KALEIDOSCOPE

PlayStation Vita takes handheld gaming to a new level

2012-04-01T21:26:00.001-07:00

Overview

The PS Vita is the most powerful, dazzling and impressive handheld games console ever built.
It packs not one but two quad-core processors, a sparkling 5-inch touchscreen OLED display, dual analogue stick controls and games that go way beyond what any other portable device is currently capable of.
That includes the Nintendo 3DS, which may wield 3D optics as its trump card, but nonetheless simply cannot compete with the Vita in terms of graphical fidelity. What the PlayStation Vita offers is more akin to a home console experience on the move, and that puts it in an elite class of one.
Of course, whether or not there is a big market for such a device is an interesting question, and we're in the process of getting some early answers. A sluggish start in Japan has been followed by some less-than-stellar sales figures in the first weeks of its UK and US launch. It doesn't come as much of a surprise.
After all, it's a luxury item launching post-Christmas into a Western world ravaged by financial floundering, and further hindered by Sony's desperate need to make money at a time when the strength of the Yen makes exported Japanese products very expensive.

Take a look at PS Vita gameplay footage, the new interface and touch controls in our video:

But we'll get to that a little later, and as far as this PlayStation Vita review goes, we're looking at the product as a stand alone piece of hardware, how it stacks up against the competition and whether or not it offers value for money.
The basics
In many ways, despite the new name, the PlayStation Vita is another revision of the Sony PSP legacy with plenty of much needed evolution on top.
The same basic form factor returns and it doesn't look too different from its predecessors. But this is a wolf in sheep's clothing. A beast among men. A veritable fire-breathing monster compared to those long-dead PSPs in the sky.

The curvy oval shape returns, and measures 7.2-inches from end to end. So it's the biggest Sony handheld ever, with a height of 3.3-inches and a thickness of 0.73.
Sony's reasoning has clearly been: if we're going to make the world's most powerful handheld console, we might as well make it the best it can possibly be. That involves packing industry-leading visuals, hence the 5-inch OLED screen which on its own is as big as the entire PSP Go console was.
We think the enlarged size is a worthwhile compromise, and this Wi-Fi only model weighs in at just 260g which is 20g lighter than the original, smaller PSP 1000. So when you pick it up you'll react to its apparent lightness.
On the table
The front of the console is a smorgasbord of hardware delights.
To the left of the screen you'll find the classic Sony D-Pad, a left analogue stick, a left speaker and the PS Home button.

To the right you'll find your classic PlayStation triangle, circle, square and X buttons, as well as a right analogue stick, right speaker, a 0.3MP front-facing camera and the Start and Select buttons you're most likely very familiar with already.

On the top side of the Vita are left and right shoulder buttons - there are no trigger buttons like you'd find on a PS3 Dualshock controller. Between the shoulders you'll find the on/off button, volume controls, the PS Vita Card slot (which we'll discuss in a moment) and a terminal to plug in any number of as-yet non-existent peripherals.

The base of the console houses the proprietary USB connector for charging and connecting to PS3 etc, as well as the headphone/microphone adapter and the Memory Card slot.

And finally, the rear of the PS Vita is home to the brand-new rear Touch Pad, a rear 0.3MP camera and a microphone.

Price
At launch the PS Vita will set back UK gamers around £209.99 (RRP £229.99), while the 3G version will launch a little later for £259.99 (£279.99). At the time of writing, the cheapest deal for the PS Vita is £197 at ASDA, while Amazon have matched that price.
There are bundle deals if you shop around, and these include different combinations of PC Sivta with memory cards and games.

Features

The PlayStation Vita's immense power is provided by the 32-bit Quad-core ARM Cortex-A9 MPCore CPU - the same beating heart you'll find in many other devices including the iPad 2. Graphical grunt is thus supplied by the A9's defacto GPU of choice, the similarly quad core PowerVR Series5XT SGXMP+ chip.
That makes the Vita more graphically capable than the iPhone 4 or the iPad 2, despite its far more modest price point.
Memory is provided by 512MB RAM and 128MB VRAM for the GPU. There were rumours prior to launch that Sony was attempting to slash that memory allocation to 256MB in order to save money, but it's a good thing it's been left in.

That's because the Vita is able to hold even a game like Uncharted: Golden Abyss in stasis while you return to the Vita menus and change some settings etc. As soon as you want to return to the game, it resumes instantaneously, even if you put the console to sleep and leave it alone for 48 hours.
It's the same seamless experience you get with Sony's other games console, the PS3 which itself only has 256MB RAM.
Screen
Of course, the big stand-out feature of the Vita is that incredible screen. It's a real stunner, and discards with LCD tech to jump straight into bed with sexier, brighter and more efficient OLED.
It's a winning feature, and it packs a qHD resolution of 640x960. That doesn't make it the sharpest screen in the business - the iPhone 4S' retina display has a pixel density of 326ppi, while the Vita rocks up with just 220ppi - but it's plenty enough to make Vita's games resonate with graphical beauty beyond anything else on any other portable device.

It's a capacitive touchscreen jobby too, which means you use gestures on the screen to navigate the PS Vita's brand new interface, instead of using the D-Pad, and most games make heavy use of that touch input too.
Underneath the screen you've also got three-axis accelerometer and gyroscopes, meaning you can control many of your games simply by moving the device in your hand.
This enables you to aim simply by moving the device around - great for games like Uncharted, though if you're sitting down you might need a swivel chair or things start to get tricky!

No internal storage
As we mentioned on the previous page, one criminal drawback is the lack of internal storage. For this, Sony really needs to take a long, hard look at itself because it's really not a very clever move. Talk about a put-off.
So in addition to the console, you'll have to fork out for one of Sony's proprietary Vita memory cards, essentially a proprietary stick similar in shape but smaller than an SD card.

When you buy games, they'll come on their own cartridge-style cards with storage space for saves and updates so if you're only gaming it's less of a concern.
The device has two ports, one for the generic memory card and one for game cartridges. So if you want to take music, pictures or videos with you, or if you want to download digital-only games from the Sony Entertainment Network, you'll have to pay extra for the Vita storage cards. There are a range of sizes planned from 2-16GB and you probably won't like the prices.
As of launch day, Amazon UK is selling the 4GB card for £15, 8GB for £28 and 16GB for £40.
We'd recommend holding off buying one in case prices come down a little - ideally you'd be much better off with the 16GB model but £40 is simply too much to pay in our eyes (it has to be said, at the time of writing, Amazon UK is offering a deal whereby you can get an 8GB Vita card for free when buying the console).
Connection-wise both models come with standard Bluetooth and WiFi connections while the 3G model also includes, well a 3G connection.
In the EU the 3G service is provided by Vodaphone, and the £279 price tag includes a free 4GB memory card, a PAYG SIM card which when topped up with £5 will get you a free downloadable game - WipEout 2048 - and 250 MB of data lasting up to 30 days with full Vodafone 3G connectivity.
The PlayStation Vita 3G will also be available at other high street and online retailers with the option to top up £5 and get the WipEout 2048 game free of charge.

Windows 8 review

2012-04-01T21:21:00.001-07:00

Windows 8: Getting started, ARM and x86

Windows 8 offers options on lock screens and more

The Windows 8 Consumer Preview (here's the Windows 8 download) updates the look of the Developer Preview, adds a lot of new features and revamps a few old ones.
The round Start button is gone, the Metro-style Start screen remains and yes, you can only pick from nine colours and five patterns for the Start screen background.
But there's far more to the Consumer Preview user interface than the Start screen, and far more to Windows 8 than the user interface.

Metro has a limited choice of colour schemes and styles

There are new ways of switching between apps, as well as more updates to the desktop tools. There are changes under the hood to file copying, power management, security, networking, hardware support and more.

Two windows; when one is the desktop, it has thumbnails of all open apps

And then there are the first real Metro apps, so you can find out what it's like to use Metro for more than just trying out Metro, and the Windows Store for the first third-party apps from real developers.

Swipe down on the start menu to see all your apps

This is the version of Windows 8 that's going to give you a real feel for what the final operating system will be like and the first version you could realistically use for day-to-day work. But will you want to?

Running the Windows 8 Consumer Preview

First of all, it's worth noting that the Consumer Preview is only for x86/64 PCs; there isn't an ARM version that you can download and try out, since there aren't any ARM devices that will run it.
That's because of the extremely custom way that ARM devices are built, where not even the way to control a physical button is standard. Microsoft isn't supporting tablets built to run Android or WebOS, either.

It's the windows 7 beta fish – metro style

Much of what we're seeing in the Consumer Preview will be the same on Windows on ARM (WOA) systems. Most stuff - from the Metro user interface to the touch gestures, to the Windows desktop and built-in Windows tools such as Explorer and Task Manager - will be practically the same. But until we see it in action, we don't know what WOA performance and battery life will be like.
Consumer Preview doesn't include the desktop Office apps that will be bundled with WOA either - and of course it runs all the x86 desktop apps that won't work on WOA.

Windows 8 on ARM: Steven Sinofsky speaks

When you download the Consumer Preview, installing is easier than usual with a beta operating system. You can start the installation directly from the web page, instead of having to download an ISO file and burn that to an optical disc.
You can still burn an ISO if you want, and the installer can also create a bootable USB stick so you can download Consumer Preview once and install it on multiple machines.

Windows 8 boots so fast you may miss the bios screen, so you can change the options for the next boot here

The tools for creating a Windows To Go USB stick aren't available yet, so you can't run Windows 8 directly from USB, but you'll get a far better feel for how Windows 8 performs if you can try it out directly on a PC.

Windows 8: Metro interface

The Metro interface doesn't look that different, but having your email, photos, appointments and friends pinned to it livens it up considerably - as does the new Metro tile for the desktop, which sports a cute Metro-ified version of the Windows 7 beta fish.
You can also pin libraries here as well as Explorer, but you have to do that from Explorer set to view the desktop rather than from within a library itself.

Pin libraries as a top level link to the start screen

The improved touch gestures also make it far easier to work with. Swipe from the right edge of the screen and you get the redesigned charm bar; Search, Share, Start, Devices and Settings.
You can do the same thing by leaving your mouse pointer in the top or bottom right corner; first the charms appear as white outlines, then if you don't move your mouse they disappear. Windows assumes you didn't want to trigger them, since you might be moving the mouse to scroll or closing a window at the side of the screen instead. If you are, you don't have to wait for the charms to vanish to do so. Move the mouse towards the charms and the black bar and charm titles draw in on screen.

Put the mouse in the corner to open the charms, move your mouse and they light up

Start, which is highlighted in the accent colour of the colour theme you choose, swaps between the Start screen and whatever you were doing last. Search is now context sensitive; if you're in IE when you choose it, you get results from Bing first.
Swipe up from the bottom on the Start screen to get a quick link to the All Apps view, which is now neatly organised into program groups, arranged alphabetically.
As you swipe across the Start menu, it stops with the group of tiles you've swiped to line up under the word Start; this bouncing into place is the promised 'speed bump' to help you navigate around. Scrolling with a mouse works far better - if you push the mouse past the edge of the screen, the tiles scroll as if you were swiping with your finger.

Put your mouse in the corner and you see this thumbnail

Drag your mouse down to see the thumbnails in the switching pane

This works so well you'll miss it in apps that don't support it, such as Photos, where you have to go back to grabbing the scrollbar or use a touch pad or Microsoft Touch Mouse, which enables you to swipe sideways.
The Semantic zoom feature now works too; pinch to shrink the tiles on the Start screen to tiny thumbnails so you can see everything at once or move an entire group. Select a group and drag it down to get the option of naming it.

Zoom out on the start menu to see more tiles and name your groups

This is also the view you get when you drag a tile you're moving to the bottom of the screen, which makes it easier to move an item a long way across the screen without disturbing the arrangement of all your tiles and groups.
As you drag a tile between two groups, when you position it between them a vertical grey bar appears to show that you're creating a new group to put it in.
Switching between apps is now far easier. You can still drag in the next app in the stack from the left edge of the screen to be full screen or to snap into a side window, but when the icon of that next app appears, you can also drag it back to the edge to get a vertical pane of thumbnails.

Switch between current apps using this thumbnail list

Moving between screens

This only shows six thumbnails of recent apps (including the desktop if that's open) plus the thumbnail for the Start menu. Tap a thumbnail to open the app or drag it to choose where on screen it appears.

Hover the mouse in the corner for this start button replacement

You can get the switching pane using a mouse by leaving the mouse pointer in the top or bottom left corner of the screen until a thumbnail appears (the next app at the top, the Start menu preview at the bottom). Drag down with the mouse and the thumbnails appear. If you want to see all current desktop apps and recent Metro apps, use Alt+Tab instead. Win+Tab makes the switching pane appear.

The new lock screen image; a coral reef where you might find a beta fish maybe?

You can close Metro apps without restoring to the task manager. Drag down from the top of the screen until the app you're looking at shrinks down to a thumbnail and keep dragging that off the screen to close it (it's a longer swipe than when you use a quick finger swipe down from the top or up from the bottom of the screen to get the menu bar inside an app).
That works with a mouse as well. Or you can use Alt+F4, just like with a desktop app.

IE10 has a spell checker that works in any app that needs is

You can type quite well on screen. The large touch keyboard is a little better laid out now, and has predictive text and spelling corrections.
The thumb keyboard layout still has the alphabet split between the two sides of the screen where it's all in reach of your thumbs, but there's now a numeric keyboard in the middle to make it faster to type passwords (or indeed, numbers) and you can resize the keyboard.

The split screen keyboard now has a numeric keypad all the time

The new notifications in Metro work well; they pop up in the top right corner of the screen where they're not likely to be in the way and you can tap for options. So the first time you put a USB stick in, you can choose whether to open Explorer or do something else, and that will happen automatically next time you insert it.

Charms in the desktop bring up desktop tools

Windows 8: Accounts and more

If you use a Windows Live account (which can be a Hotmail address or any other email address you've set up as a Windows Live account) to log in, you automatically get your contacts, calendar and messages.

The two day calendar view

If you've already linked your Twitter, Facebook, LinkedIn or Flickr accounts to Windows Live, Windows 8 uses that to put your Facebook photos in the Photos app, your Facebook friends in the People app and Facebook chat in Messaging.

See the photos you save on skydrive from your phone

The people app doesn't always make good use of the space

Much like it did in the Developer Preview, Windows 8 uses this account to take your settings, IE favourites and saved passwords to any other Windows 8 PCs you sign into with the same account, but this is now called a Microsoft account and it will enable you to download apps from the Windows Store.

Take favourites and colour schemes to other windows 8 pcs you use

You can easily switch accounts but only after you log in

If you use an account from a different provider, such as Gmail, as your login, you'll get the information from that account in Windows but you'll have to verify that before contact, calendar and message information start arriving.
When they do, you can choose which of them show notifications on the Lock screen. You can pick up to seven apps that will run in the background when your screen is off and tell you if you have new messages - one of them can show more detailed information, but so far the calendar is the only choice.

Choose what notifications you see on the lock screen; those will be the connected standby apps on new devices

This will be much more important on WOA and SoC devices that have connected standby, since these are the apps that will get updates while the rest of the system is asleep.

Choose what apps can pop up notifications

Windows Live account or not, the first account you make on a Consumer Preview system is automatically an admin account.
When you add a second account, there's no option to set it as being an administrator straight away, as you realise the first time you try to install an app and have to put in the password of the original account. You can go into the control panel to change the account type, but it's irritating not to get the option in the first place.

iPhone 5 rumours

2012-04-01T21:09:00.000-07:00

Getting ready for the next wave of iPhone excitement

As it happened, there was no iPhone 5 in 2011 after all, but the company did announce the iPhone 4S.
However, the new iPhone 5 is still on the cards - we're expecting it to debut in the middle of this year. So we've gathered together all the latest iPhone 5 rumours and rounded them up below.
First though, why not read our complete iPhone 4S review?
It's the phone that appeared when the whole world was looking forward to the iPhone 5 anyway, so make up your own mind whether to make the jump to Apple's latest now or save those pennies for the 2012 iPhone 5 release.

iPhone 5 release date

iPhone 5 news

Stay up to date on iPhone 5 with our in-depth coverage

Given the pattern of Apple's iPhone launches, we're expecting the next-gen iPhone 5 to debut in mid to late 2012. We reckon it's most likely to be shown off at Apple's Worldwide Developer Event (WWDC), which usually takes place in early June.
Rumours that we reported on 18 October claim an iPhone 5 release date of Summer 2012. Analyst Ashok Kumar claimed that the absent iPhone 5 was meant to be the big announcement at the recent event where the iPhone 4S was launched.
We also reported in February that the new iPhone would be launched in October, falling into line with the same release schedule from last year, and Macotakara 'sources' confirming the Cupertino brand would be honouring the same upgrade cycle from now on.

iPhone 5 form factor

iPhone 5 RSS feed

Constant alerts on the latest iPhone 5 news

Unlike the iPhone 4S, the new iPhone will be a completely new design from what has gone before, so that means an entirely new casing as we saw with the iPhone 3G and, later, the iPhone 4.
Interestingly, someone who claimed to have seen a larger-screened iPhone 5 prototype said in November 2011 that Steve Jobs canned the new handset and opted for the iPhone 4S because of the larger screen size of the new device. According to Business Insider, it was feared that a new size would create a two-tier iPhone ecosystem.
Beatweek also claimed in November 2011 that the 5-inch was scrapped "because Apple wouldn't be able to do it properly" this year. However, the Daily Mail (make of that what you will) then suggested that a four-inch version was likely and that Sony has already shipped top secret demo screens to Apple.

iPhone 5 specs

Based on the roadmap of mobile chip design specialist ARM (of which Apple is a licensee), we'll see a quad-core processor debut in the new iPhone 5 - probably called the Apple A6. We know that we'll see other quad core handsets debut in 2012, so it's not too much of a stretch to say that the iPhone 5 will be the same.
We had expected some kind of help in terms of predicting the iPhone 5 CPU from the launch of the new iPad, but the announcement of a slightly tweaked A5X processor really didn't help things there.

iPhone 5 will have 4G/LTE support

With many 4G handsets already announced in the US, it can't be long before the iPhone supports 4G technologies - even if we won't even have a UK spectrum auction until 2012.

