strange attractor

If it's Sunday night, it must be Denver. Jen-Luc Piquant and I flew into the Mile-High City today for the 2007 APS March Meeting. While waiting for the plane to take off, I distracted myself from the cries of the inevitable Wailing Infant by playing a little game I like to call "Spot the Physicists." It's easy enough to do so, especially since this time of year, they tend to be clutching a copy of the Bulletin of the American Physical Society containing abstracts for the meeting -- although this year, the APS only published the session titles and speakers to save the trees. The 2007 conference features some 7000 abstracts, which would pretty darned unwieldy in printed form. (In the recent past, the March meeting Bulletin was published in two parts, it had gotten so big.) One of the flight attendants must have noticed the high percentage of science types on the flight. After an impressively smooth landing, she got on the intercom to praise the pilots and remarked, "Once again, skill and technology trump fear and superstition."

It was a nicely appropriate kickoff to a conference that celebrates  the latest research in materials and condensed matter physics, biophysics, and related subfields, all of which play key enabling roles in the development of new technology. Even the tiniest, seemingly insignificant effect can turn out to be important, especially as one gets down to micro- and nano-scales. Take, for example, the case of something dubbed "the Casimir effect." Basically, it refers to the attraction between two objects should they come within, say, 1/5000 of an inch of each other. It's related to the energy inherent in the quantum vacuum. Empty space isn't as empty as one might thing, since it roils and boils with matter/antimatter pairs of virtual particles that pop into existence and just as quickly annihilate into radiation, i.e., electromagnetic waves. (There's even an ongoing debate as to whether the Casimir effect could account for the attraction between ships moored too closely together in a harbor.)

The effect gets its name from a Dutch physicist named Hendrik Casimir, who first proposed the existence of such a force (along with Dirk Polder) and proposed an experiment in 1948 to detect it. It involves two uncharged parallel metal plates. Normally there would be no electromagnetic charge to exert a force sufficient to pull the plates together or push them apart. Casimir proved that if the plates were close enough, however, there is still a tiny attractive force between them.

His explanation was that, because the parallel plates are so close together, the virtual particle pairs can't easily come between them, so there are more pairs popping into existence around the outside of the plates than between them. That imbalance creates a force that pushes the plates inward ever so slightly. The smaller the separation between the plates, the greater the inward attraction.  Really, it's quite a nifty confirmation of  Casimir's theory, and provided  critical evidence of the existence of virtual particles, which don't hang around long enough to "observe" directly via the usual means (i.e., the electromagnetic force).

In fine scientific tradition, physicists weren't content to just accept those 1948 results outright. They kept testing it, devising new, improved experiments to measure the Casimir effect more accurately. For instance, scientists at Los Alamos National Laboratory and the University of California, Riverside made some excellent measurements in 1997, followed in 2001 by the measurement of the Casimir force between parallel plates using micro-resonators, by scientists at the University of Padua.

About a month ago, the Casimir Effect was back in the news (among physics sorts) thanks to new results published in Physical Review Letters from a research group at the National Institute of Standards and Technology and the University of Colorado in Boulder, led by Nobel Laureate Eric Cornell. They were testing another prediction, this one made in 1955 by Evgeny Lifschitz, that temperature affects the Casimir force.

Cornell et al. specifically studied the Casimir-Polder force between a neutral ultracold rubidium atom and a glass surface a mere few microns away. Then they doubled the temperature of the glass to 600 degrees Kelvin. The surrounding environment was still at room temperature. The result: the sharp rise in temperature caused a threefold increase in the attractive force exerted by the glass on the rubidium atoms. I'm still a bit fuzzy as to why this happens, but the good people at Physics News Update (via the American Institute of Physics) explain it thusly:

According to quantum mechanics, the vacuum contains fleeting electromagnetic waves, in turn consisting of electric and magnetic fields. The electric fields can slightly rearrange the charge in atoms. Such 'polarized' atoms can then feel a force from an electric field. The vacuum's electric fields are altered by the presence of the glass, creating a region of maximum electric field that attracts the atoms. In addition, heat inside the glass also drives the fleeting electromagnetic waves, some of which leak onto the surface as 'evanescent waves.' These evanescent waves have a maximum electric field on the surface and further attract the atoms. Electromagnetic waves from heat in the rest of the environment would usually cancel out the thermal attraction from the glass surface. However, dialing up the temperature on the glass tilts the playing field in favor of the glass's thermal force and heightens the attraction between the wall and the atoms.

