For centuries, the far side of the Moon was called the dark side – not because it doesn’t get any sunlight, but because it was always hidden from view. Astronomers couldn’t shed any light on what it looked like – making it dark.

Today, scientists are trying to shed a little light on another darkness – dark energy. It appears to be making the universe expand faster as it ages. And it accounts for about 70 percent of all the energy and matter in the universe.

But so far, there’s no widely accepted explanation for what constitutes dark energy. Scientists have a lot of ideas, but none of them has been confirmed.

One of the leading ideas is that dark energy is constant, because it comes from the vacuum of space itself. As the universe expands, the amount of matter stays the same, but it’s spread across a greater and greater volume. That means each bit of matter feels a weaker gravitational pull from all the other matter. At the same time, as more space is created, so is more dark energy. It overpowers gravity, causing the universe to expand faster.

Some recent research has found support for that idea by looking at how the universe has expanded over the eons. But the same result could support the idea that dark energy isn’t constant – that it’s evolved over time. That has important implications for the fate of the universe – whether it will continue to expand forever, or someday collapse – ending in a “Big Crunch.”

Script by Damond Benningfield