It's been a good year for confirming (and reconfirming) older theories in physics. Last week the scientists on the MiniBooNE experiment told us that the Standard Model, while imperfect, is holding up just fine as it approaches its dotage, thanks very much for asking. (Whether or not you're pleased by that news might depend on whether you find the prospect of operating a bit outside the theoretical box exhilarating or utterly terrifying.) Gravity Probe B just gave the thumbs up to Einstein for his 1917 prediction of the geodetic effect (and I can't believe my eagle-eyed commenters missed my inadvertent typos in Saturday's post). It's also thisclose to most likely (probably, maybe) affirming the frame-dragging effect as well. Last year saw more precise measurements of Lorenz invariance and E=mc<2>, as well as an experiment by scientists at the University of Twente in the Netherlands that yielded a plausible physical explanation for the mysterious "Kaye Effect."
Many of you have probably never heard of the Kaye Effect, but trust me, it happens all the time, and nobody except physicists ever takes much notice. That's what makes physicists/scientists so special, and I don't mean that in an ironic sense. Physicists are the ones who see something in nature that's not quite right, think, "Huh... that's funny," and -- here's what sets them apart from the Average Joe/Jane -- decide to try and figure out what's actually going on, rather than just forgetting about it and going on their merry way.
They're persistent, too. Sometimes it can take a good long while between the initial observation and a scientifically plausible (and experimentally confirmed) explanation. Case in point: back in 1963, a humble physicist named Arthur Kaye (he doesn't even have a stub on Wikipedia) was experimenting with complex mixtures of viscous fluids -- things with the consistency of honey, syrup or the like -- and noticed that when he poured these substances onto a surface, the downward stream would unexpectedly produce an upward-moving jet that then merged with the incoming stream.
Essentially, as the liquid flows, its viscosity decreases. The same thing happens with shampoo, liquid hand soaps, ketchup, yogurt and certain paints, it just happens so fast -- on the order of 300 milliseconds -- that most of us aren't aware of it. Michel Verlsluis, the Twente scientist, figured out to keep the effect stable long enough to study the underlying physical mechanism: by pouring the stream onto a sloping surface. I won't go into the full explanation he proposed for the Kaye Effect, because you can find the whole story here, and watch nifty videos of the Incredible Bouncing Viscous Liquid here and here. If you happen to run into Verlsluis during your next trip to the Netherlands, I'm sure he'd be happy to tell you how to perform a similar experiment in your own bathroom.
Sometimes it works the other way around: a theorist does a bunch of calculations and concludes that, under very specific circumstances, something ought to happen. And then experimenters try to create the right conditions to prove (or disprove) the theory in the laboratory. Here at the APS April meeting in Jacksonville, the focus yesterday morning was on the recent experimental observation of the elusive "Efimov Effect." Atomically speaking, it's what happens when two atoms that normally repel each other become strongly attracted when a third atom is introduced. Three's company, two's a crowd, which flies in the face of conventional wisdom.
(Jen-Luc Piquant observes that many a straight male's favorite sexual fantasy is based on a very similar concept: "Really, honey, inviting Fergie -- of Black-Eyed Peas fame, not the former Duchess of Windsor -- to bed with us can only bring us closer!" Thanks to physics, their partners now have a handy one-word rejoinder: shrinkage. The Efimov Effect is only observed in ultracold gases, like cesium, cooled way down to a billionth of a degree above Absolute Zero. That's colder than the furthest reaches of outer space, which hover around a comfy 3 degrees Kelvin. Those kinds of temperatures aren't likely to *cough* show a guy to his best advantage. She's just sayin'....)
The man behind the Efimov Effect is a Russian physicist named Vitaly Efimov. Back in 1969, he had a shiny new PhD in theoretical nuclear physics, along with sufficient youthful optimism to make a strange prediction: even though any two in a group of three atoms will normally repel each other, under just the right kind of conditions, it should be possible to create a state of matter in which they will experience an irresistible attraction, forming an infinite number of "bound states." This struck many of his colleagues as a bit preposterous, but the math bore young Vitaly out. Time and again over the years, theorists have tried to disprove the Efimov Effect, only to further verify it. But it still hadn't been seen in a laboratory.
