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?

Isn’t it crazier if the universe had some sort of edge? What would that look like?

We don’t know. There are three possible shapes that space could make. The analogy to 2 dimensions are flat, curved away from itself (saddle shaped) or curved into itself. The first two have no end. The last would eventually connect with itself.

We can actually measure the curvature of space. And we’ve measured….no curvature. But our measurements aren’t perfect, so the universe could possibly be curved in on itself and we wouldn’t be able to detect it currently as long as it is larger than around 23 trillion light years in diameter (15 millions times the volume of the visible universe).

Edit: there is another possibility which is any random shape that isn’t uniform in every direction, like maybe a part of space is suddenly curved for hundreds of billions of light years then flattens out or curves back in the opposite direction. Or maybe space is shaped like a chess piece and we live on the flat bottom. But no evidence for that yet.

But as far as we know you could point a ship in any direction and travel forever. And the most likely thing you’d find is more of what we currently see…trillions and trillions of galaxies. Anything else (like a wall, or the end of a computer simulation) isn’t supported by science.

“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.

the amount of things humans don’t know, vastly outweigh what we think we know, and what we actually know is a small fraction of what we think we know.

There are going to be ideas we will never be able to perceive, just like there are colors, sounds, and smells we can’t perceive, we are limited by our perception. Infinity is one of those things. Our way of understanding/measuring things requires a starting/ending point, if you say there’s no beginning/end we have no way to understand/measure it.