Scientists are testing Einstein’s claim that the speed of light is constant. While the researchers found no evidence that the speed of light changes with energy, this result is null. Dramatically reinforces the limitations of quantum gravity theories that predict even the smallest violations. ScienceDaily reports: Special relativity is based on the principle that the laws of physics remain the same for all observers, regardless of how they move relative to each other. This idea is known as Lorentz invariance. Over time, Lorentz invariance became a fundamental assumption of modern physics, especially within quantum theory. […] A prediction shared by several quantum gravity models that violate Lorentz invariance is that the speed of light may depend slightly on the energy of a photon. Any such effect would have to be small to match existing experimental limits. However, it could become detectable at higher photon energies, specifically very high-energy gamma rays.
A research team led by UAB alumni Merce Guerrero and current IEEC doctoral student at UAB Anna Campoy-Ordaz set out to test this idea using astrophysical observations. The team also included Robertus Potting from the University of Algarve and Markus Gaug, a professor in the UAB Department of Physics who is also affiliated with the IEEC. Their approach is based on the great distances that light travels through the universe. If photons of different energies are emitted at the same time from a distant source, even minute differences in their velocities could lead to measurable delays in the time they reach Earth.
Using a new statistical technique, the researchers combined existing measurements of very high-energy gamma rays to examine several parameters that violate Lorentz invariance favored by theorists within the Standard Model Extension (SME). The goal was ambitious. They hoped to find evidence that Einstein’s assumptions could fail under extreme conditions. Once again, Einstein’s predictions held firm. The study did not detect any violation of Lorentz invariance. Still, the results are significant. The new analysis improves previous limits by an order of magnitude, dramatically narrowing down where the new physics could be hiding.
