Monday, April 19, 2010

A New Limit on the Light Speed Isotropy

All those theories that have the possible Lorentz violation will have to deal with a new lower and more stringent limit on light speed isotropy. A new study base on the Compton edge measurement at the ESRF has imposed a new limit on such isotropy.

Abstract: When the electrons stored in the ring of the European Synchrotron Radiation Facility (ESRF, Grenoble) scatter on a laser beam (Compton scattering in flight) the lower energy of the scattered electron spectra, the Compton Edge (CE), is given by the two body photon-electron relativistic kinematics and depends on the velocity of light. A precision measurement of the position of this CE as a function of the daily variations of the direction of the electron beam in an absolute reference frame provides a one-way test of Relativistic Kinematics and the isotropy of the velocity of light. The results of GRAAL-ESRF measurements improve the previously existing one-way limits, thus showing the efficiency of this method and the interest of further studies in this direction.

The new limit is Delta(c)/c of less than 1 e-14.


1 comment:

The Universe said...

Interesting, zapper. You'll know about the NIST fountain clock and the definition of the second:

"Since 1967, the second has been defined to be the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom..."

Lasers and a microwave cavity are employed to cause electron spin-flip hyperfine transitions. These are electromagnetic in nature, and emit light of a given "frequency", which is measured by a detector. But note that frequency is measured in Hertz, which is defined as cycles per second, and the second is what we're defining. What the detectors really do is count incoming microwave peaks. When they get to 9,192,631,770, that's a second, and then the frequency is 9,192,631,770 Hz by definition.

The second is then used to define the metre as "the distance travelled by light in free space in 1/299,792,458 of a second", and then we use these units to measure the speed of light. It's important to spot here that the motion of light is being used to define the units used to measure the motion of light. Hence the measured speed of light always comes out the same.

The situation is something like me being able to press a slow-motion button that lowers the speed of light for you and your NIST clock. I do this every day, whereupon the light moves slower, so your second is bigger. Your metre is however the same because the slower light and the bigger second cancel each other out. But you then use your bigger second on the slower light, and lo and behold, you always measure 299,792,458 m/s.

Apologies if this a doublepost, just delete it, the webpage timed out.