Ask Ethan #52: How long has the Universe been accelerating? (Synopsis)

“After all the ‘Universe’ is a hypothesis, like the atom, & must be allowed the freedom to have properties & to do things which would be contradictory & impossible for a finite material structure.” –Willem de Sitter

Dark energy was one of the biggest surprises to come along in the past generation, from a scientific standpoint. It’s only intuitive to think that the Universe — with gravity fighting the initial expansion ever since the Big Bang — and all the galaxies in it would continue to slow down over time. But with a significant positive amount of energy inherent to space itself, that simply isn’t the case.

Image credit: Large Synoptic Survey Telescope, NSF, DOE, and AURA.
Image credit: Large Synoptic Survey Telescope, NSF, DOE, and AURA.

But if we had come along when the Universe was only half its present age, not only would dark energy be virtually undetectable, but the Universe wouldn’t have even begun accelerating yet! And furthermore, even the expansion rate today — a paltry 67 km/s/Mpc — continues to drop.

Image credit: Quantum Stories, retrieved via http://cuentos-cuanticos.com/.
Image credit: Quantum Stories, retrieved via http://cuentos-cuanticos.com/.

What do we mean when we say “the Universe is accelerating,” and how long has it been doing so? Find out on this week’s Ask Ethan!