Once beam has circulated stably in both rings, some time next week the LHC team will attempt to collide protons at the injection energy of 450 GeV (a total center of mass energy of 900 GeV). While this is much less than the Tevatron is colliding presently, it could provide some sorely needed initial data for the detectors to do timing and calibration of the various subsystems. There will even hopefully be a few collision events recorded with clear “dijet” structure – collisions where quarks and/or gluons inside the protons hit head on and effectively bounce sideways into the detector, giving two back-to-back collimated sprays of particles. Pictures of such events will be great to see, at long last!

You can follow progress live on twitter: http://twitter.com/cern and I will update this post as I learn more.

10:32 PST: The LHC has gotten beam around clockwise, to Point 6! Woo hoo!

10:45 PST: Magnet quench – should be recovered soon…

11:25 PST: Beam has reached Point 7!

11:30 PST: Point 8! Next beam will be sent past Point 1 where ATLAS is…

11:39 PST Beam all the way around the ring! WOO HOO!! It’s baaaaaack! The LHC Page 1 display shows that the injection probe beam made it more than once around the machine:

11:54 PST: Next goals: do the same with the counterclockwise beam. Will they attempt RF capture tonight? Trying to find out…

13:11 PST: Turns out (no pun intended) they decided to go for RF capture of the clockwise beam rather than probe counterclockwise. They are up to 10 million turns with the RF on! Fantastic!

13:30 PST: Having captured the beam for several minutes, the LHC will now switch to counterclockwise.

14:53 PST: About to go for a full orbit of the counterclockwise beam…done!! Now to RF capture!

15:30 PST: Counterclockwise beam is RF captured! The LHC is operational…colliding beams within a week? Stay tuned.

Unfortunately the video doesn’t seem to be embeddable, but you can go to the video page and click on the “David Gross” entry. (The others are good, too!)

You all know my perspective here — time probably exists, and we should try to understand it rather than replace it. But I’ll agree with David — let’s not ignore more “practical” problems, but not be afraid to tackle the big ideas!

The AP’s study isn’t actually a “study,” per se. Rather, what the Journal of Applied Physiology published was a point-counterpoint (pdf), now freely available for anyone to read. In in, Peter Weyand and Matthew Bundle argue that Pistorius’ prosthetics are a huge advantage, particularly in what matters most: how fast he can move his legs. Weyand and Bundle say that the lightweight blades allow Pistorius “to reposition his limbs 15.7 percent more rapidly than five of the most recent former world-record holders in the 100-meter dash” [AP].

There is, however, a counterpoint to this argument in the journal piece that yesterday’s news reports neglected, coauthored by Alena Grabowski of the MIT Media Lab (who led the research on Pistorius’ blades that 80beats covered last week). Her team has found that the limiting factor determining an athlete’s top speed was how hard the foot or prosthesis hit the ground. Their study showed this “ground force” was around 9% lower in the prosthetic limb versus the unaffected leg [The Guardian]. Grabowski’s research focused on professional runners with only one prosthetic leg.

No matter, Weyand and Bundle say in a rebuttal to the counterpoint: because Pistorius swings his legs so quickly (about .28 seconds per leg, as opposed to the .36 seconds of world-class sprinters with biological legs), he needs 20 percent less ground force than an ordinary runner would to maintain the same speed. Weyand told DISCOVER that the MIT team’s research is probably correct about speed and power when it comes to runners with only one prosthetic. “One limb can’t go faster than the other,” or the runner would go in a circle. But a runner like Pistorius with two prosthetics can learn to swing both legs at the “off-the-charts” speed of .28 seconds, he says, gaining a clear advantage.

Grabowski was understandably miffed at her side’s counterargument being left out of news reports. “We’re all sort of shaking our heads,” she said. She also questioned the validity of Weyand and Bundle’s findings, saying in an email to DISCOVER that they represent an opinion and not a peer-reviewed study, that they don’t consider the starting blocks and turning inherent in a 400-meter race, and Weyand and Bundle’s assertion that Pistorius’ blades take 10 seconds off his 400-meter time “is ridiculous and not based on data.”

But, Weyand tells DISCOVER, he and Bundle got their data during direct observations of Pistorius last year, during the time he was attempting to qualify for the Beijing Olympics. At that time they arrived at the same kind of conclusion Grabowski’s side has arrived at now—that the sprinter ought not be banned. The reason for this odd twist in the story, Weyand says, is that he and Bundle were brought in by Pistorius’ law firm during a hearing last May on the question of whether to overturn a ban on Pistorius, but the hearing could only consider the evidence used to enact the ban in the first place. So, Weyand tells DISCOVER, he and Bundle’s were advocating analysis suggested the ban be overturned because its basis was shoddy insufficient scientific evidence, and at the same time their own studies convinced them that he did have a clear advantage.

To make this affair even stranger, both sides—Weyand and Bundle’s team, and Grabowski’s—all co-authored a less controversial paper earlier this year in the same journal. However, Bundle tells DISCOVER, they left the question of advantage or no advantage out of that paper because they couldn’t agree, and published this point-counterpoint instead. “The comparisons and analysis that Peter and I present in the point-counterpoint are novel, in part because our co-authors prevented them from being included in the manuscript that appeared in June,” he says. As for peer review, Bundle says his argument did receive this treatment, because the journal’s standards consider the editors’ approval of an article to be an appropriate review.

This scientist smackdown isn’t going away: Grabowski told DISCOVER she would issue a press release in response to Weyand and Bundle’s, and continue her prosthesis research. Though if there’s one thing both sides can agree on, it’s that Pistorius is a remarkable athlete, advantage or not. “What he does as an athletic feat is really an amazing thing,” Weyand says.

Related Content:
80beats: Prosthetic Legs Aren’t Better Than the Real Thing… Yet
80beats: Scientist Smackdown: All Our Stories of Lively Scientific Debate
80beats: Toddler Gets a Telescoping, Prosthetic Arm Bone That Grows With Him
Science Not Fiction: Dr. Terminator: The Prosthetics Designer Who Makes Sci-Fi Sculptures

Image: flickr/Elvar Freyr

It’s been a mixed bag so far; while I’ve had great fun interacting with people here in Australia, I’ve also been struggling with a nasty cold I picked up on the flight over. Spent yesterday mostly in bed, too fogged up to even work on my talk for Friday. But when I’ve had the strength to be up and about, it’s been a treat. Here’s an iPhone snap of the University of Sydney; that clocktower in the middle houses, appropriately enough, the Centre for Time.

One of the perks of civilization that hasn’t quite caught on in these parts is affordable internet access in hotel rooms, so don’t expect a lot of blogging over the next week or two. Instead, I can point you to a couple of recent videos. One is an extended interview for Edge, entitled Why Does the Universe Look the Way it Does? It is an interview (presented in text and video), not a carefully pre-planned document, so not all thoughts are arranged as elegantly as one might like. Here is some of the flavor:

We are in a very unusual situation in the history of science where physics has become slightly a victim of its own success. We have theories that fit the data, which is a terrible thing to have when you are a theoretical physicist. You want to be the one who invents those theories, but you don’t want to live in a world where those theories have already been invented because then it becomes harder to improve upon them when they just fit the data. What you want are anomalies given to us by the data that we don’t know how to explain.

The other one is a panel discussion on Time Since Einstein, from the World Science Festival. As the description there says, it features Roger Penrose, David Albert, and some other people it would be too exhausting to list individually. Here’s part 1 of 5:

World Science Festival 2009: Time Since Einstein, Part 1 of 5 from World Science Festival on Vimeo.

Now if only my immune system would finish off the little viral buggers inside me, I could get out and see a bit of this interesting country.

The paper describes the results of our search for Higgs bosons predicted in supersymmetric theories, in the CDF experiment at Fermilab. Alas, we didn’t see any evidence for Higgs boson production, despite earlier hints that something might lurk in our sample, and so we were able to rule out some regions of supersymmetric parameter space. We first obtained a preliminary result from this analysis in late 2007. A group of us from Rutgers University, University of Valencia, and UC Davis all worked directly on it, within our several-hundred-member collaboration, using Tevatron data recorded up through mid-2007. Since then we’ve more than tripled our data sample, but this result stuck with the data sample on which it was based and has finally reached publication.

The analysis was the topic of the Ph.D. thesis of my student Cris Cuenca, who was formally a student of my former postdoc Juan Valls at University of Valencia. Cris was a visitor in our group at UC Davis, and I was effectively his thesis advisor. After we got the preliminary results, Cris focused on writing his thesis, eventually defending it in Valencia in April 2008. One nice effect of that was that I got to visit Valencia for the first time: what a fantastic city!

Once the thesis was done, it was clear we needed to publish the result formally. In fact, we should have been already writing the paper but as usual it’s hard to find time to get started on writing projects. Here is a place we could have saved some time, though…

Anyway, I wrote a draft after the birth of our son Ian in June 2008, while helping with baby care at home. In our collaboration there is a very formal review process before submitting a paper for publication. The spokespeople of the collaboration “godparents” who perform a full internal review of the analysis and the draft of the paper. Without naming names, we got some very knowledgeable godparents who asked us hard questions. Some of these questions took weeks to answer, because more data analysis had to be performed. And some of them led to even more questions. This review process is a good thing — it ensures that the quality of the final paper is very high, and that the result is correct to the best of our ability. In fact, in the course of the review process we found that there was a minor software bug, and we repeated the full end stage of the analysis. As it turned out, the bug had very little effect on the final result but we needed to be sure. (At present there are only unknown bugs in the analysis software!)

Whenever there is a change to an analysis like this, it needs to be re-approved in our physics analysis group meetings, with two presentations: a “pre-blessing”, and then a “blessing” two weeks later. (Hey, I’m not responsible for the pseudo-religious jargon used in this process…) This eventually happened in March 2008.

With the result final and the godparents happy with the paper draft, it was time for the general collaboration review. The collaboration gets two weeks to comment on each draft. Then the authors go through comment by comment and reply to the commenters, modifying the draft as needed. The godparents reviewed our replies and then we arrive at the next draft. This part of the process can take many weeks depending on how much time the authors have two devote to the paper. Once the final draft stage is reached, a “paper reading” is scheduled at the weekly general collaboration meeting. Following the presentation of the result, the collaboration has 48 hours before the paper is submitted to the journal. For us this happened, finally, in June of this year.

