According to Chinese scientists testing Einstein's theory of relativity, the speed of light remained constant during the most powerful cosmic explosion ever observed, based on the world's most sensitive high-energy light detector.
Their study, submitted to the arXiv preprint site this month but not yet peer-reviewed, provides the latest evidence that the universe is a symmetrical place — also known as Lorentz symmetry, a pillar of Einstein's special theory of relativity — leaving scientists empty-handed in their search for violations of this symmetry.
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Nicholas Yunes, a theoretical physicist at the University of Illinois at Urbana-Champaign in the US, said that Lorentz violation was a phenomenon predicted by researchers who tried to develop a theory of quantum gravity to unify general relativity and quantum mechanics.
„If detected, such a breach would be a groundbreaking discovery that would shake the foundations of physics,” Younes said. „So far, no such breach has been found.”
Younes said the Lasso group's results put „strong constraints” on such violations, and that a linear-type Lorentz violation „probably does not exist in nature.”
In Einstein's theory of relativity, Lorentz symmetry dictates that as long as the observed object is moving at a constant speed, observers must see the same object from any direction or frame of reference.
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As a result of Lorentz symmetry, people always notice that light travels at 300 million meters per second, whether driving down the highway or flying through space in a spaceship. The constant speed of light is a cornerstone of modern physics and forms the basis of our understanding of space and time.
Every experiment conducted to date has confirmed Lorentz symmetry. However, this rule does not hold in extreme situations, such as when tiny particles burst through the vast universe with incredibly high energies, giving rise to a mysterious, unknown force.
Although such a force is very weak, it increases with the particle's energy and can accumulate to detectable levels over large travel distances, the researchers wrote.
The Lasso collaboration, with the Institute of High Energy Physics in Beijing and 280 participants from around the world, divided these photons into 10 groups according to their energy thresholds and tracked the delay as they arrived.
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The researchers' analysis of the data based on two different methods showed that changes in the speed of light at higher energies are much smaller. They found that the lower limits of energies at which Lorentz violation could occur would have been higher than current predictions.
In other words, based on the detections of gamma-ray photons, the team found no conclusive evidence to support the theory of the variable speed of light at the observed energies.
Younes said it was „particularly impressive” that the new study could constrain linear-type violations at a scale 10 times larger than the Planck size, which determines the minimum limit of the universe. Quadratic violations are also „weaker, but no less impressive, in scale,” he said.
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Lasso was built by Chinese scientists at an altitude of 4,410 meters (14,470 ft) on Mount Haixi in Dacheng County, Sichuan Province. It consists of four types of detectors, including about 5,200 electromagnetic particle detectors, 1,200 muon detectors, 18 wide-field Cherenkov telescopes, and a 78,000-square-meter (839,600 sq ft) water Cherenkov detector array.
The facility was commissioned in 2021 and operates as the world's most sensitive ultra-high-energy gamma ray detector.