Is the enlargement of the universe slowing down?

It’s broadly thought that our universe is increasing at an ever-accelerating fee. However may we now have that mistaken? That’s what a bunch of scientists from South Korea claims, however different scientists have main issues in regards to the work.

Our universe has been increasing for the reason that huge bang 13.8 billion years in the past. A number of strands of proof, together with observations of distant dying stars referred to as sort Ia supernovae, have urged that this enlargement is accelerating. One of many essential explanations for the motive force of this acceleration is a mysterious pressure referred to as darkish vitality, the invention of which gained the 2011 Nobel prize in physics.

Younger-Wook Lee at Yonsei College in South Korea and his colleagues now say this may be mistaken. Sort Ia supernovae are triggered when the remnant core of a star like our solar, often known as a white dwarf, explodes in a binary system. Astronomers use these “commonplace candles” as reliable measurements of distance throughout the cosmos as a result of they’re regarded as uniformally shiny.

However Lee and his group say the brightness varies strongly with the age of the celebrities, based mostly on their evaluation of 300 host galaxies. They are saying that distant supernovae could seem like fainter than anticipated and that is normally put right down to the accelerating enlargement of the universe, however, as soon as this “age bias” is taken into consideration, the accelerating enlargement disappears.

As a substitute, Lee says their findings counsel the enlargement of the universe started decelerating 1.5 billion years in the past, and will even reverse sooner or later, a situation referred to as the “huge crunch” by which the universe may finish in a reverse huge bang. Beforehand, he says, “a giant crunch was out of the query. However now it’s a risk.”

Adam Riess on the Area Telescope Science Institute in Maryland, one of many recipients of the 2011 Nobel prize in physics, disagrees with that declare, pointing to earlier work by the group in 2020 that had been refuted. “The identical group’s new work repeats the argument with little change,” he says, noting that making measurements of stellar ages for sort Ia supernovae at massive distances could be very troublesome. He says Lee’s group used a imply stellar age derived from the host galaxy. “The speculation behind that is weak due to a scarcity of certainty about how the [star] types,” says Riess.

There are identified points with how age impacts the brightness of sort Ia supernovae throughout the universe, says Mark Sullivan on the College of Southampton, UK, however these are already accounted for in measurements of darkish vitality. “I’m very sceptical it will result in a decelerating universe,” he says.

Upcoming observations with the Vera C. Rubin Observatory in Chile are anticipated to drastically broaden the variety of identified sort Ia supernovae within the universe, from the hundreds catalogued in the present day to tens of hundreds. That can enable us to “map the enlargement historical past” of the universe a lot additional again in time, says Sullivan, doubtlessly ruling out the claims from Lee’s group.

The precise nature of darkish vitality, nonetheless, stays mysterious. Earlier this 12 months, outcomes from the Darkish Power Spectroscopic Instrument survey indicated that darkish vitality may not be a relentless pressure, however may differ over time. Whereas that wouldn’t imply the universe was decelerating proper now, it would counsel that the enlargement fee has modified over the historical past of the universe.

“The needle is pointing much more to darkish vitality being some form of dynamical factor, not a cosmological fixed,” says Ed Macaulay at Queen Mary College of London. “Precisely what that’s, I believe, is a extremely fascinating query.”