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Space News this Week: An ESA Spacecraft, New Moon Images, and Solar-Electric Propulsion

2011-07-06T17:55:00.002+05:30

A new European re-entry vehicle, unprecedented moon images, and a call for solar electric propulsion systems.

ESA Spacecraft

ESA's Intermediate eXperimental Vehicle

The European Space Agency announced that its re-entry spacecraft, called Intermediate eXperimental Vehicle (IXV), will be ready to fly in 2013. The agency first announced the vehicle concept in 2009. Now the detailed design and technologies are ready and the agency has partnered with Thales Alenia Space Italia to manufacture the vehicle. Its first flight will be in 2013.

Europe's ambition for a spacecraft to return autonomously from low orbit is a cornerstone for a wide range of space applications, including space transportation, exploration and robotic servicing of space infrastructure.

This goal will be achieved with IXV, which is the next step from the Atmospheric Reentry Demonstrator flight of 1998. More maneuverable and able to make precise landings, IXV is the 'intermediate' element of Europe's path to future developments with limited risks.

The new spacecraft, which resembles a wing-less space shuttle and it s test vehicle, will launch aboard a small ESA rocket, reaching an altitude of 450 kilometers. It will test technologies like advanced thermal protection systems, new guidance, navigation and control systems, and will collect lots of data. It will operate autonomously. It could be proving ground for ESA to develop a vehicle that can travel to the space station or other destinations.

Moon Images

Data from seven instruments onboard NASA's Lunar Reconnaissance Orbiter (LRO), a spacecraft orbiting the moon since 2009, have provided amazing detailed images and maps of the moon's surface, showing craters and topography that have never before been seen.

According to the NASA press release,

The most precise and complete topographic maps to date of the moon's complex, heavily cratered landscape have been created from the more than 4 billion measurements -- and still counting -- taken by LRO's Lunar Orbiter Laser Altimeter (LOLA). These maps are more accurate and sample more places on the lunar surface than any available before. In fact, LOLA has taken more than 100 times more measurements than all previous lunar instruments of its kind combined, opening up a world of possibilities for future exploration and for science.

Already, researchers have used LOLA data to put together the first comprehensive set of maps of the roughness of the moon's surface. Like wrinkles on skin, the roughness of craters and other fetures on the moon's surface can reveal their age. By looking at where and how the roughness changes -- and by combining that information with contour maps that show where the high and low points are -- researchers can get important clues about the processes that shaped the moon.

Solar Electric Propulsion

To reach destinations beyond low Earth orbit spacecraft needs propulsion systems that are efficient and powerful. Chemical propulsion systems are most commonly used for spacecraft, but they require large amounts of fuel and are inefficient for deep space missions. Now NASA is seeking proposals for mission concepts of solar electric propulsion systems. The systems use solar panels to generate electricity that gives a positive charge to atoms inside a chamber, which are pulled by magnetism towards the back of the spacecraft and pushed out. The stream of atoms going out of the spacecraft gives it the thrust it needs to move through space. (The agency tested an ion-propulsion system it developed in 2009 and expects it to launch in 2013.)

More surprises for the Voyager mission at the edge of the solar system

2011-07-05T13:02:00.001+05:30

Voyager spacecrafts in the heliosheath

Unexpected observations by NASA's Voyager 1 spacecraft have astronomers once again revising their theories about the radial extent of the heliosheath – the heated outer shell of the solar system. Recent data from the spacecraft have shown a gentle decrease in the velocity of the solar wind at the heliopause – the outer boundary of the heliosheath – not the abrupt discontinuity predicted by current theories. Also, scientists looking at other data from both Voyager 1 and Voyager 2 have found that the magnetic field in the heliosheath is a tumultuous foam of magnetic bubbles, as compared to the graceful arcs of magnetic field lines they had expected.

At the edge

Ionized particles emitted at high speeds from the Sun – the solar wind – form a bubble around our solar system. The skin of the bubble, called the heliosphere, contains the heliopause, the heliosheath and the termination shock. The solar wind travels at supersonic speed until it crosses a shockwave – the termination shock where it slows down and heats up the heliosheath. The heliopause is the outer edge of the heliosheath where the solar wind slows down to zero.

Launched nearly 34 years ago, and now cruising through space some 14.4 billion kilometres from the Sun, both Voyager 1 and Voyager 2 are currently in the heliosheath. A team of scientists led by Stamatios Krimigis of the Johns Hopkins University Applied Physics Laboratory, Maryland, US have been using Voyager's Low-Energy Charged Particle instrument to determine the solar wind's velocity. Voyager 1 has crossed into an area where the velocity of the solar wind has slowed gradually to zero since 2007. As Voyager 1 has moved outwards over the past three years, the radial velocity of the wind has been decreasing almost linearly from 208,000 km/h to zero; while the transverse component that flows sideways relative to the Sun is also trending toward zero.

"This tells us that Voyager 1 may be close to the heliopause, or the boundary at which the interstellar medium basically stops the outflow of solar wind," says Krimigis. "The extended transition layer of near-zero outflow contradicts theories that predict a sharp transition to the interstellar flow at the heliopause – and means, once again, we will need to rework our models."

As velocities may fluctuate, the team looked at multiple monthly readings before confirming the velocity was actually at zero. However, scientists believe Voyager 1 has not yet crossed the heliopause into interstellar space. Crossing into interstellar space would mean a sudden drop in the density of hot particles of the heliosheath and an increase in the density of cold particles of the interstellar plasma. The researchers, writing in Nature, estimated the location of the heliopause by combining the Voyager 1 observations and energetic neutral atom images of the heliosheath from the Cassini mission. They believe that the heliopause may be as close as 18 billion kilometres, meaning that Voyager 1 could exit the transition layer and enter the galactic medium by the end of 2012. The research was published in Nature Letters.

Bubble trouble

At the same time, another team from NASA has found distinct bubbles of magnetism, each about 160 million kilometres wide, in the heliosheath. Voyager 1 entered the "foam-zone" in around 2007 and Voyager 2 followed about a year later, according to the researchers, and it would take either one of the probes weeks to cross just one bubble.

The old and the new view of the heliosheath

"The Sun's magnetic field extends all the way to the edge of the solar system," explains Merav Opher of Boston University, US. "Because the Sun spins, its magnetic field becomes twisted and wrinkled, a bit like a ballerina's skirt. Far, far away from the Sun, where the Voyagers are now, the folds of the skirt bunch up."

When a magnetic field gets severely folded, lines of magnetic force criss-cross and reorganize themselves into foamy magnetic bubbles. This magnetic reconnection is the same energetic process underlying solar flares. The actual bubbles appear to be self-contained and disconnected from the broader solar magnetic field.

Sensor readings from the spacecraft show that the Voyagers sometimes travel in and out of bubbles in the foam – zone, while at other times they seem to move through foam-free regions. This further complicates our picture of the heliosphere.

The researchers suggest that the foam zone might protect the solar system from cosmic rays, which would be trapped inside the bubbles and have to travel through individual bubbles before arriving at relatively smoother magnetic field lines to travel towards the Sun itself. "The magnetic bubbles appear to be our first line of defence against cosmic rays," points out Opher. "We haven't figured out yet if this is a good thing or not."

So far, most evidence for the bubbles comes from the Voyager energetic-particle and flow measurements and magnetic-field observations; but because the magnetic field is so weak, the data takes much longer to accurately analyse. "We'll probably discover [if our model] is correct as the Voyagers proceed deeper into the froth and learn more about its organization," says Opher. "This is just the beginning, and I predict more surprises ahead."

Watch the video below from the NASA Heliophysics and the Science Visualization Studio to find out more about the bubbles and how cosmic rays may travel through them:

Future of International Space Station

2011-07-05T12:44:00.002+05:30

The Future of the International Space Station (ISS) at this point is somewhat in doubt. The reason for that is the fact that the United States is the principle country responsible for the ISS, having absorbed the vast majority of the cost overruns that have come with the project.The fact that their commitment is uncertain is something that really does seem to be affecting
all of the plans that have been made for this space station.

In 2004, then President George W. Bush was responsible for approving a plan that would see the ISS deorbited by the United States and brought back to Earth in 2015. When the Obama Administration came to power, that plan was rejected in favour of a push to allow the ISS to stay in orbit until 2020. This plan was supported by many in the international space community including the Russians, Japanese and Europeans, all of whom have similar plans in operation to continue their own support of the ISS project until 2020.

At the moment, it seems as though the final battles will be fought within the United States. It is up to the administration to convince Congress that the ISS should be funded until that time. With the political turmoil in the country combined with a hyper-partisan attitude, it is unclear as to whether that plan will come to fruition. Even with noted people in the field such as former station commander Leroy Chiao commenting that a loss of confidence in the US ability to lead in the area of space would accompany such a decision, it seems as though this issue is one that is still up in the air.

Based on what we know now, it seems as though the ISS will definitely be around until at least 2015. Whether it makes it past that mark is seemingly dependant on what happens in the halls of Washington DC between now and then.

Aamir sweats it out for DHOOM 3

2011-07-05T11:20:00.000+05:30

Though the much talked about shoot of DHOOM 3 is scheduled to begin in February 2012, actor Aamir Khan has already been sweating out for the last six months for his role in the film.
According to reliable sources, Aamir wants to train for one full year for his role in DHOOM 3. That is the reason the actor started his rigorous workouts for his role from January 2011 to give him enough time to shape up for the role.

