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New Clue to Universe's Darkest Mystery

An astronomer says he may have found an important clue to one of the most profound mysteries in the universe: Why the stars in the sky are moving away from us at an ever increasing pace. Some scientists have suggested that the vacuum of space is filled with a weird force, called "dark energy."

But new results, presented Wednesday at the American Astronomical Society meeting in Washington, D.C., call that idea into question.

When astronomers look out into the sky, they see that everything around is moving away from us. Part of their explanation is that the universe started with a cosmic explosion, known as the Big Bang. In 1999, astronomers set out to measure the speed of expansion by looking at distant supernovae -- exploding stars -- to see how fast they were moving away.

To everyone's surprise, they found that the material isn't just coasting away from us in space, as expected in the aftermath of an explosion. It's actually picking up speed as it goes.

"Something out there is pushing the universe, making it expand, making it speed up and we don't know what this is really," says Bradley Schaefer, the Louisiana State University astronomer who presented the results.

"It's been given a name, dark energy, and you can say this dark energy is pushing the universe, pushing the acceleration," he says.

A leading notion is that dark energy is something that pervades what was thought of as empty space. It's sometimes called "quantum vacuum energy" or the "cosmological constant."

The idea is that it's a constant through all space and through all time. Schaefer decided to test this idea by probing deeper back in time, to see if the constant was the same way back then. He did this by studying objects called gamma-ray bursts.

"They're an extreme version of supernovae," says Schaefer, "and as such, they are 100 times more luminous than supernovae, and so you can see them much further out in the universe."

Early results from Schaefer's study of the movements of gamma-ray bursts suggest that dark energy is different far out in space, and therefore way back in time.

"The first result of this new method happens to be pointing toward the direction of this cosmological constant not being constant," Schaefer explains, "which would be to say it appears that the dark energy is changing with time."

Schaefer, however, stops short of making a definitive claim about the nature of the universe from these results. And his evidence is not strong enough at the moment to be absolutely convincing.

Even so, it is attracting a lot of attention at the astronomy meeting, including from heavyweights such as Michael Turner from the University of Chicago and the National Science Foundation.

"It's very intriguing," says Turner, "but I don't think it rises to the level of me being able to issue Schaefer a ticket to Sweden."

The Nobel Prize will have to wait for more convincing results, Turner says. But he adds that a breakthrough in this field would clearly be gold-medal material.

"Cosmic acceleration, I believe, is the biggest mystery in all of science."

Turner says it's hard enough for scientists to understand how the supposedly empty vacuum of space can be suffused with some form of cosmic energy. If Schaefer's data hold up and the idea of a constant and pervading energy is thrown out, then what?

"The alternatives really are mind-stretching," says Turner.

Maybe the universe contains hidden dimensions. Turner says the uncertainty about Shaefer's results won't last long; other astronomers have also been trying to measure the expansion of the universe way back in time. In a few years, Turner says we should know whether this is just a statistical fluke, or a real clue about the fabric of our universe.

Copyright 2022 NPR. To see more, visit https://www.npr.org.

Richard Harris
Award-winning journalist Richard Harris has reported on a wide range of topics in science, medicine and the environment since he joined NPR in 1986. In early 2014, his focus shifted from an emphasis on climate change and the environment to biomedical research.