Among the laws that govern the Universe, Einstein’s theory of relativity revolutionized our understanding of space and time, predicting phenomena such as time dilation. However, despite technological advances, some of these predictions remain difficult to observe, especially in the context of the early universe. Recently, a team of astrophysicists from the University of Sydney and the University of Auckland made a significant breakthrough. Using an innovative method based on the observation of distant quasars, they were able to observe time dilation in the early universe for the first time. This discovery not only confirms an important prediction of the theory of relativity, but also opens new avenues for studying the early universe, with potentially profound implications for our understanding of cosmic history. His work is published in the journal Astronomy of Nature.

According to Einstein, general relativity predicts a slowdown in ancient cosmic events compared to modern ones. This effect is known as time dilation. It is driven by the expansion of the universe, as exposed by the scientist in 1915. One consequence of the expansion of the universe is that light is stretched as it traverses the cosmos, which increases the wavelength. This effect makes old galaxies appear redder than they are, or redshifted. But time also stretches. Consider a distant object that blinks once per second. The expansion of the universe causes more than a second to pass between flashes when they hit Earth.

Astronomers have seen stars explode in slow motion before. The flash and fade occur at about half the normal rate, when the universe was half its current age. But attempts to see time dilation in the very ancient cosmos have so far failed. This is how the authors of the new study were able to identify cosmic time dilation. And this in a sample of 190 quasars located in the early universe. Quasars are extremely distant and bright objects. The team monitored them in various frequency bands over a period of two decades. Then, he was able to standardize the “tick-tock” of each one of them (fluctuation of the light emitted by these objects).

Quasars, unlike supernovae that act as a single flash of light, are more complex, like fireworks. Professor Geraint Lewis, co-author, explains in an announcement: “What we have done is unravel this firework, showing that quasars can also be used as standard time markers for the beginning of the universe. «. In fact, each quasar has a specific rate of luminosity variation. By observing these variations, researchers can infer information about the quasar itself and the surrounding universe. They determine a characteristic time scale for each of them.

They then compared them to those expected in an expanding universe based on Einstein’s theory of general relativity. The authors then found that events in the early universe seemed to unfold about five times slower than in the current universe. This means that if an event happened in one second in the early universe, it would appear to have happened in five seconds from our perspective in the current universe.

His work not only confirms Einstein’s theory of relativity, but also solves several puzzling problems. Professor Lewis said: At some level, it increases our confidence that we know how the universe works. «. He adds: “We have this picture given by Einstein and we have tested it over and over again. A good scientist does not take these things for granted. We have to keep testing. » This study confirms that quasars are consistent with the effect of time dilation over large distances of space-time. This means that quasars can be used as “cosmic clocks” to measure time in the distant universe. This consistency with the effect of time dilation increases confidence in the standard model of cosmology, which describes the evolution and large-scale structure of the universe.

Second, we can now explain time dilation in studies of the behavior of quasars. When a fluctuation in the luminosity of a distant quasar is observed, it appears to occur more slowly. It is a distance effect, which would not exist if the quasar were closer. This could help us better interpret quasar observations. Finally, it allows us to refine our theoretical models of the universe and better understand its evolution since the Big Bang. The researchers’ results reinforce the importance of constant verification of scientific theories. This is even more true for those who are widely accepted. Science is a constantly evolving process.

source: https://www.nature.com/articles/s41550-023-02029-2