Scientists have observed the distant universe running in slow motion.
It's marking the first time that the strange effect predicted by Albert Einstein approximately a century ago, has been observed in the early universe.
Astronomers found that when the universe was just 1 billion years old, or about one-tenth of its current age, events unfolded five times slower because of the way the expansion of the universe stretches time.
"We observed things changing about five times slower than they do today" said Geraint Lewis, Professor of astrophysics at the University of Sydney and lead author of this study. "It's like watching a movie in slow motion" he added.
According to Einstein's theory of general relativity, Scientists should see ancient cosmic events happen more slowly than modern ones. The effect, known as time dilation, is driven by the expansion of the universe, as explained in the scientist's fundamental exposition of gravity in 1915.
One consequence of the expansion of the universe is that light is stretched as it travels through the universe, making its wavelength longer. This effect causes ancient galaxies to appear redder, or redshifted, than they are.
But time also stretches: If a distant object like pulsar, flashes once every second, the expansion of the universe ensures that more than a second elapses between flashes until they reach Earth.
Scientists have previously observed stars explosion in slow motion, with the flash and fade unfolding at roughly half normal speed, from when the universe was just 50% its current age. But attempts to look at time dilation in the early cosmos by observing extremely bright, distant galaxies called quasars had failed to find the effect.
Lewis and his colleague Dr Brendan Brewer at the University of Auckland carried out a detailed statistical analysis on 190 quasars observed over two decades and found that, in contrast to earlier work, cosmic events in the early universe appeared to be very slow.
The key to their success, described in Nature Astronomy, was to find the equivalent of a clock ticking in the quasar's rich and erratic light display.
Lewis said that, while astronomers fully expected to see time dilation in the early cosmos and were puzzled as to why earlier work had failed to see the effect, the prediction still had to be tested.
"On some level, this builds confidence that we know how the universe operates" Lewis said. “We have this picture given by Einstein and we test it, test it and test it. A good scientist does not take these things for granted. You have to keep testing."
Pro. Brian Schmidt, an astronomer at Australian National University in Canberra, who shared the Nobel Prize in 2011 in physics for discovering the early expansion of the universe, said the theory makes progress by continually testing science's predictions.
"In this case, Lewis and colleagues have extended the study of time dilation to great distances in association with a supernova" he said. "And while they found that once again general relativity has predicted what has been observed, this clears up some potential concerns around time dilation observed in quasars from other studies". Schmidt added.