Aamir on his part has also admitted that he is training hard for the film. Says the actor, "I take out at least one hour everyday to do some serious workout in the gym for my role in DHOOM 3. Though the film will go on the floors in February 2012, I have decided to work on my body in the meantime."
It must be mentioned that unlike the earlier installments of DHOOM and DHOOM 2 that were directed by Sanjay Gadhvi, DHOOM 3 will be directed by Vijay Krishna Acharya, who had earlier directed TASHAN with Saif Ali Khan and Akshay Kumar in the lead.

Delhi Belly Movie Reviews

2011-07-05T11:12:00.001+05:30

Starring: Imran Khan, Vir Das, Kunal Roy Kapoor, Poorna Jagannathan, Shenaz Treasuryvala
Director: Abhinay Deo.

It is a cliche as old as this nation - of the many Indias that breathe under one India, Indian cinema has hardly been representative of even a few of these. Yet, one would have expected, after globalization and the emergence of a new bold, urban India, that at least this class would get representation in commercial cinema.

Though there have been successful attempts in the past, it is with "Delhi Belly" that the urban, money-is-everything, foul-mouthed India has been captured with aplomb. And that, depending upon your morality, is good or bad.

Tashi (Imran Khan), a Delhi-based journalist living filthily with two roommates, winds up with a bunch of 'desi' goons chasing him and his mates after a mix-up. The three are forced to navigate the dark underbelly to survive, while encountering one situation after another and one idiosyncratic Indian after another.

The beauty of Abhinav Deo's film is not its smooth story, loosely inspired by the type of films made famous by Guy Ritchie, 'Lock Stock..' and 'Snatch' among others, neither is it Ram Sampath's catchy music that beats to the rhythm of the film, or the slick, seamless direction, or its immaculate casting and performance or even its wickedly witty dialogues. The true beauty of the film is in all these elements together creating a madcap image of a new, unabashed, even shameless section of India.

Though Delhi is referred to in its title, it is not the real Delhi that Dibakar Banerjee captures with satirical reality in his films. Instead, it is the image of a Delhi populated by young, educated, newly 'liberated' urbanites. In that it is the splitting image of that young urban India anywhere perpetually churning like the stomach of a character in the film, a showcasing of this nations new neo-liberal underbelly.

However, the other Indias might not take kindly to the film. Hypocritical Indians okay with female infanticide and dowry would be aghast at how almost every 'bad' word that they know is spoken everywhere on the streets and in homes, finds a place in the usually moralistic Bollywood. Cinema purists too may cry foul that the film does not really have a soul and is not really trying to say anything. Though a legitimate accusation, in not having a soul and not really being concerned or serious about anything, the film holds a mirror to a large section of the country. And that is a big statement in itself.

For decades Indian cinema has been shackled with a morality that has not kept pace with the changing morality of life around. Though the morality of the film is strictly of urban, young, middle-class India, and isn't representative, it is welcome as this is the farthest Bollywood has gone to truly representing urban life. And just for that, hats off to Aamir Khan for yet again, after "Peepli Live" and "Dhobi Ghat", believing in a different kind of cinema, even while he doles out a "Ghajini" in the same breath.

The last scene of "Delly Belly" is bound to become as iconic as the one in Mahesh Bhatt's 1990 musical 'Aashiqui'. If there the lovers were so embarrassed of their surroundings that they had to kiss under a coat, here the lovers who are not even girlfriend-boyfriend are so brazen and caught in the heat of the moment that the guy kisses the girl in full view, half his body hanging out a slowly moving Maruti car symbolic of old India, unconcerned whether others are looking (which they are not). If that isn't the urban, chic, and unconcerned-about-others India that has moved away from the morality of an un-liberalized India in 'Aashiqui' then what is?

Five Year Integrated Postgraduate Programme in Management (IPGP)

2011-07-04T17:51:00.000+05:30

A Brief Note

In this brief note we articulate the rational on the design and implementation of the proposed five-year integrated postgraduate programme in management (IPGP) of IIM Indore.

IIM Indore’s vision is to have a dominant presence in every segment of management education. Operationalization of increasing the PGP batch size from 240 to 450 candidates is a step in this direction. We have launched a one-year executive education programme for the premium price segment of the management education market. Academic presence in Mumbai and Dubai is a demonstration of our desire to be globally present. We have an expanding Ph.D. programme. We have launched a 3-month Faculty Development Programme (FDP) for teachers. We have plans to launch several specialized programmes in the emerging sectors of the Indian economy like egovernance, health care etc. The proposed five-year integrated postgraduate programme in management (IPGP) is a unique and creative programme to meet the aspirations of young students to become management professionals.

This programme therefore is a strategic fit in the overall context, vision and mission of IIM, Indore. The five-year integrated postgraduate programme in management is aimed at students who have passed out class XII / Higher Secondary or equivalent from various schools in India. It is widely believed that our ability to influence the younger students is much greater if we start early. It is hoped that we will be able to shape them as outstanding leaders.

The five-year integrated residential programme is a unique opportunity for the Institute to make a contribution. It is also an interesting option for the young boys and girls to charter their profession in the area of management with a wider scholarly academic background in the social sciences setting.

The proposed batch size is 120. We have adequate infrastructural facilities for this year to start this batch size. For next year, we have to create infrastructure. We plan to do it rapidly.

Eligibility criteria for this programme are 60% aggregate marks at Secondary/ X Std/ Equivalent and at Higher Secondary/XII/+2 level/ Equivalent. Government of India reservation norms would be followed while admitting the candidates. Selection of candidates would be based on their performance in Secondary/X Std/ Equivalent and Higher Secondary/XII Std/ +2 level / Equivalent examination. Final selection will be based on academic performance, scholastic achievements, performance in SAT-1 and the performance in the Aptitude Test and Personal Interview.

The aptitude test and personal interview would be held in various centres including Bangalore, Chennai, Delhi, Hyderabad, Indore, Kolkata and Mumbai. We plan to invite roughly seven times (approximately 850 candidates) of the batch size for aptitude test and personal interview. The classes are scheduled to begin in October 2011.

Candidates can use the option of exiting the system with a degree equivalent to BBA programme of 3 years. Others who desire to continue would receive an MBA equivalent after 5 years.

Fee for the programme for the first 3 years would be Rs.300,000 per annum and for next two years would be Rs.500,000 per annum. This fee is for tuition and does not include boarding and lodging. The participants should meet any international component expenses, as a part of the programme. The participants would, also meet expenses related to the field visit if any.

Accommodation would be organized on the campus on a twin-sharing basis for the first 3 years. Single room accommodation would be made available for the 4th and 5th year of the programme on campus.

This academic programme would consist of 15 terms. Each term is for 3 months. Detailed programme design and academic curriculum will be made available by August 2011.

The broad design of the programme would include management education in social sciences setting. Accordingly, 40% of the programme would focus on subjects related to the following:

· Mathematics, Statistics, Logic and Computer Science

· Introduction to Literature and Political Science

· Civilization in History (both national and international)

· Exposure to biological sciences

· Exposure to languages (one foreign language and one Indian language) – Ordinary language and exposure to Indore by field visit.

· Soft skills: Leadership development, personality development, team work and communication both written and oral

Second module would consist of all functional areas of management like Accounting, Finance, Organizational Behaviour, Decision Science, Operations and Services Management, Marketing, Economics, Information Technology, Communication, Legal Aspects of Business, Ethics, Corporate Governance, Corporate Social Responsibility, Business Strategy and International Business. This would account for 50% of the course design.

The remaining 10% of the programme would focus on international exposure and internship in various social organizations in India.

Faculty Resources: Faculty would be drawn from various sources. They include faculty members, retired and serving teachers in top rank commerce and science colleges in India; Industry experts who have inclination to teach; Retired faculty members from central universities and state universities.

Collaboration with foreign Universities/ Colleges: We are actively exploring international participation with Universities/ Colleges based in Europe, US and Canada.