4G mobile broadband and LTE explained

Cnet.com quotes Will Strauss from analyst firm Forward Concepts, who says that the next iPhone will feature LTE technologies."They're saving iPhone 5 for the LTE version and that won't be out until next spring," said Strauss.
After the new iPad's launch brought 4G to an Apple device, it's widely expected that 4G will come to iPhone 5.

Steve Jobs' iPhone 5 legacy

Many sites have reported that Steve Jobs was working hard on the iPhone 5 project, which will apparently be a "radical redesign". We shall see... but the fact the iPhone 4S was so similar to the iPhone 4 suggests that Steve was working on something pretty special before
And if you're in a bit of a hurry, we've also got a handy iPhone 5 video detailing the latest rumours on release date, spec and more - so check if out for a quick fix of next-gen Apple fun:
The Wall Street Journal has previously reported that: "Apple is also developing a new iPhone model, said people briefed on the phone. One person familiar said the fifth-generation iPhone would be a different form factor than those that are currently available… it was unclear how soon that version would be available to Verizon or other carriers."
This has since been backed up by reports from Engadget, which state the design will be a 'total rethink'.

iPhone 5 screen

Various sources claim the iPhone 5 will feature a larger, 4-inch screen. Digitimes quotes the source as saying that Apple is expanding the screen size "to support the tablet PC market as the vendor only has a 9.7-inch iPad in the market."
On 23 May 2011, we reported on rumours that the iPhone 5 could feature a curved glass screen. These rumours also came from Digitimes, which said that Apple has purchased between 200 and 300 special glass cutting machines because they're too costly for the manufacturers to invest in.
In March 2012, new reports suggested that the new iPhone 5 would come sporting a larger 4.6-inch retina display.

iPhone 5 digital wallet - NFC

Review

iPhone 4S review

There's been some speculation that Apple might include Near Field Communication (NFC) technology in the iPhone 5, turning it into a kind of credit/debit card.
However, with the tech being inside the Google Nexus S and Samsung Galaxy Nexus, as well as a host of other top smartphones, the time for NFC may finally be here.
On 24 June 2011 it was reported that the Google Wallet mobile payment platform could feature on the new iPhone. Eric Schmidt admitted that Google is looking to port the software to other manufacturers.
However, on 31 January 2012 9to5Mac claimed to have spoken with a well-connected developer who disclosed information received from Apple iOS engineers saying they are "heavily into NFC".
The developer in question has not been named, but is working on a dedicated iOS app which includes NFC reading for mobile transactions. When questioned how confident he was on the information he had received his reply was "Enough to bet the app development on".

iPhone 5 camera

Sony makes the camera for the iPhone 4 and iPhone 4S. Speaking at a live Wall Street Journal event, Sony's Sir Howard Stringer was talking about the company's camera image sensor facility in Sendai, a town that was recently ravaged by the recent Japanese earthquake and tsunami.
According to 9to5Mac, he said something along the lines of, "Our best sensor technology is built in one of the [tsunami] affected factories. Those go to Apple for their iPhones… or iPads. Isn't that something? They buy our best sensors from us."
Sources have also suggested the new iPhone could have an 8MP camera. Indeed, Sony announced in January 2012 that it had developed new back-illuminated stacked CMOS image sensors which are smaller in size.

iPhone 5 price

If the iPhone 5 is an evolutionary step like the move from the iPhone 4 to the iPhone 4S then we'd expect the price to stay more or less the same, although in the UK higher VAT rates may well mean a higher price tag.
It's pretty much nailed on that the new iPhone will cost around £500 for a 16GB / 32GB model (depending on the capacity Apple whacks in there) and unless the iPhone 5 comes with some truly next generation technology that pricing model should hold firm.

New iPad 3 review

2012-04-01T21:06:00.000-07:00

Overview, design and feel

The new iPad, the iPad 3, the new iPad 3… call it what you want, but it's a device that from the outside looks remarkably like the iPad 2 but with an overhaul on the innards.
The question most people ask us when it comes to the new iPad is: what's different from the old one?
Well, in this case it's pretty easy: there's a Retina Display that makes everything looks superbly crisp, an updated A5X processor bringing quad-core graphics and a 5MP camera on the rear with a VGA sensor on the front.
Oh, and the iPad 3 is also the device that brings iOS 5.1 to the masses (well, it's also on the likes of the iPhone 4S and iPad 2 as well, but hey, we're not reviewing those today, and you don't really care unless it's a new iPad.)

The design of the new iPad 3 isn't really anything different from the original duo from Apple's tablet range. Actually, while we're thinking about it, it looks almost identical to the iPad 2 – to the point you'd struggle to tell them apart when turned off.
However, in the hand, there's a little bit of a difference, especially when it comes to the weight. The new iPad is nearly 60g heavier than the previous iteration, and while it's not terrible, it does add a little arm strain during a marathon movie session.

Retina Display

Before we get onto all the normal insight over the frame of the new iPad, it's worth talking about the main feature: the Retina Display.
Apple has packed a huge amount more pixels into the 9.7-inch screen - 1536 x 2048 to be exact. However, despite the fact that the Cupertino brand makes a big thing about the 330 PPI density of the iPhone 4, we're looking at a screen that's technically a lot less sharp than its smartphone brethren - around 264PPI.

Apple has got around this fact by stating that the screen is meant to be held at 15 inches from the face, rather than the 10 inches the iPhone is supposed to from your eyes, and as such the sharpness is the same.
Given the fact the term 'Retina Display' really isn't a legally binding term, we don't care. What matters is the effect - and it's one of the most impressive we've seen on a tablet to date. If someone took an iPad, printed out a really hi-res image of an iOS system and stuck it on the front, we'd struggle to tell the difference - it's superb, and even squinting up close you'll be hard pushed to notice any pixelation.
The colour reproduction will also appeal to many, as it's pretty close to reality - it lacks the punch of the Super AMOLED HD screens seen on the likes of the Samsung Galaxy Note for instance, but it will depend on personal preference as to whether that's a good thing.

We like the vivid colours of Samsung's screens, but we know plenty of people that loathe them too.
The main thing is things like internet browsing; photo viewing and movie sessions are all much, much improved over the iPad 2, and is one of the main reasons to pick up the new iPad.

Design

The new iPad, as we said, is only marginally thicker and a little heavier than the iPad 2, and if you pick it up with no knowledge of the former, you'll likely be mighty impressed.
The rest of the design is premium too - given you can be paying nearly £700 for a top end model, it needs to seem like a worthwhile investment, and it does.

The curved edges, the oleophobic scratch-proof glass and the aluminium chassis are all the kind of thing that some Android tablets have tried to ape and failed. Of course, many will prefer the feather-light frames of some of the Samsung models but, like the screen, it really comes down to personal preference.
The buttonry on the new iPad is pretty sparse though - we're talking four buttons and that's your lot.

The iconic home button is back once again, despite rumours of its demise, and is easy to reach and hit within the thick bezel.

The rest of the buttons are all clustered tightly together in the top left-hand corner of the new iPad, with the rocker/volume key, the mute/orientation switch and power/lock key all within an inch of one another.
As you can see, Apple has been pretty efficient with the button placement, with all of them performing more than one function. And they say the iPad can't multi-task... tsk.

Interface

The new iPad 3 picks up the iOS story where the iPad 2 left off - with an incremental upgrade to iOS 5.1 the main talking point.
However, before we go through what's new, we'll take a quick tour across the operating system to show just how simple it is to operate a new iPad.
The home screen is laid out in a very similar way to the iPhone, except we're seeing some much larger icons for the apps you've downloaded.

You can fill as many home screens as you like with apps as you download more from the App Store, and swiping from screen to screen on the iPad 3 is silky smooth even with loads of programs downloaded.
There's also the dock at the bottom of the display which can hold up to six regularly-used apps that are present on all home screens, which is more than the four on offer with the iPhone thanks to the extra screen real estate.

Neat freaks need not despair either: it's easy to create folders of the apps you want to lump together simply by dragging an icon and plopping it on top of another – the iPad will create a name for the group based on the content, but it's easy to rename these.
iOS 5.1 doesn't offer too much in the way of new features for the users interface, but a trick that Apple has learned from Google's Android is the notifications bar, which can be accessed simply by swiping down from the top of the screen.

This contains information on everything from unread mail messages to notifications of new moves in games you're playing with friends. It's a simple system and one that's prevalent throughout the system, even in most apps, meaning you can easily jump in and out of applications where necessary.
Speaking of which, it's worth taking a look at the multi-tasking gestures on offer, as they're pretty sensational. Using a full set of fingers on the screen allows three functions: pinching in will take you to the home screen, flicking up will enable the multi-tasking window and swiping left will let you bounce between open apps.
It really works on the new iPad, and we urge you to check it out as it really makes moving through the system easy and cool at the same time.
There's a great debate over what really constitutes multi-tasking – but in our view, the iPad does enough to warrant the title. The likes of the BlackBerry Playbook are more capable when it comes to fully running programs in the background, but most users will struggle to really notice the difference when the iPad and its Android competition are asked to jump between apps.
As mentioned, you can easy multi-finger swipe up or double tap the home button to call up a list of recently opened apps, which can be deleted from the tray by a single long press and tapping of the 'x' that appears.

Swiping right in the multi-tasking tray will also call up the music player, which allows you to see what songs are about to play, or change the volume or brightness. Not new, but the closest thing to a widget we'll get here.
The lock screen allows you to do some pretty funky stuff; double tapping the home button will call up the music player so you can switch tracks or pause without needing to open the iPad. Also, there's an option to have a slide show of your photos – although we've all got some we don't want to see cycling past at times.

The iPad interface is one that's a little hard to judge, as it's so subjective we're bound to be chastised for the manner in which we rate the OS. However, in our minds it's still a little simplistic, with no opportunity for real customisation, and that's something we've been hoping Apple will fix for years.
But then again others hate overly-complicated user interfaces, and they'll love the simple icon-centric offering. There are other foibles, like apps not re-aligning when one is deleted off a screen, but there are examples of this happening on other tablets all the time, so it's hard to criticise the iPad specifically.
Does the iPad 3 really do enough to be the poster boy for the A5X chip in terms of smoothness under the finger? Maybe, but it's nothing spectacular. The iPad 3 randomly shut down apps during use on more than one occasion, and we were often left prodding a key on the screen only to see that there was a big freeze at work.

Although Apple won't admit it, there's an increase under the hood from 512MB of RAM to 1GB – given the iPad 2 had a decent level of snap between programs, it's hard to say how this really works until put under a few months of load.
However, jumping through apps with the multi-touch gestures certainly impressed, and we're hoping this level of RAM will keep the iPad running at optimum performance for a while longer.
Basically, if you want simple and a mostly slick user interface, then you're in for a treat. It's not the most complete system out there, but iOS 5.1 is knocking the socks off the users who love the iPad experience, and don't give two hoots about Android widgets.

The history of Easter eggs

2012-04-01T06:56:00.000-07:00

It's pretty much common knowledge that Easter is a Christian celebration of Christ's rising, but this holiday also has pagan origins. Where did the colored eggs, cute little bunnies, baby chicks, leg of lamb dinners, and lilies come from? They are all symbols of rebirth and the lamb was a traditional religious sacrifice.

Easter falls in the spring, the yearly time of renewal, when the earth renews itself after a long, cold winter. The word Easter comes to us from the Norsemen's Eostur, Eastar, Ostara, and Ostar, and the pagan goddess Eostre, all of which involve the season of the growing sun and new birth. The Easter Bunny arose originally as a symbol of fertility, due to the rapid reproduction habits of the hare and rabbit.

The ancient Egyptians, Persians, Phoenicians, and Hindus all believed the world began with an enormous egg, thus the egg as a symbol of new life has been around for eons. The particulars may vary, but most cultures around the world use the egg as a symbol of new life and rebirth. A notation in the household accounts of Edward I of England showed an expenditure of eighteen pence for 450 eggs to be gold-leafed and colored for Easter gifts. The first book to mention Easter eggs by name was written five hundred years ago. Yet, a North African tribe that had become Christian much earlier in time had a custom of coloring eggs at Easter. Long hard winters often meant little food, and a fresh egg for Easter was quite a prize. Later, Christians abstained from eating meat during the Lenten season prior to Easter. Easter was the first chance to enjoy eggs and meat after the long abstinence.

Some European children go from house to house begging for Easter eggs, much like Halloween trick-or-treaters. Called pace-egging, it comes from the old word for Easter, Pasch. Many old cultures also attributed the egg with great healing powers. It is interesting to note that eggs play almost no part in the Easter celebrations of Mexico, South America, and Native American Indian cultures. Egg-rolling contests are a symbolic re-enactment of the rolling away of the stone from Christ's tomb. The decoration of small leaf-barren branches as Easter egg trees has become a popular custom in the United States since the 1990s.

Traditional Easter Foods

Although colored hard-boiled eggs are probably the first Easter food to come to mind, other foods factor into the traditional Easter meals around the world.

Hot Cross Buns are an Easter favorite in many areas. The tradition allegedly is derived from ancient Anglo-Saxons who baked small wheat cakes in honor of the springtime goddess, Eostre. After converting to Christianity, the church substituted the cakes with sweetbreads blessed by the church.

Countries around the world serve sweet cakes in the same vein, such as Czech babobka and Polish baba. The Greeks and Portugese serve round, flat loaves marked with a cross and decorated with Easter eggs. Syrian and Jordanian Christians have honey pastries.

Pretzels were first shaped to indicate the torso of a person with arms folded, praying.

The roast lamb dinner that many eat on Easter Sunday goes back earlier than Easter to the first Passover of the Jewish people. The sacrificial lamb was roasted and eaten, together with unleavened bread and bitter herbs (see Passover Seder) in hopes that the angel of God would pass over their homes and bring no harm. As Hebrews converted to Christianity, they naturally brought along their traditions with them. The Christians often refer to Jesus as The Lamb of God. Thus, the traditions merged.

In the United States, ham is a traditional Easter food. In the early days, meat was slaughtered in the fall. There was no refrigeration, and the fresh pork that wasn't consumed during the winter months before Lent was cured for spring. The curing process took a long time, and the first hams were ready around the time Easter rolled around. Thus, ham was a natural choice for the celebratory Easter dinner.

Easter

2012-04-01T06:50:00.000-07:00

Easter, which celebrates Jesus Christ's resurrection from the dead, is Christianity's most important holiday. It has been called a moveable feast because it doesn't fall on a set date every year, as most holidays do. Instead, Christian churches in the West celebrate Easter on the first Sunday following the full moon after the vernal equinox on March 21. Therefore, Easter is observed anywhere between March 22 and April 25 every year. Orthodox Christians use the Julian calendar to calculate when Easter will occur and typically celebrate the holiday a week or two after the Western churches, which follow the Gregorian calendar.

The exact origins of this religious feast day's name are unknown. Some sources claim the word Easter is derived from Eostre, a Teutonic goddess of spring and fertility. Other accounts trace Easter to the Latin term hebdomada alba, or white week, an ancient reference to Easter week and the white clothing donned by people who were baptized during that time. Through a translation error, the term later appeared as esostarum in Old High German, which eventually became Easter in English. In Spanish, Easter is known as Pascua; in French, Paques. These words are derived from the Greek and Latin Pascha or Pasch, for Passover. Jesus' crucifixion and resurrection occurred after he went to Jerusalem to celebrate Passover (or Pesach in Hebrew), the Jewish festival commemorating the ancient Israelites' exodus from slavery in Egypt. Pascha eventually came to mean Easter.
Easter is really an entire season of the Christian church year, as opposed to a single-day observance. Lent, the 40-day period leading up to Easter Sunday, is a time of reflection and penance and represents the 40 days that Jesus spent alone in the wilderness before starting his ministry, a time in which Christians believe he survived various temptations by the devil. The day before Lent, known as Mardi Gras or Fat Tuesday, is a last hurrah of food and fun before the fasting begins. The week preceding Easter is called Holy Week and includes Maundy Thursday, which commemorates Jesus' last supper with his disciples; Good Friday, which honors the day of his crucifixion; and Holy Saturday, which focuses on the transition between the crucifixion and resurrection. The 50-day period following Easter Sunday is called Eastertide and includes a celebration of Jesus' ascension into heaven.
In addition to Easter's religious significance, it also has a commercial side, as evidenced by the mounds of jelly beans and marshmallow chicks that appear in stores each spring. As with Christmas, over the centuries various folk customs and pagan traditions, including Easter eggs, bunnies, baskets and candy, have become a standard part of this holy holiday.

Why are butterflies colored?

2012-04-01T06:45:00.001-07:00

Blue Morpho butterfly (Morpho menelaus). This brilliant blue butterfly can be found in the rain forests of South America (Brazil & Guyana).

Butterflies have fascinated humankind for millennia, and have been interpreted in a variety of ways, from omens of love to personifications of the soul. Yet, the delicate beauty of iridescent butterfly wings belies their intricate structure and functionality as the perfect foil for predators.
Structural colors are created by an optical effect (such as interference, refraction, or diffraction) rather than by a pigment. They arise from the arrangement of physical structures interacting with light to produce a particular color.
Structural color is responsible for the colors of the feathers of many birds (including the blue jay, hummingbirds and pheasants), as well as certain butterfly wings and beetle shells. Variations in the spacing of the pattern often gives rise to an iridescent effect, as seen in peacock feathers, soap bubbles, films of oil, and mother-of-pearl, because the reflected color depends upon the angle of view.

Butterflies and moths

The Morpho butterflies are among the largest in the world, with a wingspan of 7.5 to 20 cm. The males have beautiful metallic blue upper wings, while the females are drab. Their iridescence stems from the microscopic structure of their wings. Pilots flying over the rain forest can occasionally see brief flashes of blue as these butterflies travel above the forest canopy.

Blue Morpho butterfly (Morpho menelaus). This brilliant blue butterfly can be found in the rain forests of South America (Brazil & Guyana).

Underside of wings. When the Morpho lands, it closes its wings tightly, showing only the brown, camouflaged undersides, so a bird that is looking for a blue butterfly can’t see it.

Iridescent surfaces, such as butterfly wings, help animals to elude potential predators. When these insects fly, the upper surface of their wings continually changes from bright blue to dull brown because the angle of the light striking the wing changes. As the butterflies move their wings up and down during flight, they seem to disappear, and then reappear a short distance away, looking like ethereal flashes of bright blue light. The dark undersides of their wings strengthen this effect. Combined with an undulating pattern of flight, this ability to change color quickly makes them difficult for predators to pursue.

