# What Drives Accelerating Expansion?

*Most recent answer: 05/01/2019*

- Jason Spielfogel (age 49)

Aliso Viejo

So far as I know gravitons and anti-gravitons are the same thing.

We're used to the effects of gravity when we have two masses that are fixed. The gravitational energy is lowered when they move nearer each other. If you have a (finite) universe with many fixed masses, its gravitational energy is lowered when it contracts.

What if instead of having fixed masses you had some sort of fixed mass *density* so that as the (finite) universe expanded it had more total mass? It turns out then that expansion would *lower* the gravitational energy, so instad of pulling the universe together gravity would push it apart.

General relativity (the modern theory of gravity) describes what happens to a universe filled with a fixed background mass density regardless of whether the universe is finite or infinite. That background density still drives accelerating expansion. We call that apparent background "dark energy".

Mike W.

*(published on 05/01/2019)*