Einstein's Physics Of Illusion

2009-11-13T11:24:00.000+05:30

Some of you may think from the title "Einstein's Physics of Illusion", that I'm going to talk about the
physics which underlies what we think of as magic. That is not what I expect to talk about. Some of you
may think that I suspect that Einstein had some special physics of illusions. If he did, I don't know
anything of it. Instead, what I want to do, with Einstein's help, is to trace our physics all the way back to
square one, and to find out whether, underlying it, there may possibly be something akin to magic.
George Valens has written a charming book called The Attractive Universe. It is subtitled "Gravity and
the Shape of Space", and on the very first page he says that when a ball is thrown straight up, after a
while it comes to a stop, changes its direction and comes back. He says it looks like magic, and probably
it is. Now what he is taking for granted is that it should have gone off on a straight path without any
change in speed or direction. But you see, that also would have been the result of magic. We do not
understand in physics why the ball comes back. But we also do not understand in our physics why the
ball should have continued without any change in the direction of its speed....
Now in the title, and in the remarks that I have made so far, what I mean by magic or illusion is
something like what happens when, in the twilight, you mistake a rope for a snake. And this sort of thing
was analyzed very carefully by some people in North India long, long ago, and they said that when you
make such a mistake there are three aspects to your mistake. First, you must fail to see the rope rightly.
Then, instead of seeing it as a rope, you must see it as something else. And finally, you had to see the
rope in first place or you never would have mistaken it for" a snake. You mistook it for a snake because
the rope was three feet long, and you're accustomed to three foot long snakes.
But before I speak further about illusion, I want to say a few words about what we do understand in
physics, and I also want to point out a few gaps in that understanding. When we talk about the universe,
or when we look out and see it, what we see is that the universe is made out of what we call matter. It's
what we call a material universe. And what we want to do, first of all, is to trace that material back, not
quite to square one, but to square two at least, We want to find out whether we can think of all these
things which we see as being made out of matter, as really being made out of only a few ingredients.
And the answer is that we can. Long ago the chemists pointed out that all these things that we see are
made out of not more than 92 ingredients. Those are the 92 chemical elements of the periodic table. It
was suggested in 1815 that all those different chemical elements are probably made out of hydrogen.
That was Prout's hypothesis, because in those days no one knew how to do it. But now, in modern times, we do know how to do it, and we do know that that's what happens. All the other chemical elements
are made out of hydrogen, and it happens in the stars"
The universe, even as it is today, consists mostly of hydrogen. And what it is doing is falling together in
the gravitational field. It falls together to galaxies and stars, and the stars are hot. Falling together by
gravity is what makes them hot. And they get hot enough inside so that the hydrogen is converted
to.helium. Now helium is a very strong atomic nucleus, and so the main line in building up the atoms of
the atomic table goes this way: First, four hydrogens make one helium. Then three heliums make one
carbon. Two heliums won't stick. That would be beryllium-8. There is no beryllium-8. It won't last. But
three heliums will stick, and that's carbon. Four is oxygen. Five is neon. That's the way it goes in the
stars; the other nuclei are built of helium nuclei. Six makes magnesium. Then silicon, sulfur, argon,
calcium, titanium, chromium and iron.
In big stars it goes like this. But in small stars like our sun it goes only up to carbon or possibly carbon
and oxygen. That's where our sun will end, at about the size of the earth, but with a density of about four
concrete mixing trucks in a one pint jar. Larger stars get too hot by their own gravitational squeeze, and
the carbon cannot cool off like that. They go right on to oxygen and so on, until they get, in the center, to
iron. Now iron is the dumbest stuff in the universe. There is no nuclear energy available to iron --
nothing by which it can fight back against gravitational collapse; so gravity collapses it, this time to the
density of a hundred thousand airplane carriers squeezed into a one pint yogurt box One hundred
thousand airplane carriers in a one pint box! And, when it collapses like that, the gravitational energy that
is released to other forms blows the outer portions of the star all over the galaxy. That's the stuff out of
which our bodies are made. Our bodies are all made out of star dust from such exploding stars.
We do know that the main ingredient of the universe is hydrogen and that the main usable energy in the
universe is gravitational. We know that the name of the game is falling together by gravity (hydrogen,
falling together by gravity), but what we don't know is why things fall together by gravity. We do know
that the stuff out of which this universe is made is hydrogen, but we do not know from where we get
the hydrogen. We know that the hydrogen is made of electrical particles, protons and electrons, and we
know that the total electrical charge of the universe is zero, but we do not know, you see, why it is made
of electricity. We do not know why it falls together. And we do not know why, when things are
moving, they should coast. There are these gaps in our understanding. We know how things coast. We
know how things fall. We know how the electrical particles behave, but we don't know any of the why
questions. We don't have any answers to the why questions.
What I want to talk about next is a discovery made by Albert Einstein when he was 26 years old and
working in the patent office in Bern. Then I want to talk about the" consequences of that discovery and,
through that, I want to trace our physics back, if possible, to answer those why questions.
Einstein noticed that we cannot have an objective universe in three dimensions. We all talk about 3-D.
Hardly anybody talks about 4-D. But the universe is 4-D. It is not possible to have a universe of space
without a universe of time. It is not possible to have space without time, or time without space, because
space and time are opposites. I don't know that Einstein ever used the language that space and time are
opposites, but if you look at his equations, it is very, very clear that that's exactly what they are. If,
between two events, the space separation between them is the same as the time separation between them,
then the total separation between them is zero. That's what we mean by opposites in this case. In
electricity if we have the same amount of plus charges as we have of minus charges, say in the same atom or the same molecule, then that atom or that molecule is neutral. There is no charge seen from
outside. Likewise here. If the space separation between, two events is just the same as the time separation
between those two events, then the total separation between those two events is zero.
I'll give you an example. Suppose we see an exploding star, say in the Andromeda galaxy. There's one
going on there right now. It's been visible for about a month or so. Now the Andromeda galaxy is two
and a quarter million light years away, and when we see the explosion now, we see it as it was two and a
quarter million years ago. You see, the space separation and the time separation are the same, which
means that the total separation between you and what you see is zero. The total separation, the real
separation, the objective separation, that is, the separation as seen by anybody, between the event
which you see and the event of your seeing it -- the separation between those two events is always zero.
What we mean when we say that the space and time separations between two events are equal is that
light could get from one of those events to the other in vacuum.
We see things out there, and we think they're really out there. But, you see, we cannot see them when
they happen. We can't see anything when it happens. We see everything in the past. We see everything a
little while ago, and always in such a way that the while ago just balances the distance away, and the
separation between the perceiver and the perceived remains always at zero.
As soon as Einstein noticed that we cannot have a universe of space without a universe of time and vice
versa, and that they are connected in this way, and that the only way to have an objective universe is in
four dimensions, and not in two or three or one -- as soon as he noticed that, he had to redo our physics.
Now relativity theory is a geometry theory. It's not something else. It's a geometry theory. It's about the
geometry of the real world. I'm sure that most if not all of you have been exposed, somewhere along your
educational careers, to the geometry of Euclid. His geometry is in two dimensions and in three, but he
didn't have any idea about introducing the fourth dimension. His geometry - is a theoretical geometry
about a theoretical space which does not, in fact, exist. Newton based his understanding of physics also
on that understanding of geometry, and Newton's physics is a theoretical physics about a theoretical
universe which does not, in fact, exist. We know now, you see, that Euclid was wrong in his
understanding of geometry, and that Newton was likewise wrong in his understanding of physics. And
we had to correct our physics in terms of Einstein's re-understanding of geometry. It was when Einstein
went through our physics with his new understanding of geometry that he saw that what we had been
calling matter or mass or inertia is really just energy. It is just potential energy. It had been suggested a
few years earlier by Swami Vivekananda that what we call matter could be reduced to potential energy.
In about 1895 he writes in a letter that he is to go the following week to see Mr. Nikola Tesla who thinks
he can demonstrate it mathematically. Without Einstein's understanding of geometry, however, Tesla
apparently failed.
It was from the geometry that Einstein saw that what we call rest mass, that which is responsible for the
heaviness of things and for their resistance to being shaken, is really just energy. Einstein's famous
equation is E = mc2. Probably most of you have seen that equation. It says that for a particle at rest, its
mass is equal to its energy. Those of you who read Einstein know that there is no "c" in that equation.
The c2 is just in case your units of space and time don't match. If you've chosen to measure space in an
arbitrary unit and time in another arbitrary unit, and if you have not taken the trouble to connect the two
units, then, for your system you have to put in the c2. If you're going to measure space in centimeters,
then time must not be measured in seconds. It must be measured in jiffies. A jiffy is the length of time it takes light to go one centimeter. Astronomers are rather broad minded people, and they have noticed that
the universe is quite a bit too big to be measured conveniently in centimeters, and quite a bit too old to be
measured conveniently in seconds; so they measure the time in years and the distance in light-years, and
the units correspond. That "c" in the equation is the speed of light in your system of units, and if you've
chosen years and light-years then the speed of light in your system is one. And if you square it, it's still
one, and the equation doesn't change. The equation simply says that energy and mass are the same thing.
Our problem now is that if we're going to trace this matter back, and find out what it is, we have first of
all to find out what kind of energy makes it massive. Now we have only a few kinds of energy to choose
from. Fortunately there are only a few: gravitational energy, kinetic energy, radiation, electricity,
magnetism and nuclear energy. But I must allay your suspicion that nuclear energy might be very
important. It is not. The nuclear energy available in this universe is very small. If all the matter in the
universe began as hydrogen gas and ended as iron, then the nuclear energy released in that change (and
that is the maximum nuclear energy available) is only one per cent of what you can get by letting that
hydrogen fall together by gravity. So nuclear energy is not a big thing, and we have only five kinds of
energy to choose from in order to find out what kind of energy makes the primordial hydrogen hard to
shake. That, you remember, was our problem.
What we want is potential energy, because the hydrogen is hard to shake even when it's not doing a
thing. So what we're after is potential energy, and that restricts it quite a bit more. Radiation has nothing
to do with that. Radiation never stands still. And kinetic energy never stands still. And even magnetic
energy never stands still. So we are left with electricity and gravity. There are only two. We don't have
any choice at all. There is just the gravitational energy and the electrical energy of this universe available
to make this universe as heavy or as massive as we find it.
Now I should remind you that the amount of energy we're talking about is very large. It's five hundred
atom bombs per pound. One quart of yogurt, on the open market, is worth one thousand atom bombs. It
just happens that we're not in the open market place. We live where we have no way to get the energy of
that yogurt to change form to kinetic energy or radiation so that we can do anything with it. It's tied up in
there in such a way that we can't get it out. But right now we're going to talk about the possibility of
getting it out. We want to talk about how this tremendous energy is tied up in there. We want to talk
about how this matter is "wound up".
First let's talk about watches. We know how they're wound up. They're wound up against a spring. Now
when we wind up a watch, what I want to know is whether it gets heavier or lighter. If we have a watch,
and if we wind it up, does it get harder to shake or easier? It gets harder to shake because when we wind
it up we put more potential energy into it, and energy is the only thing in the universe that's hard to
shake. So now we want to know in what way the whole universe is wound up to make it heavy and hard
to shake. We know that it must be wound up against electricity and gravity. The question is: How?
We need to know some details on how to wind things up. How, for instance, do you wind up against
gravity? You wind against gravity by pulling things apart in the gravitational field. They all want to go
back together again. And if the entire universe were to fall together to a single blob, the gravitational
energies that would be released to other forms would be five hundred atom bombs per pound. The
universe is wound up on gravitational energy just by being spaced away from itself against the
gravitational pull inward. And it turns out to be just the right amount. It really does account for the fact
that it's five hundred atom bombs per pound.