Parts of the wing: Wing > Scales > Veins > Ridges

Scales from the top and bottom of a Morpho wing

What is iridescence?

The wings of butterflies and moths consist of a colorless translucent membrane covered by a layer of scales (the name of the order is Lepidoptera, meaning "scaly wings"). Each scale is a flattened outgrowth of a single cell and is about 100 µm long and 50 µm wide. The scales overlap like roof tiles and completely cover the membrane, appearing as dust to the naked eye.
The iridescence is caused by multiple slit interference. Sunlight contains a full range of light wavelengths. "Interference" occurs when light hitting the wing interacts with light reflected off the wing.
Light is a wave. If the crests and the troughs of the waves are aligned, or in phase, they will cause constructive interference, and iridescence is the result. One light wave hits the first groove, and a second light wave travels half of a wavelength to another groove, and is then reflected back in phase with the first.
If the crest of one wave meets the trough of another wave (out of phase), they will cancel each other out, as destructive interference occurs.

Why does the Morpho appear blue?

Blue light has a wavelength range from 400 to 480 nm. The slits in the scales of the Morpho are 200 nm apart. Because the distance between slits corresponds to half of the wavelength of blue light, this is the wavelength that undergoes constructive interference. The slits are attached to a base of melanin, a material that absorbs light, further strengthening the blue image.

Top of wing (blue):

Underside of wing (brown):

Detailed views of scales from the wing tops, and wing undersides. Notice the veins in the magnified views.

Why are Morphos’ wing undersides brown?

The scales on the underside of the Morpho’s wing do not cause interference. This stems from normal organic pigments, rather than physical structure, and does not change with viewing angle. They resemble foliage, with lackluster browns, grays, blacks, and reds.
The iridescence is more useful on the topside of the butterfly wing, where it can be used to elude their main predators: birds. These scales also protect the wing from physical contact.
Each scale is about 70 by 200 µm, and is covered with thin parallel veins. The veins are much like ridges on a vinyl record. There are about 1,800 veins per millimeter. The texture forms a reflection grating. The veins are made of stacked chitin lamellae kept equidistant by fine braces. On the underside, the slits on the scales are 160 nm apart, less than half of any visible light wavelength, and thus do not cause visible interference.

Another interesting group of insects, the day-flying swallowtail moths from the uraniidae family, get their iridescent colors from their unusual scale design. Their scales use a combination of ridges and air pockets to produce iridescence.

Holograms

2012-04-01T06:42:00.000-07:00

Although we regularly see holograms on our credit cards, our drivers’ licenses, and our currency, surrealist Salvador Dali was among the first to incorporate holograms into fine art. The ability of holograms to play with light and create a transparent yet realistic three-dimensional world is both inviting and intriguing.
Holograms are images that allow us to reproduce the three-dimensional aspects of an object. Instead of capturing an image directly onto film as a photograph does, a hologram records an interference pattern. Transmission holograms are viewed by shining a light through the recorded hologram, while reflection holograms create an image by reflecting light from their surface. Large-scale transmission holograms are able to create an image that appears to have depth, and that changes as you move, allowing you to see around the object projected.
To record a hologram, monochromatic, coherent laser light is split into two beams. The reference beam is directed to the holographic film, while the object beam shines onto the object and is reflected onto the film. The film is exposed to an interference pattern as the two beams recombine.

Holograms are ubiquitous, with uses ranging from adding security to currency and credit or debit cards, to decorative wrapping paper. The ability to record a three-dimensional image has also been utilized in art, architecture, educational displays, and portraiture.

Dispersive Refraction

2012-04-01T06:36:00.001-07:00

Dispersive refraction effects in crystals

Crystals have their own colors (see emeralds and rubies), but dispersive refraction can enhance the appeal of a well-cut jewel.

In a well-faceted gemstone, a ray of light passing into the top of the stone undergoes total internal reflection and is returned to the eye as the "brilliance." Light reflected back towards the observer will be dispersed by refraction if the gemstone has a high refractive index.	Since the geometry of the path corresponds to that in a prism, the reflected rays are also refracted, leading to flashes of color, or the "fire" in a stone. The amount of fire depends on the magnitude of the dispersion. The diamond has a very high dispersion, the highest of any naturally occurring gemstone, as well as a very high refractive index.
More complex effects occur in crystals that have a different refractive index for different optical planes. The crystal on the right is anisotropic and creates a double image, as compared to the isotropic left-hand crystal.

"Double refraction" can be observed using crossed polarizers. Because of the asymmetrical geometry of the crystal, polarized light is separated into ordinary and extraordinary rays moving at different velocities through the crystal. The second polarizer recombines these rays to produce color by interference.

Getting rid of dispersive refraction: chromatic aberration

Light is dispersed into the colors of the spectrum by refraction. When we are using a refractive lens to enlarge an image, this becomes a problem; we don’t want to see the image with distorted colors at the edges of objects. This problem is known as chromatic aberration.
Chromatic aberration is a problem for any devices relying on lenses, such as telescopes, microscopes, and cameras. Digital cameras include software to compensate for this effect.
The magnifying lenses of early telescopes were simple convex lenses. At high magnification, refraction by these lenses dispersed the light into its component colors, haloing the stars and planets in rainbow colors and distorting the image seen.
Newton was the first to solve this problem, enlarging the image by reflection instead of refraction.

In addition to creating extra colors, dispersive refraction creates different focal lengths for different colors, so that edges in the projected image are blurred.
An image of Venus with a colored rim caused by chromatic aberration	This photograph shows uncorrected chromatic aberration. The window edges are blurred and colored.
This is the design of telescope Newton developed to overcome the chromatic aberration inherent in earlier refracting telescope designs. Note that the eyepiece is on the side of the telescope, not at the lower end as in the telescopes we use today.	Various geometries of reflecting telescopes

The essence of a reflecting telescope is that the refractive lens is eliminated and a parabolic mirror reflects the image.
There are applications that still use a refracting lens, so other methods of reducing chromatic aberration are employed. One method uses lenses of glass with different refractive indices. Joining a flint glass negative lens, which has a higher refractive index, to a crown glass positive lens, with a lower refractive index, forms a doublet lens corrected for dispersive refraction haloes.

What is Refraction?

2012-04-01T06:34:00.001-07:00

Rainbows, with their ephemeral quality and gorgeous hues, have fascinated us since the beginning of recorded time. The rainbow is deeply rooted in our history. It appears in the oldest of stories, as well as being ubiquitous in art and music.

Newton and the color spectrum: dispersive refraction

Isaac Newton established that refraction causes white light to separate into its constituent wavelengths. While he was not the first to demonstrate that a prism produces a spectrum of colored light from incident white light, he showed that a second prism could recombine the colors to create white light again. He also demonstrated that the individual colors remained constant when shone through a prism again. This was in stark contrast to the consensus that the prism itself produced colors.
Newton’s contribution created a new understanding that white light is a mixture of colored light, and that each color is refracted to a different extent. The different colors correspond to light with different wavelengths, and are refracted to differing degrees. This separation of colors is known as dispersion.
Once the colors in sunlight are separated by refraction, we are able to distinguish them in the splendor that is a rainbow.

What is refraction?

The refractive index (n) of a medium such as air or water tells us how fast light travels in that medium. It is the ratio of the speed of light in a vacuum (c) to the speed of light in this medium (v): n = c / v.
The bending of a light as it crosses the boundary into a different medium is determined by its refractive index, or how much the light is slowed down in the new medium.

We see objects "breaking" at the boundary between media of different density because of refraction. Light rays are bent, or refracted, because light travels at different speeds in different media. Unless the light ray meets the boundary at exactly 90°, the direction of travel will change and the light ray is "bent."

The relationship between the angle of incidence and speed in the first medium and the angle of refraction and the speed of the refracted light in the second medium is given by Snell’s law: n1 sin θ₁ = n2 sin θ₂ (where θ₁ = incident angle, n1 is the refractive index of the first medium, θ₂ = refracted angle, and n2 is the refractive index of the second medium).

The reason that light travels more slowly in a higher density medium is that light interacts with the particles in its path. When light traveling through space to the earth meets the atmosphere, light is absorbed and then re-emitted every time a photon of light collides with an atom of air.

Rainbows

2012-04-01T06:32:00.001-07:00

Rainbows can be seen in the spray of a waterfall. Ideal conditions for rainbows are sunlight and water droplets, usually as rain, but also in fine spray.

How is a rainbow formed?

The mechanics of rainbows have been studied since ancient times. The Greek philosophers were aware of the role of reflection in forming a rainbow, and had some understanding of the role of refraction. In the 13th century, scientists produced theories on rainbow formation, and in the 17th century, Rene Descartes sketched out the conditions required to observe a rainbow.
We see rainbows because of the geometry of raindrops. When the sun shines from behind us into the rain, incident rays of light enter the drop and are refracted inwards. They are reflected from the back surface of the raindrop, and refracted again as they exit the raindrop and return to our eyes. Refraction is responsible for splitting the sunlight into its component colors.

Descartes’ well-known sketch describes the conditions required to observe a rainbow. The sun is directly behind him, and the light reflected from the raindrops ahead of him concentrates between approximately 40.6° and 42.4°, centered on the point where the shadow of his head would be.

You perceive a rainbow from a particular position; "your" rainbow will alter as you move and will differ from others’ perceptions. Because the light from any single drop is dispersed, only one ray of a particular color reaches your eye. The violet band that you see leaves the corresponding raindrops at about 40.6°, and the red band that you see leaves its corresponding raindrops at 42.4°, so the red light is from raindrops higher in the sky relative to your eye.

Above, compare the angles from internal and double-internal reflections. There are triple- and quadruple- internal reflections as well. See up to 6 internal reflections below.
Secondary rainbows are formed by double internal reflection. Light is reflected twice from the inner surface of the raindrop before leaving the raindrop. The light is concentrated between approximately 50.4° and 53.6°, forming a secondary rainbow above the primary rainbow.

Explore for yourself the main rains through a raindrop. Notice how short and long wavelengths have slighty different angles. The primary output angle is from one reflection.

If we were able to see an entire rainbow (for example from a plane) it would form a full circle. This rainbow over the Iguazu Falls illustrates this with its extended arc.

The size of the raindrops does not affect the geometry of the rainbow, although very tiny drops, such as those in fog or mist, reduce the effect. In this case, the effect of scattering overpowers the dispersive refraction effect. A "fogbow" has the arc of a rainbow, but appears as a bright white bow without spectral colors.
The angle of the sun does affect the rainbow we see. Once the sun is higher than 42°, the rainbow arc slips below the horizon. As the sun approaches the horizon, the size of the visible arc increases, reaching a full semicircle just before sunset.
Moonbows have been observed, but as our night vision is not sensitive to color, they appear white rather than colored.

Secondary rainbows and supernumerary rainbows

The Blind Girl, by John Everett Millais, expresses the pathos of this figure, unaware of the splendor surrounding her. The artist has taken some liberties with the double rainbow here; the dramatic dark sky below the rainbow does not occur in nature.

If one rainbow is beautiful, a double rainbow is breathtaking. In fact, is possible for sunlight to be reflected three or more times in one raindrop, but third order rainbows cannot be seen. They form so close to the sun that its brightness overpowers them.
In the laboratory, it is possible to recreate multiple rainbows formed by multiple internal reflections. A spherical flask of water simulates the raindrop.
In a double rainbow, raindrops reflect the sun’s light noticeably inward from the rainbow arc, and correspondingly out of the secondary bow, so that the dark band is seen between the bows. This effect, called Alexander’s band, was first described by the Greek philosopher Alexander of Aphrodisias in the 3rd century. The sky below the primary (lower) rainbow, and above the secondary (higher) bow, is brighter as a result.
A supernumerary rainbow forms additional bands on the inner arc of the primary rainbow, or very occasionally on the outer arc of the secondary rainbow. These bands, which usually appear in pastel colors, are caused by the interference of light waves.

This photograph illustrates the actual appearance of a double rainbow, with the bright area below the primary bow and the dark Alexander band between the bows. The colors of the bright primary rainbow (lower) run from violet on the inside to red on the outside. In the secondary (higher) rainbow the color sequence is reversed, with red on the inside and violet on the outside.

The primary rainbow is brightest, with red at the top and violet at the bottom. The supernumerary bands appear up against the violet band, in pastel shades that do not follow the usual pattern of spectral color. These bands are caused by the interference of light waves, providing evidence for the wave nature of light.

How do different colorblind individuals see?

2012-04-01T06:31:00.001-07:00

Many people mistakenly think anyone labeled as "colorblind" only sees black and white - like a black and white movie or television show. On the contrary, it is extremely rare to have monochromacy - the complete absence of any color sensation. The variations in type and severity of colorblindness are explored in more detail in the section Colorblindness.


Comparison of normal and dichromat vision

Anomalous trichromacy (where vision is based on three functioning cone types, but one or more cone types are atypical) is by far the most common form of colorblindness, and in many senses it is the least severe. Its effect is to reduce the ability to discriminate between colors, but it does not eliminate color perception altogether. People with this form of colorblindness experience very little difficulty in doing tasks that require color vision. Some may not even be aware that their color perception is in any way atypical. The only problem they have is passing color vision tests.

Under poor viewing conditions, such as when driving in dazzling sunlight or in rainy or foggy weather, it is easily possible for protanomalous individuals to mistake a blinking red traffic light for a blinking yellow or amber one, or to fail to distinguish a green traffic light from the various "white" lights in store fronts, signs, and street lights. The dimming can be so pronounced that reds may be confused with black or dark gray, and red traffic lights may appear to be extinguished.

Dichromats (those with vision based on two functioning cone types) on the other hand, can be so severely color deficient as to affect their daily lives. The real problem, for protanopes (absence of L-cone), deuteranopes (absence of M-cone) and tritanopes (absence of S-cone), is there are far too many color names and no obvious basis for using one instead of another. Why call something "orange" when it doesn’t look different in any way from something else called green, tan, beige, or any of several other color names?
For the protanope, red, orange, yellow, yellow-green, and green, appear somewhat shifted toward green in hue, and all appear paler than they do to the average observer. Protanopes may learn to distinguish reds from yellows and from greens primarily on the basis of their apparent brightness or lightness, rather than any perceptible hue difference. Violet, lavender, and purple are indistinguishable from various shades of blue because their reddish components are so dimmed as to be invisible. Pink flowers, reflecting both red light and blue light, may appear blue to the protanope. In the pictures below, the orange flowers completely disappear.
The deutanope suffers the same hue discrimination problems as the protanope, but without the dimming. The names red, orange, yellow, and green mean very little. Similarly, violet, lavender, purple, and blue appear to be the same color. In the pictures below, the orange flowers completely disappear.
Tritanopes can have difficulty distinguishing green, cyan, and blue. Tritanopes can also have problems distinguishing yellow from violet. They can have pink, orange, and brown confusions. In the picture below, the orange and pink flowers look the same.

Typical	Protanope (L-cone absent)
Deutanope (M-cone absent)	Tritanope (S-cone absent)
Comparison of normal and dichromat vision

The vision simulator illustrates these differences more clearly.

Achromatopsia and monochromacy

Achromatopsia (sometimes called rod monochromacy) can be inherited (congenital), or cerebral achromatopsia can develop later in life. Because an achromat or achromatope’s vision comes entirely from the rods, it works best at low light levels, and at the periphery of view. People with the condition must wear dark sunglasses in daylight or bright indoor conditions. Congenital achromats perceive black, white, and shades of grey, but have no understanding of the concept of color. People with cerebral achromatopsia see in shades of grey, because having had color vision, they perceive the absence of color.
There are three types of cone monochromacy (all of which are rare), named according to the working cone type, e.g. blue cone monochromacy is a condition in which the L-cones and M-cones are missing, leaving just the S-cones and the rods. Because the S-cones do not contribute to our perception of brightness, blue cone monochromats have similar problems with bright lights to achromatopes, although they are able to distinguish a small range of colors. Monochromats can see during the day, but can’t distinguish between hues.

Colorblindness

2012-04-01T02:46:00.000-07:00

Could you tell the difference between a tomato, a lime, and an orange? Some colorblind people (protanopes and deutanopes) see no perceptible difference between red, orange, yellow, and green. Colors that seem so different to the average viewer appear to be the same color for this two percent of the population.

Hundreds of millions of people have vision problems. Colorblindness affects as many as 1 in 12 men and 1 in 200 women. Although colorblindness is typically the result of a genetic condition, acquired color deficiencies can stem from injury or disease. While not officially labeled colorblindness, as people age, their corneas typically turn yellowish, severely hampering their ability to see violet and blue colors.
Cataracts are another major vision problem affecting a large proportion of the population. When a person has a cataract, the lens in his or her eye is no longer entirely transparent. Because aging is the most common risk factor for the condition, increased life expectancy has made cataracts the leading cause of blindness worldwide. In the U.S., over 20 million people 40 years of age and older experience this clouding in the lens of the eye, and cataracts are estimated to be the cause of half of the cases of vision loss in white, African American, and Latino people.

Types of colorblindness

The different forms of colorblindness can be classified according to the affected cone type and the degree of deficiency. People with typical cones and light-sensitive pigments are able to see different colors by using three types of cone pigments (referred to as L for long wavelengths, M for medium wavelengths and S for short wavelengths) having different spectral sensitivity. This is called trichromacy.
Sometimes vision is based on only two types of cone pigments. This is known as dichromacy.
A mild color deficiency is present when one or more of the three light sensitive pigments in the cones are atypical and their peak sensitivity is shifted (anomalous trichromacy). This can vary from being very mild to almost as severe as dichromacy.
Total colorblindness is very rare but the effects are severe. L-cone, M-cone, or S-cone monochromacy describes a condition where only one type of cone pigment functions, and thus only a single color is perceived. In rod monochromacy or achromatopsia, there are no working cone pigments in the cones. Achromatopsia can be inherited or cerebral achromatopsia can develop. The terms protan, deutan, and tritan are used to refer to the absence of functional L-cone, M-cone, and S-cone pigments, respectively.
Protanopes (L-cone) and deutanopes (M-cone) are often referred to as red-green colorblind and tritanopes (S-cone) are often referred to as blue-yellow colorblind. This can be misleading, as tritanopes can distinguish between blue and yellow.

