Quasar 'clocks' show time running five times slower in ancient universe

In a new paper published in the journal Nature Astronomy, a team of scientists explains how they used quasars as "clocks" to take measurements of that ancient time.

"Looking back to a time when the universe was just over a billion years old, we see time appearing to flow five times slower," lead author Professor Geraint Lewis from the University of Sydney explained.

"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 scientists used observational data from 200 quasars, which are hyperactive supermassive black holes at the centers of early galaxies. Using this data, they were able to measure this immense time dilation.

What is time dilation?

Time dilation refers to the phenomenon whereby different objects experience time differently based on their relative speeds or gravitational potentials. This is observable, for example, in the fact that geosynchronous satellites experience time differently from a clock on Earth.

"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," Professor Lewis said.

"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."

Disproving earlier studies

Before the new study, scientists had used supernovae to measure time dilation dating back to roughly half the age of the universe.

Though supernovae – massive exploding stars – are incredibly bright, they are very hard to detect in the very ancient universe. Instead of using supernovae, the team behind the new paper used quasars to measure this slow-motion universe back at only a tenth of the age of the universe.

By doing so, they provided further evidence that the universe appears to be speeding 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," Professor Lewis explained. "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."

The researchers analyzed over two decades' worth of quasar data, observing the "tick" of these quasars and helping to disprove 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."