A Brief History of Black Holes

2009-11-12T11:47:00.000+05:30

It has frequently been alleged by theoretical physicists Newton’s theory of gravitation either predicts or adumbrates the black hole. This claim stems from a suggestion originally made by John Michell in 1784 that if a body is sufficiently massive, “all light emitted from such a body would be made to return to it by its own power of gravity”. The great French scientist, P. S. de Laplace, made a similar conjecture in the eighteenth century and undertook a mathematical analysis of the matter. However, contrary to popular and frequent expert opinion, the Michell-Laplace dark body, as it is actually called, is not a black hole at all. The reason why is quite simple. For a gravitating body we identify an escape velocity.

This is a velocity that must be achieved by an object to enable it to leave the surface of the host body and travel out to infinity, where it comes to rest.
Therefore, it will not fall back towards the host. It is said to have escaped the host. At velocities lower than the escape velocity, the object will leave the surface of the host, travel out to a finite distance where it momentarily comes to rest, then fall back to the host. Consequently, a suitably located observer will see the travelling object twice, once on its journey outward and once on its return trajectory. If the initial velocity is greater than or equal to the escape velocity, an observer located outside the host, anywhere on the trajectory of the travelling object, will see the object just once, as it passes by on its outward unidirectional journey. It escapes the host. Now, if the escape velocity is the speed of light, this means that light can leave the host and travel out to infinity and come to rest there. It escapes the host. Therefore, all observers located anywhere on the trajectory will see the light once, as it passes by on its outward journey. However, if the escape velocity is greater than the speed of light, then light will travel out to a finite distance, momentarily come to rest, and fall back to the host, in which case a suitably located observer will see the light twice, once as it passes by going out and once upon its return. Furthermore, an observer located at a sufficiently large and finite distance from the host will not see the light, because it does not reach him. To such an observer the host is dark: a Michell-Laplace dark body. But this does not mean that the light cannot leave the surface of the host. It can, as testified by the closer observer. Now, in the case of the black hole, it is claimed by the relativists that no object and no light can even leave the event horizon (the “surface”) of the black hole.

Therefore, an observer, no matter how close to the event horizon, will see nothing. Contrast this with the escape velocity for the Michell-Laplace dark body where, if the escape velocity is the speed of light, all observers located on the trajectory will see the light as it passes out to infinity where it comes to rest, or when the escape velocity is greater than the speed of light, so that a suitably close observer will see the light twice, once when it goes out and once when it returns. This is completely opposite to the claims for the black hole. Thus, there is no such thing as an escape velocity for a black hole, and so the Michell-Laplace dark body is not a black hole. Those who claim the Michell-Laplace dark body a black hole have not properly understood the meaning of escape velocity and have consequently been misleading as to the nature of the alleged event horizon of a black hole. It should also be noted that nowhere in the argument for the Michell-Laplace dark body is there gravitational collapse to a point-mass, as is required for the black hole.

Black Holes

2009-11-12T11:36:00.000+05:30

After a star has exhausted its nuclear fuel, it can no longer remain in equilibrium and
must ultimately undergo gravitational collapse. The star will end as a white dwarf
if the mass of the collapsing core is less than the famous Chandrashekhar limit of 1.4
solar masses. It will end as a neutron star if the core has a mass greater than the
Chandrashekhar limit and less than about 35 times the mass of the sun. It is often
believed that a core heavier than about 5 solar masses will end, not as a white dwarf
or as a neutron star, but as a black hole. However, this belief that a black hole will
necessarily form is not based on any firm theoretical evidence. An alternate possibility
allowed by the theory is that a naked singularity can form, and the purpose of the
present article is to review our current understanding of gravitational collapse and the
formation of black holes and naked singularities.
A black hole has been appropriately described by Chandrashekhar as the most
beautiful macroscopic object known to man. Only a few parameters suffice to describe
the most general black hole solution, and these objects have remarkable thermodynamic
properties. Further, excellent observational evidence for their existence has
developed over the years (Rees 1998). Thus, there can be no doubt about the reality of
black holes, and the gravitational collapse of very many sufficiently massive stars
must end in the formation of a black hole...

However, the following question is still very much open. If the collapsing core is
heavy enough to not end as a neutron star, does this guarantee that a black hole will
necessarily form? The answer to this question has to come from the general theory of
relativity, and unfortunately this remains an unsolved problem.
What we do know from general relativity about gravitational collapse is broadly
contained in the celebrated singularity theorems of Geroch, Hawking and Penrose. It
has been shown that under fairly general conditions, a sufficiently massive collapsing
object will undergo continual gravitational collapse, resulting in the formation of a gravitational singularity. The energy density of the collapsing matter, as well as the
curvature of spacetime, are expected to diverge at this singularity.
Is such a singularity necessarily surrounded by an invisible region of spacetime, i.e.
has a black hole formed? The singularity theorems do not imply so. The singularity
may or may not be visible to a far away observer. If the singularity is invisible to a far
away observer, we say the star has ended as a black hole. If it is visible, we say the
star has ended as a naked singularity. We need to have a better understanding of
general relativity in order to decide whether collapse always ends in a black hole or
whether naked singularities can sometimes form.
Given this situation, Penrose was led to ask (Penrose 1969) whether there might
exist a cosmic censor who forbids the existence of naked singularities, 'clothing each
one of them with a horizon’? Later, this led to the cosmic censorship hypothesis,
which in broad physical terms states that the generic singularities arising in the gravitational
collapse of physically reasonable matter are not naked. Till today, this
hypothesis remains unproven in general relativity, neither is it clear that the hypothesis
holds true in the theory. What is of course true is that the hypothesis forms the
working basis for all of black hole physics and astrophysics. If cosmic censorship
were to not hold, then some of the very massive stars will end as black holes, while
others could end as naked singularities. As we will argue in section 3, these two kinds
of objects have very different observational properties.
There are various very important reasons for investigating whether or not cosmic
censorship holds in classical general relativity. As we have mentioned above, the
hypothesis is vital for black hole astrophysics. Unfortunately this fact is rarely
appreciated by the astrophysics community. The hypothesis is also necessary for the
proof of the black hole area theorem. It is not clear what the status of this theorem
will be if the hypothesis were to not hold. If naked singularities do occur in classical
relativity, they represent a breakdown of predictability, because one could not predict
the evolution of spacetime beyond a naked singularity. Such singularities would then
provide pointers towards a modification of classical general relativity, so that a
suitable form of predictability is restored in the modified theory. Further, naked
singularities might be observable in nature, if they are allowed by general relativity.
Undoubtedly then, it is important to find out if the censorship hypothesis is valid.
We wish to make two further remarks. Firstly, while a great deal is known about the
properties of stationary black holes, we know very little about the process of black
hole formation. In fact we know as little about the formation of black holes as we do
about the formation of naked singularities. Secondly, it has sometimes been remarked
that a theory of quantum gravity is likely to get rid of the singularities of classical
general relativity, irrespective of whether these singularities are naked or covered.
Why then does it eventually matter whether or not cosmic censorship holds? The
answer to this legitimate objection is the following. A quantum gravity theory is
expected to smear out a classical singularity and replace it by a region of very high,
albeit finite, curvature. If the classical singularity is hidden behind a horizon (i.e. is a
black hole), this quantum smeared region remains invisible to an external observer.
However, if the classical singularity is naked, the smeared region of very high
curvature will be visible to far away observers, and the physical processes taking place
near this smeared region will be significantly different from those taking place outside
the horizon of ordinary astrophysical black holes. Hence, from such an experimental
standpoint, quantum gravity has little bearing on the question of cosmic censorship.
To put it differently, quantum gravity is not expected to restore the event horizon, if
the horizon is absent in the classical theory.
Since a theorem proving or disproving the hypothesis has not been found, attention
has shifted to studying model examples of gravitational collapse, to find out whether
the collapse ends in a black hole or a naked singularity. While specialised examples
such as have been studied are nowhere near a general proof, they are really all that we
have to go by, as of now. However, there does seem to be an underlying pattern in the
results that have been found in these examples, which gives some indication of the
general picture. It is interesting that all models studied to date admit both black hole
and naked singularity solutions, depending on the choice of initial data. In the next
section, we give a summary of what has been learnt from these examples and what
they probably tell us about cosmic censorship. In the third section we will address the
question of whether naked singularities might occur in nature, and if so, what they
would look like to an observer.

