The quasar “clocks” show the universe slowed down by a factor of 5 after the Big Bang

In a pioneering study, scientists used quasars as cosmic clocks to track the early universe in ultra-slow motion, further confirming Einstein’s theory of general relativity. By examining data from nearly 200 quasars, supermassive black holes at the centers of early galaxies, the team found that time slows down five times when the universe is over a billion years old.

Observational data from nearly 200 quasars show Einstein – again – correct about the periodic expansion of the universe.

Unlocking one of the mysteries of Einstein’s expanding universe, scientists have observed for the first time that the early universe was moving at an extremely slow rate.

Einstein’s theory of general relativity means that we should observe that the distant – and therefore ancient – universe was moving much more slowly than it is today. However, looking back at that time has proven elusive. Scientists have now cracked that mystery by using quasars as ‘clocks’.

“When we look back to a time when the universe was more than a billion years old, we see time slows down by a factor of five,” said lead author of the study, Professor Geraint Lewis of the Institute of Physics and Astronomy in Sydney. University of Sydney.

“If you were there, in this infant universe, one second would seem like a second — but from our position, more than 12 billion years into the future, that early period seems to drag on.”

The research was published on July 3 Natural Astronomy.

Geraint Lewis

Professor Geraint Lewis at the Sydney Institute of Astronomy in the School of Physics at the University of Sydney. Credit: University of Sydney

Professor Lewis and his collaborator Dr Brendan Brewer, from the University of Auckland, used data observed from nearly 200 quasars – the supermassive black holes at the centers of early galaxies – to study this time dilation.

“Thanks to Einstein, we know that time and space are intertwined, and that since time began in the singularity of the Big Bang, the universe has been expanding,” Professor Lewis said.

“This expansion of space means that our observations of the early universe must appear much slower than the present-day flow of time.

“In this paper, we establish that after about a billion years[{” attribute=””>Big Bang.”

Previously, astronomers have confirmed this slow-motion universe back to about half the age of the universe using supernovae – massive exploding stars – as ‘standard clocks’. But while supernovae are exceedingly bright, they are difficult to observe at the immense distances needed to peer into the early universe.

By observing quasars, this time horizon has been rolled back to just a tenth the age of the universe, confirming that the universe appears to speed up as it ages.

Professor Lewis said: “Where supernovae act like a single flash of light, making them easier to study, quasars are more complex, like an ongoing firework display. 

“What we have done is unravel this firework display, showing that quasars, too, can be used as standard markers of time for the early universe.”

Professor Lewis worked with astro-statistician Dr. Brewer to examine details of 190 quasars observed over two decades. Combining the observations taken at different colors (or wavelengths) – green light, red light, and into the infrared – they were able to standardize the ‘ticking’ of each quasar. Through the application of Bayesian analysis, they found the expansion of the universe imprinted on each quasar’s ticking.

“With these exquisite data, we were able to chart the tick of the quasar clocks, revealing the influence of expanding space,” Professor Lewis said.

These results further confirm Einstein’s picture of an expanding universe but contrast earlier studies that had failed to 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,” Professor Lewis said.  

“With these 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,” he said.

Reference: “Detection of the cosmological time dilation of high-redshift quasars” by Geraint F. Lewis and Brendon J. Brewer, 3 July 2023, Nature Astronomy.
DOI: 10.1038/s41550-023-02029-2

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