The Cosmos in a Test Tube

"In effect, we have made a universe in a test tube."

Richard Haley -Lancaster University

A "universe in a test tube" that could be used to prove theories of everything has been created by physicists using liquid helium and a magnetic field to build a finger-sized representation of the early cosmos.

The low-temperature team at Great Britain's Lancaster University may have found a laboratory test of the ‘untestable’ string theory, made popular by Brian Greene at Columbia University. Within string theory, a brane is a large surface embedded in higher dimensional space — our Universe could occupy such a brane.

The findings of the Lancaster University team according to nature.com could help string theorists to refine their models. A popular theory amongst string theorists is that inflation was caused by the collision of two 'branes'. A brane (derived from the word 'membrane') is a three-dimensional object suspended in a higher-dimensional space. One tenet of string theory is that a collision between a brane and an antibrane could have triggered the Big Bang itself and drove inflation of the universe.

A collision between a brane and an antibrane can leave behind topological defects, including perhaps the Big Bang itself. But however elegant this theory, the problem with string theory is that it makes no falsifiable predictions, scientists being unable to find two Universe-sized objects that you can crash into each other. According to Richard Haley, who led the team at Lancaster University, a testable model can be found in a test tube of liquid helium.

Inside the tube an isotope of helium (called helium three) forms a "superfluid", an ordered liquid where all the atoms are in the same state according to the quantum theory that rules the subatomic domain.

Haley and his group used an 8mm by 45mm cylinder filled with helium-3, an isotope of helium that contains two protons and a single neutron. When cooled to just 150 microkelvin above absolute zero, helium-3 becomes a superfluid and ghostly 'quasi-particles' are formed that can flit through the frigid liquid. And the entire system can undergo 'symmetry breaking' — a phenomenon also thought to have led to the creation of every force we see today except gravity. It also tends to settle into one of two phases, which physicists label A and B.

The team used a magnetic field to create an A-phase slice of helium-3 sandwiched between two sections of B-phase liquid. They then decreased the field and watched as the two B-phases collided.

The colliding phases were good analogues for colliding branes, Haley says. While helium-3 is radically different from the vacuum of space, the maths governing the two systems are similar.

Universe-sized brane collisions are thought to leave behind a tangle of defects called 'cosmic strings' — massive, spaghetti-like objects that would criss-cross the entire cosmos. None have been found to date, but theorists believe that their gravity waves might one day be detected by specialized instruments such as the CERN Large Hadron Collider outside Geneva, Switzerland.

The equations used to describe this superfluid turn up in many other branches of physics. "For instance, the internal structure of the superfluid mirrors very closely the structure of space-time itself, the 'background' of the universe in which we live," says Haley.

"Consequently the superfluid can be used to simulate particle and cosmic phenomena; black holes, cosmic strings and the Big Bang for instance.

"This is great for testing theories, since the equations describing helium-3 are well-established enough to say that it is the most complex system for which we already have string theory -the 'Theory of Everything'," Haley said.

Posted by Casey Kazan.

The Daily Galaxy: News from Planet Earth & Beyond

December 27, 2007

The Cosmos in a Test Tube

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