"Lasso" verifies the correctness of the space-time symmetry of Einstein's theory of relativity

◎ Science and Technology Daily reporter Lu Chengkuan

Einstein's theory of relativity holds that the fastest speed of movement of matter in the universe is the speed of light, is it possible that this limit can be broken? This problem can be tested by the breaking of Lorentz's symmetry.

Recently, the Physical Review Letters published online the latest test results of scientific experiments on the mainland. "Using the example of high-energy gamma rays observed by the high-altitude cosmic ray observatory 'Lasso' (LHAASO) in Daocheng, Sichuan, researchers from the LHAASO collaborative group examined lorentz symmetry. The experimental results increase the energy scale of Lorentz symmetry by about 10 times, which is the most rigorous test of Lorentz symmetry at present, and once again verifies the correctness of Einstein's relativistic space-time symmetry. On February 10, Bi Xiaojun, a researcher at the Institute of High Energy of the Chinese Academy of Sciences, a member of the LHAASO cooperation group and one of the corresponding authors of the paper, said.

High-altitude cosmic ray observatory "Lasso". Image source: Institute of High Energy, Chinese Academy of Sciences

This means that the speed of light is the fastest speed of matter in the universe, and this limitation cannot be broken.

So, what does Lorentz symmetry have to do with relativity?

Einstein's theory of relativity is the cornerstone of modern physics, and the principle of relativity requires that the laws of physics have Lorentz symmetry. In the more than 100 years since Einstein proposed the theory of relativity, the correctness of Lorentz's symmetry has undergone countless experimental tests.

However, there is an irreconcilable contradiction between general relativity, which describes gravity, and quantum mechanics, which describes the laws of the microscopic world. Theoretical physicists have made unremitting efforts to unify general relativity and quantum mechanics, and have proposed different theories such as string theory and loop quantum gravity. "These theories predict that Lorentz symmetry is likely to be broken at very high energies, meaning that relativity may need to be corrected at high energies." Bi Xiaojun explained.

Therefore, the experimental search for signs of Lorentz symmetry failure becomes a "breakthrough" in testing relativity and finding more fundamental physical laws.

However , extrapolating from these theories , lorentz symmetry failure is only significant under the so-called Planck energy scale , which is as high as 1019 GeV ( 1 GeV = 1 billion electron volts ) .

"Today, when artificial accelerators can only reach about 104 GeV energy, in the laboratory, the effect of this destruction is very weak, requiring extremely high experimental accuracy to be measured, making it difficult to detect." But there are very high-energy processes in celestial activity, for example, there are particles in the universe with much higher energy than artificial accelerators can accelerate, and Lorentz symmetry failure will be more pronounced and easier to detect on these high-energy particles, Bi said. As another example, although particles emitted from celestial sources carry a very weak Lorentz symmetry-breaking effect, accumulation over long distances becomes easier to detect. Therefore, astrophysical observations became a natural laboratory for looking for lorentz symmetry failure.

LHAASO is a cosmic ray observation experiment independently designed and built by the mainland, and in the process of construction in 2021, the highest energy gamma-ray photon known to mankind was detected, with an energy of 1.4 beats of electron volts (1 beat of electron volts = 1000 trillion electron volts), setting a new record, but also providing a rare opportunity to explore basic physical laws and strictly test the correctness of Lorentz symmetry.

Lorentz symmetry disruption causes high-energy photons to cease to be stable and can quickly decay into a pair of positive and negative electron pairs or 3 gamma photons.

In other words, high-energy photons automatically disappear on a journey to Earth. For observers on Earth, even if the celestial source has emitted a higher energy photon, the photon energy spectrum we measured for this celestial body is suddenly cut off at this specific energy. Bi Xiaojun explained.

LHAASO observational data show that the current gamma-ray spectrum to the beat electron volt above the continuous high energy, and no "mysterious" disappearance of high-energy gamma cases has been found. "This shows that the Lorentz symmetry is still correct close to the Planck energy scale." Bi Xiaojun said firmly.

Source: Science and Technology Daily

Editor: Zhang Shuang

Review: Julie

Final Judgement: Wang Yu