High Altitude Experiment Atop Mexican Volcano Challenges Speed of Light

The testing confirmed that the laws of physics hold no matter where you are or how fast you're moving.
Fabienne Lang
Compound graphic with a view of the sky in ultra-high energy gamma raysHAWC

New measurements from an experiment held at the top of an extinct volcano in Mexico have confirmed that there is a new limit on whether light is able to go faster than the known speed of light

Observations of record-breaking gamma rays from a distant galaxy confirmed the robustness of a piece of Einstein's theory of relativity: the Lorentz Invariance. No matter where you are or how fast you're moving, the laws of physics hold. 

The findings were published in Physical Review Letters.


The speed of light

Einstein's Lorentz Invariance predicts that the speed of light is constant everywhere in the universe. The new measurements taken from the High-Altitude Water Cherenkov (HAWC) Observatory in Puebla, Mexico, detected gamma rays from far-away galactic sources, and physicists were able to confirm, to the highest energies yet explored, that these laws of physics are true, no matter where you are or how fast you're moving.

"How relativity behaves at very high energies has real consequences for the world around us," said Pat Harding, an astrophysicist in the Neutron Science and Technology group at Los Alamos National Laboratory and a member of the HAWC scientific collaboration.

"Most quantum gravity models say the behavior of relativity will break down at very high energies. Our observation of such high-energy photons at all raises the energy scale where relativity holds by more than a factor of a hundred."

High Altitude Experiment Atop Mexican Volcano Challenges Speed of Light
The highest-energy gamma rays ever observed, Source: HAWC

The physicists were looking for a deviation from the well-established theory of Lorentz Invariance because this law suggests that it may not hold at the highest of energies. If Lorentz Invariance were not to hold true, a number of phenomena would become possibilities. For instance, gamma rays may travel at speeds faster or slower than the speed of light. 

The HAWC Gamma Ray Observatory had noticed a number of astrophysical sources that produce photons higher than 100 TeV (or one trillion times the energy of visible light). As HAWC is able to detect these gamma rays it extends the range that the Lorentz Invariance holds by a factor of 100 times

"Detections of even higher-energy gamma rays from astronomical distances will allow more stringent checks on relativity. As HAWC continues to take more data in the coming years and incorporate Los Alamos-led improvements to the detector and analysis techniques at the highest energies, we will be able to study this physics even further," said Harding.


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