Time has been observed passing more slowly in quasars within the early universe.
The observed time dilation comes as a consequence of Albert Einstein’s theory of general relativity combined with the expansion of space. “At its heart, that is one other ‘Einstein is correct again’ story,” Geraint Lewis, a cosmologist on the University of Sydney, told Space.com.
Lewis and Brendon Brewer of the University of Auckland are co-authors on a brand new paper describing the long-sought after confirmation of time dilation effects within the variability of quasars. A quasar is powered by an accreting supermassive black hole at the center of an especially energetic galaxy. Since the accretion disk across the black hole is comparatively small, fluctuations in the sunshine emitted by the quasar can happen in only days. This makes them easier to trace.
Nonetheless, within the time for the reason that light, and its fluctuations, was emitted from the 12 billion-year-old quasars, the universe has expanded greatly. Which means we’re seeing the quasars as they existed over 12 billion years ago.
“We expected quasars to also exhibit this behavior, but previous searches had failed to seek out it,” said Lewis.
Related: What’s the idea of general relativity?
A latest sample of 190 high-redshift quasars observed over 20 years by the Sloan Digital Sky Survey (SDSS), Pan-STARRS and the Dark Energy Survey, has provided Lewis and Brewer with the tools to finally detect time dilation within the variability of quasar light. The long period of observations coupled with telescopic sensitivity to the quasar fluctuations reveals the time dilation effect. Based on how slowly the fluctuations appear to be occurring, time in these quasars appears to run five times slower than it does for us in our frame of reference on Earth.
“We will pin-down the characteristics of their variability and show that quasars truly play ball with the cosmos,” said Lewis.
To be clear, time didn’t really run slow in those quasars relative to all the things around them — of their frame of reference, time ran normally. Einstein’s theory of relativity and the way he described the passage of time relies on the concept of frames of reference, and that these frames will be distinguished by their velocity relative to one another.
“The motion of distant galaxies is as a consequence of expanding space,” said Lewis. Consider that the Hubble constant describes how briskly a volume of space 3.26 million light-years across is expanding per second. That is an incremental effect, where the expanding volumes of space add up. The farther a galaxy is from us, the extra space has expanded between the galaxy and us, and the faster that galaxy appears to be moving away from us.
“A few of these quasars were moving faster than the speed of sunshine, relative to us, when the photons were emitted,” said Lewis.
As Einstein showed, strange things occur once you approach the speed of sunshine. One among these strange things is time dilation. A stationary observer on Earth would observe a clock traveling faster than them, whether on a spacecraft or in a quasar, appear to decelerate. The faster the clock is moving, the greater the effect. At velocities approaching the speed of sunshine, the effect is dramatically pronounced, leading to peculiarities reminiscent of the twin paradox.
Time dilation shouldn’t be just theoretical. It has been observed, albeit in tiny amounts, in satellites orbiting the Earth — the Global Positioning System has to take this into consideration. Cosmologically, time dilation has been observed in supernovae that exploded 6 to 7 billion years ago, but never in objects more distant than that until now.
Besides being one other successful test of Einstein’s theory of relativity, the time dilation observed within the quasars can be further evidence that we do indeed live in a universe that’s expanding because of this of the Big Bang. If the universe weren’t expanding, the quasars wouldn’t seem like moving at relativistic speeds relative to us. Lewis described the findings as “putting to bed among the more extreme ideas that had been proposed, including that cosmologists have all of it flawed, as a consequence of the previous failure to see quasar time dilation.”
The research was published on 30 June in Nature Astronomy.