BEIJING, April 9 (Xinhua) — The speed of light is the highest known speed in the universe, and near the top of an extinct volcano in Mexico, scientists are using an approach to measure an extreme condition in an attempt to find evidence that the speed of light may not be constant. Existing physics theories can explain most of the universe well, but they fail when it comes to extremes, such as how matter interacts on the surface of a black hole, or matter interacts with matter after the Big Bang.
Testing the limits of Einstein’s theory and developing a broader theory that incorporates these extremes has become a whole new field of physics. But not every test proves that modern physics theory is correct. The new experiment is probably the biggest challenge physicists face so far.
Pat Harding, an astrophysicist at Los Alamos National Laboratory and one of the study’s authors, said his instinctive reaction was shocked when the results came out. Relativity is Einstein’s most famous theory, and this new study extends the application of the theory to some energy that cannot be directly acquired on Earth or in space. In most quantum gravitational models, relativity behavior collapses at very high levels of energy, and many strange phenomena become possible, such as the possibility that high-energy ray particles may travel faster or slower than the speed of light.
Some physicists try to explain some mysterious deviations in the universe with ideas that differ slightly from existing theories, such as string theory. These deviations occur only in extreme cases, such as ultra-high-energy particles. Physicists are looking for such deviations at the high-altitude Chelenkov Observatory (HAWC) in Puebla, Mexico, to see if there is a violation of Lorentz’s invariance. Lorenz invariance is an important part of the standard model of physics, meaning that the laws of physics are the same for each stationary object (regardless of its orientation in space) or for an object in constant motion (which can be converted between a frame of stationary and motion using mathematical formulas). The result of this symmetry is that the speed of light is a constant value in a vacuum, just under 300 million meters per second.
The violation of Lorenz invariance means that high-energy cosmic rays may travel faster or slower than constant speeds of light and may have visible effects. These particles may decay or divide to reach Earth. In observational experiments, this will show a decrease in the number of photons capable of detecting a sufficiently high energy. Physicists at Mexico’s high-altitude Cherenkov Observatory are looking for this signal.
The observatory consists of hundreds of large water tanks located near the top of Mexico’s Sierra Negra volcano. High-energy gamma-ray particles produce large amounts of particles when they interact with the atmosphere, and when they interact with water, they produce small flashes. The photomultiplier tubes can convert these flashes into signals, which allow scientists to reconstruct the high-energy particles that cause the flash.
The scientists combined the method of calculating the energy of the incident photons to obtain very clear data: the number of photons did not decline. HAWC continues to look at photons from astrophysical sources with an energy of 285 TeV, more than 40 times the energy of the particle beam in the Large Hadron Collider, the most powerful particle physics experiment on Earth. The presence of these gamma rays precludes the possibility that the most energetic photons exceed the speed of light. Moreover, according to the mathematical calculations of Humberto Martinez-Huerta, a physicist at the University of Sao Paulo in Brazil, the observations increased the minimum energy scale required to violate Lorenz’s invariance theory by 100 times, in other words, the energy scale of relativity.
In short, even the most incredible high-energy light particles still travel at the speed of light, because experiments on Earth can measure them. In other words, if these high-energy particles travel faster than the speed of light, they will decay into lower-energy particles that will never reach Earth. The findings limit the expansion of the theoretical basis that physicists can extend in solving some outstanding problems, the researchers note in a paper published in physical review letters.
However, Martinez-Huerta explains that the observations do not limit all the extensions to Einstein’s theory. Perhaps a violation of Lorenz’s invariance may occur in other particles, or it may cause some photons to be slower than the speed of light.
Ralf Lehnert, a physicist at Indiana University in the United States, who was not involved in the study, said the work was reliable. He reiterated that the study was just one way to measure Lorenz’s invariance, and that, like dozens of other tests that had tried to find evidence of Lorenz’s invariance, it did not get the desired results.
Next, scientists plan to continue to expand the search. THE HAWC RESEARCHERS ADDED MORE WATER TO THE TANK AND INCREASED THE SENSITIVITY OF THE EXPERIMENT. But for now, Einstein’s theory of relativity still refuses to budge, even in the most extreme cases.