Paul M. Sutter is an astrophysicist at SUNY Stony Brook and Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of How to Die in Space.
It’s one among the foremost compelling questions you could possibly ask, one that humanity has been asking since basically beginning of time: What’s beyond the known limits? What’s past the edge of our-maps? the last word version of this question is, what lies outside the boundary of the universe? the ans-wer is … well, it’s complicated.
To answer the question of what’s outside the universe, we first-need to define exactly what we mean by “universe.” If you’re taking it to mean literally all the items that would possibly exist all of space-and-time, then there can’t be anything outside the universe. albeit you imagine the universe to possess some finite size, and you imagine something outside that volume, then whatever is outside also has got to be included within the universe.
Even if the universe may be a formless, shapeless, nameless barren of absolutely nothing, that’s still a thing and is counted on the list of “all the things” — and, hence, is, by definition, a-part of the universe.
If the universe is infinite in size, you don’t actually need to stress about this conundrum. The universe, being all there, is infinitely big and has no edge, so there’s no outside to even mention .
Oh, sure, there is an outside to our observable patch of the universe. The cosmos is merely so old, and light only travels so fast. So, within the history of the universe, we haven’t received light from every single galaxy. the present width of the observable universe is about 90 billion light-years. And presumably, beyond that boundary, there’s a bunch of other random stars and galaxies.
But past that? It’s hard to inform .
The case of the curvature
Cosmologists aren’t sure if the universe is infinitely big or simply extremely large. To calculate the universe, astronomers instead check out its curvature. The geometric curve on large scales of the universe tells us about its overall shape. If the universe is perfectly geometrically flat, then it are often infinite. If it’s curved, like Earth’s surface, then it’s finite volume.
Current observations and measurements of the curvature of the universe indicate that it’s almost perfectly flat. you would possibly think this suggests the universe is infinite. But it’s not that easy. Even within the case of a flat universe, the cosmos doesn’t need to be infinitely big. Take, for instance , the surface of a cylinder. it’s geometrically flat, because parallel lines drawn on the surface remain parallel (that’s one among the definitions of “flatness”), and yet it’s a finite size. Same might be true of the universe: It might be completely flat yet closed on itself.
But albeit the universe is finite, it doesn’t necessarily mean there’s a edge or outside . It might be that our three-dimensional universe is embedded in some larger, multidimensional construct. That’s perfectly fine and is indeed a part of some exotic models of physics. But currently, we’ve no way of testing that, and it doesn’t really affect the day-to-day operations of the cosmos.
And I know this is often extremely headache-inducing, but albeit the universe features a finite volume, it doesn’t need to be embedde
A matter of perspective
When you imagine the universe, you would possibly consider an enormous ball that’s crammed with stars, galaxies and every one kinds of interesting astrophysical objects. you’ll imagine how it’s looks from the outside, like an astronaut views the globe of the world from a serene orbit above.
But the universe doesn’t need that outside perspective so as to exist. The universe simply is. it’s entirely mathematically self-consistent to define a three-dimensional universe without requiring an outside to-that-universe. once you imagine the universe as a ball floating within the middle of nothing, you’re playing a mental trick on yourself that the mathematics doesn’t require.
Granted, it sounds impossible for there to be a finite universe that has nothing outside it. And not even “nothing” within the sense of an empty void — completely and totally mathematically undefined. In fact, asking “What’s outside the universe?” is like asking “What sound does the colour purple make?” It’s a nonsense question, because you’re trying to mix two unrelated concepts.
It could alright be that our universe does indeed have an “outside.” But again, this doesn”t need to be the case. There’s nothing in mathematics that describes the universe that demands an outside.
If all this sounds complicated and confusing, don’t worry. the whole point of developing sophisticated mathematics is to possess tools that give us the power to grapple with concepts beyond what we can imagine. And that’s one among the powers of modern’ cosmology: It allows us to review the unimaginable.
Learn more by listening to the episode “What’s outside the universe?” on the Ask a Spaceman podcast, available on iTunes and askaspaceman.com. Thanks to Mitchell L. for the questions that led to this piece!