We heard back from PRL in late July, with blind referee comments to address. There then ensued a back-and-forth between us and the referees, answering questions, making changes to our submission, and eventually reaching agreement that the paper would be published in PRL. This happened a few weeks ago, and our paper has now appeared in what I think is still considered to be the most prestigious journal in our field, though Nature possibly tops it. (That might inspire a comment flame war but I hope not…)

Maybe this is an extreme example, and I certainly will endeavor to bring results to publication much more quickly in the future. (I always say that.) Certain results, if they are “hot”, can be published on a fast track in CDF, within weeks, but that is quite rare.

Many will, no doubt, argue that print media of almost every form is on the way out. Will this happen to print science journals? I do think there is a strong need for blindly refereed publication of scientific results, even though many scientists have reviewed these papers by the time they are submitted.

And clearly once the LHC experiments have physics results to publish, we will need a very rapid means of getting them into print. For any striking new discovery we’ll want to have a paper submitted for publication when we announce the result…this is in contrast to the case of not-very-striking results, where we announce the results at conferences first and publish later. The reason is that the experiments will try to establish scientific priority by publishing striking results before the other one does, but I have to wonder, in the modern age of electronic media and collaborations with thousands of members, whether simply announcing or presenting the the result in public doesn’t accomplish that anyway. If ATLAS says they see a resonance in muon pairs at 1.5 TeV mass and so does CMS, the same week, will we really say “ATLAS found it first” or “ATLAS was the one to discover it and CDF confirmed it?” I hope the science mainstream media don’t present such a thing that way…but more than that I just hope this is a problem we will actually face!

Rosetta, a European Space Agency craft, captured this view of the crescent Earth from about 400,000 miles away. The unmanned probe, which is busy chasing comets, was making its third flypast since it was launched in 2004. The close approach gave it a speed boost to send it on its mission to Comet Churyumov-Gerasimenko [Scientific American].

This will be Rosetta’s final visit to its home planet, having already executed a flyby of the asteroid Steins, a gravity assist with Mars, and two previous swoops past the Earth, gathering images all the way. Now it’s off to the comet.

Rosetta is carrying a fridge-sized lab, Philae, that it will send down to the comet. Anchored by tiny hooks, Philae will look for clues about the Solar System’s primal past, exploring a theory that comets are primitive rubble left over from the making of the Solar System [AFP].

While we bid safe travels to Rosetta, it could tell us something about the Earth itself on this final pass. Scientists notice unexpected behavior in spacecraft that make gravitational assists with our planet: Rosetta itself behaved exactly as expected in 2007 flyby but picked up an extra speed boost of 1.8 millimeters per second on its initial maneuver in 2005, leading some mission scientists to speculate that the Earth’s rotation might be distorting space-time more than they thought. “Some studies have looked for answers in new interpretations of current physics. If this proves correct, it would be absolutely groundbreaking news” [MSNBC], says Rosetta flight dynamics specialist Trevor Morley.

Related Content:
Bad Astronomy: Rosetta Takes Some Home Pictures
Bad Astronomy: Earth From Rosetta, from its 2007 flyby.
Bad Astronomy: Rosetta Swings By Mars!
DISCOVER: To Catch a Comet, which anticipated Rosetta, Stardust, and other comet-chasing missions.

Image: ESA

Looking online I find basically no research or anything written on this subject, but I am quite certain that just about everyone has some picture of time in their heads. For me, it’s quite a visual one, and past events and for that matter future ones are all attached to my mental picture of the time continuum. My notion of all history, from my own to that of the universe is inextricably linked with my internal mental images of time.

The thing is, as I have reflected on how I actually internally visualize time, I have found it to be somewhat bizarre. Or maybe not – I don’t really know because I haven’t really explored this in one-on-one conversation with others and haven’t learned from anything written out there just how different my picture is from others’. So here goes…I hope those of you out there who are intrigued or inspired by this will share their own images.

The main thing is that my mental picture of time changes depending on the time scale involved, from a microsecond to a minute to an hour, day, week, month, year, or many years. Starting at the largest time scales, those of the cosmos, when I am looking back in time over billions of years I imagine the classical, boring sort of “time as a line” progressing from left to right, straight across my mental image. As we zoom in to more recent cosmological time, though, millions of years, the line becomes more of a curve, and curving toward me. But then, very oddly (and this pattern will repeat itself) when we get to the much more recent past, say the last few thousand years, the curve is revealed to be more of a strip of sorts and moving from down and to the right (that’s the best way I can express it) toward the upper left.

It’s really strange: if I think of a time, say, 20 000 years ago, in my mental field of view it’s definitely off to the right, and as I refer to more recent times, the ribbon is such that more recent times are to the left of earlier times.

But this is not absolute: as we get to the last 2000 or so years, the earlier part is sort of coming straight at me, eventually becoming (you got it) a ribbon coming from the lower left to the upper right again. If I am considering the period from the Renaissance to the present, for example, I see a more distant past as actually more distant, off to the left, coming closer in more recent times an moving left to right. The future, on this time scale, goes off to my right sort of behind me (where I can’t see – duh!)

Okay I have probably lost at least 2/3 of the people who started reading this. Huh? Either this is so alien to how they think of time they don’t really see what I am seeing, or don’t care, or think that this is so off that wall it’s not worth reading further.

So, for the rest of you, the next part is where it gets kind of interesting. My mental timeline/ribbon, which has been snaking from left to right and back across my mental field of view, does a few more twists. As I think of the time scale of my life which began in the early 1960’s (okay, 1959), those early 60’s years are sort of again coming straight at me, becoming a left-to-right ribbon in the 70’s and then definitely right-to-left by the mid 80’s. The years from then to now flow from far away and to the right to nearby toward the left. But they don’t cross the center of my mental picture – that’s the present.

If we zoom in further, say to the past several years, the ribbon is a string of months going back. As I view earlier and earlier months they recede, up and to the right, and merge with the ribbon of the decades. Events, major and minor, are recallable by zooming into my past picture of then-present time. They are all there (the ones I remember, anyway), and freakily often I can remember the exact dates and times they occurred.

Last week to a few months ago is definitely on that ribbon, stretching up and to the right as we go further into the past. But then we get to yesterday, today, and tomorrow. Here the ribbon, which is segmented by lines marking the days, does a weird thing. For a given day, the ribbon starts out straight in front of me, going up, as if I had to climb it, the hours marked off by lines. The ribbon climbs up, into the darkness, reaching a peak and then, after midnight, descending down into the next day, week, month, and year, away from me, off into the distance in the left part of my mental view of time.

The future, the near future anyway (years) is definitely to the left in my mind’s eye. (And no, this whole post is not some sort of allegory of my personal political evolution…) The long term future is unpopulated by memories or images of expectations or hopes, and snakes off to the right.

All this changes when we are talking about smaller time scales. As I zoom into the present hour, to finer and finer scales it becomes more and more a straight line extending from left to right. I can zoom in from here to any micro-time scale and it stays the same. Somehow the left-right snaking curve is attached to particular memories, including my memories of historical events about which I have learned. Micro-time is so non-specific that it doesn’t trigger the snaky ribbon time view.

Another oddity about me in particular is that I actually find it hard to use a standard calendar to keep track of appointments, important meetings etc. I don’t see time on that seven-day table! But with a few anchor dates in the future, gotten from standard calendars, I can quickly calculate intervening dates and their days of the week. If I know I have an appointment on December 4, and an exam to give on December 7, I can see in my head what days they are and I do rather well remembering them. But at this moment, for example, I cannot tell you what day of the week Christmas is (though I know next January 18 is a Monday…)

I know there will be plenty of eye-rolling at this possibly boring description of my mental view of time, but, as I say, I hope it will trigger lots of you out there to share your own. If you really think about it (and I bet you probably have not) you so have *some* sort of picture in your head. What is it?

In the study, researchers exposed a thin “barrier” of four layers of cancer cells to cobalt-chromium ions or particles. Cells close to the nanoparticles experienced signs of mitochondrial damage. But even cells on the other side of the barrier suffered some DNA damage, the team found, despite the fact that there was no evidence that the metals themselves moved through the cells to the other side of the barrier [ScienceNOW Daily News]. Interesting indeed, but experts are pointing out that this set-up is not entirely relevant to humans, or any living organism for that matter.

The nanoparticles used in the study, cobalt-chromium particles, are not used in any medical treatments, but are used in larger pieces to make replacement hips. Hundreds of thousands of people receive cobalt-chromium implants every year, and there has been no evidence of ill effects reported [New Scientist]. Experts also point out that the experiment exposed cells to the nanoparticles at concentrations that were thousands of times higher than what would ever be seen in the body; remember the maxim that “the dose makes the poison.” Finally, the cells used to construct the barrier are human cancer cells (BeWo cells for the jargon-minded) that have been adapted to life in the petri dish, so they aren’t exactly like cells in the body.

Artificial set up or not, if the nanoparticles didn’t cross the barrier, then how was DNA damaged on the other side? The researchers suggested that the nanoparticles created a cascading chemical change. This is the part that is likely to whet the appetites of other scientists in the field. It looks like the nanoparticles set off a series of signals within the cells of the barrier, that ultimately led to the release of DNA-damaging [molecules] through two specific channels at the edge of the barrier [The Great Beyond]. When the researchers then blocked these channels in a subsequent experiment—poof!—the damage didn’t happen.

The researchers who conducted the experiments have responded to the criticism by saying that they only intended to study how the nanoparticles would interact with the physical barrier; they say they didn’t set out to conduct a realistic assessment of potential dangers posed by the particles. Hopefully, other research groups will set out to do just that. Scientists already suspect that nanoparticles can cause damage in some circumstances, and the need for more research is obvious.

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80beats: Nanotech Products on the Market May Have Unknown Health and Safety Risks
DISCOVER: Nano Risks Worry Scientists

Image: Wikimedia Commons / Nandiyanto

The rehabilitation of the beleaguered Large Hadron Collider was on hold tonight after the failure of one of its powerful cooling units caused by an errant chunk of baguette.

According to Popular Science:

[A] bird dropped some bread on a section of outdoor machinery, eventually leading to significant over heating in parts of the accelerator. The LHC was not operational at the time of the incident, but the spike produced so much heat that had the beam been on, automatic failsafes would have shut down the machine.

The overheating shouldn’t postpone the LHC’s reactivation at the end of the month, but all the delays and mishaps are adding to our paranoid, sci-fi suspicion: Is the LHC being sabotaged from the future? See this Cosmic Variance post for an authoritative take on such a possibility.

