Einstein’s Theory of Relativity Goes Through the Observation of LHAASO
Scientists from the Institute of High Energy Physics of the Chinese Academy of Sciences analyzed the validity of the relativity theory with the highest possible accuracy in a study entitled “Exploring Lorentz Invariance Violation from Ultrahigh-Energy γRays Observed by LHAASO,” which was published in the most recent issue of Physical Review Letters.
According to Einstein’s theory of relativity, the speed of light is the fastest speed of matter in the Universe. Whether that limit is breakable can be tested by examining Lorentz symmetry breaking or Lorentz invariance violation.
“Utilizing the world’s highest-energy gamma rays observed by the Large High Altitude Air-shower Observatory (LHAASO), a large-scale cosmic ray experiment in Daocheng, Sichuan province, China, we tested Lorentz symmetry.
The outcome improves the breaking energy scale of Lorentz symmetry by dozens of times compared to the previous best outcome. This is one of the most rigorous tests of a Lorentz symmetry breaking form, confirming once again the validity of Einstein’s relativistic space-time symmetry,” said Prof. Bi Xiaojun, among the paper’s corresponding authors. Prof. BI is a scientist at the Institute of High Energy Physics and a member of the LHAASO collaboration.
What is the connection between Lorentz symmetry and the theory of relativity?
Einstein’s relativity theory, the foundation of modern physics, requires that physical laws have Lorentz symmetry. In over 100 years since Einstein proposed his relativity theory, the validity of Lorentz symmetry has gone through numerous experimental tests.
Nonetheless, there is an irreconcilable contradiction in between general relativity, which explains gravity, and quantum mechanics, which describes the laws of the microscopic world. To unify general relativity and quantum mechanics, theoretical physicists made unremitting efforts and have actually created theories such as string theory and loop quantum gravity theory. These theories predict that Lorentz symmetry is most likely to be broken at really high energies, indicating that relativity might need to be changed.
As a result, it is essential to test the relativity theory and develop more fundamental laws of physics by trying to find signals of Lorentz symmetry breaking. Nonetheless, according to these theories, the effect of Lorentz symmetry breaking is just significant at the so-called Planck energy scale, which is up to 1019 GeV (1 GeV = 1 billion electron volts).
Considering that artificial accelerators can just get to around 104 GeV, the effects of Lorentz symmetry breaking are too weak to be tested in laboratories. However, there are extremely violent astrophysical processes in the Universe where particles can be sped up to energies much higher than what artificial accelerators can get to. For that reason, astrophysical observations are a natural laboratory for finding the effects of Lorentz symmetry breaking.
LHAASO is a large-scale cosmic ray experiment in China. Throughout the construction process in 2021, the globe’s highest energy gamma-ray event was recorded by LHAASO, with its energy up to 1.4 PeV (1 PeV = 1015 electron volts). Establishing a world record also provided an important possibility for exploring the fundamental laws of physics, such as Lorentz symmetry.
Lorentz symmetry breaking might cause high-energy photons to become unstable, swiftly decaying into an electron-positron pair or into three photons. “To put it simply, the high-energy photons immediately vanish on their journey to Earth if Lorentz symmetry is broken, which suggests the energy spectrum we measured needs to be abbreviated at a particular energy,” claimed Prof. Bi.
The data from LHAASO reveal that the existing gamma-ray spectrum continues to high energies above PeV, and no “mysterious” disappearance of any type of high-energy gamma-ray events has been located. This outcome shows that Lorentz symmetry is still maintained when approaching the Planck energy scale.
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