In this experiment by researchers at Hebrew University, the Open University of Israel, Sapienza University of Rome, and University of Montpellier in France, in the emitted gamma rays of such a burst, some 7+ billion years ago, it was concluded at the Fermi Large Area Telescope (LAT) [ http://fermi.gsfc.nasa.gov/ ] of gamma-ray burst GRB090510, on this 100th birthday of Einstein's Special and General Relativity Theories, that the speed of light is indeed universally constant thus upholding Lorentz invariance.
This result of the constancy of the speed of light was tested for differing electromagnetic energies or frequencies at the small quantum Planck scale of spacetime foam, the latter of which is yet to be finally determined whether or not it truly exists.
The release date of this experiment occurred on March 14, 2015 which incidentally coincides with Pi - Day where the '15' in the pi number of 3.1415 ... occurs only once in a century.
Prof. Tsvi Piran, the Schwartzmann University Chair at the Hebrew University’s Racah Institute of Physics and a leader of the research: "When we began our analysis, we didn’t expect to obtain such a precise measurement ... This new limit is at the level expected from quantum gravity theories and can direct us how to combine Quantum Theory and Relativity."
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