Related Content:
Discoblog: LHC Collisions to Commence Next Week…Hopefully
Discoblog: You Say Large Hadron Collider, I Say Sizeable Particle Crasher
Discoblog: While LHC Scientists Were Drinking Champagne, Hackers Were Attacking
Cosmic Variance: Spooky Signals from the Future Telling Us to Cancel the LHC!

Image: CERN

The telescope detected and studied a gamma ray burst, one of the massively bright and powerful explosions that occurs when stars go supernova in distant galaxies. Astronomers were interested in the gamma rays of differing energies and wavelengths that were generated by the explosion, and that raced each other across the universe. After a journey of 7.3 billion light-years, they all arrived within nine-tenths of a second of one another in a detector on NASA’s Fermi Gamma-Ray Space Telescope, at 8:22 p.m., Eastern time, on May 9 [The New York Times].

The researchers were wondering if certain gamma rays with both high energies and short wavelengths would arrive last, at the back of the pack. That would suggest that they had violated one of the principles set out in Einstein’s theory of relativity: that the speed of light is always constant. If researchers could detect a significant lag in some gamma rays, it would also give fresh hope to those ambitious researchers searching for a theory of everything.

At present, two separate theories dominate the world of physics. General relativity explains gravity and the motion of large objects such as planets, stars and galaxies, whereas quantum-mechanics explains the behaviour of very small things such as atoms. Both theories do well at explaining their respective worlds, but they don’t fit together mathematically. The problem is as fundamental as it gets: the two see space and time very differently [Nature News].

Einstein’s general relativity relies on space-time being smooth and continuous, while quantum mechanics suggests that the universe is made up of countless tiny grains of space-time. If the latter model is true, researchers theorized that the lumpy nature of space-time could interfere with the travel of some gamma rays. In simplified terms, that’s because higher energy photons have shorter wavelengths, which makes them more likely to bump into tiny lumps in spacetime and to be slowed by those structures. The slowdown would be tiny, but the lower velocity of high-energy photons could in principle be detectable over a journey of several billion light-years [Science News].

But the study of the Fermi Telescope’s results, published in Nature, declares that since all the gamma rays arrived within nine-tenths of a second apart, they must have all traveled at almost exactly the same speed. That suggests either that space-time is smooth and continuous, as general relativity proposed, or that the grains of space-time are smaller than we ever thought possible, and are having only the most minuscule effect on light waves. Researchers say the grains could theoretically be smaller than one-hundred-thousandth of a trillionth of the size of a proton [Science News].

Physicists working with the Fermi Telescope will keep looking for new evidence. But for now, says study coauthor Peter F. Michelson, “I take it as a confirmation that Einstein is still right” [The New York Times].

Related Content:
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80beats: First Map of the “Gamma Ray Universe” Produced

Image: NASA. Gamma ray bursts are the universe’s brightest explosions.

The Fermi Haze: A Gamma-Ray Counterpart to the Microwave Haze
Authors: Gregory Dobler, Douglas P. Finkbeiner, Ilias Cholis, Tracy R. Slatyer, Neal Weiner

Abstract: The Fermi Gamma-Ray Space Telescope reveals a diffuse inverse Compton signal in the inner Galaxy with the same spatial morphology as the microwave haze observed by WMAP, confirming the synchrotron origin of the microwaves. Using spatial templates, we regress out pi0 gammas, as well as ICS and bremsstrahlung components associated with known soft-synchrotron counterparts. We find a significant gamma-ray excess towards the Galactic center with a spectrum that is significantly harder than other sky components and is most consistent with ICS from a hard population of electrons. The morphology and spectrum are consistent with it being the ICS counterpart to the electrons which generate the microwave haze seen at WMAP frequencies. In addition to confirming that the microwave haze is indeed synchrotron, the distinct spatial morphology and very hard spectrum of the ICS are evidence that the electrons responsible for the microwave and gamma-ray haze originate from a harder source than supernova shocks. We describe the full sky Fermi maps used in this analysis and make them available for download.

In English: if the dark matter is a weakly-interacting massive particle (WIMP), individual WIMPs should occsasionally annihilate with other WIMPs, giving off a bunch of particles, including electron/positron pairs as well as high-energy photons (gamma rays). Indeed, searching for such gamma rays was one of the primary motivations behind the Fermi mission (formerly GLAST). And it makes sense to look where the dark matter is most dense, in the center of the galaxy. But it’s a very hard problem, for a simple reason — there’s lots of radiation coming from the center of the galaxy, most of which has nothing to do with dark matter. Subtracting off these “backgrounds” (which would be very interesting in their own right to galactic astronomers) is the name of the game in this business.

But Doug Finkbeiner at Harvard has for a while now been suggesting that there was already evidence for something interesting going on near the galactic center — not in the form of high-energy photons, but in the form of low-energy photons. The so-called WMAP haze is alleged to be radiation emitted when high-energy electrons are being accelerated by magnetic fields, leading to low-energy photons (synchrotron radiation). And Finkbeiner and collaborators claim that a careful analysis of data from WMAP (whose primary mission was to observe the cosmic microwave background) reveals exactly the kind of radiation you would expect from annihilations near the galactic center.

If that model is right, it gives us some guidance about what to look for in the gamma rays themselves, which Fermi is now observing. And according to this new paper, this is what we see.

That’s one of many images, and has been extensively processed; see paper for details. The new paper claims that there is an excess of gamma rays, and that it has just the right properties to be arising from the same population of electrons that gave rise to the WMAP haze. These much higher-energy photons arise from inverse Compton scattering — electrons bumping into photons and pushing them to higher energies — rather than synchrotron emission. So we’re not talking about gammas that are produced by dark-matter annihilations, but ones that might arise from electrons and positrons that are produced by such annihilations. The authors pointedly do not claim that what we see must arise from dark matter, or even delve very deeply into that possibility.

There have been speculations that the microwave haze could indicate new physics, such as the decay or annihilation of dark matter, or new astrophysics. We do not speculate in this paper on the origin of the haze electrons, other than to make the general observation that the roughly spherical morphology of the haze makes it difficult to explain with any population of disk objects, such as pulsars. The search for new physics – or an improved understanding of conventional astrophysics – will be the topic of future work.

That’s as it should be; whether or not the gamma-ray haze is real is a separate question from whether dark matter is the culprit. But on a blog we can speculate just a bit. Therefore I’m going to go out on a limb and say: maybe it is! Or maybe not. But a wide variety of promising experimental techniques are attacking the problem of detecting the dark matter, and we’ll be hearing a lot more in the days to come.

The light from the distant explosion, called a gamma-ray burst, first reached Earth on April 23 and was detected by NASA’s Swift satellite. Gamma-ray bursts are thought to be associated with the formation of star-sized black holes as massive stars collapse. Within hours, telescopes around the world were turned on the burst — the most violent explosions in the universe — observing its fading afterglow to glean clues about its source and location [SPACE.com].

As explained in two papers in Nature, the astronomers determined that the explosion happened just 630 million years after the Big Bang during a period of time known as the cosmic dark ages. In that era of primal darkness, the first generation of stars were born. The earliest stars are thought to have been massive, short-lived balls of hydrogen and helium, whereas their offspring incorporated heavier elements formed in the first generation’s explosive demise [Scientific American]. Because the recently viewed blast resembles more recent gamma ray bursts, researchers say the star was probably part of the second or third generations of stars.

Says study coauthor Dale Frail: “The primal cosmic darkness was being pierced by the light of the first stars and the first galaxies were beginning to form. The star that exploded in this event was a member of one of these earliest generations of stars” [SPACE.com]. Researchers plan to train the Hubble Space Telescope on the ancient galaxy where the star exploded in an attempt to learn more about the universe’s first stars.

Related Content:
80beats: World’s Biggest Telescope Will Provide “Baby Pictures” of the Universe
80beats: First Map of the “Gamma Ray Universe” Produced
80beats: Scientists May Have Detected the Death Throes of the Universe’s First Stars

Image: NASA/Swift/Stefan Immler

Now, via Dan Vergano’s Twitter feed, I see a story in Nature News to the effect that things have become murky once again. The proposals got too expensive, so NASA turned to the European Space Agency for help, but ended up giving away things the DOE thought were in their domain, so they threatened to take their toys and go home, giving up on the idea of a satellite altogether.

The story is complicated by disagreement over how important it is to measure the dark energy equation-of-state parameter, the number characterizing how quickly the energy density changes (if at all). It’s frequently said that “we know nothing” about dark energy, but that’s not true; we know that it’s smoothly distributed and nearly-constant in density through time. We even have a very natural candidate for what it is: the vacuum energy. There is of course the problem that the vacuum energy is much smaller than it should be, but that problem is there whether it’s strictly zero or just really small. Other models still have that problem, and tend to add other fine-tunings on top. It would be great, and we would certainly learn a lot, if the dark energy were not simply vacuum energy; but right now we have no compelling reason to think it’s not, so it’s a bit of a long shot.

Federal experts believe that a major earthquake could trigger fires at Los Alamos National Laboratory, releasing radioactive materials and endangering lives. The rupture of a seismic fault that runs underneath the lab would shake the ground more than scientists previously thought, according to a new report (PDF). A natural disaster here would be bad news, since the lab, just west of Santa Fe, is the main plutonium factory in the United States, believed to hold thousands of pounds of plutonium for use in nuclear weapons

Researchers study plutonium inside glove boxes—a Hollywood movie staple, consisting of a sealed enclosure with gloves so that someone outside the box can work on dangerous materials inside. A major earthquake would shake the ground enough to topple the glove boxes, says the new study. Some glove boxes are enormous and even contain furnaces to cast and mold plutonium. If one of these were to crash, the resulting fire would be uncontrollable and would create a vaporized plutonium cloud that could drift outside of the lab, says the safety report. In a worst-case scenario, a fire could release so much airborne plutonium that a person on the boundary of the lab would get a dose of radiation—potentially many thousands of times greater than a chest X-ray—that could be fatal in weeks, according to individuals knowledgeable about the study [Los Angeles Times].

The amount of vaporized plutonium could potentially be as much as 100 times more than the level allowed by the Department of Energy. Los Alamos responded to the report by saying they have taken many actions in the past year to increase fire safety including repacking plutonium into containers that would survive the accident. The lab also installed ventilation filters that perform at higher temperatures, improved the fire suppression system, implemented new controls for combustibles, added fire extinguishers to critical areas and developed plans to support firefighter response [AP].

