What does spacetime look like

[samsara15]

If we could see spacetime (from an outside point of view), what would it look like? An expanding globe of lights (stars and galxies)? Or is there so little luminous matter that we wouldn't see much at all? We certainly couldn't see empty space, or gravitational fields. So what would we see?

[Bad jcsd]

Why it would look like any pseudo-Rimeannian manifold with a metric of signature +2 does from the outside

[Bad jcsd]

The problem is it doesn't make much sense to talk about outside of spacetime as if indeed such a thing exists we have no conception of it.

[Ut]

With a little bit of imagination, I can picture it as a pseudo-Rimeannian manifold with a metric of signature -2! Fear my superior brain!

[HerrProfessorDoktor]

Since photons and all other particles require the quantum vacuum as a medium to exist (as I understand it), and there is no "border" of the Universe for them to travel out of (as pointed out here), I'm pretty sure you would see nothing at all optically, nor would you be able to detect any other particles escaping from it.

However, it seems possible you could detect our universe if its geometry influenced the topology of your own spacetime equivalent. Say, if you were in an intersecting brane or something else that hasn't been thought of yet.

I'm not sure how much you would be able to figure out about the properties of our universe from that influence. We would just be annoying dark matter forever screwing up your observations.

[Evan]

If you were somehow outside the edge of our expanding universe then you would not see anything at all. How could you? It hasn't reached you yet. If it has then you aren't outside it anymore, are you?

[Bozola]

It looks like David Hasselhoff.

[HerrProfessorDoktor]

It looks like David Hasselhoff.

Funny, whenever I try to look at him I can't focus me eyes, as if the light is going around or right through him. And yet, I can feel his influence...

[samsara15]

I understand that you CANT (or couldn't) see it, but the point was, if you could imagine what it actually looks like, what would it look like. Those manifolds are hard to visualize.

[Evan]

No, they are impossible to visualize. They are mathematical constructs. In programming I can create a one dimensional array, a two dimensional array and a three dimensional array. All of those are easy to visualize. I can also create a 4, 5, 6 etc dimensional arrays. These you cannot visualize.

[HerrProfessorDoktor]

Well, it's possible to "get" dimensions above 3, and you may be able to partially visualize 4. But once you get above 4 I don't know how you could do it. You can project its effects on 3-space, as many good sci-fi stories have done, but that just dances around the issue.

And sorry samsara15, you mentioned luminosity in the original post, so I took the literal interpretation.

[Mr. Milton Banana]

It looks like David Hasselhoff.

***shudder***

Thanks for that mental image. Now, I'll have to go back into therapy.

:P

[Mr. Milton Banana]

It looks like David Hasselhoff.

Funny, whenever I try to look at him I can't focus me eyes, as if the light is going around or right through him. And yet, I can feel his influence...

Pot has that influence too, I understand.

:P

[Bad jcsd]

No, they are impossible to visualize. They are mathematical constructs. In programming I can create a one dimensional array, a two dimensional array and a three dimensional array. All of those are easy to visualize. I can also create a 4, 5, 6 etc dimensional arrays. These you cannot visualize.

Here's an interesting thing an n x n x n x n.... array is actually pretty simalir to a tensor of rank m (where m would be the number of 'n's') on an n-dimensioanl vector space (though the space of m (q,r) tensors wher q + r = m is itself an n^m dimensional vector space!).

[Bad jcsd]

The problem is that even visualizing the x,t plane in Minkowski space is next to impossible as it is flat but non-Euclidean (for example the cocnept of a non-zero* but null seperation is something that is alien in Euclidena space).

*by non-zero I mena in the snse that the dispalcement vector rperesnting the speration is a null vector, but not a zero vector, as the seperation IS actually zero.