Einstein’s theory is a theory which explains how mass and energy interact with the fabric of space-time, creating a phenomenon known to us as gravity. Physicists have tested and retested his theory and the outcome has always been outstandingly accurate, yet they suspect that there exists an underlying quantum mechanical description of gravity, referred to as quantum gravity. Some Quantum Gravity theories consider that the speed of light might be energy dependant. This hypothetical phenomenon is called Lorentz invariance violation. Its effects are thought to be too tiny to be measured unless they are accumulated over a very long time. One solution to achieve that is using signals from astronomical sources of gamma rays. Gamma-ray bursts are powerful and far away cosmic explosions, which emit highly variable and extremely energetic signals. They are therefore excellent laboratories for experimental tests on quantum gravity. The higher energy photons are expected to be more influenced by the quantum gravity effects, and there should be plenty of those – these travel billions of years before reaching Earth, which enhances the effect.
Gamma-ray bursts are detected on a daily basis with satellite detectors, which observe at lower energies than ground-based telescopes like MAGIC. After a cosmic cataclysm detected by MAGIC, scientists found out that they were looking for signals in the wrong domain for over 20 years. This type of high radiation gamma-ray burst had never been detected before and supported the theory that the speed of light was constant in a vacuum. Naturally, the MAGIC scientists wanted to use this unique observation to hunt for effects of quantum gravity. However, the signal that was recorded with the MAGIC telescopes decayed monotonically with time. While this was an interesting finding for astrophysicists studying gamma-ray bursts, it was not favourable for the violation testing. When comparing the arrival times of two gamma-rays of different energies, one assumes they were emitted instantaneously from the source. However, researchers’ knowledge of processes in astronomical objects is still not precise enough to pinpoint the emission time of any given photon and A careful analysis then revealed no energy-dependent time delay in arrival times of gamma rays, and Einstein still holds the legitimate description of gravity.
Writer: Ariya Gupta
17/07/2020
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