Dark energy — which causes the expansion of the universe — may be changing

Transcript

ARI SHAPIRO, HOST:

Now let's lift up from Earth for a big-picture look at the changing universe. Astronomers know that the universe is expanding and picking up speed as it does so. But what is this cosmic acceleration? The answer begins with Einstein, as NPR's Regina Barber explains for Short Wave's series Space Camp.

REGINA BARBER, BYLINE: Over 100 years ago, Albert Einstein was figuring out how the universe works, developing his theories of relativity by toying around with mathematical equations. At the time, people, including him, thought that the universe was static. But the equations he created to explain the universe implied that it had to be expanding, which went against the current thinking. And it bothered Einstein.

BRIAN NORD: And so he added a fudge factor. It was meant to counteract the expansion so that you would get this static universe.

BARBER: Brian Nord is a cosmologist at Fermilab, and he says that Einstein later removed the fudge factor because he couldn't ignore the original conclusion of the equation or the data, that the universe was indeed expanding. As more and more data became available over the decades, scientists realized that this fudge factor was actually useful to explain that the universe is not only expanding but doing so faster and faster over time.

NORD: You know, it's a shame. If he had gotten this right in the first place, he might have been famous.

BARBER: (Laughter).

Fortunately for Einstein, his fudge factor now has a name - dark energy. Conventional thinking is that it's constant and about 70% of the universe. If you're having difficulty imagining this, Brian says to imagine the fabric of space-time, the universe, as a body of water.

NORD: One way to figure out how that fabric or body of water is changing is to look at buoys. And so in the late '90s, two competing teams of cosmologists were looking at supernovae, often referred to as exploding stars. And so they observed as many of these supernovae as they could at distances away from Earth to see, oh, how are these buoys moving? Are they moving because space-time is itself changing? And that's indeed what they found - that the best fit to the data is that these supernovae are moving away from us faster and faster.

BARBER: OK, got you. So, like, basically, because we can't measure cosmic acceleration itself - that's the water - like, we measure the movement of supernovae. That's the buoys. But just like you'd need a lot of buoys to measure, like, the whole sea, it seems that we need, like, a lot of supernovae to be able to prove anything about, like, cosmic acceleration.

NORD: Yeah.

BARBER: And that's where astronomers are now, looking for buoys to give us different hints 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 after all. It may be changing.

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

Regina Barber, NPR News.

SHAPIRO: And special thanks to The U.S. Space & Rocket Center, home of Space Camp.

(SOUNDBITE OF JOHN WILLIAMS' "THE IMPERIAL MARCH") Transcript provided by NPR, Copyright NPR.