The warning was delivered by Defense Nuclear Facilities Safety Board, an auditing agency that oversees federal nuclear programs; the board urged Energy Secretary Stephen Chu to act quickly to improve safety at Los Alamos. The laboratory will present a formal response to the report later this week.

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Image: Los Alamos National Laboratory

The LHC machine commissioning will pick up where it left off more than a year ago, and the plan is, if all goes well, to collide beams of protons in the experiments at a center of mass energy of 7 TeV (3.5 TeV per beam) before the end of the year. The luminosity will not be large at first, but should increase steadily with time until next fall, when the long shutdown to retrofit the remaining magnets with new quench detection and helium pressure relief systems begins. By that point the experiments hope to have accumulated upwards of 200 pb^-1 of integrated luminosity. This initial data sample is sorely needed to shake down the detectors and start tuning up the event reconstruction and analysis. And who knows, maybe we’ll see something totally unexpected. (Please, no black hole comments!)

The next main milestone will be beam circulating around the whole ring and captured by the RF system. That should happen by mid-November. Fingers crossed!

But experts aren’t sure what they’ll find inside the dump. At the very least, there is probably a truck down there that was contaminated in 1945 at the Trinity test site, where the world’s first nuclear explosion seared the sky and melted the desert sand 200 miles south of here during World War II [The New York Times]. It may also contain explosive chemicals that could have become more dangerous over the years of burial.

While the Los Alamos dump was alone on a mesa when it was established in 1944, the town has since grown up around it. Today several businesses are across the street from the site, so experts took extra precautions before starting the remediation effort. The team members pored over wartime classified documents and interviewed old-timers to learn what materials might have found their way into the dump, and took soil samples to test their estimates of how much plutonium might be buried there. They debriefed a laboratory worker who, as a young man, once fell into it [The New York Times].

Stimulus money has also gone to other facilities that worked on nuclear weapons. About $1.9 billion has gone to the Hanford site in Washington, where an earlier stage of the cleanup unearthed a metal safe with a glass jug inside. Inside that jug was plutonium left over from the first batch of weapons-grade plutonium ever made. Another batch of Hanford plutonium was used in the nuclear bomb that fell on the Japanese city of Nagasaki. Another $1.6 billion has been dedicated to cleaning up the Savannah River site in South Carolina, where nuclear materials were processed in the 1950s.

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Image: Department of Energy. The Trinity test was the first test of a nuclear weapon.

Science fiction has long tackled the biggest questions about the human condition: What is reality? What makes us human? What is consciousness?

So to Susan Schneider, an assistant professor of philosophy at the University of Pennsylvania, sci-fi seemed a logical way to illustrate some of the existential conundrums of philosophers over the ages, from Plato to René Descartes to David Chalmers.

“Science fiction fires the imagination and can get across conceptual ideas and thought experiments, or scenarios, that test philosophical theories,” she says. “Consider Isaac Asimov and his stories about robots and what happens if they become conscious. What does that tell us about the notion of a person?”

In her new book, Science Fiction and Philosophy: From Time Travel to Superintelligence (Wiley-Blackwell Publishing, 2009), Schneider mines time travel, artificial intelligence, robot rights, teleportation, and genetic modification to discuss the nature of space and time, free will, transhumanism, the self, neuroethics, and reality.

Each chapter tackles a different philosophical question via essays by Schneider and academic colleagues with titles like “Could I be in a Matrix or a Computer Simulation?” and “Free Will and Determinism in the World of Minority Report.” These discussions draw parallels between such sci-fi stalwarts as Star Trek, Blade Runner, and Brave New World, and philosophical classics like Plato’s The Republic and Descartes’ Meditations on First Philosophy.

The book sprang from a 2007 undergraduate Penn course of the same name, which she plans to resume in the 2010-2011 school year. The course grew of out of Schneider’s quest for a compelling way to introduce students to philosophy, plus her own research on the nexus of philosophy and cognitive science.

“Cognitive science regards thinking as computational. I examine how it shapes our understanding of the mind, the self, and consciousness,” says Schneider. “If both computers and humans arrive at answers in a computational manner, then how much of a difference is there between us and them? Not all philosophical questions involve cognitive science. But the area of philosophy I’m most interested in—the nature of our minds and thinking—is in constant dialogue with cognitive science.”

— Guest-blogger Susan Karlin

This was my last meeting – I have served on the committee for six years. The membership rotates roughly every two years. I had been an external reviewer and problem writer for a couple years, and was then asked to serve on the committee. I am sworn to secrecy about a lot of the details, for good reason, but let me try to tell you from my perspective as an exam writer how to study for this dreaded event in your physics education.

Firstly, there’s the format. The exam is 100 questions long, and you have 170 minutes to do it. This is, therefore, different from just about every other physics exam you have had in college, where you have, say, four to six problems in an hour-long exam. The GRE Physics problems (or “items” in assessment world jargon) are short, to-the-point questions, and just about all of them are short calculations, if any, and take little time once you see what to do. Writing such questions is a difficult thing to do, let me tell you. We are continually amazed how, after about six levels of review, we can find issues of clarity, reasoning, and even sometimes basic physics correctness in the items submitted to the pool. All the committee members spend a lot of time each year reviewing hundreds of problems, looking for flaws, but more often than you would think the face-to-face meeting in Princeton with the ETS folks reveals something previously overlooked. It’s a really interesting process.

For each new exam form we eventually arrive at 100 items that test mastery of a clear physics concept or idea, and there is, yes, a certain amount of memorization required in terms of the basic equations learned in undergraduate physics. But there are many problems that can be done using just concepts, and many that can be done with simple dimensional analysis. When there are numerical solutions (and many if not most are in that category) the numbers are chosen so as to allow easy arithmetic – no calculators are allowed.

My first piece of advice to students studying for this exam is to focus on reviewing the textbook from your freshman introductory physics course. In my years on the GRE committee, when I have needed to consult a text, it is that text at least 80% of the time. If you master every example in there and review the basic equations, you will do really well on the GRE. I have found that only a small fraction of the items on the GRE are actually from upper-level topics like stat mech, quantum, and special topics (solid state, nuclear, particle, cosmology, etc.) And presumably you have been studying the advanced topics more recently anyway. I think the single biggest mistake students make in studying for the GRE is to focus on too-advanced subjects.

The other piece of advice I give students is to be disciplined in your approach to actually taking the exam. You only have an average of 1.7 minutes per problem! If you get bogged down on a long algebraic calculation, you risk not being able to complete the exam, including items that you would correctly answer in a few seconds. So when you take the exam, read each problem, answer it if you can do so reasonably quickly and then put an X on the problem number. If you think the problem will take some time or a long calculation, put a circle around the number and come back to it in a second pass through the whole thing. But pIck off the easy ones first! It also helps build confidence as you go through.

Also realize that the GRE penalizes random guessing: your raw score is the number correct minus the 1/4 times the number incorrect. As a result it’s no better to guess than to leave an answer blank if you cannot eliminate some of the five choices. But if you can eliminate some, then by all means guess! Look carefully at the possible answers – sometimes just the units, or magnitude, or mathematical form can give you a way to guess more astutely.

So just what is the GRE measuring? A critic might point out that it measures the ability to work under pressure, memorization, and quick mathematical reasoning and calculation. Though these are good qualities for a physicist to have, they are by no means the only qualities required for a successful career. I would argue further, though, that the Physics GRE really does test knowledge about basic physics and the ability to analyze physical situations accurately.

So then how important is the Physics GRE for your career? It turns out that it is in fact quite important. Some of the top programs in the US even go to the extent of requiring a GRE score above some threshold for considering the applicant. I have served on our graduate admissions committee for five years now, and I can tell you that we regard the GRE as just one piece of information telling us how likely a student is to thrive in our program. We do see a clear correlation between an incoming graduate student’s Physics GRE score and their score on the other dreaded exam in a physics student’s career, the Ph.D. written preliminary exam, which is a very different beast. (There was, a few years back, some lore that the GRE Verbal score was a better predictor than the GRE Physics score, and there is a correlation, but not as strong as with the GRE Physics score.)

In considering an applicant we look at a number of things, including the applicant’s own statement, experience, letters of recommendation, and their undergraduate transcript, in addition to the GRE general and subject scores, to get an idea of the whole student. My own observation is that students below about the 30% level have a very hard time attaining a Ph.D., though this is by no means absolute. I am sure there are tons of very successful physicists out there who, for whatever reason, scored poorly on this peculiar exam and went on to great careers.

So, to of those of you facing this exam in a few weeks, I wish you good luck! Review your intro course, get a good night’s sleep before the exam, and make sure you pick off all the easy problems that you can!

The Lucasian Professorship was established in 1663 and previous holders have included Isaac Newton [BBC News]; it’s considered one of the most prestigious academic posts in the world. Hawking held the job for 30 years, but stepped down in September following his 67th birthday, in accordance with a university rule.

Green is one of the founders of string theory, which many physicists believe paves the way to understanding all of nature’s forces, including electromagnetism, the strong force that holds atomic nuclei together, the weak force that governs certain forms of radiation, and gravity that keeps our feet on the ground and the Earth in orbit around the Sun [The Guardian]. Its goal is to unify the two fundamental physics theories of the 20th century: quantum mechanics, which governs the behavior of subatomic particles, and Einstein’s cosmological theory of general relativity.

String theory, which is formulated in ten dimensions with the extra dimensions ‘compactified’ at very high energy, has met with many successes over the years. It has, for example, been shown to contain all the known particles of the so-called standard model of particle physics [Cambridge Network].

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Image: University of Cambridge

Yes, that’s a pretty suave picture of me on the image capture. What can I say? I’m just one of those lucky folks with an effortless magic in front of the camera.

If you prefer to get your talks about entropy unadulterated by voice and motion, and don’t mind a more technical presentation, I’ve put the slides from my recent Caltech colloquium online. These are aimed basically at grad students in physics, so there is an equation or two, and the caveats are spelled out more clearly. But the punchline is the same.

The basis of the experiment was a refutation of a rule of magnetism observed in our day-to-day lives: No matter how many times you divide a magnet, the resulting fragments will always have both north and south poles. But more than 70 years ago, physicist Paul Dirac theorized that elementary particles should exist that have only a north or south pole, and dubbed these theoretical particles magnetic monopoles. Last month, researchers got closer to spotting a monopole than ever before, when they created ripples that had the same magnetic properties as monopoles.

