Scientists have used quasars as ‘cosmic clocks’ to prove the universe is speeding up as it ages – adding support to Albert Einstein’s general theory of relativity.
They found about one billion years after the Big Bang, time flowed about five times slower than it does now.
Quasars, beams fuelled by supermassive black holes, are the most powerful known objects in the universe.
Combining the observations taken at different colours or wavelengths – green light, red light and into the infrared – the team were able to standardise the ‘ticking’ of each quasar.
Statistical analysis identified the expansion of the universe imprinted on each quasar’s ticking, showing they, and the universe, once moved much more slowly.
‘Looking back to a time when the universe was just over a billion years old, we see time appearing to flow five times slower,’ said lead author Professor Geraint Lewis, of Sydney University in Australia.
‘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.’
The Big Bang is grounded in Einstein’s general theory of relativity.
The German physicist reckoned the universe started in a dense mass of energy that exploded – and has been spreading faster ever since.
It means we should observe the distant – and therefore ancient – cosmos running much slower than now.
The ground-breaking study, published in the journal Nature Astronomy, suggests he was right.
Professor Lewis and Dr Brendon Brewer, of Auckland University in New Zealand, used observations of 190 quasars from early galaxies.
‘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 Professor Lewis.
‘This expansion of space means that our observations of the early universe should appear to be much slower than time flows today.
‘In this paper, we have established that back to about a billion years after the Big Bang.’
The slow-motion universe had previously only been traced back to about half its age using supernovae – massive exploding stars – as ‘standard clocks’.
By observing quasars, the time horizon has been rolled back to just a tenth the age of the universe – confirming it appears to speed up.
‘Where supernovae act like a single flash of light, making them easier to study, quasars are more complex, like an ongoing firework display,’ said Professor Lewis.
‘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.
‘With these exquisite data, we were able to chart the tick of the quasar clocks, revealing the influence of expanding space.’
The results also contradict 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,’ added Professor Lewis.
‘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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