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chris_mackintosh Mon, Dec 31, 2007
A Test for String Theory After All? Or Just PR?

A letter published this week in Nature is causing a bit of a stir among physicists, with press releases promising that scientists "may have found a laboratory test of the 'untestable' string theory."

If literally true, this would be huge, Nobel-prize level news, with mind-boggling consequences for our understanding of a radically expanded universe. But while interesting, it's probably none of that.

The experiment in question comes from the UK's Lancaster University, where a group of low-temperature physicists are studying a real-world phenomenon they believe is an analog for one of the oddest ideas in modern physics.

In some versions of string theory, our entire universe is described as being embedded on a gigantic "brane" (the term comes from the word "membrane," but think bigger, with more dimensions), which may have counterparts that float through or simply exist in a higher-dimensional space, and might even encounter "antibranes."

In part because these theoretical constructs would all exist outside the confines of what we think of as our world, these ideas have been viewed as nearly, if not wholly, impossible to test.
The Lancaster physicist are looking at the problem from an unusual angle, however. Their experiment involves cooling helium-3 isotopes very close to zero degrees Kelvin, where it changes into into a superfluid state. Here it has interesting properties, such as the absence of friction as it flows.

Then they add a magnetic field, which creates a separate region within the fluid. The interface between these two regions behaves very much like a two-dimensional brane, they say.
In a press release, the university touts this as a possible "test" for string theory. Nature itself is more cautious on its Web site, calling it a possible "laboratory analogue." String theory critic Peter Woit, a Columbia University mathematical physicist, calls these claims simple "dishonest nonsense."

It strikes me that this experiment may well be interesting, but that these striking claims risk mistaking an interesting metaphor for actual proof. Analogues, to use Nature's term, can certainly shed light on related issues, but don't serve as hard laboratory proof of anything.