In a groundbreaking study, scientists used quasars as cosmic clocks to observe the early universe traveling in extremely slow motion, validating Einstein’s theory of general relativity. By examining data from nearly 200 quasars, supermassive black holes at the centers of early galaxies, the team found that time seemed to flow five times slower when the universe was just over a billion years old.
Observational data from nearly 200 quasars shows that Einstein was right – once again – about the time expansion of the universe.
Scientists have noticed for the first time that the early universe was moving in extremely slow motion, unlocking one of the mysteries of Einstein’s expanding universe.
Einstein’s general theory of relativity means that we should observe the distant – and therefore ancient – universe working much more slowly than it does today. However, looking back at that time has proven elusive. Scientists have now been able to solve this mystery by using quasars as “clocks”.
said lead author of the study, Professor Geraint Lewis from the University of Sydney’s School of Physics and the Sydney Institute of Astronomy.
“If you were out there, in this infant universe, one second would seem like one second — but from our location, more than 12 billion years in the future, that early time seems to be getting delayed.”
The research was published July 3 in natural astronomy.
Professor Geraint Lewis is at the Sydney Institute of Astronomy in the University of Sydney’s School of Physics. Credit: University of Sydney
Professor Lewis and his co-author, Dr Brendon Brewer of the University of Auckland, used observed data from nearly 200 quasars – supermassive black holes at the centers of early galaxies – to analyze this time dilation.
“Thanks to Einstein, we know that time and space are entwined, and since the dawn of time in the Big Bang singularity, the universe has been expanding,” said Professor Lewis.
“This expansion of space means that our observations of the early universe should appear to be much slower than today’s time flows.
“In this paper, we prove it back to about a billion years later[{” attribute=””>Big Bang.”
Previously, astronomers have confirmed this slow-motion universe back to about half the age of the universe using supernovae – massive exploding stars – as ‘standard clocks’. But while supernovae are exceedingly bright, they are difficult to observe at the immense distances needed to peer into the early universe.
By observing quasars, this time horizon has been rolled back to just a tenth the age of the universe, confirming that the universe appears to speed up as it ages.
Professor Lewis said: “Where supernovae act like a single flash of light, making them easier to study, quasars are more complex, like an ongoing firework display.
“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.”
Professor Lewis worked with astro-statistician Dr. Brewer to examine details of 190 quasars observed over two decades. Combining the observations taken at different colors (or wavelengths) – green light, red light, and into the infrared – they were able to standardize the ‘ticking’ of each quasar. Through the application of Bayesian analysis, they found the expansion of the universe imprinted on each quasar’s ticking.
“With these exquisite data, we were able to chart the tick of the quasar clocks, revealing the influence of expanding space,” Professor Lewis said.
These results further confirm Einstein’s picture of an expanding universe but contrast 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,” he said.
Reference: “Detection of the cosmological time dilation of high-redshift quasars” by Geraint F. Lewis and Brendon J. Brewer, 3 July 2023, Nature Astronomy.
DOI: 10.1038/s41550-023-02029-2