The new study, published in Nature, describes the phenomenon in a strange, crystalline material known as spin ice. These crystals are made up of pyramids of charged atoms, or ions, arranged in such a way that when cooled to exceptionally low temperatures, the materials show tiny, discrete packets of magnetic charge. Now one of those teams has gone on to show that these “quasi-particles” of magnetic charge can move together, forming a magnetic current just like the electric current formed by moving electrons [BBC News].

To study the phenomenon in greater detail, the research team injected muons – short-lived cousins of electrons – into the spin ice. When the muons decayed, they emitted positrons in directions influenced by the magnetic field inside the spin ice. This revealed that the monopoles were not only present but were moving [New Scientist]. The ripples of distinct north or south charges moved about at random until a magnetic field was applied, which caused the charges to flow through the crystal as a current.

This may seem like fairly abstract research, but physicist Steven Bramwell swears that it could have practical applications–they’ll just be a ways down the road. Data is stored on computer hard discs by magnetising their surfaces in patterns that represent 1s and 0s. Bramwell speculates that monopoles could one day be used as a much more compact form of memory than anything available today, given that the monopoles are only about the size of an atom. “It is in the early stages, but who knows what the applications of magnetricity could be in 100 years time,” he says [New Scientist].

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Image: ISIS. Atom-sized north and south poles in spin ice drift in opposite directions when a magnetic field is applied.

Since I am quoted (in a rather non-committal way) in the essay, it’s my responsibility to dig into the papers and report back. And my message is: relax! Western civilization will survive. The theory is undeniably crazy — but not crackpot, which is a distinction worth drawing. And an occasional fun essay about speculative science in the Times is not going to send us back to the Dark Ages, or even rank among the top ten thousand dangers along those lines.

The standard Newtonian way of thinking about the laws of physics is in terms of an initial-value problem. You specify the state of the system (positions and velocities) at one moment, then the laws of physics tell you how it will evolve into the future. But there is a completely equivalent alternative, which casts the laws of physics in terms of an action principle. In this formulation, we assign a number — the action — to every possible history of the system throughout time. (The choice of what action to assign is simply the choice of what laws of physics are operative.) Then the allowed histories, the ones that “obey the laws of physics,” are those for which the action is the smallest. That’s the “principle of least action,” and it’s a standard undergraduate exercise to show that it’s utterly equivalent to the initial-value formulation of dynamics.

In quantum mechanics, as you may have heard, things change a tiny bit. Instead of only allowing histories that minimize the action, quantum mechanics (as reformulated by Feynman) tells us to add up the contributions from every possible history, but give larger weight to those with smaller actions. In effect, we blur out the allowed trajectories around the one with absolutely smallest action.

Nielsen and Ninomiya (NN) pull an absolutely speculative idea out of their hats: they ask us to consider what would happen if the action were a complex number, rather than just a real number. Then there would be an imaginary part of the action, in addition to the real part. (This is the square-root-of-minus-one sense of “imaginary,” not the LSD-hallucination sense of “imaginary.”) No real justification — or if there is, it’s sufficiently lost in the mists that I can’t discern it from the recent papers. That’s okay; it’s just the traditional hypothesis-testing that has served science well for a few centuries now. Propose an idea, see where it leads, toss it out if it conflicts with the data, build on it if it seems promising. We don’t know all the laws of physics, so there’s no reason to stand pat.

NN argue that the effect of the imaginary action is to highly suppress the probabilities associated with certain trajectories, even if those trajectories minimize the real action. But it does so in a way that appears nonlocal in spacetime — it’s really the entire trajectory through time that seems to matter, not just what is happening in our local neighborhood. That’s a crucial difference between their version of quantum mechanics and the conventional formulation. But it’s not completely bizarre or unprecedented. Plenty of hints we have about quantum gravity indicate that it really is nonlocal. More prosaically, in everyday statistical mechanics we don’t assign equal weight to every possible trajectory consistent with our current knowledge of the universe; by hypothesis, we only allow those trajectories that have a low entropy in the past. (As readers of this blog should well know by now; and if you don’t, I have a book you should definitely read.)

To make progress with this idea, you have to make a choice for what the imaginary part of the action is supposed to be. Here, in the eyes of this not-quite-expert, NN seem to cheat a little bit. They basically want the imaginary action to look very similar to the real action, but it turns out that this choice is naively ruled out. So they jump through some hoops until they get a more palatable choice of model, with the property that it is basically impotent except where the Higgs boson is concerned. (The Higgs, as a fundamental scalar, interacts differently than other particles, so this isn’t completely ad hoc — just a little bit.) Because they are not actually crackpots, they even admit what they’re doing — in their own words, “Our model with an imaginary part of the action begins with a series of not completely convincing, but still suggestive, assumptions.”

Having invoked the tooth fairy twice — contemplating an imaginary part of the action, then choosing its form so as to only be relevant where the Higgs is concerned — they consider consequences. Remember that the effect of the imaginary action is non-local in time — it depends on what happens throughout the history of the universe, not just here and now. In particular, given their assumptions, it provides a large suppression to any history in which large numbers of Higgs bosons are produced, even if they won’t be produced until some time in the future.

So this model makes a strong prediction: we’re not going to be producing any Higgs bosons. Not because the ordinary dynamical equations of physics prevent it (e.g., because the Higgs is just too massive), but because the specific trajectory on which the universe finds itself is one in which no Higgses are made.

That, of course, runs into the problem that we have every intention of making Higgs bosons, for example at the LHC. Aha, say NN, but notice that we haven’t yet! The Superconducting Supercollider, which could have found the Higgs long ago, was canceled by Congress. And in their December 2007 paper — before the LHC tried to turn on — they very explicitly say that a “natural” accident will come along and break the LHC if we try to turn it on. Well, we know how that turned out.

But NN have an ingenious suggestion for saving us from future accidents at the LHC — which, as they warn, could endanger lives. They propose a card game with more than a million cards, almost all of which say “go ahead, no problem.” But one card says “don’t turn on the LHC!” In their model, the nonlocal effect of the imaginary part of the action is to ensure that the realized history of the universe is one in which the LHC never turns on; but it doesn’t matter why it doesn’t turn on. If we randomly pick one out of a million cards, and honestly promise to follow through on the instructions on the card we pick, and we happen to pick the card that says not to turn it on, and we therefore don’t — that’s a history of the universe that is completely unsuppressed by their mechanism. And if we choose a card that says “go ahead,” well then their theory is falsified. (Unless we try to go ahead and are continually foiled by a series of unfortunate accidents.) Best of all, playing the card game costs almost nothing. But for it to work, we have to be very sincere that we won’t turn on the LHC if that’s what the card says. It’s only a million-to-one chance, after all.

Note that all of this “nonlocal in time,” “receiving signals sent from the future” stuff is a bit of a red herring, at least at the classical level. We often think that the past is set in stone, while the future is still to be determined. But that’s not how the laws of physics operate. If we knew the precise state of the universe, and the exact laws of physics, the future would be as utterly determined as the present (Laplace’s Demon). We only think otherwise because our knowledge of the present state is highly imperfect, consisting as it does as a few pieces of information about the coarse-grained state. (We don’t know the position and velocity of every particle in the universe, or for that matter in any macroscopic object.) So there’s no need to think of NN’s imaginary action as making reference to what happens in the future — all the necessary data are in the present state. What seems weird to us is that the NN mechanism makes crucial use of detailed, non-macroscopic information about the present state; information to which we don’t have access. (Such as, “does this subset of the universe evolve into the Large Hadron Collider?”) That’s not how the physics we know and love actually works, but the setup doesn’t actually rely on propagation of signals backwards in time.

At the end of the day: this theory is crazy. There’s no real reason to believe in an imaginary component to the action with dramatic apparently-nonlocal effects, and even if there were, the specific choice of action contemplated by NN seems rather contrived. But I’m happy to argue that it’s the good kind of crazy. The authors start with a speculative but well-defined idea, and carry it through to its logical conclusions. That’s what scientists are supposed to do. I think that the Bayesian prior probability on their model being right is less than one in a million, so I’m not going to take its predictions very seriously. But the process by which they work those predictions out has been perfectly scientific.

There is another reasonable question, which is whether an essay (not a news story, note) like this in a major media outlet contributes to the erosion of trust in scientists on the part of the general public. I would love to see actual data one way or the other, which went beyond “remarkably, the view of the common man aligns precisely with the view I myself hold.” My own anecdotal observations are pretty unambiguous — the public loves far-out speculations like this, and happily eats them up. (See previous mocking quote, now applied to myself.) It’s always important to distinguish as clearly as possible between what is crazy-sounding but well-established as true — quantum mechanics, relativity, natural selection — and what is crazy-sounding and speculative, even if it’s respectable speculation — inflation, string theory, exobiology. But if that distinction is made, I’ve always found it pretty paternalistic and condescending to claim that we should shield the public from speculative science until it’s been established one way or the other. The public are grown-ups, and we should assume the best of them rather than the worst. There’s nothing wrong with letting them in on the debates about crazy-sounding ideas that we professional scientists enjoy as our stock in trade.

The disappointing thing about the responses to the article is how non-intellectual they have been. I haven’t heard “the NN argument against contributions to the imaginary action that are homogeneous in field types is specious,” or even “I see no reason whatsoever to contemplate imaginary actions, so I’m going to ignore this” (which would be a perfectly defensible stance). It’s been more like “this is completely counter to my everyday experience, therefore it must be crackpot!” That’s not a very sciencey attitude. It certainly would have been incompatible with all sorts of important breakthroughs in physics through the years. The Nielsen/Ninomiya scenario isn’t going to be one of those breakthroughs, I feel pretty sure. But it’s sensible enough that it merits disagreement on the basis of rational arguments, not just rolling of eyes.

The lab experiment simulates a cosmological black hole, where the intense gravity curves space-time, sucking in any matter or radiation that gets too close. Not even light can escape a black hole (hence the name). The researchers couldn’t duplicate the intense gravity, but they could build a metamaterial with a physical structure that would make light curve into its central core, never to return. The device they built works only with microwaves so far, but the researchers say a visible light black hole is the next step.

The device consists of 60 layers of circuit board arranged in concentric rings. The layers are coated in copper and etched with intricate patterns that interact with light waves at microwave frequency. “When the incident electromagnetic wave hits the device, the wave will be trapped and guided in the shell region towards the core of the black hole, and will then be absorbed by the core,” says Cui. “The wave will not come out from the black hole.” In their device, the core converts the absorbed light into heat [New Scientist]. The research paper, which has been posted on the preprint server arXiv but hasn’t yet been published, notes that the scientists measured microwaves going in, and found none coming out.

