The expansion is not the kind of expansion you're thinking of. It isn't like a sphere getting bigger. It's more like every ruler in the Universe is getting smaller, so all measurements of distance stretch to be longer even though nothing "really" moved.

There is, as far as we are aware, no edge to the Universe even if it turns out not to be infinite (which current evidence suggests that it probably is). If the Universe were finite, it would be more like the surface of the Earth where you could get back to where you started after going "all the way around".

The edge of the universe is not necessarily observable for us. But the edge of the universe that is observable to us is not only far away, it is far away in time, more primordial than anything.

According to our current observation and understanding, the universe is expanding and accelerating. That is to say that is expanding ever faster, to the point that at the edge of our observable universe it expands faster than the speed of light. That creates a kind of spacial horizon we cannot observe beyond, because light coming from the other side will never reach us. And this horizon is drawing ever nearer to us. Eventually, many of billions of years in the future an observer from our galaxy, may not be able to see past our galaxy.

With some of these questions you could say we have working assumptions rather than absolute knowledge. To have an edge there would , I think, have to something that wasn't universe but the universe seems like all the space/time there is.

Though we don't know for sure , there is some reason for thinking it might also be infinite in size. There is in edge in the sense of the limit of our ability to observe. The observable universe has for us increased in size as telescopes get better though you could say that its also a sort of illusion since the further we look , the further back in the universe's history we are seeing. We are seeing it as was. We can only see as far as light has had time to travel. The limit is called the cosmic horizon.

And we also have some reason to think its pretty much the same everywhere in general. Though some bits are clumping together the space between is increasing everwhere. At one point in the past it infected very fast , slowed down and is now accelerating again. But as far as we know whereever you were in the universe you would look out and observe something similar to another observer. If the universe continue expanding its possible that we could imagine one day an observer looks out and sees nothing because all the stars would be too far away for light to reach them.

It’s like asking the question what’s at the edge of the earth? The answer is more earth. Just because you can’t see over the horizon doesn’t mean that’s all there is.

Similar with the universe - we can only see as far as light can travel in the amount of time since the universe began, just under 14 billion years. That’s like the horizon. But if you were able to magically teleport to 14 billion light years away from here, you’d still be able to see 14 billion light years in every direction. Similar to how if you teleported to the horizon on earth, you’d still just see the same distance to the horizon in every direction.

It’s more complicated because we are 3 dimensional beings in a 3 dimensional space, versus being 3 dimensional beings looking at the 2 dimensional surface of a sphere. If we were 4 dimensional beings, we could look at the 3D universe from a vantage point that would make it just as obvious that there’s no edge as it’s obvious to you that there’s no edge of a globe. But we aren’t 4 dimensional beings so we have to use analogies to understand without using math.

The way to understand expansion is that everything is getting further away from everything else. No matter where you are, everything else that exists is all moving away from you.

The short answer: uncertainty.

Depending on the nature if the universe's genesis, it is possible that parts of it exists beyond the light cone which defines the bounds of what we could possibly observe.

Hm. So is there a hypothetical shape of the universe?

That’s where it gets complicated. We don’t know because we can only observe 13.7 billion light years in every direction. So what we see is a sphere with us at the center. But there are some other things that suggest that the universe is a hypersphere or a hypertoroid.

It’s not possible for us to picture these objects except by approximation, or with math, or with analogies. But a short explanation: A sphere is a circle extended into an additional dimension. You can visualize that. A hypersphere is a sphere extended into an additional dimension. Can’t visualize it, but that’s what it means.

A torus is a donut shape, so a hypertoroid is a donut extended into an additional dimension.

There are videos about hypercubes, and hyperspheres, which attempt to help picture what it’s like, but because our minds operate in 3 dimensions, it’s not capable of truly comprehending these 4 dimensional objects.

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