Where Are the Boundaries of the Universe and How Can We Measure Them?

[anuraj.b]

where is end of universe and how can measure it?

 

[PeterDonis]

where is end of universe and how can measure it?

There isn't one.

 

[Bandersnatch]

Hi anuraj.b,

The universe is very much unlike a stick, and more like a sphere. It doesn't have ends.

But it's not really like a sphere either, as it doesn't have edges.

The bottom line being, there's little point in trying to apply common sense intuitions to cosmological scales.

To find out what we do know about the shape and size of the universe, start by reading the faq in the cosmology section(https://www.physicsforums.com/showthread.php?t=506986) and the sticky thread on the balloon analogy (https://www.physicsforums.com/showthread.php?t=261161).
Mordred wrote a very informative post about the geometry of the universe, to be seen here: https://www.physicsforums.com/showthread.php?t=694499

A forum search in the cosmo section might help as well.

That should be enough reading to help you ask more precise questions in the future.

 

[PeterDonis]

But it's not really like a sphere either, as it doesn't have edges.

Neither does a sphere. Perhaps what you meant to say is that, at least on our best current understanding, the universe is spatially infinite, whereas a sphere is not.

 

[Bandersnatch]

Neither does a sphere. Perhaps what you meant to say is that, at least on our best current understanding, the universe is spatially infinite, whereas a sphere is not.

Sorry, my English is failing me. Should I have said "boundaries"? I think it should be boundaries.

 

[WannabeNewton]

A sphere has no boundary either if by boundary you mean manifold boundary (which is the one we care about in GR). I think you are confusing balls with spheres.

 

[PeterDonis]

Sorry, my English is failing me. Should I have said "boundaries"? I think it should be boundaries.

As WannabeNewton said, spheres don't have boundaries either. The key difference between a sphere and what I called a "spatially infinite" space, like we currently think the universe is, is that a sphere is a compact manifold, whereas a spatially infinite space is not.

(Actually, if Wikipedia is correct--which is not something that should be taken for granted--a sphere is a "closed manifold", i.e., a compact manifold without boundary. I've seen the term "compact" used to mean this as well, so I'm not sure what the most-used terminology is. The key is that both a sphere and a spatially infinite space are manifolds without boundary, so the presence or absence of a boundary isn't what differentiates them--it's that only the sphere is compact.)