Making a similar device that captures visible light will be quite a challenge, as visible light has a wavelength orders of magnitude smaller than that of microwave radiation. This will require the etched structures to be correspondingly smaller. Cui is confident that they can do it. “I expect that our demonstration of the optical black hole will be available by the end of 2009,” he says [New Scientist].

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Images: Qiang Cheng and Tie Jun Cui

So here is a new such test, courtesy of Rachel Bean of Cornell. She combines a suite of cosmological data, especially measurements of weak gravitational lensing from the Hubble Space Telescope, to see whether GR correctly describes the behavior of large-scale structure in the universe. And the surprising thing is — it doesn’t. At the 98% confidence level, Rachel finds that general relativity is inconsistent with the data. I’m not sure why we haven’t been reading about this in the science media or even on other blogs — it’s certainly a newsworthy result. Admittedly, the smart money is still that there is some tricky thing that hasn’t yet been noticed and Einstein will eventually come through the victor, but this is serious work by a respected cosmologist. Either the result is wrong, and we should be working hard to find out why, or it’s right, and we’re on the cusp of a revolution.

Here is the abstract:

A weak lensing detection of a deviation from General Relativity on cosmic scales
Authors: Rachel Bean

Abstract: We consider evidence for deviations from General Relativity (GR) in the growth of large scale structure, using two parameters, γ and η, to quantify the modification. We consider the Integrated Sachs-Wolfe effect (ISW) in the WMAP Cosmic Microwave Background data, the cross-correlation between the ISW and galaxy distributions from 2MASS and SDSS surveys, and the weak lensing shear field from the Hubble Space Telescope’s COSMOS survey along with measurements of the cosmic expansion history. We find current data, driven by the COSMOS weak lensing measurements, disfavors GR on cosmic scales, preferring η < 1 at 1 < z < 2 at the 98% significance level.

Let’s see if we can’t unpack the basic idea. The real problem in testing GR in cosmology is that any particular kind of spacetime curvature can be a solution to Einstein’s theory — all you need are the right sources of matter and energy. So in order to do a real test, you need to have some confidence that you understand what is creating the gravitational field — in the Solar System it’s the Sun and planets, in the binary pulsar it’s two neutron stars, and in the early universe it’s radiation. For large-scale structure things are a bit less clear — there’s ordinary matter, and dark matter, and of course dark energy.

Nevertheless, even though there are some things we don’t know about dark matter and dark energy, there are some things we think we do know. One of those things is that they don’t create any “anisotropic stress” — basically, a force that pulls different sides of things in different directions. Given that extremely reasonable assumption, GR makes a powerful prediction: there is a certain amount of curvature associated with space, and a certain amount of curvature associated with time, and those two things should be equal. (The space-space and time-time potentials φ and ψ of Newtonian gauge, for you experts.) The curvature of space tells you how meter sticks are distorted relative to each other as they move from place to place, while the curvature of time tells you how clocks at different locations seem to run at different rates. The prediction that they are equal is testable: you can try to measure both forms of curvature and divide one by the other. The parameter η in the abstract is the ratio of the space curvature to the time curvature; if GR is right, the answer should be one.

There is a straightforward way, in principle, to measure these two types of curvature. A slowly-moving object (like a planet moving around the Sun) is influenced by the curvature of time, but not by the curvature of space. (That sounds backwards, but keep in mind that “slowly-moving” is equivalent to “moves more through time than through space,” so the curvature of time is more important.) But light, which moves as fast as you can, is pushed around equally by the two types of curvature. So all you have to do is, for example, compare the gravitational field felt by slowly-moving objects to that felt by a passing light ray. GR predicts that they should, in a well-defined sense, be the same.

We’ve done this in the Solar System, of course, and everything is fine. But it’s always possible that some deviation from Einstein shows up at much larger distance and weaker gravitational fields than we have access to in our local neighborhood. That’s basically what Rachel’s paper does, considering different measures of the statistical properties of large-scale structure and comparing them to the predictions of a phenomenological model of the gravitational field. A crucial role is played by gravitational lensing, since that’s where the deflection of light comes in.

And here is the answer: the likelihood, given the data, for different values of 1/η, the ratio of the time curvature to the space curvature. The GR prediction is at 1, but the data show a pronounced peak between 3 and 4, and strongly disfavor the GR prediction. If both the data and the analysis are okay, there would be less than a 2% chance of obtaining this result. Not as good as 0.01%, but still pretty good.

So what are we supposed to make of this? Don’t get me wrong: I’m not ready to bet against Einstein, at least not yet. Mostly my pro-Einstein prejudice comes from long experience trying to come up with alternative theories of gravity that are simultaneously logically sensible and observationally consistent; it’s just very hard to do. But more generally, good scientists naturally have a strong suspicion of any claimed observational result that purports to overthrow an extremely well-established theory. That’s just common sense, not hidebound establishmentarianism; most such anomalies eventually go away.

But that doesn’t mean that you ignore anomalies; you just treat them with caution. In this case, there could be an unrecognized systematic error in the data set, or a subtle error in the analysis. Given 1:1 odds, that’s certainly where the smart money would bet right now. It’s also possible that the fault lies with dark matter or dark energy, not with gravity — but it’s hard to see how that could work, to be honest. Happily, it’s an empirical question — more data and more analysis will either reinforce the result, or make it go away. After all, some anomalies turn out to be frighteningly real. This one is worth taking seriously, to say the least.

Once again, scientists are trying to read your mind. Specifically, they are using fMRI (functional magnetic resonance imaging) to see what areas of the brain people use to process numbers, and even to determine what number a person just viewed.

Test subjects were shown images with either an amount of something—in this case a bunch of dots—or a numeral like 2, 4, or 6. Scientists suspected that our brains use overlapping areas to process quantities and their symbolic representations, however the findings suggest that people process the fundamental idea of a quantity differently from the way they process a symbol representing that quantity [Science News]. When a test subject looked at two dots and later at the number 2, different areas of the brain were activated, researchers report in Current Biology.

Scientists already knew that the the frontal and parietal lobes of the brain are involved in number processing. Monitoring those areas, researchers saw distinct activity patterns associated with specific numerals and dot quantities, and used the info to determine what number the test subjects had just seen.

When it came to small numbers of dots, the researchers found that brain activity patterns changed gradually in a way that reflected the ordered nature of the numbers. For example, one might be able to conclude that the pattern for six is between that for five and seven. In the case of the numerals, the researchers could not detect this same gradual change. This suggests their methods simply might not be sensitive enough to detect this progression yet, or that these symbols are in fact coded as more precise, discrete entities in the brain [LiveScience].

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Image: Current Biology / Eger, et al.

NEW YORK — Citing the extremely low level of entropy present before a normal set of football downs, scientists from the NFL’s quantum mechanics and cosmology laboratories spoke Monday of a theoretical proto-down before the first. “Ultimately, we believe there are an infinite number of proto-downs played before the first visible snap,” lead NFL scientist Dr. Oliver Claussen said during a press conference, adding that the very last yocto-down is a by-product of leftover fourth downs from this universe, as well as those from a theoretical universe running along an arrow of time concurrent to our own.

Probably some enthusiastic football coach is going to try to cash in by writing a book about the idea, while others fulminate on the sidelines about how such irresponsible speculation is destroying the game. (Thanks to Ahmet Toker and Tom Fishman.)

“Everything happens to everybody sooner or later if there is time enough.” — George Bernard Shaw, Back to Methuselah

“Time is the longest distance between two places.” — Tennessee Williams, The Glass Menagerie

“The future’s not ours to see.” — Doris Day

“Time rushes toward us with its hospital tray of infinitely varied narcotics, even while it is preparing us for its inevitably fatal operation.” — Tennessee Williams, The Rose Tattoo

“Time, you old gypsy man,
Will you not stay,
Put up your caravan
Just for one day?”
– Ralph Hodgeson

“Time present and time past
Are both perhaps present in time future,
And time future contained in time past.
If all time is eternally present
All time is unredeemable.”
– T.S. Eliot, “Burnt Norton” (Four Quartets)

“Time is the substance from which I am made. Time is a river that carries me along, but I am the river; it is a tiger that devours me, but I am the tiger; it is a fire that consumes me, but I am the fire.” — Jorge Luis Borges, Labyrinths.

Apparently you have to be extremely careful when it comes to poetry; fair use doesn’t necessarily extend very far.

Over the past week, four papers have shown up on astro-ph using new WFC3 data of the Hubble Ultra Deep Field (see the prescient comment by Brian Mingus in the original blog post):

Bouwens et al
Oesch et al
Bunker et al
McLure et al

All of these papers are based upon data released on September 9th, from a large “Treasury” program to extend the wavelength coverage of the Hubble Deep Field. The first two papers were produced by the team that actually proposed the observations, and the second two were from groups that were sitting around eagerly waiting for the first group’s data to be publicly released¹.

All of the papers deal with the statistics and properties of extremely high redshift (i.e. distant and young) galaxies. The dominant technique for finding high redshift galaxies has been looking for “drop out” galaxies. These are galaxies that have essentially zero flux in blue filters, due to absorption from intergalactic gaseous Hydrogen, and significant flux in all redder filters (at wavelengths that are largely unaffected by the same gas). Higher redshift galaxies “drop out” of progressively redder filters, because the rest frame (un-redshifted) wavelength at which the gas absorbs the galaxy’s light appears redshifted to longer and longer (redder) wavelengths for highly redshifted galaxies. This technique was pioneered by Guhathakurta, Tyson, & Majewski in 1990, and put on the map as a technique for galaxy selection by Chuck Steidel throughout the 90’s.

These early works looked for “U-band dropouts”, which turn out to be star forming galaxies at a redshift of 3 (about 2.5 billion years after the big bang). Subsequently, people had the bright idea to just keep pushing the drop out technique to redder wavelengths, to look for ever more distant galaxies. However, this comes at a cost, since more distant galaxies tend to be much fainter, so you need to work harder to have statistically significant detections in the red filters, and strong contraints on the absence of detections in bluer filters. The new WFC3 data pushes this technique out of the optical and into the infrared, selecting galaxies at redshifts from 6 to 9, when the universe was 0.5-1 billion years old. (Note: in the picture above, each successive column shows an image taken at redder and redder wavelengths. The likely distant galaxies are those that show up in the rightmost three columns but none of the leftmost columns)

The new papers all find that at these early times, the star formation rate of the universe is on the rise. This isn’t too surprising, given that you’re getting so close to the beginning of the universe — early on, structure hasn’t really had much time to form, so naturally you should find that fewer galaxies have yet had time to go about their business.