Visual Quantum Mechanics The Next Generation

2009-11-07T21:38:00.000+05:30

A large number of devices detect the presence of light. These range from the “switches”
which automatically turn on the street lights when it gets dark to the receiving end of the
scanners at the grocery store check out counter to the detectors in a CD player. All of
these devices work because light striking a material deposits energy in that material and
causes a change in the motion of the electrons. The detection of this change helps determine
how dark it is, how much your potato chips cost, and what sound should be produced
by the stereo.
The basic process behind all of these devices is the photoelectric effect. This effect was
first explained by Albert Einstein in 1905 and is cited as the reason for his Nobel Prize.
(When Einstein was awarded the Noble Prize, the Theory of Relativity was very controversial,
so it was not included as the reason.) We will study this photoelectric effect in this
experiment....

We have not studied the photoelectric effect in class, so you will need a little background
information to understand the measurements which you will need to complete. In this
experiment we will look at a situation similar to the one that Einstein originally explained.
It uses rather high-energy visible and ultraviolet light. In many devices today, particularly
CD players and grocery store scanners, the energy of the light is much lower.
The photons of the light source have the energy;
Ephoton = hfphoton h = 6.626 x 10-34 J•sec = 4.136 x 10-15 eV•sec
where E is the energy of the photon, f is the frequency of the light and h is Planck’s Constant.
The frequency of light can be found from the wavelength by:
f = c/λ c = 3.00 (10)8 m/sec
When an electron gets enough energy from a photon, the electron can be ejected from
the metal. However, the electrons are bound in the metal so some of this energy must
be used to overcome this binding. For bound electrons their maximum kinetic energy
will be less than the energy of the light photon. Because interactions with the metal will
differ from different electrons, not all of them will have the same kinetic energy even
though they have absorbed the same total energy from the photon. We relate the kinetic
energy of the ejected electron to energy of the photon as:
KEmax = Ephoton - Wo = hf – Wo
Here, Ephoton is the energy of a photon, h is Planck’s constant, f is the frequency of the
light, KEmax is the maximum kinetic energy of the electron released from the metal, Wo is
the energy needed to eject an electron from the metal.

Modern device that use the photoelectric effect are frequently called photocells. These
devices include a metal that will emit the electrons when light strikes it and another metal
plate. The energy of photoelectrons can be changed by placing a voltage across the two
metal plates. As the electron moves between these plates, it gains or loses energy which
depends on the voltage applied to the plates. (An energy gain occurs when the electron
is traveling toward the positive plate; a loss occurs when it is traveling toward the negative
plate.). In next part of this experiment we will use this fact to determine the kinetic
energy of the electrons.

"Ether and the Theory of Relativity"

2009-11-05T00:33:00.000+05:30

HOW does it come about that alongside of the idea of ponderable matter, which is derived by abstraction from everyday life, the physicists set the idea of the existence of another kind of matter, the ether? The explanation is probably to be sought in those phenomena which have given rise to the theory of action at a distance, and in the properties of light which have led to the undulatory theory. Let us devote a little while to the consideration of these two subjects.
Outside of physics we know nothing of action at a distance. When we try to connect cause and effect in the experiences which natural objects afford us, it seems at first as if there were no other mutual actions than those of immediate contact, e.g. the communication of motion by impact, push and pull, heating or inducing combustion by means of a flame, etc. It is true that even in everyday experience weight, which is in a sense action at a distance, plays a very important part. But since in daily experience the weight of bodies meets us as something constant, something not linked to any cause which is variable in time or place, we do not in everyday life speculate as to the cause of gravity, and therefore do not become conscious of its character as action at a distance.....
It was Newton's theory of gravitation that first assigned a cause for gravity by interpreting it as action at a distance, proceeding from masses. Newton's theory is probably the greatest stride ever made in the effort towards the causal nexus of natural phenomena. And yet this theory evoked a lively sense of discomfort among Newton's contemporaries, because it seemed to be in conflict with the principle springing from the rest of experience, that there can be reciprocal action only through contact, and not through immediate action at a distance.
It is only with reluctance that man's desire for knowledge endures a dualism of this kind. How was unity to be presented in his comprehension of the forces of nature? Either by trying to look upon contact forces as being themselves distant forces which admittedly are observable only at a very small distance – and this was the road which Newton's followers, who were entirely under the spell of his doctrine, mostly preferred to take; or by assuming that the Newtonian action at a distance is only apparently immediate action at a distance, but in truth is conveyed by a medium permeating space, whether by movements or by elastic deformation of this medium. Thus the endeavour toward a unified view of the nature of forces leads to the hypothesis of an ether. This hypothesis, to be sure, did not at first bring with it any advance in the theory of gravitation or in physics generally, so that it became customary to treat Newton's law of force as an axiom not further reducible. But the ether hypothesis was bound always to play some part in physical science, even if at first only a latent part.
When in the first half of the nineteenth century the far-reaching similarity was revealed which subsists between the properties of light and those of elastic waves in ponderable bodies, the ether hypothesis found fresh support. It appeared beyond question that light must be interpreted as a vibratory process in an elastic, inert medium filling up universal space. It also seemed to be a necessary consequence of the fact that light is capable of polarisation that this medium, the ether, must be of the nature of a solid body, because transverse waves are not possible in a fluid, but only in a solid. Thus the physicists were bound to arrive at the theory of the quasi-rigid luminiferous ether, the parts of which can carry out no movements relatively to one another except the small movements of deformation which correspond to light-waves.
This theory – also called the theory of the stationary luminiferous ether – moreover found a strong support in an experiment which is also of fundamental importance in the special theory of relativity, the experiment of Fizeau, from which one was obliged to infer that the luminiferous ether does not take part in the movements of bodies. The phenomenon of aberration also favoured the theory of the quasi-rigid ether.
The development of the theory of electricity along the path opened up by Maxwell and Lorentz gave the development of our ideas concerning the ether quite a peculiar and unexpected turn. For Maxwell himself the ether indeed still had properties which were purely mechanical although of a much more complicated kind than the mechanical properties of tangible solid bodies. But neither Maxwell nor his followers succeeded in elaborating a mechanical model for the ether which might furnish a satisfactory mechanical interpretation of Maxwell 's laws of the electro-magnetic field. The laws were clear and simple, the mechanical interpretations clumsy and contradictory. Almost imperceptibly the theoretical physicists adapted themselves to a situation which, from the standpoint of their mechanical programme, was very depressing. They were particularly influenced by the electro-dynamical investigations of Heinrich Hertz. For whereas they previously had required of a conclusive theory that it should content itself with the fundamental concepts which belong exclusively to mechanics (e.g. densities, velocities, deformations, stresses) they gradually accustomed themselves to admitting electric and magnetic force as fundamental concepts side by side with those of mechanics, without requiring a mechanical interpretation for them. Thus the purely mechanical view of nature was gradually abandoned. But this change led to a fundamental dualism which in the long-run was insupportable.
A way of escape was now sought in the reverse direction, by reducing the principles of mechanics to those of electricity, and this especially as confidence in the strict validity of the equations of Newton's mechanics was shaken by the experiments with b-rays and rapid kathode rays.
This dualism still confronts us in unextenuated form in the theory of Hertz, where matter appears not only as the bearer of velocities, kinetic energy, and mechanical pressures , but also as the bearer of electromagnetic fields. Since such fields also occur in vacuo – i.e. in free ether – the ether also appears as bearer of electromagnetic fields. The ether appears indistinguishable in its functions from ordinary matter. Within matter it takes part in the motion of matter and in empty space it has everywhere a velocity; so that the ether has a definitely assigned velocity throughout the whole of space. There is no fundamental difference between Hertz's ether and ponderable matter (which in part subsists in the ether).
The Hertz theory suffered not only from the defect of ascribing to matter and ether, on the one hand mechanical states, and on the other hand electrical states, which do not stand in any conceivable relation to each other; it was also at variance with the result of Fizeau's important experiment on the velocity of the propagation of light in moving fluids, and with other established experimental results.
Such was the state of things when H. A. Lorentz entered upon the scene. He brought theory into harmony with experience by means of a wonderful simplification of theoretical principles. He achieved this, the most important advance in the theory of electricity since Maxwell, by taking from ether its mechanical, and from matter its electromagnetic qualities. As in empty space, so too in the interior of material bodies, the ether, and not matter viewed atomistically, was exclusively the seat of electromagnetic fields. According to Lorentz the elementary particles of matter alone are capable of carrying out movements; their electromagnetic activity is entirely confined to the carrying of electric charges. Thus Lorentz succeeded in reducing all electromagnetic happenings to Maxwell's equations for free space.
As to the mechanical nature of the Lorentzian ether, it may be said of it, in a somewhat playful spirit, that immobility is the only mechanical property of which it has not been deprived by H. A. Lorentz. It may be added that the whole change in the conception of the ether which the special theory of relativity brought about, consisted in taking away from the ether its last mechanical quality, namely, its immobility. How this is to be understood will forthwith be expounded.
The space-time theory and the kinematics of the special theory of relativity were modelled on the Maxwell-Lorentz theory of the electromagnetic field. This theory therefore satisfies the conditions of the special theory of relativity, but when viewed from the latter it acquires a novel aspect. For if K be a system of co-ordinates relatively to which the Lorentzian ether is at rest, the Maxwell-Lorentz equations are valid permanently with reference to K . But by the special theory of relativity the same equations without any change of meaning also hold in relation to any new system of co-ordinates K' which is moving in uniform translation relatively to K . Now comes the anxious question: – Why must I in the theory distinguish the K system above all K' systems, which are physically equivalent to it in all respects, by assuming that the ether is at rest relatively to the K system?
For the theoretician such an asymmetry in the theoretical structure, with no corresponding asymmetry in the system of experience, is intolerable. If we assume the ether to be at rest relatively to K , but in motion relatively to K' , the physical equivalence of K and K' seems to me from the logical standpoint, not indeed downright incorrect, but nevertheless inacceptable.

