Scientists using quasars as cosmic clocks have observed that when the universe was just a billion years old, time ran five times slower, helping to confirm Einstein's general theory of relativity and the expansion of the universe.
By studying distant supernovae, it's been well established that the universe has been expanding since the Big Bang 13.8 billion years ago. As it does so, the galaxies have been spreading away from one another across four dimensions, allowing for no objective center to the expansion.
As they spread, they move faster in relation to one another. One thing this does is cause the spectra of stars and other objects to shift red-ward due to the Doppler effect, which can be measured, so scientists can clock the spread. The other thing it does is that, eventually, the expansion becomes so fast at the edge of the universe, which we see as the distant past, that relativistic effects become apparent, causing shifts in how fast time passes compared to us.
Led by Professor Geraint Lewis from the School of Physics and Sydney Institute for Astronomy at the University of Sydney, a team of scientists used data collected over 20 years from 190 quasars, hyperactive supermassive black holes that are on the edge of the universe, to learn more about how time and space are intertwined.
By using quasar data from the green, red, and infrared bands of the spectrum and applying Bayesian analysis, which can update the probability of a hypothesis as more evidence or information becomes available, the team could statistically calibrate the 'ticking' of each quasar, turning them into clocks to measure the time dilation.
The result is that the passage of time in the past was different than it is today, with each ancient second corresponding to five of ours. Because we're talking about relativity, how this looks depends on where you are. To us, it looks like ancient time is passing more slowly, but if you were in the vicinity of one of these ancient galaxies, each second would seem normal while ours appear to be running five times as fast.
"With these exquisite data, we were able to chart the tick of the quasar clocks, revealing the influence of expanding space," said Professor Lewis, discussing earlier studies that couldn't identify the time dilation of distant quasars. "These earlier studies led people to question whether quasars are truly cosmological objects, or even if the idea of expanding space is correct. With this new data and analysis, however, we've been able to find the elusive tick of the quasars and they behave just as Einstein's relativity predicts."
The research was published in Nature Astronomy, and the video below discusses the time dilation effect.
Source: University of Sydney
