A new study, published in Nature Astronomy, has found evidence of cosmic time dilation in 190 quasars observed over 20 years in different wavelengths. Cosmic time dilation is the phenomenon predicted by Albert Einstein’s relativity theory, which states that time flows slower in distant parts of the universe.
The researchers, from the University of Sydney and the University of Auckland, used quasars as cosmic clocks to measure how time changed with the expansion of the universe. Quasars are extremely bright and energetic black holes at the centres of galaxies, and can be seen from billions of light-years away.
The study revealed that time appeared to run five times slower when the universe was about one billion years old, compared to today. This is more than twice the slowdown detected by previous studies using supernovas, which are massive exploding stars.
The lead author of the study, Geraint Lewis, an astrophysicist at the University of Sydney, explained that this does not mean that time was actually different in those distant regions.
“If I could magically transport you back 10 billion years and drop you next to one of these quasars, and you’ve got a stopwatch, time would just be normal,” he told AFP.
“One second would be one second.”
He added that this effect is only observable from our perspective, as we look back in time and space.
“Everything looks like it’s slowed down” from here, he said.
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Quasars had failed to measure time dilation in previous trials, which led to some “peculiar proposals,” Mr Lewis said.
Some of these proposals questioned the distance of quasars or even suggested that “something fundamental was wrong” with cosmology, he said.
But the new study “restores everything to its proper place,” Mr Lewis said.
It also showed that “Einstein was right once more,” he added.
The researchers succeeded where others had not because they had much more data on quasars, Lewis explained. Recent progress in the statistical analysis of randomness also helped.
The researchers had to make sense of the chaotic explosions that happened when the black holes consumed material, to turn quasars into clocks with observable ticks.
Mr Lewis likened it to watching a fireworks show, where the big flashes seem random but different components are “illuminating and dimming on their own timescales”.
“We have untangled this fireworks show, demonstrating that quasars can also be used as standard indicators of time for the early universe.”