All in all, these are nice results doing just what the new data was designed to do.

¹ In Jackson Hole, I once saw a bald eagle sitting high in a tree above a stream. There was an osprey sitting lower down the same tree. The river guide said the eagle waits for the osprey to catch a fish, and then just steals the fish from the osprey.

² After posting this, I found a nice write-up by Ron Cowan here, as well as discussion of the result from the always lovely Peter Coles here. There’s also a cute discussion of the stress involved in such publications over at andxyl’s place.

In the study, published in Nature, researchers used high-speed video to find out what was happening. Drops of liquid usually form tight spheres, but as two electrically charged droplets come close to each other, the spheres begin to warp — and at very short distances, a small bridge of fluid forms between the drops. When the electrical charge is low, that bridge grows until the drops merge together, but when the charge is high, something else happens: the bridge allows the droplets to exchange their charge and then snaps. The water flows back into the bubbles, and by the time the two drops collide, they are back in their spherical shape. Rather than merging, their surface tension causes them to bounce off one another like beach balls [Nature].

The work may sound more like a fun lab trick than vitally important science, but researcher William Ristenpart explains that the findings have implications for many high-tech industries that use electric fields to manipulate tiny water drops. For example, the discovery probably explains why the petroleum industry has not been able to achieve greater efficiencies in the electrostatic removal of water from crude oil, Ristenpart says, a process that has been used for nearly a century, though he adds that the process is extremely difficult to observe because of the opaqueness of the oil [ScienceNOW Daily News].

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Image: W.D.Ristenpart and B.Hamlin, U.C.Davis. The top sequence shows the normal action of a drop, while the lower sequence shows the drop bouncing away.

Or more precisely, from Physics Buzz:

Assuming you’re not in a big lecture hall and the professor shuts the door at the start of class, how long does it take for you and your classmates to deplete the oxygen enough to feel it?

The mathletes at the Buzz make a few assumptions about the classroom, but in a 16-foot by 16-foot classroom with a 10-foot ceiling, packed with 34 bleary-eyed students and one Red Bull fueled professor the answer is…2 hours and 51 minutes!

Of course you’ll probably be brain dead long before that point.

Check their math here and then tell us why they’re right or wrong, or if you’ve ever survied such a physics marathon.

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Image: flickr / Rober S. Donovan

The physicist Erwin Schrödinger came up the the feline thought experiment in the 1930s, presenting it as a caution against applying quantum rules to the real, ‘classical’ world…. At its most fundamental level, quantum mechanics says that particles can only exist in discrete states. For example, researchers can measure the direction a particle spins as either ‘up’ or ‘down’, but nothing in between. Yet, as long as no one is looking, the particle exists in a combination of both states simultaneously, a strange blend known as a superposition [Nature News].

Schrödinger proposed an experiment where a cat would be put in box containing a vial of poison gas. A hammer would be suspended ready to smash down on the vial if triggered by the decay of a single atom of radioactive material. If no one looked inside the box, Schrödinger said, the radioactive atom would be in a superposition–both intact and decayed–and therefore the cat would exist in two states as well, being simultaneously alive and dead.

To take a step towards this logical impossibility, researchers propose in a paper posted on the arXiv pre-print server that they start with a much smaller living organism, a virus–although other researchers point out that there is still debate over whether viruses are truly alive. Still, the researchers say that since they think they’ve figured out a way to conduct an experiment putting a single virus in a superposition, it may as well be tried.

The proposed experiment would involve trapping a single virus in a vacuum chamber, and then gradually cooling it and slowing it down until it rests, motionless, in its lowest possible energy state. Finally a single photon, a light particle, would be beamed into the chamber, and as long as nobody peeked inside the chamber the virus would be placed in a superposition of two states: both moving and not.

Researcher Oriol Romero-Isart, one of paper’s coauthors, say the experiment would only work if the virus has certain properties: if it’s dielectric (meaning it doesn’t conduct electricity), can survive the vacuum and appears transparent to laser light, which would otherwise rip it apart. As luck would have it, Romero-Isart and co say that several viruses fit the bill. The common flu virus is known to be able to survive in a vacuum, seems to have the required dielectric properties and may well be transparent to a careful choice of laser light. The tobacco mosaic virus, to all intents and purposes a dielectric rod, looks like another good candidate [Technology Review].

Some experts say the experiment may have limited use. Physicist Martin Plenio (who’s not involved in the proposed research) says there’s no reason to think that a virus will behave differently than an inorganic molecule, but he still thinks that testing relatively large objects, whether viruses or molecules, could prove interesting. According to quantum mechanics, it should be possible for macroscopic objects like cars and people to enter superpositions, but that never appears to happen. Studying relatively large objects, says Plenio, may help physicists learn where the quantum world ends and the our macroscopic world begins [Nature News].

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The Loom: Schrodinger’s Tat (science tattoo)

Image: Wikimedia Commons

In fact our original idea wasn’t merely the idea of dark photons, it was dark atoms — having dark matter bear a close family resemblance to ordinary matter, all the way to having most of its mass be in the form of composite objects consisting of one positively-charged dark particle (a “dark proton”) and one negatively-charged dark particle (a “dark electron”). We thought about it a very tiny bit, but didn’t pursue the idea and only mentioned it in passing at the very end of our paper. There is an informal rule in theoretical physics that you should only invoke the tooth fairy (propose an extremely speculative idea or hope for some possible but unprovable result) once per paper, so we stuck with only a single kind of charged dark particle.

But once someone invokes the tooth fairy in their paper, anyone who writes another paper gets to invoke the tooth fairy for themselves. (That’s just how the rule works.) And the good news is that it’s now been done:

Atomic Dark Matter
Authors: David E. Kaplan, Gordan Z. Krnjaic, Keith R. Rehermann, Christopher M. Wells

Abstract: We propose that dark matter is dominantly comprised of atomic bound states. We build a simple model and map the parameter space that results in the early universe formation of hydrogen-like dark atoms. We find that atomic dark matter has interesting implications for cosmology as well as direct detection: Protohalo formation can be suppressed below $M_{proto} \sim 10^3 – 10^6 M_{\odot}$ for weak scale dark matter due to Ion-Radiation interactions in the dark sector. Moreover, weak-scale dark atoms can accommodate hyperfine splittings of order $100 \kev$, consistent with the inelastic dark matter interpretation of the DAMA data while naturally evading direct detection bounds.

(Note that one of the authors has been a guest-blogger here at CV.) It looks like a great paper, and they seem to have done a careful job at chasing down some of the interesting implications of dark atoms. In fact the idea might be more robust than that of the one in our paper; the fact that dark atoms are neutral lets you slip loose of some of the more inconvenient observational bounds. And the last sentence of the abstract points to an intriguing consequence: by giving the dark matter particles some structure, you might be able to explain the intriguing DAMA results while remaining consistent with other (thus far negative) direct searches for dark matter. Stay tuned; that dark sector may turn out to be a pretty exciting place after all.

Every magnet has a north and a south pole; if you break a magnet into hundreds of pieces, each fragment will also have a north and a south pole of its own. But researchers think that magnetic monopoles exist–particles with only a north or south pole–and there are several reasons physicists would like to see them. In 1931, famed British theorist Paul Dirac argued that the existence of monopoles would explain the quantization of electric charge: the fact that every electron has exactly the same charge and exactly the opposite charge of every proton [ScienceNOW Daily News].

Scientists have scoured the world and the cosmos looking for such particles, says Jonathan Morris, coauthor of one of the two new studies published in Science. “People have been looking for monopoles in cosmic rays and particle accelerators — even Moon rocks” [Nature News], he says. And while the two research groups didn’t quite find the elusive particles, they did detect ripples in strange materials known as spin ices, and found that the ripples have the same magnetic properties as monopoles.

The two groups both used spin ices (one group used holmium titanate and the other used dysprosium titanate), which are man-made solid materials in which the magnetic ions line up like the hydrogen ions in water ice. The magnetic ions sit at the tips of four-sided pyramids or tetrahedra connected corner to corner…. At temperatures near absolute zero, they should organize themselves by a simple rule: In each tetrahedron, two ions point their north poles inward toward the center and two point outward [ScienceNOW Daily News]. But when researchers heated the materials slightly, the tidy magnetic properties of the spin ice was disrupted.

The heating caused tiny flaws in which one ion flipped, leaving its tetrahedron with three ions pointing their north poles inward; that meant the adjacent tetrahedron had only one ion pointing its north poles inward. These lopsided tetrahedrons act, respectively, like north and south magnetic poles. One imbalanced tetrahedron affects another, and the imbalance can flow through the material. These ripples create concentrations of either north or south poles, which amounts, essentially, to magnetic monopoles.

But to physicists like Kimball Milton, the experiments didn’t come close to achieving the ultimate goal of detecting a monopole particle. “I might object to [the researchers] saying ‘genuine magnetic monopoles’, because when you say genuine, that implies to me it’s a point particle, and it’s not,” Milton says. “It’s an effective excitation that at some level looks like a monopole, but it’s not really fundamentally a monopole” [Scientific American].

Looks like there are plenty more monopole hunting expeditions in our future.

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Image: T. Fennell, et al. / Science

Actually here they are described as “freaky observers,” rather than the more conventional “freak observers.” That description brings to mind Smoove B rather than Ludwig Boltzmann, but who knows? Maybe unlikely thermal fluctuations tend to be pretty kinky.

And yes, before you all start in: we know that Boltzmann Brains don’t really make for a credible alien menace, if you insist on being persnickety about what they supposedly really represent. It’s not that they “perceive” a universe more chaotic than ours — it’s that they would dominate the total number of observers if the universe really were more chaotic than ours. (Which it isn’t!) Also, they would tend to dissolve back into the chaos from which they came, rather than staging a coordinated attack on our homeland. Still! What a novel challenge for the Allies’ greatest hero.

Via Hero Complex come these ingenious public service announcements and travel posters from a near future in which time travel is possible and robots are self-cleaning. Designed by artist Amy Martin, the posters are $20 each and proceeds benefit 826LA, a non-profit writing center for kids 6 to 18.

I predict we’re going to look back at the release of the original, Swedish Let the Right One In as the vampires’ artistic high point. I also predict that the release of the American version will mark the end of the whole bloody, sexy craze.

