The concept that time appeared to be slower in the past has been supported by observations of ancient astronomical objects that seem to evolve at a fifth of the rate we see today. This phenomenon is a direct result of the expansion of the universe since the big bang. As the universe expands, light from cosmic events that occurred in the distant past must travel longer distances to reach Earth, thus taking more time to arrive. Consequently, events that are far away or occurred a long time ago appear to unfold more slowly compared to similar events happening nearby in the present. However, it is important to note that this does not mean that time in the early universe actually moved in slow motion. If someone were present billions of years ago, they would have perceived time moving at a normal pace.
Since the 1990s, astrophysicists have observed this time dilation in distant supernovae, with the oldest one examined dating back to roughly half the age of the universe, appearing to evolve at 60% of the speed we see today. Now, Geraint Lewis at the University of Sydney, Australia, and Brendon Brewer at the University of Auckland, New Zealand, have discovered an even more extreme version of this time dilation in the early universe.
Lewis and Brewer focused their study on quasars, which are objects found at the center of some galaxies. Quasars consist of a supermassive black hole surrounded by a disc of hot plasma that emits high-energy particles. They are among the oldest known objects in the universe, with the earliest detected quasar emerging approximately 600 million years after the big bang.
While quasars have the potential to be used to investigate time dilation in the early universe due to their age, their unpredictable nature poses significant challenges, unlike supernovae.
To overcome this challenge, Lewis and Brewer analyzed data from 190 quasars. They grouped quasars based on their brightness and redshift, which is the stretching of light from distant objects into longer, redder wavelengths. By comparing the quasars within each group, they identified similar patterns of activity over a specific time period, treating these patterns as a standard clock.
Through this analysis, the researchers determined that the earliest quasar, which existed around one billion years after the beginning of the universe, appeared to run five times more slowly than quasars observed today. This observation represents the earliest evidence of cosmological time dilation.
Bruno Leibundgut at the European South Observatory, who was part of the team that first observed this phenomenon in supernovae three decades ago, emphasizes the significance of the Lewis and Brewer study, demonstrating that quasars, which have long been regarded as “ultimate cosmological sources,” also exhibit time dilation as predicted by theory and previously observed in other objects.
