Results 1 to 15 of 15

Thread: What does spacetime look like

  1. #1
    Join Date
    Jul 2002
    Posts
    149

    What does spacetime look like

    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?

  2. #2
    Join Date
    Dec 2004
    Posts
    275
    Why it would look like any pseudo-Rimeannian manifold with a metric of signature +2 does from the outside

  3. #3
    Join Date
    Dec 2004
    Posts
    275
    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.

  4. #4
    Join Date
    Feb 2004
    Posts
    2,479
    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!

  5. #5
    Join Date
    Dec 2004
    Posts
    102
    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.

  6. #6
    Join Date
    Sep 2004
    Posts
    1,550
    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?

  7. #7
    Join Date
    Mar 2002
    Posts
    586
    It looks like David Hasselhoff.

  8. #8
    Join Date
    Dec 2004
    Posts
    102
    Quote Originally Posted by Bozola
    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...

  9. #9
    Join Date
    Jul 2002
    Posts
    149
    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.

  10. #10
    Join Date
    Sep 2004
    Posts
    1,550
    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.

  11. #11
    Join Date
    Dec 2004
    Posts
    102
    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.

  12. #12
    Join Date
    Jan 2004
    Posts
    374
    Quote Originally Posted by Bozola
    It looks like David Hasselhoff.
    ***shudder***

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

    :P

  13. #13
    Join Date
    Jan 2004
    Posts
    374
    Quote Originally Posted by HerrProfessorDoktor
    Quote Originally Posted by Bozola
    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

  14. #14
    Join Date
    Dec 2004
    Posts
    275
    Quote Originally Posted by 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.
    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!).

  15. #15
    Join Date
    Dec 2004
    Posts
    275
    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.

Similar Threads

  1. spacetime contraction
    By tommac in forum Space/Astronomy Questions and Answers
    Replies: 10
    Last Post: 2008-Jun-18, 07:43 PM
  2. Up and Down in Spacetime...
    By Occams Ghost in forum Science and Technology
    Replies: 57
    Last Post: 2008-Feb-24, 06:59 PM
  3. The curvature of spacetime
    By afterburner in forum Space/Astronomy Questions and Answers
    Replies: 158
    Last Post: 2006-Jun-09, 12:33 AM
  4. SpaceTime
    By Chook in forum Space/Astronomy Questions and Answers
    Replies: 23
    Last Post: 2004-Jan-14, 12:53 AM
  5. SpaceTime
    By Chook in forum Astronomy
    Replies: 0
    Last Post: 1970-Jan-01, 12:00 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •