GabyNew research suggests that in the aftermath of the Big Bang, time in the universe ran about five times slower than it does today. Researchers reached that conclusion by observing quasars — the brightest sources of light and radio waves in the cosmos.
Quasars as “clocks” for measuring time in the past
Gerraint Lewis, the study’s lead author and an astrophysicist, says humans still don’t fully understand time or its limits. Time travel remains a fantasy. But this new research helps us better understand how the universe expanded after the Big Bang.
The team used quasars as a kind of clock to measure time in the distant past. Located at the centers of galaxies, these objects are trillions of times brighter than the Sun.
In a study led by Professor Lewis, the team examined the brightness of 190 quasars across the universe — from relatively young ones (observed 2.45 billion years ago) to the oldest that formed shortly after the Big Bang (about 12.17 billion years ago). They collected wavelength-spanning data over two decades.
They made up to 200 observations of each quasar. Comparing brightness across different wavelengths, they found that fluctuations in the oldest quasars unfolded about five times more slowly than in the youngest ones.
Time is complicated, even for physicists
Einstein’s general theory of relativity says that space and time are linked, and that the universe has been expanding in all directions since the Big Bang. Professor Lewis says that this expansion explains why time appeared to pass more slowly earlier in the universe’s history than it does today.
But Lewis stresses this isn’t the same as ordinary slow motion. If you could be in the newborn universe, one second there would feel like one second.
From our present perspective, that early time appears stretched. So, from today’s point of view, a second back then would stretch out to five seconds. Professor Lewis explains that in modern physics, time is a complicated concept.
In everyday life we don’t notice the link between time and space. But there is a clear example: the way an ambulance siren stretches as the vehicle speeds past. The ambulance is analogous to a distant galaxy, and the siren’s sound stands in for light.
The light is emitted normally at its source, but we observe it stretched. The same stretching happens to time. Because light takes time to cross cosmic distances, observing distant objects is like looking back in time.
Supernovae and quasars used to study cosmic time
Earlier, the Daily Mail reported that scientists had documented a slowdown in time about 7 billion years ago based on observations of supernovae. Locally, time passes normally at both locations, but because of relative motion and cosmic expansion between Earth and the supernova, those events appear to us to unfold in slow motion.
Because astronomers know how long a supernova’s light curve should last, they can spot these explosions at great distances. Those distant supernovae appear to evolve more slowly from our viewpoint.
But individual supernovae are too faint to see beyond certain distances, which limits their usefulness for probing the very early universe.
Quasars are bright enough to be seen back to the universe’s early stages. As Lewis explains, a supernova is like a single flash, while a quasar is more like a continuous fireworks display — its brightness fluctuates in small but sometimes sharp jumps, like a volatile stock.
Quasar flicker confirms relativity’s time dilation
Earlier studies suggested quasar variability didn’t show time dilation. But those studies were smaller and relied on much shorter observation periods.
The new, longer dataset shows that ancient quasars do indeed flicker more slowly than modern ones, matching the time dilation predicted by Einstein’s relativity. That’s why, Lewis says, quasar brightness is such a useful observable for studying time across cosmic history.