Well, I trust that clears everything up for everyone. The non-scientists reading this are probably wondering, "Why should we care?" That's a very good question. Back in the late 19th century, Nikola Tesla put forth the notion that the vacuum held enormous reservoirs of energy, which he believed to be sufficient to revolutionize human society if we could only figure out how to harness it. His instincts were right about there being energy in the vacuum, but not about how much there might be: the estimates I've heard peg the Casimir to be equivalent to the weight of 1/30,000th of an ant. Scaled up to macroscale units of measurement, even if we could release (and harness) the energy stored in a single cubic meter of the quantum vacuum, it would yield maybe one ten-billionth of a joule. That's not even sufficient to light a tiny 10-watt bulb.

Okay, so if the Casimir force is so darned small it can't really have a significant effect, why bother studying it? Well, it does have a significant effect at very small scales. In fact, the Casimir effect sometimes causes the moving parts in nano- and microelectromechanical systems (NEMS and MEMS) to stick together, so gaining a more detailed understanding this bizarre force could have practical benefits. On a more esoteric level, many tabletop experiments designed to test for exotic new forces can also be stymied if the Casimir effect isn't taken into full account. Virtual particle pairs popping up near the event horizon of a black hole are believed to result in the "Hawking radiation" that causes these objects to evaporate -- the smaller the black hole, the shorter the time it takes for it to wink out of existence. And vacuum energy is one of the leading contenders for the mysterious dark energy physicists believe is causing the expansion of our universe to accelerate. Wouldn't you like to know how the universe will end? We'll be long dead before that happens, but still... the point is, this strangely attractive force matters.

There might not be any papers this week in Denver about the Casimir effect, but there will be papers providing research updates on graphene and "metamaterials" (those with negative indices of refraction); medical physics; pattern formation in granular media; and bubble logic, to name a few. Jen-Luc Piquant and I will be reporting on some of the science stories in play this week; so will the folks at Physics Buzz.  While you're waiting -- because writing blog posts takes time -- check out the latest Philosophia Naturalis carnival at GeekCounterpoint, and the new carnival on women in science and technology.  Stay tuned!

Comments

[Phil Plait, aka The Bad Astronomer]

The game of spotting a physicist (or more appropriately in my case, an astronomer) at the airport while heading to a meeting is common amongst our kind. I am quite good at it, as is my wife, in fact. I call this innate ability "nerdar".

[Jim Kakalios]

Of course, this would be the year I skip the March meeting, and thus miss another chance to meet you in person!

On the plus side - it's nice to have a week free of seminars and meetings, as many of my colleagues are in Denver. Now to get into the lab and get ahead of them!

I'll be in DC at the end of April, to give a talk as part of the DOE's sponsored National Science Bowl competition. If you're around then, please say hey.

and Phil - "nerdar" - excellent!

Jim

[Stephen]

So, how much for an airline ticket for Jen-Luc Piquant? Does she travel light?

As i recall, Hobbes always went for free when Calvin traveled. Two for the price of one. Well, Calvin's folks paid for the whole trip. So, maybe there's a free launch after all.

[Jay Cummings]

Ah, yes, spot the physicist. At my very first APS meeting in Crystal City VA (Washington DC) in the mid-eighties, my wife and toddler daughter came along. After checking in at the hotel, I didn't know what to do next. My wife said, "Why don't you ask that guy over there? He has a beard and a plaid shirt." Of course he was able to point me toward the meeting registration. I myself, though bearded, was attired in a suit, so of course nobody could possibly have identified me as a physicist... right.

[JoAnne]

So, did the meeting participants miss the abstract book, or did they manage OK without it? I'm on the APS cmtte for meetings (how obscure is that?) and was the one who argued to do away with the abstract book. So, thanks for any feedback!

[Jennifer Ouellette]

I'm adding "nerdar" to my lexicon.

Jim: Alas, I am moving to Los Angeles permanently on April 25. one of these days we'll both be in the same city at the same time!

As for the March Meeting Bulletin changes, I can't speak for the meeting attendees, but my fellow science writers/reporters sorely missed the pocket session guide...

[Calvin]

Hmm, spotting a scientist on a plane. Sounds easy enough. But can you tell the scientist from the serial killer?

http://www.malevole.com/mv/misc/killerquiz/

I found this a few years back and your posting reminded me of it. I know it's about computer scientists and not physicists, but the species are very closely related, are they not?