Mysteries of the Universe

2009-11-03T23:41:00.000+05:30

There are few scientists of whom it can be said that their mistakes are more interesting
than their colleagues' successes, but Albert Einstein was one. Few "blunders" have had a
longer and more eventful life than the cosmological constant, sometimes described as the
most famous fudge factor in the history of science, that Einstein added to his theory of
general relativity in 1917. Its role was to provide a repulsive force in order to keep the
universe from theoretically collapsing under its own weight. Einstein abandoned the
cosmological constant when the universe turned out to be expanding, but in succeeding
years, the cosmological constant, like Rasputin, has stubbornly refused to die, dragging
itself to the fore, whispering of deep enigmas and mysterious new forces in nature,
whenever cosmologists have run into trouble reconciling their observations of the
universe with their theories.
This year the cosmological constant has been propelled back into the news as an
explanation for the widely reported discovery, based on observations of distant exploding
stars, that some kind of "funny energy" is apparently accelerating the expansion of the
universe. "If the cosmological constant was good enough for Einstein," the cosmologist
Michael Turner of the University of Chicago remarked at a meeting in April, "it should
be good enough for us."
Einstein has been dead for 43 years. How did he and his 80-year-old fudge factor come to
be at the center of a revolution in modern cosmology?
The story begins in Vienna with a mystical concept that Einstein called Mach's principle.
Vienna was the intellectual redoubt of Ernst Mach (1838-1916), a physicist and
philosopher who bestrode European science like a Colossus. The scale by which
supersonic speeds are measured is named for him. His biggest legacy was philosophical;
he maintained that all knowledge came from the senses, and campaigned relentlessly
against the introduction of what he considered metaphysical concepts in science, atoms
for example.
Mysteries of the Universe

Another was the notion of absolute space, which formed the framework of Newton's
universe. Mach argued that we do not see "space," only the players in it. All our
knowledge of motion, he pointed out, was only relative to the "fixed stars." In his books
and papers, he wondered if inertia, the tendency of an object to remain at rest or in
motion until acted upon by an outside force, was similarly relative and derived somehow
from an interaction with everything else in the universe.
"What would become of the law of inertia if the whole of the heavens began to move and
stars swarmed in confusion?" he wrote in 1911. "Only in the case of a shattering of the
universe do we learn that all bodies, each with its share, are of importance in the law of
inertia.".....

Mach never ventured a guess as to how this mysterious interaction would work, but
Einstein, who admired Mach's incorrigible skepticism, was enamored of what he
sometimes called Mach's principle and sometimes called the relativity of inertia. He
hoped to incorporate the concept in his new theory of general relativity, which he
completed in 1915. That theory describes how matter and energy distort or "curve" the
geometry of space and time, producing the phenomenon called gravity.
In the language of general relativity, Mach's principle required that the space-time
curvature should be determined solely by other matter or energy in the universe, and not
any initial conditions or outside influences -- what physicists call boundary conditions.
Among other things, Einstein took this to mean that it should be impossible to solve his
equations for the case of a solitary object -- an atom or a star alone in the universe --
since there would be nothing to compare it to or interact with.
So Einstein was surprised a few months after announcing his new theory, when Karl
Schwarzschild, a German astrophysicist serving at the front in World War I, sent him just
such a solution, which described the gravitational field around a solitary star. "I would
not have believed that the strict treatment of the point mass problem was so simple,"
Einstein said.
Perhaps spurred in part by Schwarzschild's results, Einstein turned his energies in the fall
of 1916 to inventing a universe with boundaries that would prevent a star from escaping
its neighbors and drifting away into infinite un-Machian loneliness. He worked out his
ideas in a correspondence with a Dutch astronomer, Willem de Sitter, which are to be
published this summer by the Princeton University Press in Volume 8 of "The Collected
Papers of Albert Einstein." Like most of his colleagues at the time, Einstein considered

the universe to consist of a cloud of stars, namely the Milky Way, surrounded by vast
space. One of his ideas envisioned "distant masses" ringing the outskirts of the Milky
Way like a fence. These masses would somehow curl up space and close it off.
His sparring partner de Sitter scoffed at that, arguing these "supernatural" masses would
not be part of the visible universe. As such, they were no more palatable than Newton's
old idea of absolute space, which was equally invisible and arbitrary.
In desperation and laid up with gall bladder trouble in February of 1917, Einstein hit on
the idea of a universe without boundaries, in which space had been bent around to meet
itself, like the surface of a sphere, by the matter within. "I have committed another
suggestion with respect to gravitation which exposes me to the danger of being confined
to the nut house," he confided to a friend.
This got rid of the need for boundaries -- the surface of a sphere has no boundary. Such a
bubble universe would be defined solely by its matter and energy content, as Machian
principles dictated. But there was a new problem; this universe was unstable, the bubble
had to be either expanding or contracting. The Milky Way appeared to be neither
expanding nor contracting; its stars did not seem to be going anywhere in particular.
Here was where the cosmological constant came in. Einstein made a little mathematical
fix to his equations, adding "a cosmological term" that stabilized them and the universe.
Physically, this new term, denoted by the Greek letter lambda, represented some kind of
long range repulsive force, presumably that kept the cosmos from collapsing under its
own weight.
Admittedly, Einstein acknowledged in his paper, the cosmological constant was "not
justified by our actual knowledge of gravitation," but it did not contradict relativity,
either. The happy result was a static universe of the type nearly everybody believed they
lived in and in which geometry was strictly determined by matter. "This is the core of the
requirement of the relativity of inertia," Einstein explained to de Sitter. "To me, as long
as this requirement had not been fulfilled, the goal of general relativity was not yet
completely achieved. This only came about with the lambda term."
The joke, of course, is that Einstein did not need a static universe to have a Machian one.
Michel Janssen, a Boston University physicist and Einstein scholar, pointed out,
"Einstein needed the constant not because of his philosophical predilections but because
of his prejudice that the universe is static."

Moreover, in seeking to save the universe for Mach, Einstein had destroyed Mach's
principle. "The cosmological term is radically anti-Machian, in the sense that it ascribes
intrinsic properties (energy and pressure-density) to pure space, in the absence of matter,"
said Frank Wilczek, a theorist at the Institute for Advanced Study in Princeton.
In any event, Einstein's new universe soon fell apart. In another 10 years the astronomer
Edwin Hubble in California was showing that mysterious spiral nebulae were galaxies far
far away and getting farther -- in short that the universe might be expanding.
De Sitter further confounded Einstein by coming up with his own solution to Einstein's
equations that described a universe that had no matter in it at all.
"It would be unsatisfactory, in my opinion," Einstein grumbled, "if a world without
matter were possible."
De Sitter's empty universe was also supposed to be static, but that too proved to be an
illusion. Calculations showed that when test particles were inserted into it, they flew
away from each other. That was the last straw for Einstein. "If there is no quasi-static
world," he said in 1922, "then away with the cosmological term."
In 1931, after a trip to the Mount Wilson observatory in Pasadena, Calif., to meet Hubble,
Einstein turned his back on the cosmological constant for good, calling it "theoretically
unsatisfactory anyway."
He never mentioned it again.
In the meantime, the equations for an expanding universe had been independently
discovered by Aleksandr Friedmann, a young Russian theorist, and by the Abbe Georges
Lemaitre, a Belgian cleric and physicist. A year after his visit with Hubble, Einstein
threw his weight, along with de Sitter, behind an expanding universe without a
cosmological constant.
But the cosmological constant lived on in the imagination of Lemaitre, who found that by
judicious application of lambda he could construct universes that started out expanding
slowly and then sped up, universes that started out fast and then slowed down, or one that
even began expanding, paused, and then resumed again.
This last model beckoned briefly to some astronomers in the early 1950's, when
measurements of the cosmic expansion embarrassingly suggested that the universe was

