The force that makes up more than half of the universe

- [Dominic] Back in 1998, scientists were trying to figure out what's the fate of the universe?

The question led them to one of the biggest discoveries of the last 50 years.

Here's what they wanted to know.

The universe is expanding now, but will it keep on going?

Or will gravity slow it down and make it shrink, crushing everything in the universe?

Astronomers looked at extremely far away, but very bright objects called supernovas to find out how fast different parts of the universe were expanding.

The results were shocking.

- And my jaw just dropped.

- [Dominic] The farthest away supernovas they tracked were moving faster than they expected.

They realize the universe is not just expanding, it's accelerating in its expansion.

Something weird and mysterious must be stretching empty space apart.

And they call that thing dark energy.

And it seems like the more empty space there is, the more dark energy there is, which creates more empty space, which creates more dark energy and on and on and on and on and on.

Right now, dark energy makes up about 70% of the universe, and scientists still don't know exactly what it is, but what we do know is that the bigger the universe gets, the faster it expands, and someday far in the future, space will expand so much that scientists in one galaxy will never be able to see extremely distant galaxies like we do today.

The universe will be expanding faster than the speed of light.

So the light from those very distant galaxies will never reach each other.

Luckily, we still live in a time when we can see extremely distant galaxies and their exploding stars and learn about dark energy.