Starts With A Bang

Ask Ethan: Is The Universe Finite Or Infinite? (Synopsis)

If you look farther and farther away, you also look farther and farther into the past. The earlier you go, the hotter and denser, as well as less-evolved, the Universe turns out to be. The part that we can see is limited and finite. But what about what lies beyond? Image credit: NASA / STScI / A. Feild (STScI).

“If the doors of perception were cleansed every thing would appear to man as it is, Infinite. For man has closed himself up, till he sees all things thro’ narrow chinks of his cavern.” -William Blake

When it comes to the ultimate question of the size of the Universe, we have to look to greater scales than what we can possibly observe. Although we can place constraints on how big the unobservable Universe must be, coming up with a lower limit to its overall size, there’s a bigger question that we don’t yet know the answer to: is it finite in size, or is it truly infinite?

The observable Universe might be 46 billion light years in all directions from our point of view, but there’s certainly more, unobservable Universe just like ours beyond that. Image credit: Wikimedia Commons users Frédéric MICHEL and Azcolvin429, annotated by E. Siegel.

Beyond what we can see, there ought to be more Universe just like our own, originating from either the same Big Bang, or possibly, if inflation is correct, from other Big Bangs at later or earlier times. And thanks to the ideas of eternal inflation, we have very, very large numbers for what’s possible as far as size goes. But there’s a long way from very large to infinite, and determining whether that’s true is a very difficult prospect.

Inflation causes space to expand exponentially, which can very quickly result in any pre-existing curved space appearing flat. Image credit: E. Siegel (L); Ned Wright’s cosmology tutorial (R).

So what can we say about the conditions under which the Universe is either finite or infinite in extent? Find out on this week’s Ask Ethan!