Universe ran in 'slow motion' soon after the Big Bang

Scientists from Australia and New Zealand have observed the early universe running in extreme slow motion, confirming the time-dilation expectations of Einstein’s theory of general relativity. Their results have been published in the journal Nature Astronomy.

Einstein’s theory means that we should observe the distant — and hence ancient — universe running much slower than the present day. However, peering back that far in time has previously proven elusive. Scientists have now cracked that mystery by using quasars — the supermassive black holes at the centres of early galaxies — as ‘clocks’.

“Thanks to Einstein, we know that time and space are intertwined and, since the dawn of time in the singularity of the Big Bang, the universe has been expanding,” said lead author Professor Geraint Lewis, from The University of Sydney.

“This expansion of space means that our observations of the early universe should appear to be much slower than time flows today.”

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.

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

“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.”

Lewis worked with astro-statistician Dr Brendon Brewer, from The University of Auckland, to examine details of 190 quasars observed over two decades. Combining the observations taken at different colours (or wavelengths) — green light, red light and into the infrared — they were able to standardise 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,” Lewis said.

“Looking back to a time when the universe was just over a billion years old, we see time appearing to flow five times slower.

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

These results further confirm Einstein’s picture of an expanding universe but contrast with earlier studies that had failed to identify the time dilation of distant quasars. According to Lewis, “These earlier studies led people to question whether quasars are truly cosmological objects, or even if the idea of expanding space is correct.

“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.”

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