From M.I.T.: “Superfluid turbulence through the lens of black holes”

Study finds behavior of the turbulent flow of superfluids is opposite that of ordinary fluids.

July 25, 2013
Jennifer Chu, MIT News Office

“A superfluid moves like a completely frictionless liquid, seemingly able to propel itself without any hindrance from gravity or surface tension. The physics underlying these materials — which appear to defy the conventional laws of physics — has fascinated scientists for decades.

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Black hole physics shows that superfluids in turbulence behave much like cigarette smoke. Image: Christine Daniloff

Think of the assassin T-1000 in the movie “Terminator 2: Judgment Day” — a robotic shape-shifter made of liquid metal. Or better yet, consider a real-world example: liquid helium. When cooled to extremely low temperatures, helium exhibits behavior that is otherwise impossible in ordinary fluids. For instance, the superfluid can squeeze through pores as small as a molecule, and climb up and over the walls of a glass. It can even remain in motion years after a centrifuge containing it has stopped spinning.

Now physicists at MIT have come up with a method to mathematically describe the behavior of superfluids — in particular, the turbulent flows within superfluids. They publish their results this week in the journal Science.

‘Turbulence provides a fascinating window into the dynamics of a superfluid,’ says Allan Adams, an associate professor of physics at MIT. ‘Imagine pouring milk into a cup of tea. As soon as the milk hits the tea, it flares out into whirls and eddies, which stretch and split into filigree. Understanding this complicated, roiling turbulent state is one of the great challenges of fluid dynamics. When it comes to superfluids, whose detailed dynamics depend on quantum mechanics, the problem of turbulence is an even tougher nut to crack.’

To describe the underlying physics of a superfluid’s turbulence, Adams and his colleagues drew comparisons with the physics governing black holes. At first glance, black holes — extremely dense, gravitationally intense objects that pull in surrounding matter and light — may not appear to behave like a fluid. But the MIT researchers translated the physics of black holes to that of superfluid turbulence, using a technique called holographic duality.

Consider, for example, a holographic image on a magazine cover. The data, or pixels, in the image exist on a flat surface, but can appear three-dimensional when viewed from certain angles. An engineer could conceivably build an actual 3-D replica based on the information, or dimensions, found in the 2-D hologram.

‘If you take that analogy one step further, in a certain sense you can regard various quantum theories as being a holographic image of a world with one extra dimension,’ says Paul Chesler, a postdoc in MIT’s Department of Physics.

Taking this cosmic line of reasoning, Adams, Chesler and colleagues used holographic duality as a ‘dictionary’ to translate the very well-characterized physics of black holes to the physics of superfluid turbulence.

To the researchers’ surprise, their calculations showed that turbulent flows of a class of superfluids on a flat surface behave not like those of ordinary fluids in 2-D, but more like 3-D fluids, which morph from relatively uniform, large structures to smaller and smaller structures. The result is much like cigarette smoke: From a burning tip, smoke unfurls in a single stream that quickly disperses into smaller and smaller eddies. Physicists refer to this phenomenon as an “energy cascade.”

‘For superfluids, whether such energy cascades exist is an open question,’ says Hong Liu, an associate professor of physics at MIT. ‘People have been making all kinds of claims, but there hasn’t been any smoking-gun type of evidence that such a cascade exists. In a class of superfluids, we produced very convincing evidence for the direction of this kind of flow, which would otherwise be very hard to obtain.’”

See the full article here.


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