Cone type	Generic defect name	Anomalous trichromacy name	Dichromacy name
L-cone	Protan	Protanomaly	Protanopia
M-cone	Deutan	Deutanomaly	Deutanopia
S-cone	Tritan	Tritanomaly	Tritanopia

Microgravity

2012-04-01T02:39:00.003-07:00

In earth’s gravity, buoyant convection develops when hot, less dense combustion products rise.

Does a candle burn the same on a space station as it does on earth?

Candle flames behave differently in outer space (microgravity) than they do on earth, primarily because microgravity provides an environment that lacks buoyant convection, which normally plays an important role in maintaining and shaping a flame on earth.
What is microgravity? Astronauts on the International Space Station are orbiting the earth in free fall the space station, the astronauts and everything on board are all "falling" around the earth at the same rate. This creates the floating sensation we think of as zero gravity, or more correctly, microgravity. The astronauts experience a sense of weightlessness, but it is gravity that holds the space station in its orbit.
In earth’s gravity, buoyant convection develops when hot, less dense combustion products rise. The flow that results draws cooler surrounding air to the base of the flame, supplying it with the oxidizer (in this case, oxygen) that the flame requires to maintain itself. Combustion products (carbon dioxide, water vapor, and soot) are carried away from the flame by the same convective flow, which is the dominant transport mechanism in the flame.

Candle flames on earth (left) have several different temperatures within the flame; on a space station (right), there is no buoyant convection, and the flame burns slower and hotter.

In microgravity, however, the process is not the same. There is no buoyant convection, and the transport of combustion products and oxygen occurs by the much slower process of molecular diffusion. This diffusion occurs when there is a high concentration of combustion products and a low concentration of oxygen close to the flame and a high concentration of oxygen farther away from the flame. The combustion products migrate away from the flame and the oxygen migrates toward the flame. The diffusive transport rates in microgravity are much lower than the transport rates due to natural convection in earth’s gravity. As a result, a flame in microgravity will often appear to burn less vigorously than a flame on Earth, and it will assume a spherical shape that diffuses equally in all directions, rather than the more elongated shape that is characteristic of flames in earth’s gravity.

Why are fire and flames colored?

2012-04-01T02:38:00.000-07:00

From ancient times, when fire helped ensure human survival, to today’s romantic candlelit dinner, the magic and mystery of flames have entranced and enchanted us.
The concept of color temperature has permeated our everyday language. For example, we use the term "red hot" to qualify everything from a fashion trend, to a spicy food, to a temperature hot enough to melt iron. However, terms related to color temperature can lead to confusion, especially when talking about flames themselves. Incandescence does color a flame, but it is not the only source of its color.

A rainbow of neon tubes displays the variety of colors available through gas excitation.

Gas excitations

Gas excitations are responsible for vivid examples of colored light. Arc lighting, sparks, neon lights, sodium or mercury vapor lamps, and the aurora rely on gas excitations for their striking colors. Lightning and fireworks, while obtaining their bright white colors from incandescence, also display a range of other colors obtained through gas excitations. Scientists use the same phenomenon to identify different elements in flame tests.

Why are beetle shells colored?

2012-04-01T02:36:00.001-07:00

Most insect structural colors are in the green-blue-violet range, but red, gold, and copper colors may also be produced in this way. The shade of color and its intensity are determined by several factors, including the thickness and spacing of the layers of the scales, or epicuticle, the number of these layers, and the angle of the incoming light.

Although we often think of beetles as garden pests or garden protectors, many cultures use parts of dazzling, colorful beetles as ornamentation for ceremonial costumes and headdresses, as well as in prized jewelry. Just as structural color is responsible for the beautiful shimmering blue of neotropical Morpho butterflies, it is also responsible for the glistening iridescent colors of many tropical beetles.
The epicuticle, or outermost surface, of iridescent beetles is made of many stacks of slanting, plate-like layers, which are oriented in different directions. These layers bend, and then reflect the incoming light in the same way as the ridges of iridescent butterfly and moth scales. Similarly, they produce structural colors by interference in the same way as butterfly wings. A layer of pigment below the refractive plates of beetles and the ridges of iridescent butterfly scales enhances the effect of the iridescence. In some species, the epicuticle acts as a reflection diffraction grating to cause iridescence. The exact mechanism of the structural color for many species is an open topic of research.

The leafy environment of some beetles is often illuminated by intermittent flashes of sunlight as breezes move through the trees. The glistening surfaces of these beetles blend in well with the beetles’ surroundings.

Why are many tropical beetles iridescent?

Unlike birds, most insects do not use showy color to attract mates; instead, the primarily rely on chemical attraction. It might seem that the colorful appearance of these beetles would advertise their presence to predators; in fact, these creatures are surprisingly well camouflaged.

Iridescence

2012-04-01T02:32:00.000-07:00

Iridescence as a result of interference

We’re captivated when we see something in nature with a multitude of colors, or when the colors seem to change depending on our point of view. Whether we’re looking at pearl and mother-of-pearl, the transparent wings of houseflies and dragonflies, the near-metallic colors of scales on beetles and butterflies , or the feathers of hummingbirds and peacocks , we are immediately drawn to their iridescence (from the Latin word, "iris," meaning rainbow).
Although the iridescence of these natural wonders are a result of "structural colors," rather than pigment molecules, iridescence takes other forms as well. For example, light waves can interfere with one another, causing the iridescent colors you see in a layer of oil on a wet pavement or in the surface of a soap bubble.
Other examples of iridescence caused by interference include ice and crumpled cellophane, which will produce iridescent colors in polarized white light. Because they are optically anisotropic (they have different optical properties for light from different directions), they undergo double refraction. In contrast, the iridescent colors in opals, CDs, and DVDs that change with viewing angle is attributed to diffraction (the diffracted rays interfere to produce the colors).

What is interference?

Two light waves of the same wavelength can interact to reinforce each other if they are in phase, or cancel each other out if they are out of phase. Some cases of interference occur in combination with diffraction (see opal), while others involve interference in the absence of diffraction.

Constructive vs. destructive interference: light waves 1 and 2 produce constructive reinforcement if they are in phase (A). Crests align with crests and troughs align with troughs, reinforcing one another. Destructive cancellation is observed when they are out of phase (B). The crests of wave 1 align with the troughs of wave 2, canceling one another.

Interference of light beams reflected from the front and back surfaces of a thin parallel film. This effect can be seen in soap bubbles. As either the angle, the thickness of the film, or the wavelength changes, the wavelength and the color of light produced by constructive interference changes.

The French scientist Augustin-Jean Fresnel performed the first clear demonstration of interference without diffraction in about 1815. He used a monochromatic light source reflected in two mirrors; the mirrors were made of black glass to reflect light only at the front surface and were placed at a small angle to each other to produce two overlapping beams of light on a screen. The result was a series of "interference fringes" consisting of alternate bands of light and dark. If either mirror was covered or removed, the fringes disappeared and only the uniform light from the other mirror remained.
The ability of lasers to produce monochromatic light has opened up the study of interference, and led to the wide use of a variety of interference-based devices. Interferometers, such as the Twyman-Green interferometer and the Fabry-Perot etalon (using multiple reflective surfaces), are used for precise comparison of waves in applications ranging from oceanography to measurements at the microscopic scale.

Green metallic-like reflection of a photographic flash from the eyes of a cat, caused by multiple thin-film interference.

Iridescence in the animal kingdom

Structural colors occur naturally in a rich variety of systems, usually involving multiple-layered structures that provide thin-film interference. The layers may be composed of keratin, chitin, calcium carbonate, mucus, and so on. Frequently, a dark layer of melanin forms a backing to intensify the observed color by absorbing the non-reflected light.
The eyes of many nocturnal animals contain multilayer structures that improve night vision and produce iridescent metallic-like reflections.
Several species of stomatopod crustaceans, a family of tropical marine predators, have colored display surfaces that change dramatically when viewed with a linear polarizing filter. If the angle of polarization is changed, the uropods and antennal scales change from red-orange to faint purple. Researchers are studying the cause of this color (perhaps interference, perhaps a pigment), and whether the animals use these signals to communicate.

Bubbles

2012-04-01T02:28:00.000-07:00

Bubbles capture the essence of childlike wonder, perfectly formed, evanescent and rich with ephemeral color. They also demonstrate a plethora of useful scientific principles, including surface tension, ratios of surface area to volume, and interference colors.

What is a soap bubble?

A soap bubble is a very thin sheet of water sandwiched between two layers of soap molecules. The film of soapy water surrounds a bubble of air. Soap molecules have one end that repels water, and one that attracts it, and these molecules move to the inner and outer surfaces, thrusting their water-repelling ends out into the air, and their "heads" inwards. Without such molecules on the surface, the bubble would spontaneously break apart into tiny water droplets. Surface tension causes the bubble to be spherical, which is the shape that gives the minimum surface energy - the lowest ratio of surface area to volume.

Why are soap bubbles colored?

The thickness of the film - or rather, its thinness - determines whether iridescence is apparent. Light is reflected from both the inner and outer surface of the soap bubble.

When an incoming ray of light strikes the outer surface of a bubble, part of the light ray is reflected immediately, while the other part is transmitted into the soap film. After reaching the inner surface of the film, this transmitted light ray is reflected back toward the outer surface. When it leaves the bubble, it travels in the same direction as the ray that was immediately reflected and is, therefore, parallel to that ray.

If these two rays of light are reflected back so that their wavelengths are "out of phase" with each other, the second ray will partly cancel out the reflection of the first ray. This is called destructive interference, which results in a reduction of color intensity. If, however, the wavelengths of the two reflected rays are "in phase," they will enhance each other. This is called constructive interference.

The light rays that are reflected off the inner surface of the bubble travel further than the light rays that are reflected off the outer surface. Some wavelengths will interfere destructively and others constructively, depending on the extra distance traveled by a transmitted-and-reflected ray. Whether the reflected rays are in or out of phase with each other depends on the extra distance (through the film and back) that the second ray must travel before rejoining the first ray. This distance depends on the angle of the incident light and the thickness of the film.
White light is made up of different colors, corresponding to specific wavelengths. As the film thickness changes, the extra distance the ray must travel changes. Interference is constructive when the total extra distance matches a specific wavelength of light, and is destructive when it is half a wavelength. So if white light shines on a bubble, the film reflects light of a specific hue, and this hue changes with the film’s thickness.
The iridescence of a soap bubble, which seems to contain a wealth of changing color, stems from light striking the bubble from varied angles. The path length varies with the angle of incident light, giving varying path differences for the internally and externally reflected rays at different points on the bubble. This means that, even if the soap film is of uniform thickness, different colors can be seen. Light entering the bubble directly travels a shorter path than light entering at a wider angle. This allows different wavelengths to undergo constructive and destructive interference, so different colors are perceived.

David Stein holds the Guinness World Record for the longest bubble, over 15 m long.

Cluster of soap bubbles. A variety of beautiful colors appear in the swirls. Often, just before bursting, the swirls will appear black.

Changing color

The colors of a bubble are dependent on the thickness of the film. A bubble becomes thinner and thinner as it dries out (due to evaporation), before finally popping. As the surface film of the bubble becomes increasingly thinner, a change in overall color can be seen. Thick walls cancel out longer wavelengths in the red range. As the bubble film gets thinner, yellow wavelengths are cancelled out. As it gets even thinner, green light is lost. Beyond this point, even shorter wavelengths in the blue wavelength range disappear.
The resulting colors are a combination of the colors that do not undergo destructive interference and their degrees of constructive interference. Blue-green colors dominate in thicker films and yellow hues in thinner films. Eventually, the film becomes too thin to create interference of visible wavelengths, as all wavelengths are cancelled out. At this point the bubble appears colorless. Against a black background the bubble surface could appear black.

Railway air brake

2012-04-01T01:46:00.001-07:00

An air brake is a conveyance braking system actuated by compressed air. Modern trains rely upon a fail-safe air brake system that is based upon a design patented by George Westinghouse on March 5, 1872. The Westinghouse Air Brake Company (WABCO) was subsequently organized to manufacture and sell Westinghouse's invention. In various forms, it has been nearly universally adopted.
The Westinghouse system uses air pressure to charge air reservoirs (tanks) on each car. Full air pressure signals each car to release the brakes. A reduction or loss of air pressure signals each car to apply its brakes, using the compressed air in its reservoirs

Background

Prior to the introduction of air brakes, stopping a train was a difficult business. In the early days when trains consisted of one or two cars and speeds were low, the engine driver could stop the train by reversing the steam flow to the cylinders, causing the locomotive to act as a brake. However, as trains got longer, heavier and faster, and started to operate in mountainous regions, it became necessary to fit each car with brakes, as the locomotive was no longer capable of bringing the train to a halt in a reasonable distance.
The introduction of brakes to railcars necessitated the employment of additional crew members called brakemen, whose job it was to move from car to car and apply or release the brakes when signaled to do so by the engineer with a series of whistle blasts. Occasionally, whistle signals were not heard, incorrectly given or incorrectly interpreted, and derailments or collisions would occur because trains were not stopped in time.
Brakes were manually applied and released by turning a large brake wheel located at one end of each car. The brake wheel pulled on the car's brake rigging and clamped the brake shoes against the wheels. As considerable force was required to overcome the friction in the brake rigging, the brakeman used a stout piece of wood called a "club" to assist him in turning the brake wheel.
The job of a passenger train brakeman wasn't too difficult, as he was not exposed to the weather and could conveniently move from car to car through the vestibules, which is where the brake wheel was (and still is, in many cases) located. Also, passenger trains were not as heavy or lengthy as their freight counterparts, which eased the task of operating the brakes.
A brakeman's job on a freight train was far more difficult, as he was exposed to the elements and was responsible for many more cars. To set the brakes on a boxcar (UIC: covered wagon) the brakeman had to climb to the roof ("coon the buggy" in railroad slang) and walk a narrow catwalk to reach the brake wheel while the car was swaying and pitching beneath his feet. There was nothing to grasp other than the brake wheel itself, and getting to the next car often required jumping. Needless to say, a freight brakeman's job was extremely dangerous, and many were maimed or killed in falls from moving trains.
Complicating matters, the manually operated brakes had limited effectiveness and controlling a train's speed in mountainous terrain was a dicey affair. Occasionally, the brakemen simply could not set enough brakes to a degree where they were able to reduce speed while descending a grade, which usually resulted in a runaway—followed by a disastrous wreck.
When adopted, the Westinghouse system had a major effect on railroad safety. Reliable braking was assured, reducing the frequent accidents that plagued the industry. Brakemen were no longer required to risk life and limb to stop a train, and with the engineer now in control of the brakes, misunderstood whistle signals were eliminated. As a result, longer and heavier trains could be safely run at higher speeds.
During his lifetime, Westinghouse made many improvements to his invention. The United States Congress passed the Safety Appliance Act in 1893 making the use of some automatic brake system mandatory. By 1905, over 2,000,000 freight, passenger, mail, baggage and express railroad cars and 89,000 locomotives in the United States were equipped with the Westinghouse Automatic Brake.

Overview

A comparatively simple brake linkage

In the air brake's simplest form, called the straight air system, compressed air pushes on a piston in a cylinder. The piston is connected through mechanical linkage to brake shoes that can rub on the train wheels, using the resulting friction to slow the train. The mechanical linkage can become quite elaborate, as it evenly distributes force from one pressurized air cylinder to 8 or 12 wheels.
The pressurized air comes from an air compressor in the locomotive and is sent from car to car by a train line made up of pipes beneath each car and hoses between cars. The principal problem with the straight air braking system is that any separation between hoses and pipes causes loss of air pressure and hence the loss of the force applying the brakes. This deficiency could easily cause a runaway train. Straight air brakes are still used on locomotives, although as a dual circuit system, usually with each bogie (truck) having its own circuit.
In order to design a system without the shortcomings of the straight air system, Westinghouse invented a system wherein each piece of railroad rolling stock was equipped with an air reservoir and a triple valve, also known as a control valve.

Rotair Valve Westinghouse Air brake Company

The triple valve is described as being so named as it performs three functions: Charging air into an air tank ready to be used, applying the brakes, and releasing them. In so doing, it supports certain other actions (i.e. it 'holds' or maintains the application and it permits the exhaust of brake cylinder pressure and the recharging of the reservoir during the release). In his patent application, Westinghouse refers to his 'triple-valve device' because of the three component valvular parts comprising it: the diaphragm-operated poppet valve feeding reservoir air to the brake cylinder, the reservoir charging valve, and the brake cylinder release valve. When he soon improved the device by removing the poppet valve action, these three components became the piston valve, the slide valve, and the graduating valve.

If the pressure in the train line is lower than that of the reservoir, the brake cylinder exhaust portal is closed and air from the car's reservoir is fed into the brake cylinder to apply the brakes. This action continues until equilibrium between the brake pipe pressure and reservoir pressure is achieved. At that point, the airflow from the reservoir to the brake cylinder is lapped off and the cylinder is maintained at a constant pressure.

If the pressure in the train line is higher than that of the reservoir, the triple valve connects the train line to the reservoir feed, causing the air pressure in the reservoir to increase. The triple valve also causes the brake cylinder to be exhausted to atmosphere, releasing the brakes.

As the pressure in the train line and that of the reservoir equalize, the triple valve closes, causing the air pressure in the reservoir and brake cylinder to be maintained at the current level.

Unlike the straight air system, the Westinghouse system uses a reduction in air pressure in the train line to apply the brakes. When the engineer (driver) applies the brake by operating the locomotive brake valve, the train line vents to atmosphere at a controlled rate, reducing the train line pressure and in turn triggering the triple valve on each car to feed air into its brake cylinder. When the engineer releases the brake, the locomotive brake valve portal to atmosphere is closed, allowing the train line to be recharged by the compressor of the locomotive. The subsequent increase of train line pressure causes the triple valves on each car to discharge the contents of the brake cylinder to atmosphere, releasing the brakes and recharging the reservoirs.
Under the Westinghouse system, therefore, brakes are applied by reducing train line pressure and released by increasing train line pressure. The Westinghouse system is thus fail safe—any failure in the train line, including a separation ("break-in-two") of the train, will cause a loss of train line pressure, causing the brakes to be applied and bringing the train to a stop, thus preventing a runaway train.
Modern air brake systems are in effect two braking systems combined:

The service brake system, which applies and releases the brakes during normal operations, and
The emergency brake system, which applies the brakes rapidly in the event of a brake pipe failure or an emergency application by the engineer.

When the train brakes are applied during normal operations, the engineer makes a "service application" or a "service rate reduction”, which means that the train line pressure reduces at a controlled rate. It takes several seconds for the train line pressure to reduce and consequently takes several seconds for the brakes to apply throughout the train. In the event the train needs to make an emergency stop, the engineer can make an "emergency application," which immediately and rapidly vents all of the train line pressure to atmosphere, resulting in a rapid application of the train's brakes. An emergency application also results when the train line comes apart or otherwise fails, as all air will also be immediately vented to atmosphere.
In addition, an emergency application brings in an additional component of each car's air brake system: the emergency portion. The triple valve is divided into two portions: the service portion, which contains the mechanism used during brake applications made during service reductions, and the emergency portion, which senses the immediate, rapid release of train line pressure. In addition, each car's air brake reservoir is divided into two portions—the service portion and the emergency portion—and is known as the "dual-compartment reservoir”. Normal service applications transfer air pressure from the service portion to the brake cylinder, while emergency applications cause the triple valve to direct all air in both the service portion and the emergency portion of the dual-compartment reservoir to the brake cylinder, resulting in a 20–30% stronger application.
The emergency portion of each triple valve is activated by the extremely rapid rate of reduction of train line pressure. Due to the length of trains and the small diameter of the train line, the rate of reduction is high near the front of the train (in the case of an engineer-initiated emergency application) or near the break in the train line (in the case of the train line coming apart). Farther away from the source of the emergency application, the rate of reduction can be reduced to the point where triple valves will not detect the application as an emergency reduction. To prevent this, each triple valve's emergency portion contains an auxiliary vent port, which, when activated by an emergency application, also locally vents the train line's pressure directly to atmosphere. This serves to propagate the emergency application rapidly along the entire length of the train.
Use of distributed power (i.e., remotely controlled locomotive units midtrain and/or at the rear end) mitigates somewhat the time-lag problem with long trains, because a telemetered radio signal from the engineer in the front locomotive commands the distant units to initiate brake pressure reductions that propagate quickly through nearby cars.

Enhancements

Electro-pneumatic or EP brakes are a type of air brake that allows for immediate application of brakes throughout the train instead of the sequential application. EP brakes have been in use in German high-speed trains (most notably the ICE) since the late 1980s, and in British practice since 1949, fully described in Electro-pneumatic brake system on British railway trains. Electro-pneumatic brakes are currently in testing in North America and South Africa in captive service ore and coal trains.
Passenger trains have had for a long time a 3-wire version of the Electro-pneumatic brake, which gives seven levels of braking force. In most cases the system is not fail-safe, with the wires being energized in sequence to apply the brakes, but the conventional automatic air brake is also provided to act as a fail safe, and in most cases can be used independently in the event of a failure of the EP brakes.
In North America, WABCO supplied HSC (High Speed Control) brake equipment for several post-World War II streamlined passenger trains. This was an electrically controlled overlay on conventional D-22 passenger and 24-RL locomotive brake equipment. On the conventional side, the control valve set a reference pressure in a volume, which set brake cylinder pressure via a relay valve. On the electric side, pressure from a second straight-air trainline controlled the relay valve via a two-way check valve. This "straight air" trainline was charged (from reservoirs on each car) and released by magnet valves on each car, controlled electrically by a 3 wire trainline, in turn controlled by an "electro-pneumatic master controller" in the controlling locomotive. This controller compared the pressure in the straight air trainline with that supplied by a self lapping portion of the engineers valve, signaling all of the "apply" or "release" magnets valves in the train to open simultaneously, changing the pressure in the "straight air" trainline much more rapidly and evenly than possible by simply supplying air directly from the locomotive. The relay valve was equipped with four diaphragms, magnet valves, electric control equipment, and an axle-mounted speed sensor, so that at speeds over 60 mph full braking force was applied, and reduced in steps at 60, 40 and 20 mph, bringing the train to a gentle stop. Each axle was also equipped with anti-lock brake equipment. The combination minimized braking distances, allowing more full-speed running between stops. The "straight air" (electro-pneumatic trainline), anti-lock, and speed graduating portions of the system were not dependent on each other in any way, and any or all of these options could be supplied separately.^[2]
Later systems replace the automatic air brake with an electrical wire (in the UK, at least, known as a "round the train wire") that has to be kept energized to keep the brakes off.
More recent innovations are electronically controlled pneumatic brakes where the brakes of all the wagons (cars) and locomotives are connected by a kind of local area network, which allows individual control of the brakes on each wagon, and the reporting back of performance of each wagon's brakes.

Limitations

The Westinghouse air brake system is very trustworthy, but not infallible. Recall that the car reservoirs recharge only when the brake pipe pressure is higher than the reservoir pressure, and that the car reservoir pressure will rise only to the point of equilibrium. Fully recharging the reservoirs on a long train can require considerable time (8 to 10 minutes in some cases^[3]), during which the brake pipe pressure will be lower than locomotive reservoir pressure.
If the brakes must be applied before recharging has been completed, a larger brake pipe reduction will be required in order to achieve the desired amount of braking effort, as the system is starting out at a lower point of equilibrium (lower overall pressure). If many brake pipe reductions are made in short succession ("fanning the brake" in railroad slang), a point may be reached where car reservoir pressure will be severely depleted, resulting in substantially reduced brake cylinder piston force, causing the brakes to fail. On a descending grade, the unfortunate result will be a runaway.
In the event of a loss of braking due to reservoir depletion, the engineer (driver) may be able to regain control with an emergency brake application, as the emergency portion of each car's dual-compartment reservoir should be fully charged—it is not affected by normal service reductions. The triple valves detect an emergency reduction based on the rate of brake pipe pressure reduction. Therefore, as long as a sufficient volume of air can be rapidly vented from the brake pipe, each car's triple valve will cause an emergency brake application. However, if the brake pipe pressure is too low due to an excessive number of brake applications, an emergency application will not produce a large enough volume of air flow to trip the triple valves, leaving the engineer with no means to stop the train.
To prevent a runaway due to loss of brake pressure, dynamic (rheostatic) braking can be utilized so the locomotive(s) will assist in retarding the train. Often, blended braking, the simultaneous application of dynamic and train brakes, will be used to maintain a safe speed and keep the slack stretched as the train crests a grade.
Another solution to loss of brake pressure is the two-pipe system, fitted on most modern passenger stock and many freight wagons. In addition to the traditional brake pipe, this enhancement adds the main reservoir pipe, which is continuously charged with air directly from the locomotive's main reservoir. The main reservoir is where the locomotive's air compressor output is stored, and is ultimately the source of compressed air for all systems that use it.
Since the main reservoir pipe is kept constantly pressurized by the locomotive, the car reservoirs can be charged independently of the brake pipe, this being accomplished via a check valve to prevent backfeeding into the pipe. This arrangement helps to reduce the above described pressure loss problems, and also reduces the time required for the brakes to release, since the brake pipe only has to recharge itself.
Main reservoir pipe pressure can also be used to supply air for auxiliary systems such as pneumatic door operators or air suspension. Nearly all passenger trains (all in the UK and USA), and many freights, now have the two-pipe system.

Accidents

The air brake can fail if one of the cocks where the pipes of each carriage are joined together is accidentally closed. In this case, the brakes on the wagons behind the closed cock will fail to respond to the driver's command. This happened in 1953 to the Federal Express, a Pennsylvania Railroad train pulling in to Washington DC's Union Station, causing the train to crash into the passenger concourse and fall through the floor. Similarly, in the Gare de Lyon train accident a valve was accidentally closed by the crew, reducing braking power.
There are a number of safeguards that are usually taken to prevent this sort of accident happening. Railroads have strict government-approved procedures for testing the air brake systems when making up trains in a yard or picking up cars en route. These generally involve connecting the air brake hoses, charging up the brake system, setting the brakes and manually inspecting the cars to ensure the brakes are applied, and then releasing the brakes and manually inspecting the cars to ensure the brakes are released. Particular attention is usually paid to the rearmost car of the train, either by manual inspection or via an automated end-of-train device, to ensure that brake pipe continuity exists throughout the entire train. When brake pipe continuity exists throughout the train, failure of the brakes to apply or release on one or more cars is an indication that the cars' triple valves are malfunctioning. Depending on the location of the air test, the repair facilities available, and regulations governing the number of inoperative brakes permitted in a train, the car may be set out for repair or taken to the next terminal where it can be repaired.

Standardization

The modern air brake is not identical with the original airbrake as there have been slight changes in the design of the triple valve, which are not completely compatible between versions, and which must therefore be introduced in phases. That said, the basic air brakes used on railways worldwide are remarkably compatible.

Vacuum brakes

The main competitor to the air brake is the vacuum brake, which operates on negative pressure. The vacuum brake is a little simpler than the air brake, with an ejector with no moving parts on steam engines or a mechanical or electrical "exhauster" on a diesel or electric locomotive replacing the air compressor. Disconnection taps at the ends of cars are not required as the loose hoses are sucked onto a mounting block.
However, the maximum pressure is limited to atmospheric pressure, so that all the equipment has to be much larger and heavier to compensate. This disadvantage is made worse at high altitude. The vacuum brake is also considerably slower acting in both applying and releasing the brake; this requires a greater level of skill and anticipation from the driver. Conversely, the vacuum brake had the advantage of gradual release long before the Westinghouse automatic air brake, which was originally only available in the direct-release form still common in freight service.
A primary fault of vacuum brakes is the inability to easily find leaks. In a positive air system, a leak is quickly found due to the escaping pressurized air. This problem left the British railways in a terrible condition, where trains would have to be stopped at the top of grades to set the manual brakes on each car. Purchase and maintenance of a mechanical air pump on hundreds of engines is nothing compared to keeping the vacuum line in good order across a fleet of tens of thousands of freight cars.
Electro-vacuum brakes have also been used with considerable success on South African electric multiple unit trains. Despite requiring larger and heavier equipment as stated above, the performance of the electro-vacuum brake approached that of contemporary electro-pneumatic brakes. However, their use has not been repeated.

Air brake (road vehicle)

2012-04-01T01:40:00.000-07:00

Air brakes are used in trucks, buses, trailers, and semi-trailers. George Westinghouse first developed air brakes for use in railway service. He patented a safer air brake on March 5, 1872. Originally designed and built for use on railroad train application, air brakes remain the exclusive systems in widespread use. Westinghouse made numerous alterations to improve his air pressured brake invention, which led to various forms of the automatic brake and the subsequent use on heavier road vehicles.

Compressed air brake system

Compressed air brake systems are typically used on heavy trucks and buses. The system consists of service brakes, parking brakes, a control pedal, an engine-driven air compressor and a compressed air storage tank. For the parking brake, there is a disc or drum brake arrangement which is designed to be held in the 'applied' position by spring pressure. Air pressure must be produced to release these "spring brake" parking brakes. For the service brakes (the ones used while driving for slowing or stopping) to be applied, the brake pedal is pushed, routing the air under pressure (approx 100-125psi) to the brake chamber, causing the brake to reduce wheel rotation speed. Most types of truck air brakes are drum units, though there is an increasing trend towards the use of disc brakes in this application. The air compressor draws filtered air from the atmosphere and forces it into high-pressure reservoirs at around 120 PSI. Most heavy vehicles have a gauge within the driver's view, indicating the availability of air pressure for safe vehicle operation, often including warning tones or lights. Setting of the parking/emergency brake releases the pressurized air pressure in the lines between the compressed air storage tank and the brakes, thus actuating the (spring brake) parking braking hardware. An air pressure failure at any point would apply full spring brake pressure immediately.

Design and function

A compressed air brake system is divided into a supply system and a control system. The supply system compresses, stores and supplies high-pressure air to the control system as well as to additional air operated auxiliary truck systems (gearbox shift control, clutch pedal air assistance servo, etc.).

Supply system

" Over simplified" air brake diagram on a commercial road vehicle (does not show all air reservoirs and all applicable air valves).

The air compressor is driven off of the engine either by crankshaft pulley via a belt or directly off of the engine timing gears. It is lubricated and cooled by the engine lubrication and cooling systems. Compressed air is first routed through a cooling coil and into an air dryer which removes moisture and oil impurities and also may include a pressure regulator, safety valve and a smaller purge reservoir. As an alternative to the air dryer, the supply system can be equipped with an anti freeze device and oil separator. The compressed air is then stored in a reservoir (also called a wet tank) from which it is then distributed via a four way protection valve into the front and rear brake circuit air reservoir, a parking brake reservoir and an auxiliary air supply distribution point. The system also includes various check, pressure limiting, drain and safety valves.

Control system

The control system is further divided into two service brake circuits: the parking brake circuit and the trailer brake circuit. This dual brake circuit is further split into front and rear wheel circuits which receive compressed air from their individual reservoirs for added safety in case of an air leak. The service brakes are applied by means of a brake pedal air valve which regulates both circuits. The parking brake is the air operated spring brake type where its applied by spring force in the spring brake cylinder and released by compressed air via hand control valve. The trailer brake consists of a direct two line system: the supply line (marked red) and the separate control or service line (marked blue). The supply line receives air from the prime mover park brake air tank via a park brake relay valve and the control line is regulated via the trailer brake relay valve. The operating signals for the relay are provided by the prime mover brake pedal air valve, trailer service brake hand control (subject to a country's relevant heavy vehicle legislation) and the prime mover park brake hand control.

Park brake valve
Spring brake cylinder
Air brake foot valve
Trailer brake relay valve
Truck air compressor
Air dryer
Air brake relay valve
Four way protection valve

Exposed Physical Structure

It has been suggested that this article or section be merged into Air brake (aircraft). (Discuss) Proposed since August 2011.

This example of the air brake consists of a physical structure on the exterior of a vehicle that will increase the vehicle's drag coefficient, and therefore slow it down. Air brakes of this sort are ineffective at normal road vehicle speeds, and therefore are reserved for vehicles which need to quickly decelerate from high speeds, such as race and high performance sports cars.

The Bugatti Veyron's hydraulic rear spoiler/air brake in the wing position.

Many high performance sports and racing cars utilize air brakes in order to slow the cars down from high speeds. The Bugatti Veyron, one of the fastest production cars in the world, features a rear spoiler which, at speeds above 200 km/h (120 mph), also acts as an air brake, snapping to a 55° angle in 0.4 seconds once the brake pedal is pressed, providing an additional 0.68 g (6.66 m/s²) of deceleration (equivalent to the stopping power of an ordinary hatchback). Top Fuel Dragsters and other drag racing cars that routinely reach speeds greater than 150 miles per hour use a physical air brake via a parachute(s) after the completion of a race.
In 1994, NASCAR introduced roof flaps to the cars, which are designed to keep cars from becoming airborne and possibly flipping. Following Rusty Wallace's crash at Talladega, Penske Racing designed the original roof flaps.^[3] NASCAR team owner Jack Roush helped improve on the design of the roof flaps, in conjunction with Embry-Riddle Aeronautical University, Daytona, Florida, USA. During a spin, the car rotates it eventually reaches an angle where the oncoming air reacts with the profile of the vehicle in the same manner as a wing. If the speed is high enough, air flowing over this aerofoil shape will create sufficient lift to force the car to become airborne. To prevent this, NASCAR developed a set of flaps that are recessed into pockets on the roof of the car. As a car is turned around and reaches an angle where significant lift occurs, the low pressure above the flaps causes them to deploy. The first flap, oriented 140 degrees from the centerline of the car, typically deploys first. After flap deployment, higher pressure air is forced through an air tube which connects to a second flap, deploying it. This second flap ensures that, should the car continue to spin, no further lift will be created as the vehicle's angle changes. The deployment of these flaps eliminates most of the lift on the vehicle. The roof flaps generally keep the cars on the ground as they spin, although it is not guaranteed.

Big Bang Theory

2012-03-31T10:42:00.000-07:00

The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe.^[1] According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the Universe to cool and resulted in its present continuously expanding state. According to the most recent measurements and observations, the Big Bang occurred approximately 13.75 billion years ago,^[2]^[3] which is thus considered the age of the Universe.^[4]^[5] After its initial expansion from a singularity, the Universe cooled sufficiently to allow energy to be converted into various subatomic particles, including protons, neutrons, and electrons. While protons and neutrons combined to form the first atomic nuclei only a few minutes after the Big Bang, it would take thousands of years for electrons to combine with them and create the first atoms, the building blocks of matter. The first element produced was hydrogen, along with traces of helium and lithium. Giant clouds of these primordial elements would coalesce through gravity to form stars and galaxies, and the heavier elements would be synthesized either within stars or during supernovae.
The Big Bang is a well-tested scientific theory which is widely accepted within the scientific community because it is the most accurate and comprehensive explanation for the full range of phenomena astronomers observe. Since its conception, abundant evidence has arisen to further validate the model.^[6]^[7] Georges Lemaître first proposed what would become the Big Bang theory in what he called his "hypothesis of the primeval atom." Over time, scientists would build on his initial ideas to form the modern synthesis. The framework for the Big Bang model relies on Albert Einstein's general relativity and on simplifying assumptions (such as homogeneity and isotropy of space). The governing equations had been formulated by Alexander Friedmann. In 1929 Edwin Hubble discovered that the distances to far away galaxies were generally proportional to their redshifts—an idea originally suggested by Lemaître in 1927. Hubble's observation was taken to indicate that all very distant galaxies and clusters have an apparent velocity directly away from our vantage point: the farther away, the higher the apparent velocity.^[8]
If the distance between galaxy clusters is increasing today, everything must have been closer together in the past. This idea has been considered in detail back in time to extreme densities and temperatures,^[9]^[10]^[11] and large particle accelerators have been built to experiment on and test such conditions, resulting in significant confirmation of this model. On the other hand, these accelerators have limited capabilities to probe into such high energy regimes. There is little evidence regarding the absolute earliest instant of the expansion. Thus, the Big Bang theory cannot and does not provide any explanation for such an initial condition; rather, it describes and explains the general evolution of the universe going forward from that point on. The observed abundances of the light elements throughout the cosmos closely match the calculated predictions for the formation of these elements from nuclear processes in the rapidly expanding and cooling first minutes of the universe, as logically and quantitatively detailed according to Big Bang nucleosynthesis.
Fred Hoyle is credited with coining the term Big Bang during a 1949 radio broadcast. It is popularly reported that Hoyle, who favored an alternative "steady state" cosmological model, intended this to be pejorative, but Hoyle explicitly denied this and said it was just a striking image meant to highlight the difference between the two models.^[12]^[13]^[14] After the discovery of the cosmic microwave background radiation in 1964, and especially when its spectrum (i.e., the amount of radiation measured at each wavelength) was found to match that of thermal radiation from a black body, most scientists were fairly convinced by the evidence that some version of the Big Bang scenario must have occurred.

History and development

The Big Bang theory developed from observations of the structure of the Universe and from theoretical considerations. In 1912 Vesto Slipher measured the first Doppler shift of a "spiral nebula" (spiral nebula is the obsolete term for spiral galaxies), and soon discovered that almost all such nebulae were receding from Earth. He did not grasp the cosmological implications of this fact, and indeed at the time it was highly controversial whether or not these nebulae were "island universes" outside our Milky Way.^[15]^[16] Ten years later, Alexander Friedmann, a Russian cosmologist and mathematician, derived the Friedmann equations from Albert Einstein's equations of general relativity, showing that the Universe might be expanding in contrast to the static Universe model advocated by Einstein at that time.^[17] In 1924 Edwin Hubble's measurement of the great distance to the nearest spiral nebulae showed that these systems were indeed other galaxies. Independently deriving Friedmann's equations in 1927, Georges Lemaître, a Belgian physicist and Roman Catholic priest, proposed that the inferred recession of the nebulae was due to the expansion of the Universe.^[18]
In 1931 Lemaître went further and suggested that the evident expansion of the universe, if projected back in time, meant that the further in the past the smaller the universe was, until at some finite time in the past all the mass of the Universe was concentrated into a single point, a "primeval atom" where and when the fabric of time and space came into existence.^[19]
Starting in 1924, Hubble painstakingly developed a series of distance indicators, the forerunner of the cosmic distance ladder, using the 100-inch (2,500 mm) Hooker telescope at Mount Wilson Observatory. This allowed him to estimate distances to galaxies whose redshifts had already been measured, mostly by Slipher. In 1929 Hubble discovered a correlation between distance and recession velocity—now known as Hubble's law.^[8]^[20] Lemaître had already shown that this was expected, given the Cosmological Principle.^[21]
In the 1920s and 1930s almost every major cosmologist preferred an eternal steady state Universe, and several complained that the beginning of time implied by the Big Bang imported religious concepts into physics; this objection was later repeated by supporters of the steady state theory.^[22] This perception was enhanced by the fact that the originator of the Big Bang theory, Monsignor Georges Lemaître, was a Roman Catholic priest.^[23] Arthur Eddington agreed with Aristotle that the universe did not have a beginning in time, viz., that matter is eternal. A beginning in time was "repugnant" to him.^[24]^[25] Lemaître, however, thought that

If the world has begun with a single quantum, the notions of space and time would altogether fail to have any meaning at the beginning; they would only begin to have a sensible meaning when the original quantum had been divided into a sufficient number of quanta. If this suggestion is correct, the beginning of the world happened a little before the beginning of space and time.^[26]

During the 1930s other ideas were proposed as non-standard cosmologies to explain Hubble's observations, including the Milne model,^[27] the oscillatory Universe (originally suggested by Friedmann, but advocated by Albert Einstein and Richard Tolman)^[28] and Fritz Zwicky's tired light hypothesis.^[29]
After World War II, two distinct possibilities emerged. One was Fred Hoyle's steady state model, whereby new matter would be created as the Universe seemed to expand. In this model the Universe is roughly the same at any point in time.^[30] The other was Lemaître's Big Bang theory, advocated and developed by George Gamow, who introduced big bang nucleosynthesis (BBN)^[31] and whose associates, Ralph Alpher and Robert Herman, predicted the cosmic microwave background radiation (CMB).^[32] Ironically, it was Hoyle who coined the phrase that came to be applied to Lemaître's theory, referring to it as "this big bang idea" during a BBC Radio broadcast in March 1949.^[33]^{[notes 1]} For a while, support was split between these two theories. Eventually, the observational evidence, most notably from radio source counts, began to favor Big Bang over Steady State. The discovery and confirmation of the cosmic microwave background radiation in 1964^[35] secured the Big Bang as the best theory of the origin and evolution of the cosmos. Much of the current work in cosmology includes understanding how galaxies form in the context of the Big Bang, understanding the physics of the Universe at earlier and earlier times, and reconciling observations with the basic theory.
Significant progress in Big Bang cosmology have been made since the late 1990s as a result of advances in telescope technology as well as the analysis of data from satellites such as COBE,^[36] the Hubble Space Telescope and WMAP.^[37] Cosmologists now have fairly precise and accurate measurements of many of the parameters of the Big Bang model, and have made the unexpected discovery that the expansion of the Universe appears to be accelerating.

Timeline of the Big Bang

Extrapolation of the expansion of the Universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past.^[38] This singularity signals the breakdown of general relativity. How closely we can extrapolate towards the singularity is debated—certainly no closer than the end of the Planck epoch. This singularity is sometimes called "the Big Bang",^[39] but the term can also refer to the early hot, dense phase itself,^[40]^{[notes 2]} which can be considered the "birth" of our Universe. Based on measurements of the expansion using Type Ia supernovae, measurements of temperature fluctuations in the cosmic microwave background, and measurements of the correlation function of galaxies, the Universe has a calculated age of 13.75 ± 0.11 billion years.^[41] The agreement of these three independent measurements strongly supports the ΛCDM model that describes in detail the contents of the Universe.
The earliest phases of the Big Bang are subject to much speculation. In the most common models the Universe was filled homogeneously and isotropically with an incredibly high energy density and huge temperatures and pressures and was very rapidly expanding and cooling. Approximately 10⁻³⁷ seconds into the expansion, a phase transition caused a cosmic inflation, during which the Universe grew exponentially.^[42] After inflation stopped, the Universe consisted of a quark–gluon plasma, as well as all other elementary particles.^[43] Temperatures were so high that the random motions of particles were at relativistic speeds, and particle–antiparticle pairs of all kinds were being continuously created and destroyed in collisions. At some point an unknown reaction called baryogenesis violated the conservation of baryon number, leading to a very small excess of quarks and leptons over antiquarks and antileptons—of the order of one part in 30 million. This resulted in the predominance of matter over antimatter in the present Universe.^[44]
The Universe continued to grow in size and fall in temperature, hence the typical energy of each particle was decreasing. Symmetry breaking phase transitions put the fundamental forces of physics and the parameters of elementary particles into their present form.^[45] After about 10⁻¹¹ seconds, the picture becomes less speculative, since particle energies drop to values that can be attained in particle physics experiments. At about 10⁻⁶ seconds, quarks and gluons combined to form baryons such as protons and neutrons. The small excess of quarks over antiquarks led to a small excess of baryons over antibaryons. The temperature was now no longer high enough to create new proton–antiproton pairs (similarly for neutrons–antineutrons), so a mass annihilation immediately followed, leaving just one in 10¹⁰ of the original protons and neutrons, and none of their antiparticles. A similar process happened at about 1 second for electrons and positrons. After these annihilations, the remaining protons, neutrons and electrons were no longer moving relativistically and the energy density of the Universe was dominated by photons (with a minor contribution from neutrinos).
A few minutes into the expansion, when the temperature was about a billion (one thousand million; 10⁹; SI prefix giga-) kelvin and the density was about that of air, neutrons combined with protons to form the Universe's deuterium and helium nuclei in a process called Big Bang nucleosynthesis.^[46] Most protons remained uncombined as hydrogen nuclei. As the Universe cooled, the rest mass energy density of matter came to gravitationally dominate that of the photon radiation. After about 379,000 years the electrons and nuclei combined into atoms (mostly hydrogen); hence the radiation decoupled from matter and continued through space largely unimpeded. This relic radiation is known as the cosmic microwave background radiation.^[47]

The Hubble Ultra Deep Field showcases galaxies from an ancient era when the Universe was younger, denser, and warmer according to the Big Bang theory.

Over a long period of time, the slightly denser regions of the nearly uniformly distributed matter gravitationally attracted nearby matter and thus grew even denser, forming gas clouds, stars, galaxies, and the other astronomical structures observable today. The details of this process depend on the amount and type of matter in the Universe. The four possible types of matter are known as cold dark matter, warm dark matter, hot dark matter and baryonic matter. The best measurements available (from WMAP) show that the data is well-fit by a Lambda-CDM model in which dark matter is assumed to be cold (warm dark matter is ruled out by early reionization^[48]), and is estimated to make up about 23% of the matter/energy of the universe, while baryonic matter makes up about 4.6%.^[41] In an "extended model" which includes hot dark matter in the form of neutrinos, then if the "physical baryon density" Ω_bh² is estimated at about 0.023 (this is different from the 'baryon density' Ω_b expressed as a fraction of the total matter/energy density, which as noted above is about 0.046), and the corresponding cold dark matter density Ω_ch² is about 0.11, the corresponding neutrino density Ω_vh² is estimated to be less than 0.0062.^[41]
Independent lines of evidence from Type Ia supernovae and the CMB imply that the Universe today is dominated by a mysterious form of energy known as dark energy, which apparently permeates all of space. The observations suggest 73% of the total energy density of today's Universe is in this form. When the Universe was very young, it was likely infused with dark energy, but with less space and everything closer together, gravity had the upper hand, and it was slowly braking the expansion. But eventually, after numerous billion years of expansion, the growing abundance of dark energy caused the expansion of the Universe to slowly begin to accelerate. Dark energy in its simplest formulation takes the form of the cosmological constant term in Einstein's field equations of general relativity, but its composition and mechanism are unknown and, more generally, the details of its equation of state and relationship with the Standard Model of particle physics continue to be investigated both observationally and theoretically.^[21]
All of this cosmic evolution after the inflationary epoch can be rigorously described and modeled by the ΛCDM model of cosmology, which uses the independent frameworks of quantum mechanics and Einstein's General Relativity. As noted above, there is no well-supported model describing the action prior to 10⁻¹⁵ seconds or so. Apparently a new unified theory of quantum gravitation is needed to break this barrier. Understanding this earliest of eras in the history of the Universe is currently one of the greatest unsolved problems in physics.

Underlying assumptions

The Big Bang theory depends on two major assumptions: the universality of physical laws, and the cosmological principle. The cosmological principle states that on large scales the Universe is homogeneous and isotropic.
These ideas were initially taken as postulates, but today there are efforts to test each of them. For example, the first assumption has been tested by observations showing that largest possible deviation of the fine structure constant over much of the age of the universe is of order 10⁻⁵.^[49] Also, general relativity has passed stringent tests on the scale of the solar system and binary stars while extrapolation to cosmological scales has been validated by the empirical successes of various aspects of the Big Bang theory.^{[notes 3]}
If the large-scale Universe appears isotropic as viewed from Earth, the cosmological principle can be derived from the simpler Copernican principle, which states that there is no preferred (or special) observer or vantage point. To this end, the cosmological principle has been confirmed to a level of 10⁻⁵ via observations of the CMB.^{[notes 4]}^{[citation needed]} The Universe has been measured to be homogeneous on the largest scales at the 10% level.^[50]^{[better source needed]}

FLRW metric

Main articles: Friedmann–Lemaître–Robertson–Walker metric and Metric expansion of space

General relativity describes spacetime by a metric, which determines the distances that separate nearby points. The points, which can be galaxies, stars, or other objects, themselves are specified using a coordinate chart or "grid" that is laid down over all spacetime. The cosmological principle implies that the metric should be homogeneous and isotropic on large scales, which uniquely singles out the Friedmann–Lemaître–Robertson–Walker metric (FLRW metric). This metric contains a scale factor, which describes how the size of the Universe changes with time. This enables a convenient choice of a coordinate system to be made, called comoving coordinates. In this coordinate system the grid expands along with the Universe, and objects that are moving only due to the expansion of the Universe remain at fixed points on the grid. While their coordinate distance (comoving distance) remains constant, the physical distance between two such comoving points expands proportionally with the scale factor of the Universe.^[51]
The Big Bang is not an explosion of matter moving outward to fill an empty universe. Instead, space itself expands with time everywhere and increases the physical distance between two comoving points. Because the FLRW metric assumes a uniform distribution of mass and energy, it applies to our Universe only on large scales—local concentrations of matter such as our galaxy are gravitationally bound and as such do not experience the large-scale expansion of space.

Horizons

Main article: Cosmological horizon

An important feature of the Big Bang spacetime is the presence of horizons. Since the Universe has a finite age, and light travels at a finite speed, there may be events in the past whose light has not had time to reach us. This places a limit or a past horizon on the most distant objects that can be observed. Conversely, because space is expanding, and more distant objects are receding ever more quickly, light emitted by us today may never "catch up" to very distant objects. This defines a future horizon, which limits the events in the future that we will be able to influence. The presence of either type of horizon depends on the details of the FLRW model that describes our Universe. Our understanding of the Universe back to very early times suggests that there is a past horizon, though in practice our view is also limited by the opacity of the Universe at early times. So our view cannot extend further backward in time, though the horizon recedes in space. If the expansion of the Universe continues to accelerate, there is a future horizon as well.^[52]

Observational evidence

The earliest and most direct kinds of observational evidence are the Hubble-type expansion seen in the redshifts of galaxies, the detailed measurements of the cosmic microwave background, the abundance of light elements (see Big Bang nucleosynthesis), and today also the large scale distribution and apparent evolution of galaxies^[53] which are predicted to occur due to gravitational growth of structure in the standard theory. These are sometimes called "the four pillars of the Big Bang theory".^[54]

Hubble's law and the expansion of space

Main articles: Hubble's law and Metric expansion of space

Observations of distant galaxies and quasars show that these objects are redshifted—the light emitted from them has been shifted to longer wavelengths. This can be seen by taking a frequency spectrum of an object and matching the spectroscopic pattern of emission lines or absorption lines corresponding to atoms of the chemical elements interacting with the light. These redshifts are uniformly isotropic, distributed evenly among the observed objects in all directions. If the redshift is interpreted as a Doppler shift, the recessional velocity of the object can be calculated. For some galaxies, it is possible to estimate distances via the cosmic distance ladder. When the recessional velocities are plotted against these distances, a linear relationship known as Hubble's law is observed:^[8]

v = H₀D,

where

v is the recessional velocity of the galaxy or other distant object,
D is the comoving distance to the object, and
H₀ is Hubble's constant, measured to be 70.4 +1.3
−1.4 km/s/Mpc by the WMAP probe.^[41]

Hubble's law has two possible explanations. Either we are at the center of an explosion of galaxies—which is untenable given the Copernican principle—or the Universe is uniformly expanding everywhere. This universal expansion was predicted from general relativity by Alexander Friedmann in 1922^[17] and Georges Lemaître in 1927,^[18] well before Hubble made his 1929 analysis and observations, and it remains the cornerstone of the Big Bang theory as developed by Friedmann, Lemaître, Robertson and Walker.
The theory requires the relation v = HD to hold at all times, where D is the comoving distance, v is the recessional velocity, and v, H, and D vary as the Universe expands (hence we write H₀ to denote the present-day Hubble "constant"). For distances much smaller than the size of the observable Universe, the Hubble redshift can be thought of as the Doppler shift corresponding to the recession velocity v. However, the redshift is not a true Doppler shift, but rather the result of the expansion of the Universe between the time the light was emitted and the time that it was detected.^[55]
That space is undergoing metric expansion is shown by direct observational evidence of the Cosmological principle and the Copernican principle, which together with Hubble's law have no other explanation. Astronomical redshifts are extremely isotropic and homogenous,^[8] supporting the Cosmological principle that the Universe looks the same in all directions, along with much other evidence. If the redshifts were the result of an explosion from a center distant from us, they would not be so similar in different directions.
Measurements of the effects of the cosmic microwave background radiation on the dynamics of distant astrophysical systems in 2000 proved the Copernican principle, that, on a cosmological scale, the Earth is not in a central position.^[56] Radiation from the Big Bang was demonstrably warmer at earlier times throughout the Universe. Uniform cooling of the cosmic microwave background over billions of years is explainable only if the Universe is experiencing a metric expansion, and excludes the possibility that we are near the unique center of an explosion.

Cosmic microwave background radiation

Main article: Cosmic microwave background radiation

WMAP image of the cosmic microwave background radiation

During the first few days of the Universe, the Universe was in full thermal equilibrium, with photons being continually emitted and absorbed, giving the radiation a blackbody spectrum. As the Universe expanded, it cooled to a temperature at which photons could no longer be created or destroyed. The temperature was still high enough for electrons and nuclei to remain unbound, however, and photons were constantly "reflected" from these free electrons through a process called Thomson scattering. Because of this repeated scattering, the early Universe was opaque to light.
When the temperature fell to a few thousand Kelvin, electrons and nuclei began to combine to form atoms, a process known as recombination. Since photons scatter infrequently from neutral atoms, radiation decoupled from matter when nearly all the electrons had recombined, at the epoch of last scattering, 379,000 years after the Big Bang. These photons make up the CMB that is observed today, and the observed pattern of fluctuations in the CMB is a direct picture of the Universe at this early epoch. The energy of photons was subsequently redshifted by the expansion of the Universe, which preserved the blackbody spectrum but caused its temperature to fall, meaning that the photons now fall into the microwave region of the electromagnetic spectrum. The radiation is thought to be observable at every point in the Universe, and comes from all directions with (almost) the same intensity.
In 1964 Arno Penzias and Robert Wilson accidentally discovered the cosmic background radiation while conducting diagnostic observations using a new microwave receiver owned by Bell Laboratories.^[35] Their discovery provided substantial confirmation of the general CMB predictions—the radiation was found to be isotropic and consistent with a blackbody spectrum of about 3 K—and it pitched the balance of opinion in favor of the Big Bang hypothesis. Penzias and Wilson were awarded a Nobel Prize for their discovery.

The cosmic microwave background spectrum measured by the FIRAS instrument on the COBE satellite is the most-precisely measured black body spectrum in nature.^[57] The data points and error bars on this graph are obscured by the theoretical curve.

