One of the great mysteries of the universe is how it expands. The phenomenon causing this expansion is known as dark energy — and recently scientists have begun to wonder if it’s changing.
ARI SHAPIRO, HOST:
Now let’s rise above Earth to look at the big picture of the changing universe. Astronomers know that the universe is expanding and gaining speed as it does so. But what is this cosmic acceleration? The answer starts with Einstein, as NPR’s Regina Barber explains for Short Wave’s Space Camp series.
REGINA BARBER, BYLINE: More than 100 years ago, Albert Einstein was figuring out 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 suggested that it must be expanding, which contradicts current thinking. And this troubled Einstein.
BRIAN NORD: And so he added a make-believe factor. It was meant to counteract the expansion so you get this static universe.
BARBER: Brian Nord is a cosmologist at Fermilab, and he says Einstein later dropped the make-believe 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 fiction factor was actually helpful in explaining that the universe was not only expanding, but doing so faster and faster over time.
NORD: You know, it’s a shame. If he’d gotten this right in the first place, maybe he’d be famous.
BRIZNAR: (Laughter).
Fortunately for Einstein, his fudge factor now has a name – dark energy. Traditional thinking is that it is constant and makes up about 70% of the universe. If you have a hard time visualizing this, Brian says to imagine the fabric of space-time, the universe, as a body of water.
NORD: One way to understand how that fabric or body of water is changing is to look at the buoys. So in the late 1990s, two competing teams of cosmologists looked at supernovae, often called exploding stars. And so they observed as many of these supernovae as possible at distances from Earth to see, oh, how do these buoys move? Are they moving because space-time itself is changing? And that’s really what they found — that the best fit with the data is that these supernovae are moving away from us faster and faster.
BRIZNAR: Okay, I got you. So, in general, since we can’t measure cosmic acceleration itself – that’s water – for example, we measure the motion of supernovae. These are the buoys. But just like you need a lot of buoys to measure, say, the whole sea, it seems like we need, like, a lot of supernovae to be able to prove something about, like, cosmic acceleration.
NORD: Yes.
BARBER: And that’s exactly where astronomers are now, looking for buoys to give us different hints about how spacetime is expanding. And there is the possibility of a new complication. A new paper came out earlier this year suggesting that dark energy may not be permanent after all. It can change.
Both scenarios have major implications for the end of the entire universe. If dark energy is a constant cosmic acceleration, that means the universe will die what astrophysicists call heat death. Everything is moving further apart. Galaxies and black holes fade and matter decays. It will be cold and lonely. But if dark energy changes, that fate may change as well. 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 US Space and Rocket Center, home of Space Camp.
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