Ask Ethan: Are There Different Types Of Time And Space? (Synopsis) [Starts With A Bang]

“A human being is part of a whole, called by us the Universe, a part limited in time and space. He experiences himself, his thoughts and feelings, as something separated from the rest a kind of optical delusion of his consciousness. This delusion is a kind of prison for us, restricting us to our personal desires and to affection for a few persons nearest us. Our task must be to free ourselves from this prison by widening our circles of compassion to embrace all living creatures and the whole of nature in its beauty.” -Albert Einstein

If you’re talking to someone across the same room, what the two of you perceive as time and space might match up perfectly, to the limit of what each of you can measure. But if one of you moves quickly relative to the other, if you experience different gravitational fields or spacetime curvatures, or if the space of the Universe between you is expanding, times and distances will cease to line up.

This isn’t a flaw of yours in any way, but rather an inevitable feature of special and general relativity. Observers in different locations can never agree on definitions of distance and time, particularly in an expanding Universe. So we invent some alternate definitions for differently scaled types of distance and time: conformal time and comoving distance, to help us understand what’s going on in the Universe.

Here’s what they mean and why we do it, only on this week’s Ask Ethan!