In 1989 NASA launched the Cosmic Background Explorer satellite (COBE), and the initial findings, released in 1990, were consistent with the Big Bang's predictions regarding the CMB. COBE found a residual temperature of 2.726 K and in 1992 detected for the first time the fluctuations (anisotropies) in the CMB, at a level of about one part in 10⁵.^[36] John C. Mather and George Smoot were awarded the Nobel Prize for their leadership in this work. During the following decade, CMB anisotropies were further investigated by a large number of ground-based and balloon experiments. In 2000–2001 several experiments, most notably BOOMERanG, found the Universe to be almost spatially flat by measuring the typical angular size (the size on the sky) of the anisotropies. (See shape of the Universe.)
In early 2003 the first results of the Wilkinson Microwave Anisotropy Probe (WMAP) were released, yielding what were at the time the most accurate values for some of the cosmological parameters. This spacecraft also disproved several specific cosmic inflation models, but the results were consistent with the inflation theory in general,^[37] it confirms too that a sea of cosmic neutrinos permeates the Universe, a clear evidence that the first stars took more than a half-billion years to create a cosmic fog. A new space probe named Planck, with goals similar to WMAP, was launched in May 2009. It is anticipated to soon provide even more accurate measurements of the CMB anisotropies. Many other ground- and balloon-based experiments are also currently running; see Cosmic microwave background experiments.
The background radiation is exceptionally smooth, which presented a problem in that conventional expansion would mean that photons coming from opposite directions in the sky were coming from regions that had never been in contact with each other. The leading explanation for this far reaching equilibrium is that the Universe had a brief period of rapid exponential expansion, called inflation. This would have the effect of driving apart regions that had been in equilibrium, so that all the observable Universe was from the same equilibrated region.

Abundance of primordial elements

Main article: Big Bang nucleosynthesis

Using the Big Bang model it is possible to calculate the concentration of helium-4, helium-3, deuterium and lithium-7 in the Universe as ratios to the amount of ordinary hydrogen, H.^[46] All the abundances depend on a single parameter, the ratio of photons to baryons, which itself can be calculated independently from the detailed structure of CMB fluctuations. The ratios predicted (by mass, not by number) are about 0.25 for 4He/H, about 10⁻³ for 2H/H, about 10⁻⁴ for 3He/H and about 10⁻⁹ for 7Li/H.^[46]
The measured abundances all agree at least roughly with those predicted from a single value of the baryon-to-photon ratio. The agreement is excellent for deuterium, close but formally discrepant for 4He, and a factor of two off for 7Li; in the latter two cases there are substantial systematic uncertainties. Nonetheless, the general consistency with abundances predicted by BBN is strong evidence for the Big Bang, as the theory is the only known explanation for the relative abundances of light elements, and it is virtually impossible to "tune" the Big Bang to produce much more or less than 20–30% helium.^[58] Indeed there is no obvious reason outside of the Big Bang that, for example, the young Universe (i.e., before star formation, as determined by studying matter supposedly free of stellar nucleosynthesis products) should have more helium than deuterium or more deuterium than 3He, and in constant ratios, too.

Galactic evolution and distribution

Main articles: Large-scale structure of the cosmos, Structure formation, and Galaxy formation and evolution

This panoramic view of the entire near-infrared sky reveals the distribution of galaxies beyond the Milky Way. The galaxies are color coded by redshift.

Detailed observations of the morphology and distribution of galaxies and quasars provide strong evidence for the Big Bang. A combination of observations and theory suggest that the first quasars and galaxies formed about a billion years after the Big Bang, and since then larger structures have been forming, such as galaxy clusters and superclusters. Populations of stars have been aging and evolving, so that distant galaxies (which are observed as they were in the early Universe) appear very different from nearby galaxies (observed in a more recent state). Moreover, galaxies that formed relatively recently appear markedly different from galaxies formed at similar distances but shortly after the Big Bang. These observations are strong arguments against the steady-state model. Observations of star formation, galaxy and quasar distributions and larger structures agree well with Big Bang simulations of the formation of structure in the Universe and are helping to complete details of the theory.^[59]^[60]

Primordial gas clouds

In 2011 astronomers have found pristine clouds of the primordial gas that formed in the first few minutes after the Big Bang. The composition of the gas matches theoretical predictions, providing direct evidence in support of the modern cosmological explanation for the origins of elements in the universe. The researchers discovered the two clouds of pristine gas by analyzing the light from distant quasars, using the HIRES spectrometer on the Keck I Telescope at the W. M. Keck Observatory in Hawaii. They saw absorption lines in the spectrum where the light was absorbed by the gas, and that allows them to measure the composition of the gas.^[61]^[62]

Other lines of evidence

The age of Universe as estimated from the Hubble expansion and the CMB is now in good agreement with other estimates using the ages of the oldest stars, both as measured by applying the theory of stellar evolution to globular clusters and through radiometric dating of individual Population II stars.^[63]
The prediction that the CMB temperature was higher in the past has been experimentally supported by observations of very low temperature absorption lines in gas clouds at high redshift.^[64] This prediction also implies that the amplitude of the Sunyaev–Zel'dovich effect in clusters of galaxies does not depend directly on redshift. Observations have found this to be roughly true, but this effect depends on cluster properties that do change with cosmic time, making precise measurements difficult.^[65]^[66]

Features, issues and problems

While scientists now support the Big Bang model over other cosmological models, the scientific community was once divided between supporters of the Big Bang and those of alternative cosmological models. Throughout the historical development of the subject, problems with the Big Bang theory were posed in the context of a scientific controversy regarding which model could best describe the cosmological observations. With the overwhelming consensus in the community today supporting the Big Bang model, many of these problems are remembered as being mainly of historical interest; the solutions to them have been obtained either through modifications to the theory or as the result of better observations.
The core ideas of the Big Bang—the expansion, the early hot state, the formation of helium, the formation of galaxies—are derived from many observations that are independent from any cosmological model; these include the abundance of light elements, the cosmic microwave background, large scale structure, and the Hubble diagram for Type Ia supernovae.
Precise modern models of the Big Bang appeal to various exotic physical phenomena that have not been observed in terrestrial laboratory experiments or incorporated into the Standard Model of particle physics. Of these features, dark matter is currently the subject to the most active laboratory investigations.^[67] Remaining issues, such as the cuspy halo problem and the dwarf galaxy problem of cold dark matter, are not fatal to the dark matter explanation as solutions to such problems exist which involve only further refinements of the theory. Dark energy is also an area of intense interest for scientists, but it is not clear whether direct detection of dark energy will be possible.^[68]
On the other hand, inflation and baryogenesis remain somewhat more speculative features of current Big Bang models: they explain important features of the early universe, but could be replaced by alternative ideas without affecting the rest of the theory.^{[notes 5]}^{[citation needed]} Viable, quantitative explanations for such phenomena are still being sought. These are currently unsolved problems in physics.

Horizon problem

Main article: Horizon problem

The horizon problem results from the premise that information cannot travel faster than light. In a Universe of finite age this sets a limit—the particle horizon—on the separation of any two regions of space that are in causal contact.^[69] The observed isotropy of the CMB is problematic in this regard: if the Universe had been dominated by radiation or matter at all times up to the epoch of last scattering, the particle horizon at that time would correspond to about 2 degrees on the sky. There would then be no mechanism to cause wider regions to have the same temperature.
A resolution to this apparent inconsistency is offered by inflationary theory in which a homogeneous and isotropic scalar energy field dominates the Universe at some very early period (before baryogenesis). During inflation, the Universe undergoes exponential expansion, and the particle horizon expands much more rapidly than previously assumed, so that regions presently on opposite sides of the observable Universe are well inside each other's particle horizon. The observed isotropy of the CMB then follows from the fact that this larger region was in causal contact before the beginning of inflation.
Heisenberg's uncertainty principle predicts that during the inflationary phase there would be quantum thermal fluctuations, which would be magnified to cosmic scale. These fluctuations serve as the seeds of all current structure in the Universe. Inflation predicts that the primordial fluctuations are nearly scale invariant and Gaussian, which has been accurately confirmed by measurements of the CMB.
If inflation occurred, exponential expansion would push large regions of space well beyond our observable horizon.

Flatness (oldness) problem

Main article: Flatness problem

The overall geometry of the Universe is determined by whether the Omega cosmological parameter is less than, equal to or greater than 1. Shown from top to bottom are a closed Universe with positive curvature, a hyperbolic Universe with negative curvature and a flat Universe with zero curvature.

The flatness problem (also known as the oldness problem) is an observational problem associated with a Friedmann–Lemaître–Robertson–Walker metric.^[69] The Universe may have positive, negative or zero spatial curvature depending on its total energy density. Curvature is negative if its density is less than the critical density, positive if greater, and zero at the critical density, in which case space is said to be flat. The problem is that any small departure from the critical density grows with time, and yet the Universe today remains very close to flat.^{[notes 6]} Given that a natural timescale for departure from flatness might be the Planck time, 10⁻⁴³ seconds, the fact that the Universe has reached neither a heat death nor a Big Crunch after billions of years requires some explanation. For instance, even at the relatively late age of a few minutes (the time of nucleosynthesis), the Universe density must have been within one part in 10¹⁴ of its critical value, or it would not exist as it does today.^[70]
A resolution to this problem is offered by inflationary theory. During the inflationary period, spacetime expanded to such an extent that its curvature would have been smoothed out. Thus, it is theorized that inflation drove the Universe to a very nearly spatially flat state, with almost exactly the critical density.

Magnetic monopoles

Main article: Magnetic monopole

The magnetic monopole objection was raised in the late 1970s. Grand unification theories predicted topological defects in space that would manifest as magnetic monopoles. These objects would be produced efficiently in the hot early Universe, resulting in a density much higher than is consistent with observations, given that searches have never found any monopoles. This problem is also resolved by cosmic inflation, which removes all point defects from the observable Universe in the same way that it drives the geometry to flatness.^[69]
A resolution to the horizon, flatness, and magnetic monopole problems alternative to cosmic inflation is offered by the Weyl curvature hypothesis.^[71]^[72]

Baryon asymmetry

Main article: Baryon asymmetry

It is not yet understood why the Universe has more matter than antimatter.^[44] It is generally assumed that when the Universe was young and very hot, it was in statistical equilibrium and contained equal numbers of baryons and antibaryons. However, observations suggest that the Universe, including its most distant parts, is made almost entirely of matter. A process called baryogenesis was hypothesized to account for the asymmetry. For baryogenesis to occur, the Sakharov conditions must be satisfied. These require that baryon number is not conserved, that C-symmetry and CP-symmetry are violated and that the Universe depart from thermodynamic equilibrium.^[73] All these conditions occur in the Standard Model, but the effect is not strong enough to explain the present baryon asymmetry.

Globular cluster age

In the mid-1990s observations of globular clusters appeared to be inconsistent with the Big Bang. Computer simulations that matched the observations of the stellar populations of globular clusters suggested that they were about 15 billion years old, which conflicted with the 13.7 billion year age of the Universe. This issue was generally resolved in the late 1990s when new computer simulations, which included the effects of mass loss due to stellar winds, indicated a much younger age for globular clusters.^[74] There still remain some questions as to how accurately the ages of the clusters are measured, but it is clear that these objects are some of the oldest in the Universe.

Dark matter

Main article: Dark matter

A pie chart indicating the proportional composition of different energy-density components of the Universe, according to the best ΛCDM model fits – roughly 95% is in the exotic forms of dark matter and dark energy

During the 1970s and 1980s, various observations showed that there is not sufficient visible matter in the Universe to account for the apparent strength of gravitational forces within and between galaxies. This led to the idea that up to 90% of the matter in the Universe is dark matter that does not emit light or interact with normal baryonic matter. In addition, the assumption that the Universe is mostly normal matter led to predictions that were strongly inconsistent with observations. In particular, the Universe today is far more lumpy and contains far less deuterium than can be accounted for without dark matter. While dark matter was initially controversial, it is now indicated by numerous observations: the anisotropies in the CMB, galaxy cluster velocity dispersions, large-scale structure distributions, gravitational lensing studies, and X-ray measurements of galaxy clusters.^[75]
The evidence for dark matter comes from its gravitational influence on other matter, and no dark matter particles have been observed in laboratories. Many particle physics candidates for dark matter have been proposed, and several projects to detect them directly are underway.^[76]

Dark energy

Main article: Dark energy

Measurements of the redshift–magnitude relation for type Ia supernovae indicate that the expansion of the Universe has been accelerating since the Universe was about half its present age. To explain this acceleration, general relativity requires that much of the energy in the Universe consists of a component with large negative pressure, dubbed "dark energy". Dark energy is indicated by several other lines of evidence. Measurements of the cosmic microwave background indicate that the Universe is very nearly spatially flat, and therefore according to general relativity the Universe must have almost exactly the critical density of mass/energy. But the mass density of the Universe can be measured from its gravitational clustering, and is found to have only about 30% of the critical density.^[21] Since dark energy does not cluster in the usual way it is the best explanation for the "missing" energy density. Dark energy is also required by two geometrical measures of the overall curvature of the Universe, one using the frequency of gravitational lenses, and the other using the characteristic pattern of the large-scale structure as a cosmic ruler.
Negative pressure is a property of vacuum energy, but the exact nature of dark energy remains one of the great mysteries of the Big Bang. Possible candidates include a cosmological constant and quintessence. Results from the WMAP team in 2008, which combined data from the CMB and other sources, indicate that the contributions to mass/energy density in the Universe today are approximately 73% dark energy, 23% dark matter, 4.6% regular matter and less than 1% neutrinos.^[41] The energy density in matter decreases with the expansion of the Universe, but the dark energy density remains constant (or nearly so) as the Universe expands. Therefore matter made up a larger fraction of the total energy of the Universe in the past than it does today, but its fractional contribution will fall in the far future as dark energy becomes even more dominant.
In the ΛCDM, the best current model of the Big Bang, dark energy is explained by the presence of a cosmological constant in the general theory of relativity. However, the size of the constant that properly explains dark energy is surprisingly small relative to naive estimates based on ideas about quantum gravity. Distinguishing between the cosmological constant and other explanations of dark energy is an active area of current research.

The future according to the Big Bang theory

Main article: Ultimate fate of the universe

Before observations of dark energy, cosmologists considered two scenarios for the future of the Universe. If the mass density of the Universe were greater than the critical density, then the Universe would reach a maximum size and then begin to collapse. It would become denser and hotter again, ending with a state that was similar to that in which it started—a Big Crunch.^[52] Alternatively, if the density in the Universe were equal to or below the critical density, the expansion would slow down, but never stop. Star formation would cease as all the interstellar gas in each galaxy is consumed; stars would burn out leaving white dwarfs, neutron stars, and black holes. Very gradually, collisions between these would result in mass accumulating into larger and larger black holes. The average temperature of the Universe would asymptotically approach absolute zero—a Big Freeze. Moreover, if the proton were unstable, then baryonic matter would disappear, leaving only radiation and black holes. Eventually, black holes would evaporate by emitting Hawking radiation. The entropy of the Universe would increase to the point where no organized form of energy could be extracted from it, a scenario known as heat death.
Modern observations of accelerated expansion imply that more and more of the currently visible Universe will pass beyond our event horizon and out of contact with us. The eventual result is not known. The ΛCDM model of the Universe contains dark energy in the form of a cosmological constant. This theory suggests that only gravitationally bound systems, such as galaxies, would remain together, and they too would be subject to heat death, as the Universe expands and cools. Other explanations of dark energy—so-called phantom energy theories—suggest that ultimately galaxy clusters, stars, planets, atoms, nuclei and matter itself will be torn apart by the ever-increasing expansion in a so-called Big Rip.^[77]

Speculative physics beyond Big Bang theory

This is an artist's concept of the Universe expansion, where space (including hypothetical non-observable portions of the Universe) is represented at each time by the circular sections. Note on the left the dramatic expansion (not to scale) occurring in the inflationary epoch, and at the center the expansion acceleration. The scheme is decorated with WMAP images on the left and with the representation of stars at the appropriate level of development.

While the Big Bang model is well established in cosmology, it is likely to be refined in the future. Little is known about the earliest moments of the Universe's history. The equations of classical general relativity indicate a singularity at the origin of cosmic time, although this conclusion depends on several assumptions. Moreover, general relativity must break down before the Universe reaches the Planck temperature, and a correct treatment of quantum gravity may avoid the would-be singularity.^[78]
Some proposals, each of which entails untested hypotheses, are:

models including the Hartle–Hawking no-boundary condition in which the whole of space-time is finite; the Big Bang does represent the limit of time, but without the need for a singularity.^[79]
Big Bang lattice model ^[80] states that the Universe at the moment of the Big Bang consists of an infinite lattice of fermions which is smeared over the fundamental domain so it has both rotational, translational and gauge symmetry. The symmetry is the largest symmetry possible and hence the lowest entropy of any state.

brane cosmology models^[81] in which inflation is due to the movement of branes in string theory; the pre-Big Bang model; the ekpyrotic model, in which the Big Bang is the result of a collision between branes; and the cyclic model, a variant of the ekpyrotic model in which collisions occur periodically. In the latter model the Big Bang was preceded by a Big Crunch and the Universe endlessly cycles from one process to the other.^[82]^[83]^[84]
eternal inflation, in which universal inflation ends locally here and there in a random fashion, each end-point leading to a bubble universe expanding from its own big bang.^[85]^[86]

Proposals in the last two categories see the Big Bang as an event in a much larger and older Universe, or multiverse, and not the literal beginning.

Religious and philosophical implications

Main article: Religious interpretations of the Big Bang theory

The Big Bang is a scientific theory, and as such is dependent on its agreement with observations. But as a theory which addresses the origins of reality it carries theological implications regarding the concept of creation ex nihilo (a Latin phrase meaning "out of nothing");^[87]^[88]^[89] according to the Oxford professor Peter Harrison, discussions of the Big Bang's religious implications "constitute one of the liveliest areas of contemporary science-religion interchange."^[90]

Lighter

2012-03-31T10:26:00.000-07:00

A lighter is a portable device used to generate a flame. It consists of a metal or plastic container filled with a flammable fluid or pressurized liquid gas, a means of ignition, and some provision for extinguishing the flame.