Sometimes it takes so long for theories to find experimental verification because the technology just doesn't exist. That was certainly the case with Bose-Einstein condensates (BECs), a new state of matter first predicted by Albert Einstein and the Indian physicist Satyendra Bose in the 1920s. All matter exhibits wave/particle duality. At normal temperatures atoms behave a lot like billiard balls, bouncing off one another and any containing walls. Lowering the temperature reduces their speed. If the temperature gets low enough (billionths of a degree above absolute zero) and the atoms are densely packed enough, their wave nature kicks in. The different matter waves will be able to “sense” one another and coordinate themselves as if they were one big “superatom.”
Eric Cornell and Carl Wieman created the first BEC, using a combination of laser and magnetic cooling equipment. They created a laser trap by cooling about 10 million rubidium gas atoms; the cooled atoms were then held in place by a magnetic field. This can be done because most atoms act like tiny magnets; they contain spinning charged particles (electrons). But the atoms still weren’t cold enough to form a BEC, so the two men added a second step, evaporative cooling, in which a web of magnetic fields conspire to kick out the hottest atoms so that the cooler atoms can move more closely together. It works in much the same way that evaporative cooling occurs with your morning cup of coffee; the hotter atoms rise to the top of the magnetic trap and “jump out” as steam.
Wieman and Cornell made physics history at 10:54 AM on June 5, 1995, producing a BEC of about 2000 rubidium atoms that lasted 15-20 seconds. Shortly thereafter, an MIT physicist named Wolfgang Ketterle achieved a BEC in his laboratory. Wieman, Cornell and Ketterle shared the 2001 Nobel Prize in Physics for their achievement. And BECs turned out to be the key to experimentally verifying the Efimov Effect, since they spawned a huge new field of research into the properties of ultracold gases. Chris Greene of the the University of Colorado was the first (with a co-author) to predict that ultracold gases were just the ticket for achieving such an odd state in the laboratory.
Enter Austrian physicist Rudolf Grimm, who met Efimov at a workshop in Seattle in 2005, and was inspired to try his own hand at verifying the Efimov effect. Grimm's group at the University of Innsbruck took three cesium atoms, placed them in a vacuum chamber, and then used a combination of laser cooling and evaporative cooling to bring the temperature down to -459.6 degrees F. The technique is almost identical to how a BEC is created, and had BECs not become almost commonplace in physics over the last decade, Efimov's odd theory might never have been verified. Within a year of meeting Efimov, his team had created the Efimov effect in their lab. The trick is to get the gas to the very edge of condensation, without it ever turning into an actual BEC.
According to Grimm, the atoms in an Efimov state resemble something called a Borromean ring: three interlocking circles that are found on the coat of arms of a 15th century Italian noble family called Borromeo (I know -- duh). Among the many interpretations, it can be said to represent the inter-marriages that had bound the Borromeos inseparably to two other noble families. In physics, one could say the three rings -- or atoms, or particles -- are entangled, such that if you pick up any one of them, the other two will follow, and if you cut one, the other two will fall apart.
Possibly the most exciting thing about this experimental result is that it should be pretty much universal: we should be able to create this state out of any set of three particles at ultracold temperatures, and it's a harbinger of an emerging new field devoted to studying the quantum mechanical behavior of just a few interacting particles.
The Efimov Effect may even make it possible to engineer the most fundamental properties of matter way down at the subatomic level, giving scientists unprecedented control and the ability to create all kinds of new exotic molecules that couldn't otherwise exist. The University of Chicago's Cheng Chin, one of Grimm's collaborators, has said as much in various press releases: "This so-called quantum control over the fundamental properties of matter now seems feasible. We're not limited to the properties of, say, aluminum, or the properties of the copper of these particles. We are really creating a new state in which we can control their properties."
Pretty cool, huh? Even if it is awfully esoteric.... But the best part, in Jen-Luc's opinion, is the pretty pictures Greene showed, modeling the Efimov state of matter: