Dark energy, which is driving the expansion of the universe, could change

admin October 06, 2024

One of the great mysteries of the universe is how it is expanding. The phenomenon causing this expansion is known as dark energy. Recently, scientists have begun to wonder if this phenomenon is changing.

ARI SHAPIRO, HOST:

Now, let’s lift up Earth for a moment to look at the evolution of the universe as a whole. Astronomers know that the universe is expanding and accelerating. But what is this cosmic acceleration? The answer starts with Einstein, as NPR’s Regina Barber explains in Short Wave’s Space Camp series.

REGINA BARBER, BYLINE: More than 100 years ago, Albert Einstein was trying to understand how the universe worked, developing his theories of relativity by playing with mathematical equations. At the time, people, including him, thought the universe was static. But the equations he created to explain the universe implied that it had to be expanding, which went against the thinking of the time. And that bothered Einstein.

BRIAN NORD: So he added a blur factor. It was supposed to counteract the expansion so that you get this static universe.

BARBER: Brian Nord is a cosmologist at Fermilab, and he says that Einstein eventually removed the error factor because he couldn’t ignore the initial conclusion of the equation or the data, which was that the universe was indeed expanding. Over the decades, as more and more data became available, scientists realized that this error factor was actually useful in explaining that the universe is not only expanding, but it’s expanding faster and faster over time.

NORD: It’s a shame. If he had managed to do that from the beginning, he might have become famous.

BARBER: (Laughs).

Luckily for Einstein, his confounding factor now has a name: dark energy. Conventional thinking is that it is constant and makes up about 70 percent of the universe. If you have trouble imagining this, Brian suggests thinking of the structure of spacetime—the universe—as a body of water.

NORD: One way to understand how this matter or this mass of water is moving is to look at buoys. So in the late 1990s, two competing teams of cosmologists were looking at supernovae, which are often called exploding stars. So they looked at as many supernovae as they could at distances far from Earth to see, oh, how are these buoys moving? Is it because spacetime itself is changing? And that’s actually what they found – that the best fit to the data is that these supernovae are moving away from us faster and faster.

BARBER: Okay, I got you. So basically, since we can’t measure cosmic acceleration itself – that’s water – we measure the motion of supernovae. Those are the buoys. But just like you’d need a lot of buoys to measure, say, the entire sea, it seems like we need a lot of supernovae to be able to prove anything about cosmic acceleration.

NORTH: Yeah.

BARBER: And that’s where astronomers are right now, looking for beacons that will give us clues about how space-time is expanding. And there’s a possibility of a new complication. Earlier this year, a new paper came out suggesting that dark energy may not be constant. It may change.

Either scenario has big implications for the end of the entire universe. If dark energy is a constant cosmic acceleration, that means the universe will die by what astrophysicists call heat death. Everything moves further and further apart. Galaxies and black holes disappear, and matter disintegrates. It will be cold and lonely. But if dark energy changes, that fate could change, too. To figure it all out, scientists will need a lot more buoys, or hope that humanity lives long enough to find out.

Regina Barber, NPR News.

SHAPIRO: And a special thanks to the U.S. Space & Rocket Center, which houses Space Camp.

(EXCERPT FROM “THE IMPERIAL MARCH” BY JOHN WILLIAMS)

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