only two billion years old -- younger Earth. A group of astronomers visited Einstein in
Princeton and suggested that resuscitating the cosmological constant could resolve the
age discrepancy. Einstein turned them down, saying that the introduction of the
cosmological constant had been the biggest blunder of his life. George Gamow, one of
the astronomers, reported the remark in his autobiography, "My World Line," and it
became part of the Einstein legend.
Einstein died three years later. In the years after his death, quantum mechanics, the
strange set of rules that describe nature on the subatomic level (and Einstein's bete noire)
transformed the cosmological constant and showed just how prescient Einstein had been
in inventing it. The famous (and mystical in its own right) uncertainty principle decreed
that there is no such thing as nothing, and even empty space can be thought of as foaming
with energy.
The effects of this vacuum energy on atoms had been detected in the laboratory, as early
as 1948, but no one thought to investigate its influence on the universe as a whole until
1967, when a new crisis, an apparent proliferation of too-many quasars when the universe
was about one-third its present size, led to renewed muttering about the cosmological
constant. Jakob Zeldovich, a legendary Russian theorist who was a genius at marrying
microphysics to the universe, realized that this quantum vacuum energy would enter into
Einstein's equations exactly the same as the old cosmological constant.
The problem was that a naive straightforward calculation of these quantum fluctuations
suggested that the vacuum energy in the universe should be about 118 orders of
magnitude (10 followed by 117 zeros) denser than the matter. In which case the
cosmological constant would either have crumpled the universe into a black hole in the
first instant of its existence or immediately blown the cosmos so far apart that not even
atoms would ever have formed. The fact that the universe had been sedately and happily
expanding for 10 billion years or so, however, meant that any cosmological constant, if it
existed at all, was modest.
Even making the most optimistic assumptions, Dr. Zeldovich still could not make the
predicted cosmological constant to come out to be less than a billion times the observed
limit.
Ever since then, many particle theorists have simply assumed that for some as-yetunknown
reason the cosmological constant is zero. In the era of superstrings and
ambitious theories of everything tracing history back to the first micro-micro second of
unrecorded time, the cosmological constant has been a trapdoor in the basement of

physics, suggesting that at some fundamental level something is being missed about the
world. In an article in Reviews of Modern Physics in 1989, Steven Weinberg of the
University of Texas referred to the cosmological constant as "a veritable crisis," whose
solution would have a wide impact on physics and astronomy.
Things got even more interesting in the 1970's with the advent of the current crop of
particle physics theories, which feature a shadowy entity known as the Higgs field, which
permeates space and gives elementary particles their properties. Physicists presume that
the energy density of the Higgs field today is zero, but in the past, when the universe was
hotter, the Higgs energy could have been enormous and dominated the dynamics of the
universe. In fact, speculation that such an episode occurred a fraction of a second after
the Big Bang, inflating the wrinkles out of the primeval chaos -- what Dr. Turner calls
vacuum energy put to a good use -- has dominated cosmology in the last 15 years.
"We want to explain why the effective cosmological constant is small now, not why it
was always small," Dr. Weinberg wrote in his review. In their efforts to provide an
explanation, theorists have been driven recently to talk about multiple universes
connected by space-time tunnels called wormholes, among other things.
The flavor of the crisis was best expressed, some years ago at an astrophysics conference
by Dr. Wilczek. Summing up the discussions at the end of the meeting, he came at last to
the cosmological constant. "Whereof one cannot speak, thereof one must be silent," he
said, quoting from Ludwig Wittgenstein's "Tractatus Logico-Philosophicus."
Now it seems that the astronomers have broken that silence.

The Speed of Light

2009-11-03T23:23:00.000+05:30

The approximate speed of light was already known to us back in the time of Isaac Newton. Astronomers were able to use the rotation of planets and their moons as an incredibly precise system of "clockwork", and the precision of these measurements was so exact that they could identify the changes in apparent timings caused by light taking longer to reach us from more distant parts of the solar system. The critical measurement was that of the eclipse of the moons of Jupiter -- Roemer noted that the eclipses were seen slightly earlier when Jupiter was nearer to us, and slightly later when the planet was further away.
Newton's quoted estimates in Opticks of light taking seven or eight minutes to reach us from the Sun, along with an estimated distance of the Sun of seventy million miles, would have given an estimated speed of light of 150,000-160,000 miles per second. More modern values of a bit over eight minutes (~500 seconds) and just over 93 million miles give us a speed of around 186,000 miles per second, so the old figures weren't that far off
James Maxwell's work on electricity and magnetism in the mid-Nineteenth Century then led to a prediction of the existence of electromagnetic waves that just happened to propagate at the same speed as light. Maxwell argued that light was an electromagnetic wave, and that visible light consisted of electromagnetic radiation whose wavelengths happened to be in a suitable range for human eyes to be able to detect it.
Maxwell's work suggested that the speed of light should be constant, but didn't tell us exactly what sort of lightspeed constancy ought to be involved.....

G. F.Fitzgerald and H.A. Lorentz pointed out, around the turn of the Twentieth Century, that if lightspeed was absolutely fixed with respect to a background frame, but observers moving with respect to that background frame contracted (and perhaps time-dilated) in a particular way, then it'd be impossible for them to use round-trip measurements of the speed of light to work out whether they were "moving" or "stationary".
Einstein then took this system of "Lorentzian electrodynamics" and rederived it in more minimal form to produce his special theory of relativity. If we said that light was globally constant for all inertial observers, then the effects associated with Lorentz's "special factor" would absorb the disagreements that we'd otherwise expect between these observers, over whose frame was the "real" frame for the propagation of light. Although it seemed impossible for the same lightbeam to have the same totally-constant speed in everybody's different frames, special relativity's redefinitions of distances and times created a system in which this could work.
If a lightbeam links two agreed events, special relativity says that two differently-moving observers can disagree as to the distance that they believe the lightbeam "really" traveled and the amount of time that it "really" took to do it, but the combination of those two things, modified by the appropriate Lorentz factors, would combine to produce the same nominal value for the speed of the lightbeam for both observers. For this system to work, we need the lightbeam to travel in a simple way that isn't disturbed by the motion of any nearby objects ... we say that the geometry of spacetime, as defined by lightbeams, is "flat" for all observers with simple inertial motion.
When Einstein wanted to extend the principle of relativity to deal with all forms of motion, he immediately ran into a problem. Gravity bends lightbeams, and a lightbeam that seems straight and constant for an inertial observer can appear to mark out a variable-speed curved path for an accelerating observer. So special relativity's concept of lightspeed constancy didn't work in a more ambitious theory that also had to be able to deal with accelerations and gravitational effects. Gravity didn't just appear to alter light-distances, it mangled clockrates too, so for two different observers drifting in deep space in different gravitational environments, their different rates of timeflow could lead them to assign different speeds to the same lightbeam. These effects also cause a lightbeam to take longer to cross a more "gravitationally-dense" region than one in which the background gravitational field intensity is weaker ("Shapiro effect").
Under general relativity, the user can respond to these variations by deciding to define distances and times locally. It's no longer necessary for us to apply the earlier SR idea that lightspeed has to be globally constant across the region, it turns out that Nature is happy to violate that rule, as long as lightspeed is still locally constant. So if an observer is drifting in a strong-gravity region where gravitational time dilation is causing their clocks to run at half the speed that we'd otherwise expect, then the same slowing effect should make light move across the region at half the usual speed as well. Someone far outside the region might argue that light is appearing to cross the region more slowly than usual, but to a local observer, whose local references are warped by the same degree as the propagation of light, the speed of adjacent light seems to be exactly right. If it seems to have a different speed somewhere else, well, that's someone else's problem.
It could now be argued that since we had learnt that only local c-constancy was necessary (and that SR's "law" of the propagation of light wasn't a law after all), perhaps the geometrical basis of the earlier and more restricted"special" theory wasn't valid. Einstein preempted this argument by designing his general theory to reduce to the special theory over small regions of spacetime. He then argued that the special theory wasn't invalidated by general relativity, but instead lived on within it as a limiting case
Towards the end of his life, Einstein wrote that he no longer considered the decision to construct general relativity as a two-stage model, with "curvature" arguments built on top of a flat-spacetime "SR" foundation, as justifiable. It had been the best that could be achieved at the time, but with the benefit of hindsight it didn't deem to be defensible. Quite what Einstein may have meant by this, what the alternative might have been, and what the implications might be of having a general theory that didn't have a forced reduction to special relativity, still seem to be unresolved questions.

"Relativity and the Problem of Space"

2009-11-03T01:43:00.000+05:30

IT is characteristic of Newtonian physics that it has to ascribe independent and real existence to space and time as well as to matter, for in Newton's law of motion the idea of acceleration appears. But in this theory, acceleration can only denote "acceleration with respect to space". Newton's space must thus be thought of as "at rest", or at least as "unaccelerated", in order that one can consider the acceleration, which appears in the law of motion, as being a magnitude with any meaning. Much the same holds with time, which of course likewise enters into the concept of acceleration.
Newton himself and his most critical contemporaries felt it to be disturbing that one had to ascribe physical reality both to space itself as well as to its state of motion; but there was at that time no other alternative, if one wished to ascribe to mechanics a clear meaning.
It is indeed an exacting requirement to have to ascribe physical reality to space in general, and especially to empty space. Time and again since remotest times philosophers have resisted such a presumption. Descartes argued somewhat on these lines: space is identical with extension, but extension is connected with bodies; thus there is no space without bodies and hence no empty space. The weakness of this argument lies primarily in what follows. It is certainly true that the concept extension owes its origin to our experiences of laying out or bringing into contact solid bodies. But from this it cannot be concluded that the concept of extension may not be justified in cases which have not themselves given rise to the formation of this concept. Such an enlargement of concepts can be justified indirectly by its value for the comprehension of empirical results.
The assertion that extension is confined to bodies is therefore of itself certainly unfounded. We shall see later, however, that the general theory of relativity confirms Descartes' conception in a roundabout way.
What brought Descartes to his remarkably attractive view was certainly the feeling that, without compelling necessity, one ought not to ascribe reality to a thing like space, which is not capable of being "directly experienced"......

