In January 2019, researchers detected gamma-ray burst (GRB) 190114C. They caught this quick explosion right in the act and observed the most energetic photons ever seen from a gamma-ray burst. This incredible event has now been used to test Einstein’s theory of general relativity.
One of the cornerstones of special relativity, and crucial to the general relativity framework, is that the speed of light in a vacuum is a constant. General relativity is our best description of gravity. It has been tested time and time again, even with a supermassive black hole. So far, it has passed all the tests, including this one as reported in Physical Review Letters.
That said, we know that the theory is limited as we are yet to find a theory that encompasses both gravity and the other forces in the universe described by quantum mechanics. Several theories try to provide such a bridge and one group of those theories is known as quantum gravity. This is where things get interesting. Some quantum gravity theories don’t require the speed of light to be constant.
The hypothetical effect, known as Lorentz invariance violation (LIV), is dependent on the energy of the light in question. The effect is tiny and is only clearly visible over time. That’s why a cosmic source producing photons at high-energy, such as a GRB, is ideal. GRB 190114C is particularly apt as its photons reached the level of teraelectronvolt energies (TeV, 1000 billion times more energetic than the visible light).
"We were all very happy and feel privileged to be in the position to perform the first study on Lorentz invariance violation ever on GRB data in TeV energy range, and to crack the door open for future studies!" co-author Cedric Perennes, a postdoctoral researcher at the University of Padova, explained in a statement.
While the team was unable to prove physics beyond general relativity, they certainly put more stringent constraints on quantum gravity theories. The astronomers plan to continue to use the MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescope on the Canary Islands to discover more GRBs.
"This time, we observed a relatively nearby GRB. We hope to soon catch brighter and more distant events, which would enable even more sensitive tests," Oscar Blanch, spokesperson of the MAGIC collaboration, concluded.