The older a person is, the faster time passes, scientists agree. But our entire universe apparently experiences a similar effect – even though it is a matter of the human psyche and physics in the cosmos. It was described by Geraint Lewis of the University of Sydney, Australia, and statistician Brendon Brewer of the University of Auckland.
“If we look back to when the universe was just over a billion years old, we see that time seems to pass five times slower there,” explains Lewis. “If you were there, in this baby universe, one second would seem like one second – but from our position, more than 12 billion years into the future, this early time seems to really drag on.”
It is not very noticeable in our daily life, but space and time in the universe are inextricably linked. Thanks to this, we can observe the accelerating expansion of the universe. Light from much greater distances expands as space expands, shifting toward longer and redder wavelengths the greater the distance from the source.
This is called the Doppler Effect and we can observe it here on Earth. Scientists often help themselves by comparing it to the sound of an ambulance – it seems to expand as the ambulance moves away from us. In this analogy, the ambulance becomes a distant galaxy and the siren is the light. At the source, the radiation is normal, but from our point of view, the whole thing will spread out.
Something similar should happen – and does happen – with time. Time passes normally for us. To someone lingering in the vicinity of a supernova explosion, time would also appear to pass normally. But given the relative speed between the two points, it appears to us that the supernova explosion is in slow motion.
Quasars in the early universe are thought to exhibit a similar effect. Quasars are galaxies that have an actively feeding supermassive black hole at their center – it absorbs the surrounding matter. The feeding process produces large amounts of light as the material around the black hole heats up. “While supernovae behave as a single flash of light, which makes them easy to study, quasars are more complex, like a continuous firework display,” explains Lewis. “However, we were able to decipher this behavior and show that even quasars can be used as standard time markers for the early universe.”
A journey against the tide of time
Lewis and his colleagues studied a sample of 190 quasars from 2.45 to 12.17 billion years ago (the Big Bang occurred 13.8 billion years ago), taking data at different wavelengths over two decades. They had approximately 200 observations for each quasar, which allowed a detailed reconstruction of their fluctuations.
Previously, scientists thought that the variability of quasars did not show time dilation effects, but the samples were small and observed over a much shorter time period. By dramatically expanding both the number of quasars and the length of observations, astronomers have now discovered that old quasars do indeed appear to oscillate more slowly compared to newer ones.
“Previous studies have led people to question whether quasars are really cosmological objects, or even whether the idea of expanding space is correct,” adds Lewis. “However, thanks to these new data and analyses, we have managed to find previously unrecorded behavior of quasars, and they behave exactly as Einstein’s theory of relativity predicts.”
2023-07-04 13:06:00
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