[1Old Pro]

I tend to view space/universe, as nothingness with galaxies floating around in it. If it's expanding, what is it expanding into? If it's not expanding, what lies beyond the furthest edge? Is there just a big wall, and the universe is just contained in a big box?

Yep, very confusing. Is the universe flat? Could we fall over the edge?

[DesertRhino]

You win the day. It’s not a flat earth... it’s a flat universe. LOL

[Boogieman]

“Is the universe flat?”

The prevailing conception is that spacetime is a curved 4 dimensional surface. So imagine a curved 2 dimensional surface, like the outside of a globe, where the 2 dimensional plane wraps around a 3 dimensional shape. Now imagine the 3 dimensional world we know (ignoring time) and then try to imagine that world is similarly curved around some hypothetical 4 dimensional object.

There’s plenty of debate still about exactly what kind of 4-d shape the universe would be wrapped around though. Maybe it’s a hypersphere. Or maybe we’re on the INSIDE of a hypersphere, or maybe it’s a hyperdonut, etc.

[Harmless Teddy Bear]

Is the universe flat? Could we fall over the edge?

If the universe is flat then somewhere there is a cat that is batting us toward the edge.