Ask Ethan #52: How long has the Universe been accelerating?
"What it tells us is that space between galaxies — or between any structures that aren’t gravitationally bound to either one another or mutually bound to an even larger structure — is going to expand. If we want to learn how that space is going to expand, meaning at what rate, we need to know two pieces of information:
1. What the expansion rate is at any point in our cosmic history, and
2. What types and ratios of matter-and-energy are present in our Universe.
That’s it! If we can figure out those two pieces of information, we can figure out not only the fate of our Universe, but what the expansion rate was, is and will be at all times since the Big Bang.”
The Universe has always had dark energy in it, but it’s only started accelerating recently. Thanks to the precision measurements of Planck, we can finally know exactly when the transition from a decelerating Universe to an accelerating one happened. Come find out on this week’s Ask Ethan!