Ultra-relativistic neutrinos blasted into space during gamma-ray bursts are slowed down by the effects of quantum gravity. That is the conclusion of physicists in Italy, Poland and Norway, who have spotted seven neutrinos that arrived on Earth later than expected, compared to their companion gamma rays.
Quantum theory does a fantastic job of describing interactions that involve three out of the four known forces of nature. However, there is no theory today that adequately describes the quantum nature of gravity. While theories of quantum gravity have been proposed, they tend to make predictions that cannot currently be tested by experiment or observation.
One prediction that physicists have a chance of confirming today is that particles moving very near to the speed of light will lose energy because of a quantum gravitational effect. The faster the particle is moving, the more the effect is enhanced. While the effect is extremely small, if the particles are created in an astrophysical event billions of light–years away, the cumulative result would be a delay that could be measured when the particles arrive on Earth.
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