Einstein’s
theory of relativity is the cornerstone of modern physics. It requires that
physical laws have Lorentz symmetry. Since Einstein proposed his theory of
relativity, the validity of Lorentz symmetry has undergone numerous
experimental tests.
The theory
of relativity suggests that light is the fastest speed of matter in the
Universe. Whether that limit is breachable can be tested by examining Lorentz
symmetry breaking or Lorentz invariance violation.
In a new
study, scientists- from the Institute of High Energy Physics of the Chinese Academy of Sciences– examined the validity of the theory of relativity with the
highest accuracy.
They used
the highest-energy gamma rays observed by the Large High Altitude Air-shower
Observatory (LHAASO) to test Lorentz symmetry. The outcomes improve the
breaking energy scale of Lorentz symmetry dozens of times compared with the
previous best result.
Prof. BI
Xiaojun, one of the paper’s corresponding authors, said, “This is the most
rigorous test of a Lorentz symmetry breaking form, confirming once again the
validity of Einstein’s relativistic space-time symmetry.”
It is
crucial to test the theory of relativity and develop more fundamental laws of
physics by looking for signals of Lorentz symmetry breaking. However, according
to these theories, the effect of Lorentz symmetry breaking is only significant
at the so-called Planck energy scale, which is up to 1019 GeV (1 GeV = 1
billion electron volts).
The
effects of Lorentz symmetry breaking are too weak to be tested in labs. But
there are very violent astrophysical processes in the Universe where particles
can be accelerated to energies much higher than what man-made accelerators can
reach. Therefore, astrophysical observations are a natural laboratory for looking
for the effects of Lorentz symmetry breaking.
LHAASO is
a large-scale cosmic ray experiment in China. In 2021, it recorded the world’s
highest energy gamma-ray event with its energy up to 1.4 PeV (1 PeV = 1015
electron volts). Simultaneously, it offers an excellent opportunity to explore
the fundamental laws of physics, such as Lorentz symmetry.
Prof. BI
said, “Lorentz symmetry breaking may cause high-energy photons to become
unstable, rapidly decaying into an electron-positron pair or three photons. In
other words, the high-energy photons automatically disappear on their journey
to Earth if Lorentz symmetry is broken, which implies the energy spectrum we
measured should be truncated at a particular energy.”
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