The psychological origin of the idea of space, or of the necessity for it, is far from being so obvious as it may appear to be on the basis of our customary habit of thought. The old geometers deal with conceptual objects (straight line, point, surface), but not really with space as such, as was done later in analytical geometry. The idea of space, however, is suggested by certain primitive experiences. Suppose that a box has been constructed.
Objects can be arranged in a certain way inside the box, so that it becomes full. The possibility of such arrangements is a property of the material object "box", something that is given with the box, the "space enclosed" by the box. This is something which is different for different boxes, something that is thought quite naturally as being independent of whether or not, at any moment, there are any objects at all in the box. When there are no objects in the box, its space appears to be "empty".
So far, our concept of space has been associated with the box. It turns out, however, that the storage possibilities that make up the box-space are independent of the thickness of the walls of the box. Cannot this thickness be reduced to zero, without the "space" being lost as a result? The naturalness of such a limiting process is obvious, and now there remains for our thought the space without the box, a self-evident thing, yet it appears to be so unreal if we forget the origin of this concept. One can understand that it was repugnant to Descartes to consider space as independent of material objects, a thing that might exist without matter. (At the same time, this does not prevent him from treating space as a fundamental concept in his analytical geometry.) The drawing of attention to the vacuum in a mercury barometer has certainly disarmed the last of the Cartesians. But it is not to be denied that, even at this primitive stage, something unsatisfactory clings to the concept of space, or to space thought of as an independent real thing.
The ways in which bodies can be packed into space (e.g. the box) are the subject of three-dimensional Euclidean geometry, whose axiomatic structure readily deceives us into forgetting that it refers to realisable situations.
If now the concept of space is formed in the manner outlined above, and following on from experience about the "filling" of the box, then this space is primarily a bounded space. This limitation does not appear to be essential, however, for apparently a larger box can always be introduced to enclose the smaller one. In this way space appears as something unbounded.
I shall not consider here how the concepts of the three-dimensional and the Euclidean nature of space can be traced back to relatively primitive experiences.
Rather, I shall consider first of all from other points of view the rôle of the concept of space in the development of physical thought.
When a smaller box s is situated, relatively at rest, inside the hollow space of a larger box S, then the hollow space of s is a part of the hollow space of S, and the same "space", which contains both of them, belongs to each of the boxes. When s is in motion with respect to S, however, the concept is less simple. One is then inclined to think that s encloses always the same space, but a variable part of the space S. It then becomes necessary to apportion to each box its particular space, not thought of as bounded, and to assume that these two spaces are in motion with respect to each other.
Before one has become aware of this complication, space appears as an unbounded medium or container in which material objects swim around. But it must now be remembered that there is an infinite number of spaces, which are in motion with respect to each other.
The concept of space as something existing objectively and independent of things belongs to pre-scientific thought, but not so the idea of the existence of an infinite number of spaces in motion relatively to each other.
This latter idea is indeed logically unavoidable, but is far from having played a considerable rôle even in scientific thought.
But what about the psychological origin of the concept of time? This concept is undoubtedly associated with the fact of "calling to mind", as well as with the differentiation between sense experiences and the recollection of these. Of itself it is doubtful whether the differentiation between sense experience and recollection (or simple re-presentation) is something psychologically directly given to us. Everyone has experienced that he has been in doubt whether he has actually experienced something with his senses or has simply dreamt about it. Probably the ability to discriminate between these alternatives first comes about as the result of an activity of the mind creating order.
An experience is associated with a "recollection", and it is considered as being "earlier" in comparison with present "experiences". This is a conceptual ordering principle for recollected experiences, and the possibility of its accomplishment gives rise to the subjective concept of time, i.e. that concept of time which refers to the arrangement of the experiences of the individual.
What do we mean by rendering objective the concept of time? Let us consider an example. A person A ("I") has the experience "it is lightning". At the same time the person A also experiences such a behaviour of the person B as brings the behaviour of B into relation with his own experience "it is lightning". Thus it comes about that A associates with B the experience "it is lightning". For the person A the idea arises that other persons also participate in the experience "it is lightning". "It is lightning" is now no longer interpreted as an exclusively personal experience, but as an experience of other persons (or eventually only as a "potential experience"). In this way arises the interpretation that "it is lightning", which originally entered into the consciousness as an "experience", is now also interpreted as an (objective) "event". It is just the sum total of all events that we mean when we speak of the "real external world".
We have seen that we feel ourselves impelled to ascribe a temporal arrangement to our experiences, somewhat as follows. If b is later than a and c later than b then c is also later than a ("sequence of experiences").
Now what is the position in this respect with the "events" which we have associated with the experiences? At first sight it seems obvious to assume that a temporal arrangement of events exists which agrees with the temporal arrangement of the experiences. In general, and unconsciously this was done, until sceptical doubts made themselves felt. In order to arrive at the idea of an objective world, an additional constructive concept still is necessary: the event is localised not only in time, but also in space.
In the previous paragraphs we have attempted to describe how the concepts space, time and event can be put psychologically into relation with experiences. Considered logically, they are free creations of the human intelligence, tools of thought, which are to serve the purpose of bringing experiences into relation with each other, so that in this way they can be better surveyed.
The attempt to become conscious of the empirical sources of these fundamental concepts should show to what extent we are actually bound to these concepts. In this way we become aware of our freedom, of which, in case of necessity, it is always a difficult matter to make sensible use.
We still have something essential to add to this sketch concerning the psychological origin of the concepts space-time-event (we will call them more briefly "space-like", in contrast to concepts from the psychological sphere). We have linked up the concept of space with experiences using boxes and the arrangement of material objects in them. Thus this formation of concepts already presupposes the concept of material objects (e.g. ''boxes"). In the same way persons, who had to be introduced for the formation of an objective concept of time, also play the rôle of material objects in this connection. It appears to me, therefore, that the formation of the concept of the material object must precede our concepts of time and space.
All these space-like concepts already belong to pre-scientific thought, along with concepts like pain, goal, purpose, etc. from the field of psychology. Now it is characteristic of thought in physics, as of thought in natural science generally, that it endeavours in principle to make do with "space-like" concepts alone, and strives to express with their aid all relations having the form of laws. The physicist seeks to reduce colours and tones to vibrations, the physiologist thought and pain to nerve processes, in such a way that the psychical element as such is eliminated from the causal nexus of existence, and thus nowhere occurs as an independent link in the causal associations. It is no doubt this attitude, which considers the comprehension of all relations by the exclusive use of only space-like concepts as being possible in principle, that is at the present time understood by the term "materialism" (since "matter" has lost its rôle as a fundamental concept).
Why is it necessary to drag down from the Olympian fields of Plato the fundamental ideas of thought in natural science, and to attempt to reveal their earthly lineage? Answer: in order to free these ideas from the taboo attached to them, and thus to achieve greater freedom in the formation of ideas or concepts. It is to the immortal credit of D. Hume and E. Mach that they, above all others, introduced this critical conception.
Science has taken over from pre-scientific thought the concepts space, time, and material object (with the important special case "solid body") and has modified them and rendered them more precise. Its first significant accomplishment was the development of Euclidean geometry, whose axiomatic formulation must not be allowed to blind us to its empirical origin (the possibilities of laying out or juxtaposing solid bodies). In particular, the three-dimensional nature of space as well as its Euclidean character are of empirical origin (it can be wholly filled by like constituted "cubes").
The subtlety of the concept of space was enhanced by the discovery that there exist no completely rigid bodies.
All bodies are elastically deformable and alter in volume with change in temperature. The structures, whose possible congruences are to be described by Euclidean geometry, cannot therefore be represented apart from physical concepts. But since physics after all must make use of geometry in the establishment of its concepts, the empirical content of geometry can be stated and tested only in the framework of the whole of physics.
In this connection atomistics must also be borne in mind, and its conception of finite divisibility; for spaces of sub-atomic extension cannot be measured up.
Atomistics also compels us to give up, in principle, the idea of sharply and statically defined bounding surfaces of solid bodies. Strictly speaking, there are no precise laws, even in the macro-region, for the possible configurations of solid bodies touching each other.
In spite of this, no one thought of giving up the concept of space, for it appeared indispensable in the eminently satisfactory whole system of natural science.
Mach, in the nineteenth century, was the only one who thought seriously of an elimination of the concept of space, in that he sought to replace it by the notion of the totality of the instantaneous distances between all material points. (He made this attempt in order to arrive at a satisfactory understanding of inertia).