I’m having hard time getting my head around the fact that there is no end to space. Is there really no end to space at all? How do we know?

Question

I’m having hard time getting my head around the fact that there is no end to space. Is there really no end to space at all? How do we know?

In: 7083

Answer 1

“Space” is where everything is, so, by definition, there is no end. You can’t go outside “everything” because you yourself are a thing.

That said, if you’re on foot and you walk out your front door and go east and only ever go directly east, you will eventually walk into your back door. That’s because the surface of the Earth is continuous and curved. There’s an open question as to whether all of space is also curved in such a way that moving in an apparently straight line brings one back to the origin. In which case, yeah, you could argue “there’s no end to space” just the same as there’s no end to the planet Earth. In that case, there’s no edge to stumble off of; no wall you could spray paint your name onto.

But even if there’s some kind of outer edge of “everything,” could you ever GET THERE? One argument is, “can’t ever get to the end, so, practically, there isn’t one.” This is a more compelling argument than you might think because it’s not a matter of just building a faster or more durable space ship and getting there some day. And that’s because space is expanding.

Expanding like a balloon that’s inflating. Space is physically stretching, in all directions at all times. (Indeed, a guy called Richard Muller makes a good argument that time is a result of space stretching. Whoah.) So, going back a bit, what if the Earth was like a balloon and was inflating? You could head east out the front door and NEVER run into your back door, no matter how long you walked. In which case, there’s no end you could ever get to! And then you have to ask yourself, “What’s the difference between no end and no end I can ever get to?”

EDIT Muller not Miller

EDIT 2: “How do we know?” I didn’t really address the second question until a later comment. We know that space behaves the same way everywhere. Light travels through it at the same speed; mass bends it; there’s matter in it or not. Logically, that right there is how you can be sure there’s no end or edge. Because if there were, then space would behave differently at the edge! Stuff would bounce off without colliding with other stuff (Mr. Newton would be so disappointed), or light would not travel that way, pissing off Messers Young, Einstein, and others.

EDIT 3: Wow, as the poet says, “I’m wanted, dread and alive!” Thanks for the award.