So what’s next for fans of the undead? Zombies.

Anticipating public demand for a government response to the growing threat, mathematicians at the University of Ottawa have published an epidemiological model of an outbreak of zombie infection. [viaTalking Squid]

This comes just a few months after the Boston Police confirmed via Twitter that they would promptly inform the public in the event of a zombie attack. [via Consumerist]

And we’re just one month away from the release of the new Woody Harrelson movie Zombieland. I’m telling you, people. Zombies.

It may seem a somewhat surprising first, since atoms have been imaged for decades. The earliest pictures of individual atoms were captured in the 1970s by blasting a target – typically a chunk of metal – with a beam of electrons, a technique known as transmission electron microscopy (TEM)…. But strange though it might seem, imaging larger molecules at the same level of detail has not been possible – atoms are robust enough to withstand existing tools, but the structures of molecules are not [New Scientist].

In the new study, published in Science, researchers used an atomic force microscope to image the molecule in unprecedented resolution. The measurement requires extremes of precision. In order to avoid the effects of stray gas molecules bounding around, or the general atomic-scale jiggling that room-temperature objects experience, the whole setup has to be kept under high vacuum and at blisteringly cold temperatures [BBC News]; 5 Kelvin, to be exact. Rather than relying on an optical system to produce pictures, atomic force microscopes use a probe that narrows to an atomic-scale tip, and measures the forces of attraction between the tip and the molecule’s components.

Lead researcher Leo Gross was able to get the shot of pentacene because he stuck a molecule of carbon monoxide (CO) on the tip of the probe. Previously, there have been problems with the tips accidentally sticking to the molecules, and dragging them around the surface during the imaging process. ‘The CO doesn’t bond to the pentacene molecule,’ Gross says, and this means the tip can get very close to the molecule and therefore provide a better image [Chemistry World].

Gross hopes his technique of imaging molecules will help in the nascent field of “molecular electronics”, a potential future for electronics in which individual molecules serve as switches and transistors [BBC News]. In June, Gross released another study showing that atomic force microscopy could image the amount of charge on single atoms. “Now we would like to combine these two works, to observe the transport of charge through molecules on the single electron scale” [Chemistry World], he says.

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Image: Science / AAAS

But a solution to the arrow-of-time dilemma would certainly be nice, quantum or otherwise, so the paper has received a bit of attention (Focus, Ars Technica). Unfortunately, I don’t think this paper qualifies.

The arrow-of-time dilemma, you will recall, arises from the tension between the apparent reversibility of the fundamental laws of physics (putting aside collapse of the wave function for the moment) and the obvious irreversibility of the macroscopic world. The latter is manifested by the growth of entropy with time, as codified in the Second Law of Thermodynamics. So a solution to this dilemma would be an explanation of how reversible laws on small scales can give rise to irreversible behavior on large scales.

The answer isn’t actually that mysterious, it’s just unsatisfying. Namely, the early universe was in a state of extremely low entropy. If you accept that, everything else follows from the nineteenth-century work of Boltzmann and others. The problem then is, why should the universe be like that? Why should the state of the universe be so different at one end of time than at the other? Why isn’t the universe just in a high-entropy state almost all the time, as we would expect if its state were chosen randomly? Some of us have ideas, but the problem is certainly unsolved.

So you might like to do better, and that’s what Maccone tries to do in this paper. He forgets about cosmology, and tries to explain the arrow of time using nothing more than ordinary quantum mechanics, plus some ideas from information theory.

I don’t think that there’s anything wrong with the actual technical results in the paper — at a cursory glance, it looks fine to me. What I don’t agree with is the claim that it explains the arrow of time. Let’s just quote the abstract in full:

The arrow of time dilemma: the laws of physics are invariant for time inversion, whereas the familiar phenomena we see everyday are not (i.e. entropy increases). I show that, within a quantum mechanical framework, all phenomena which leave a trail of information behind (and hence can be studied by physics) are those where entropy necessarily increases or remains constant. All phenomena where the entropy decreases must not leave any information of their having happened. This situation is completely indistinguishable from their not having happened at all. In the light of this observation, the second law of thermodynamics is reduced to a mere tautology: physics cannot study those processes where entropy has decreased, even if they were commonplace.

So the claim is that entropy necessarily increases in “all phenomena which leave a trail of information behind” — i.e., any time something happens for which we can possibly have a memory of it happening. So if entropy decreases, we can have no recollection that it happened; therefore we always find that entropy seems to be increasing. Q.E.D.

But that doesn’t really address the problem. The fact that we “remember” the direction of time in which entropy is lower, if any such direction exists, is pretty well-established among people who think about these things, going all the way back to Boltzmann. (Chapter Nine.) But in the real world, we don’t simply see entropy increasing; we see it increase by a lot. The early universe has an entropy of 10⁸⁸ or less; the current universe has an entropy of 10¹⁰¹ or more, for an increase of more than a factor of 10¹³ — a giant number. And it increases in a consistent way throughout our observable universe. It’s not just that we have an arrow of time — it’s that we have an arrow of time that stretches coherently over an enormous region of space and time.

This paper has nothing to say about that. If you don’t have some explanation for why the early universe had a low entropy, you would expect it to have a high entropy. Then you would expect to see small fluctuations around that high-entropy state. And, indeed, if any complex observers were to arise in the course of one of those fluctuations, they would “remember” the direction of time with lower entropy. The problem is that small fluctuations are much more likely than large ones, so you predict with overwhelming confidence that those observers should find themselves in the smallest fluctuations possible, freak observers surrounded by an otherwise high-entropy state. They would be, to coin a pithy phrase, Boltzmann brains. Back to square one.

Again, everything about Maccone’s paper seems right to me, except for the grand claims about the arrow of time. It looks like a perfectly reasonable and interesting result in quantum information theory. But if you assume a low-entropy initial condition for the universe, you don’t really need any such fancy results — everything follows the path set out by Boltzmann years ago. And if you don’t assume that, you don’t really explain our universe. So the dilemma lives on.

In the following audio you can listen in on what amounted to a 20-minute chat with David Tennant (The Doctor, obviously) and Julie Gardner (executive producer and now head of drama for BBC Worldwide) and five reporters. You’ll here Tennant and Gardner talk about shooting “Planet of the Dead,” the sadness of ending their time working with the Doctor, their futures, and the possibility of Tennant attending the next day’s panel naked. Both are charming, and I think you’ll enjoy it.

(The recording is a little noisy at the start, but on the upside, you’ll get to hear Tennant expressing amazement at all the recorders paced in front of him. Also, you’ll hear a lot of reporters asking questions, but no, none of them are me.)

The Audio Charm of Dr. Who, David Tennant

Among the things we learned:

• X-Men’s Storm would need to consume 120,000 in food calories or have a nuclear reactor in her stomach to generate the minimum 500 million joules of energy needed to shoot lightning bolts from her body. On the plus side, such a metabolism definitely helps one stay in movie shape.
• In Mission Impossible, Tom Cruise survives a 2,200-g mid-air body slam (where g is the acceleration due to Earth’s gravity, 9.8 meters per second squared), but Newton’s second law doesn’t fare so well. “A force to the head exceeding 150 g’s is usually fatal.” Usually, sure. All that Scientology in his noggin probably helped cushion the blow…
• Best physics flick went to 2001: A Space Odyssey for the jogging sequence in the rotating circular space station, while raspberries went to Armageddon, The Day After Tomorrow and The Core for such travesties as exploding fireballs on an asteroid with no atmosphere. Star Trek got a (dis)honorable mention for phasers that took a half-second to reach their targets. “You’d be better off with a gun,” he noted disdainfully.

After the session, Weiner noted the rising trend of scientists—James Kakalios (The Physics of Superheroes, Lawrence Krauss (Physics of Star Trek) and our own Phil Plait—using pop culture to teach science literacy. “The public’s view of the world is so shaped by popular culture, we have to start to make those connections and show what’s real and what’s not,” he said.

—Guest-blogger Susan Karlin

* Folks in LA can catch Weiner when he hosts “When Worlds Collide: The Science of Movies” panel at the Academy of Motion Pictures Arts & Sciences Aug 6.

If a nanoparticle field emission thruster (the aforementioned NanoFET) has been a subject of investigation for University of Michigan electrical engineer Brian Gilchrist for several years now. Gilchrist, joined by a team of scientists, has published and presented papers (pdf) at conferences (pdf) around the country, trying to show the theory of how electronically charged nanotubes could enable a spaceship to achieve astonishing speeds.

As Gilchrist envisions it, a nanoFET engine would be installed as a series of flat plates around our spaceship—let’s say the Millennium Falcon. So instead of the white glare of rockets pointed off the back of the Falcon as it flees TIE fighters, there would be a series of flat panels that resemble the silicon wafers that go into microchips (the MEMS production process would be very similar). Each panel would be covered in round discs, each 10 centimeters in diameter, which in turn would be comprised of thousands of emitters, each roughly 100 micrometers in diameter.

Each emitter works a bit like an tiny particle accelerator: The anode of the emitter charges the nanoparticles, which are then accelerated and then shot out a tube by a strong magnetic field generated by a stack of microchip-like components. “In that a particle accelerator uses an electrical field to propel charged particles to high speeds — that’s exactly what we’re doing,” Gilchrist told MSNBC. Thanks to Newton’s third law, as the ship ejects particles in one direction, the ship moves in the opposite direction. Eject long, thin nanotubes for high-efficiency, slow acceleration; use short, thick nanotubes for better acceleration at greater cost of energy. The NanoFet could potentially eject nearly any type of nanoparticle that would take a charge.

The nanoFET is also remarkable flexible and scalable. A plate of nearly any size could be placed more or less anywhere on the object to be propelled, and each plate could be nearly any size. So instead of the Millennium Falcon merely being the fastest hunk of junk in the galaxy, it could also be astonishingly maneuverable, with smaller plates on different parts of the hull to establish tight turns and sudden changes in direction.

The only real downside is that nanoFETs are not imagined to provide the kind of high acceleration needed to break Earth’s gravity and escape orbit. But once in space, a ship equipped with nanoFET would have an extremely thin and lightweight engine with a commensurately compact fuel source. The nanoFET would be able achieve nearly constant acceleration. Do that for long enough, and speeds of 90 percent of light speed might become possible. Just think, if the Americans in Armageddon had a nanoFET powered space ship available to get out and intercept that asteroid, that whole Affleck-Armageddon fiasco could have been avoided. And wouldn’t we all want that?