For years, physicists have attempted to explain dark energy - a mysterious influence that pushes space apart faster than gravity can pull the things in it together. But physics isn’t always about figuring out what things are. A lot of it is figuring out what things cause.
And in a recent paper, a group of physicists asked this very question about dark energy, and found that in some cases, it might cause time to go forward.
When you throw a ball into the air, it starts with some initial speed-up, but then it slows as Earth’s gravity pulls it down. If you throw it fast enough (about 11 km per second, for those who want to try), it’ll never slow down enough to turn around and start falling back towards you, but it’ll still move more slowly as it moves away from you, because of Earth’s gravity.
Physicists and astronomers in the 1990s expected something similar to have occured after the big bang - an event that threw matter out in all directions. The collective gravity from all that matter should have slowed it all down, just like the Earth slows down the ball. But that’s not what they found.
Instead, everything seems to have sped up. There’s something pervading the Universe that physically spreads space apart faster than gravity can pull things together. The effect is small - it’s only noticeable when you look at far-away galaxies - but it’s there. It’s become known as dark energy - "dark", because no one knows what it is.
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