One of the great mysteries of the universe is how it is expanding. The phenomenon that causes this expansion is known as dark energy, but recently scientists have begun to suspect that it may be changing.
ARI SHAPIRO, HOST:
Now, let’s step away from Earth and put the changes in the universe into perspective. Astronomers know that the universe is expanding, and it’s speeding up. But what is this cosmic acceleration? The answer starts with Einstein. NPR’s Regina Barber explains in her Shortwave series “Space Camp.”
REGINA BARBER, BYLINE: More than 100 years ago, Albert Einstein was developing his theory of relativity, tinkering with mathematics to try to understand how the universe works. At the time, people, including Einstein himself, thought the universe was stationary. But the mathematics he created to explain it suggested that the universe must be expanding, which went against the thinking of the time. And it troubled Einstein.
Brian Nold: So he added some fudge factor to counteract the expansion and make it a static universe.
BARBER: Cosmologist Brian Nord at Fermi National Accelerator Laboratory says that Einstein later removed this fudge factor because he couldn’t ignore the original conclusion of his equations and data, which was that the universe is indeed expanding. As more and more data became available over the decades, scientists realized that this fudge factor actually helped explain not only that the universe is expanding, but that it’s expanding faster and faster over time.
Nord: Too bad. If he’d gotten this right the first time, he could have been famous.
Barber: (Laughs).
Luckily for Einstein, his fudge factor now has a name: dark energy. Conventional wisdom holds that dark energy is a constant, making up about 70% of the universe. If you have trouble picturing this, Bryan suggests imagining the fabric of space-time — the universe — as a ball of water.
Nord: One of the ways we can find out how that structure, that body of water, is changing is by observing the buoys. In the late 1990s, two competing teams of cosmologists were looking at supernovae, also known as exploding stars. They looked at as many supernovae as they could at distances from Earth to see how the buoys were moving. Could the buoys be moving because space-time itself is changing? And actually what they found was that the best fit with the data was that these supernovae were moving away from us faster and faster.
Barber: Okay. So basically, you can’t measure the acceleration of the universe, so you measure the motion of water, or supernovae. That’s the buoy. But just like you need a lot of buoys to measure the entire ocean, it seems like you need a lot of supernovae to prove anything about the acceleration of the universe.
Nord: That’s right.
Barber: Astronomers are now looking for buoys that might give us other hints about how space-time is expanding, and potentially new complications. Earlier this year, a new paper came out suggesting that dark energy might not be constant after all. It might be changing.
Either scenario has huge implications for the end of the universe as a whole. If dark energy is the constant acceleration of the universe, then the universe will die in what astrophysicists call heat death. Everything will drift apart. Galaxies and black holes will disappear, matter will collapse. It will be a cold, lonely place. But if dark energy is changing, then that fate could change too. To figure it all out, scientists will need more buoys, or hope that humanity lives long enough to figure it out.
Regina Barber, NPR News.
SHAPIRO: And a special thanks to the U.S. Space and Rocket Center, the host of Space Camp.
(From John Williams’ “Empire Marches On”)
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