posted on Jan, 26 2004 @ 07:48 AM
A quantum gyroscope could tell us if the entire Universe is in a spin, according to new research by scientists.
Physicists used to think it made no sense to say the Universe was or was not rotating. "Rotating relative to what?" asked the Austrian physicist
Ernst Mach in 1893. Then Einstein came along.
According to his general theory of relativity, if most of the matter in the Universe happens to be spinning, all of space-time will be pulled round
with it. If this is the case, the Universe must have been spinning ever since the earliest moments after the big bang.
Any overall rotation should appear as strange effects on the paths of free particles, but physicists have never previously come close to working out
how to measure this. Now a team led by Wolfgang Schleich at the University of Ulm in Germany have suggested a way to adapt the ring-laser gyros
currently used to track rotation in aircraft and satellites.
These devices fire laser beams in opposite directions around a fibre-optic ring. If a plane is turning, the laser beam travelling with the rotation
has to travel further to catch up with its starting point, so it arrives later than the beam travelling against the rotation. When the beams meet,
they create an interference pattern from which it is possible to work out the difference in the arrival times of the two beams, and hence the rate of
Shleich points out that the same principle also works with cold atom beams, and because atoms move more slowly than light, the shift is more obvious.
This should allow far slower rates of rotation to be measured.
The European Space Agency is already planning to launch a cold atom gyro called HYPER into space, with the aim of measuring whether any rotation is
associated with the Earth's gravitational field. This will provide the first test of the prediction, which flows from Einstein's general theory,
that nearby space should be dragged round by the Earth's spin
In July's New Journal of Physics (vol 4, p 37), Schleich shows that the accuracy of HYPER could be improved by a factor of 10 billion, which should
be enough to measure the rotation of the Universe.
The trick is to get both the cold atom beams into the same quantum state. The beams should then be absolutely identical, so any shift observed when
they interfere would have to be due to rotation, rather than random noise (see graphic). "There's a real beauty in the way quantum mechanics makes
these gyros more accurate," Schleich says.
Arnaud Landragin, who works for HYPER at the Paris Observatory, says it should be possible to replace the beams with a quantum fluid called a
Bose-Einstein condensate, which will have the effect Schleich wants. "It's along the same lines, it's just more difficult," he says.
The first step will be to get the quantum gyro working on the ground, says Landragin, although the adaptations necessary may not be ready in time for
HYPER's launch in 2010.