Fierce black holes reveal ‘time dilation’ – 7/3/2023 – Science

Time is a slippery thing, as deep thinkers like physicist Albert Einstein and, well, fictional time traveler Doctor Who clearly understood. The latter, in a 2007 episode of the British science fiction series, accurately described time as wobbly.

Scientists returned to that point on Monday in a study that used observations of a ferocious class of black holes called quasars to demonstrate “time dilation” in the early Universe, showing how time passed at just about one-fifth of the speed it passes today. The observations date back to approximately 12.3 billion years ago, when the Universe was approximately one-tenth of its current age.

Quasars, which are among the brightest objects in the Universe, were used as a “clock” in the study to measure time in the past. Quasars are tremendously active, supermassive black holes millions to billions of times the mass of our Sun, usually residing in the centers of galaxies. They gobble up matter drawn by their immense gravitational pull and release torrents of radiation, including jets of high-energy particles, as a glowing disk of matter swirls around them.

The researchers used observations involving the brightness of 190 quasars across the Universe, dating to around 1.5 billion years after the Big Bang event that gave rise to the cosmos. They compared the brightness of these quasars at various wavelengths with quasars existing today, finding that certain fluctuations that occur over a given amount of time today did so five times slower in the oldest quasars.

Einstein, in his general theory of relativity, showed that time and space are intertwined and that the Universe has been expanding in all directions since the Big Bang.

Astrophysicist Geraint Lewis, from the University of Sydney, Australia, lead author of the study published in the journal Nature Astronomy, said that this continuous expansion explains how time flowed more slowly in the early history of the Universe compared to today.

“In modern physics, time is a tricky thing,” said Lewis. “Dr. Who was right, this time is best described as ‘wobbly, opportune things’. It means that we really don’t understand time and its limitation, and some things are still not ruled out.”

By looking at distant objects, scientists are able to “go back in time” because of the time it takes light to travel through space.

“The statistical properties of light variations contain a time scale — a typical time for fluctuations to have a particular statistical property. And that’s what we use to define the ticking of each quasar,” added Lewis.