History

The first lighters were invented in the 16th century and were converted flintlock pistols that used gunpowder. One of the first lighters was invented by the German chemist named Johann Wolfgang Döbereiner in 1823 and was often called Döbereiner's lamp.^[1] This lighter worked by a reaction of hydrogen to platinum sponge, which gave off a great amount of heat. The device was very large and highly dangerous and fell out of production by the end of the 19th century.^[1]
The patenting of ferrocerium (often misidentified as flint) by Carl Auer von Welsbach in 1903 has made modern lighters possible. When scratched, it produces a large spark which is responsible for lighting the fuel of many lighters, and is suitably inexpensive for use in disposable items.
Using Carl Auer von Welsbach's flint, companies like Ronson were able to develop practical and easy to use lighters. In 1910 Ronson released the first Pist-O-Liter and in 1913 the company developed its first lighter, called the "Wonderlite", which was a permanent match style of lighter.^[2]
The Zippo lighter and company were invented and founded by George G. Blaisdell in 1932. The Zippo was noted for its reliability, "Life Time Warranty" and marketing as "Wind-Proof".^[3] Most early Zippos used naphtha as a fuel source.
In the 1950s there was a switch in fuel choice from naphtha to butane, as butane allows for a controllable flame and has less odour.^[4] This also led to the use of piezoelectric spark, which replaced the need for a flint wheel in some lighters and was used in many Ronson lighters.

Operation

Naphtha (very similar to gasoline) based lighters employ a saturated cloth wick and fibre packing to absorb the fluid and prevent it from leaking. They employ an enclosed top to prevent the volatile liquid from evaporating, and to conveniently extinguish the flame. Butane lighters have a valved orifice that meters the butane gas as it escapes.
A spark is created by striking metal against a flint, or by pressing a button that compresses a piezoelectric crystal (piezo ignition), generating an electric arc. In naphtha lighters, the liquid is sufficiently volatile, and flammable vapour is present as soon as the top of the lighter is opened. Butane lighters combine the striking action with the opening of the valve to release gas. The spark ignites the flammable gas causing a flame to come out of the lighter which continues until either the top is closed (naphtha type), or the valve is released (butane type).
A metal enclosure with air holes generally surrounds the flame, and is designed to allow mixing of fuel and air while making the lighter less sensitive to wind. The high energy jet in butane lighters allows mixing to be accomplished by using Bernoulli's principle, so that the air hole(s) in this type tend to be much smaller and farther from the flame.
Specialized "windproof" butane lighters are manufactured for demanding conditions such as shipboard, high altitude, and wet climates. Some dedicated models double as synthetic rope cutters. Such lighters are often far hotter than normal lighters (those that use a "soft flame") and can burn in excess of 1100 °C. Contrary to common misconception, the windproof capabilities are not achieved from "higher pressure" fuel. Windproof lighters use the same fuel (butane) as standard lighters, and therefore develop the same vapour pressure. The difference is that windproof lighters mix the fuel with air, and may also pass the butane/air mixture through a catalytic coil. An electric spark starts the initial flame, and soon after the coil is hot enough to sustain a catalytic reaction and cause the fuel/air mixture to burn on contact. In essence, the flame is constantly reignited by the coil.

Other types

Permanent match

A typical form of lighter is the everlasting match, consisting of a naphtha fuel-filled metal shell and a separate threaded metal rod assembly —the "match"— serving as the striker and wick. This "metal match" is stored screwed into the fuel storage compartment, the shell. (see photo)
The fuel-saturated striker/wick assembly is unscrewed to remove, and scratched against a flint on the side of the case to create a spark. Its concealed wick catches fire, resembling a match. The flame is extinguished by screwing the "match" back into the shell, where it absorbs fuel for the next use. An advantage over other naphtha lighters is that the fuel compartment is sealed shut with a rubber o-ring, which slows or stops fuel evaporation.

Flame-less lighter

A flame-less lighter is the safe alternative to traditional lighters. The flameless lighter uses an enclosed heating element, thus, the device does not emit an open flame. Typical flameless heating elements are an electrically heated wire or an artificial coal.
Flameless lighters are designed for use in any environment where an open flame must not exist or where conventional lighters or matches are not permitted.
Many advertised so-called flameless lighters are not flameless at all, but the flame is invisible. If a piece of paper can be easily ignited, it is probably not a true flameless lighter, and certainly not safe in explosive environments and so forth.

Automobile lighter

Some automobiles are equipped with an electric lighter housed in a 12 V receptacle. Its electric heating element becomes hot in seconds upon activation. The car lighter was claimed to have been invented by Alexander Kucala, a tavern owner/ inventor, on the south side of Chicago in the early 1920's called the AL Lighter.

Safety

Two technical standards relate to the safety of lighters: the International Standard EN ISO 9994:2002^[5] and the European standard EN 13869:2002.^[6]
The International Standard establishes non-functional specifications on quality, reliability and safety of lighters and appropriate test procedures. For instance, a lighter should generate flame only through positive action on the part of the user, two or more independent actions by the user, or an actuating force greater than or equal to 15 N. The standard also specifies other safety features, such as the lighter's maximum flame height and its resistance to elevated temperatures, dropping, and damages from continuous burning. However, the standard does not include child resistance specifications.
The European standard EN 13869:2002^[6] establishes child-resistance specifications and defines as novelty lighters those that resemble another object commonly recognized as appealing to children younger than 51 months, or those that have entertaining audio or animated effects.
As matches, lighters, and other heat sources are the leading causes of fire deaths for children,^[7] many jurisdictions, such as the EU,^[8] have forbidden the marketing of novelty or non-child resistant lighters. Examples of child resistance features, include the use of a smooth or shielded spark wheel. Many people remove the child proofing from lighters by prying off the metal with scissors or keys, making the lighter easier to ignite.
In 2005 the fourth edition of the ISO standard was released (ISO9994:2005). The main change to the 2004 Standard is the inclusion of specifications on safety symbols.

Why is the Sky Blue

2012-03-30T06:56:00.001-07:00

A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.

The white light from the sun is a mixture of all colours of the rainbow. This was demonstrated by Isaac Newton, who used a prism to separate the different colours and so form a spectrum. The colours of light are distinguished by their different wavelengths. The visible part of the spectrum ranges from red light with a wavelength of about 720 nm, to violet with a wavelength of about 380 nm, with orange, yellow, green, blue and indigo between. The three different types of colour receptors in the retina of the human eye respond most strongly to red, green and blue wavelengths, giving us our colour vision.

Tyndall Effect

The first steps towards correctly explaining the colour of the sky were taken by John Tyndall in 1859. He discovered that when light passes through a clear fluid holding small particles in suspension, the shorter blue wavelengths are scattered more strongly than the red. This can be demonstrated by shining a beam of white light through a tank of water with a little milk or soap mixed in. From the side, the beam can be seen by the blue light it scatters; but the light seen directly from the end is reddened after it has passed through the tank. The scattered light can also be shown to be polarised using a filter of polarised light, just as the sky appears a deeper blue through polaroid sun glasses.
This is most correctly called the Tyndall effect, but it is more commonly known to physicists as Rayleigh scattering—after Lord Rayleigh, who studied it in more detail a few years later. He showed that the amount of light scattered is inversely proportional to the fourth power of wavelength for sufficiently small particles. It follows that blue light is scattered more than red light by a factor of (700/400)⁴ ~= 10.

Dust or Molecules?

Tyndall and Rayleigh thought that the blue colour of the sky must be due to small particles of dust and droplets of water vapour in the atmosphere. Even today, people sometimes incorrectly say that this is the case. Later scientists realised that if this were true, there would be more variation of sky colour with humidity or haze conditions than was actually observed, so they supposed correctly that the molecules of oxygen and nitrogen in the air are sufficient to account for the scattering. The case was finally settled by Einstein in 1911, who calculated the detailed formula for the scattering of light from molecules; and this was found to be in agreement with experiment. He was even able to use the calculation as a further verification of Avogadro's number when compared with observation. The molecules are able to scatter light because the electromagnetic field of the light waves induces electric dipole moments in the molecules.

Why not violet?

If shorter wavelengths are scattered most strongly, then there is a puzzle as to why the sky does not appear violet, the colour with the shortest visible wavelength. The spectrum of light emission from the sun is not constant at all wavelengths, and additionally is absorbed by the high atmosphere, so there is less violet in the light. Our eyes are also less sensitive to violet. That's part of the answer; yet a rainbow shows that there remains a significant amount of visible light coloured indigo and violet beyond the blue. The rest of the answer to this puzzle lies in the way our vision works. We have three types of colour receptors, or cones, in our retina. They are called red, blue and green because they respond most strongly to light at those wavelengths. As they are stimulated in different proportions, our visual system constructs the colours we see.

Response curves for the three types of cone in the human eye

When we look up at the sky, the red cones respond to the small amount of scattered red light, but also less strongly to orange and yellow wavelengths. The green cones respond to yellow and the more strongly scattered green and green-blue wavelengths. The blue cones are stimulated by colours near blue wavelengths, which are very strongly scattered. If there were no indigo and violet in the spectrum, the sky would appear blue with a slight green tinge. However, the most strongly scattered indigo and violet wavelengths stimulate the red cones slightly as well as the blue, which is why these colours appear blue with an added red tinge. The net effect is that the red and green cones are stimulated about equally by the light from the sky, while the blue is stimulated more strongly. This combination accounts for the pale sky blue colour. It may not be a coincidence that our vision is adjusted to see the sky as a pure hue. We have evolved to fit in with our environment; and the ability to separate natural colours most clearly is probably a survival advantage.

A multicoloured sunset over the Firth of Forth in Scotland.

Sunsets

When the air is clear the sunset will appear yellow, because the light from the sun has passed a long distance through air and some of the blue light has been scattered away. If the air is polluted with small particles, natural or otherwise, the sunset will be more red. Sunsets over the sea may also be orange, due to salt particles in the air, which are effective Tyndall scatterers. The sky around the sun is seen reddened, as well as the light coming directly from the sun. This is because all light is scattered relatively well through small angles—but blue light is then more likely to be scattered twice or more over the greater distances, leaving the yellow, red and orange colours.

A blue haze over the mountains of Les Vosges in France.

Blue Haze and Blue Moon

Clouds and dust haze appear white because they consist of particles larger than the wavelengths of light, which scatter all wavelengths equally (Mie scattering). But sometimes there might be other particles in the air that are much smaller. Some mountainous regions are famous for their blue haze. Aerosols of terpenes from the vegetation react with ozone in the atmosphere to form small particles about 200 nm across, and these particles scatter the blue light. A forest fire or volcanic eruption may occasionally fill the atmosphere with fine particles of 500—800 nm across, being the right size to scatter red light. This gives the opposite to the usual Tyndall effect, and may cause the moon to have a blue tinge since the red light has been scattered out. This is a very rare phenomenon, occurring literally once in a blue moon.

Opalescence

The Tyndall effect is responsible for some other blue coloration's in nature: such as blue eyes, the opalescence of some gem stones, and the colour in the blue jay's wing. The colours can vary according to the size of the scattering particles. When a fluid is near its critical temperature and pressure, tiny density fluctuations are responsible for a blue coloration known as critical opalescence. People have also copied these natural effects by making ornamental glasses impregnated with particles, to give the glass a blue sheen. But not all blue colouring in nature is caused by scattering. Light under the sea is blue because water absorbs longer wavelength of light through distances over about 20 metres. When viewed from the beach, the sea is also blue because it reflects the sky, of course. Some birds and butterflies get their blue colorations by diffraction effects.

Why is the Mars sky red?

Images sent back from the Viking Mars landers in 1977 and from Pathfinder in 1997 showed a red sky seen from the Martian surface. This was due to red iron-rich dusts thrown up in the dust storms occurring from time to time on Mars. The colour of the Mars sky will change according to weather conditions. It should be blue when there have been no recent storms, but it will be darker than the earth's daytime sky because of Mars' thinner atmosphere.

Hydophone: Designs And Principle

2012-03-30T00:51:00.001-07:00

Introduction

Any systems (except for communication) which employ underwater acoustics energy are called sonar. It is a branch of applied acoustics that utilizes water as propagating medium [1]. Receiver (hydrophone) is compulsory for every sonar system to detect underwater sound. Only active sonar system utilizes transmitter [2]. Sonar system manipulates longitudinal characteristics of acoustical waves underwater. Longitudinal (irrotational) parameters include pressure, particle displacement, particle velocity, medium density, specific impedance, energy transfer speed, wavelength and temperature [3]. Physics behind sonar receiver is as simple as converting acoustics signal into electrical signals. The design should comply correct resolution and enough sensitivity to detect not only transmitted signal by transmitter (in active sonar system), but whole underwater noises within desired range. Hydrophones age nearly reach 100 years. From the first design patented in 1919 until the latest one; there were just too great advancements made in both performance and size, only a little will be discuss here.

Materials and Designs

The heart of hydrophone is piezoelectric (pressure-electric) device/material. Piezoelectric effect occurs naturally in a material when it physical dimensions changes upon application of pressure and produces electrical field. Piezoelectric effect is also reversible theoretically and in many occasions practically. This effect could be achieved using mechanically assemble components. However, in natural piezoelectric materials, effect occurs when a material consist of innumerable electric dipoles. A stress could cause a deformation of a material and reorientation of the dipoles induces net charges between electrodes. Several piezoelectric materials (not natural) are lead zirconate titanate ceramic (Pb(Zr,Ti)O3) or PZT, lead metaniobate (PbNb2O6), barium titanite (BaTiO3) and lithium niobate (LiNbO3). Certain PZT can be doped for better piezoelectric properties.

One of the earliest hydrophones [4] was sealed in the container for complete submersible operation as shown in Fig. 1. It contains circular metal diaphragm placed in the circular rim and tightly attached to the metal plate, with button type microphone placed in the center chamber.

Conducting leads was attached as output terminals and sent from container through water-proof clamp. Operating principles is very simple. Acoustics pressure will vibrate the diaphragm. Vibrating diaphragm then generates sound inside the center chamber, and the secondary generated sounds will be detected by microphone.

This design suffered from several weaknesses. It confused by the noise generated by ship engine. Proper calibration could not be done properly since it contains moving mechanical parts as transducer which worsens the resolution and sensitivity. During 1950s, capacitive-type hydrophone was introduced [5]. Details cross-section design of hydrophone shows in Fig. 2.

Fig. 1: First patented hydrophone design.

When immersed in the water, any pressure changes detected by bag, as a diaphragm. Capacitance between water and electrode will change as the function of the pressure, since the size of air cells also changed. Capacitance changes are then converted in electrical signal by any method. Compare to the previous design, it was simpler and cheaper, but lack of versatility when only capable of detecting low frequency signal. During 1960s, hydrophone design is totally depends on piezoelectric materials [6]. Almost all design follows the same pattern as shown in Fig. 3. This design employs a stack of piezoelectric plates as active material. By using stacked configuration, higher capacitance or lower impedance is obtainable. Cover and housing usually is made from flexible material such as rubber to sustain hydrostatic pressure. Fluid medium fills the entire volume between stack and cover. Produced electrical field by plates was sent through electrodes to the pre-amplifier, filter and conditioning circuits.

Arrays

Arrays are transducer assemblies with more than one element. These elements may be in line, rectangular and square in shapes, ring shaped and circular array. Hydrophone array also may be a combination of one of those for example linear array in three-dimensional arrangements. By using array, signals can be added from the desired direction while subtracted signals from other directions. Usually, array of hydrophones (and transmitter) is controlled by beamformer. Studying array requires deeper knowledge in signal processing. It deals with complicated mathematical model, complex analyses and parametric estimation, depending to the type of array [7-9].

Submarine Principles and Design

2012-03-30T00:47:00.000-07:00

A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has only limited underwater capability.

The term submarine most commonly refers to large crewed autonomous vessels; however, historically or more casually, submarine can also refer to medium sized or smaller vessels (midget submarines, wet subs), Remotely Operated Vehicles or robots.

The word submarine was originally an adjective meaning "under the sea” and so consequently other uses such as "submarine engineering" or "submarine cable" may not actually refer to submarines at all. Submarine was shortened from the term "submarine boat", and is often further shortened to "sub".

Submarines are referred to as "boats" for historical reasons because vessels deployed from a ship are referred to as boats. The first submarines were launched in such a manner. The English term U-boat for a German submarine comes from the German word for submarine, U-Boot, itself an abbreviation for Unterseeboot ("undersea boat"). [wikipedia].

The submarine operates using the Archimedes' principle by manipulating the buoyancy.

The buoyancy is controlled by the ballast tank system. A submarine resting on the surface has positive buoyancy, which means it is less dense than the water around it and will float. At this time, the ballast tanks are mainly full of air. To submerge, the submarine must have negative buoyancy. Vents of the ballast tanks are opened.

Seawater coming in through the flood ports forces air out the vents, and the submarine begins to sink. The submarine ballast tanks now filled with seawater is denser than the surrounding water. The exact depth can be controlled by adjusting the water to air ratio in the ballast tanks. Submerged,

the submarine can obtain neutral buoyancy. That means the weight of the submarine equals the amount of water it displaces. The submarine will neither rise nor sink in this state. To make the submarine rise again, compressed air is simply blown into the tanks forcing the seawater out. The submarine gains positive buoyancy becomes less dense than the water and rises.

In current design concept of the submarines modularity at design level, construction and manufacturing contributes the main factor for efficiency in building a submarine.
For example Malaysian Scorpene Submarines constructions are being held at France and Spain shipyards. Beside the modularity the main factor for safety design is to improve acoustic detection by improving the sonar performances, data computations performances, reduce the hydrodynamics and self noise.
In most submarines design all the equipments shall not linked directly to the pressure hull and elastic mounting system to reduce the vibration level on ship. Some design used the suspended platforms and cradles to fit these requirements.

Sonar stands for (Sound Navigation & Ranging) are the main navigation subsystem for submarine. It becomes an eye for the submarine during underwater operation since there is no direct manual visibility.
For underwater applications the acoustic signals are being manipulated for ensuring safety for the submarine to avoid any obstacles and threats.
The main functions for sonar subsystem are for detection in active or passive mode, tracking, localization, acoustic classification and obstacle avoidance.

Cylindrical Array: Main sonar for medium range detection.

Frank Array: Second main sonar for long range detection.

Distributed Array: Sonar for short and medium range detection.

Intercept Array: Sensor for pulse detection.

Active Array: Sonar for active ranging.

Mine Avoidance Array: Sonar for short range and objects detection.