Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Shape of the Universe

  1. Jul 15, 2004 #1
    I don't want to know the working theory for what the universe looks like, but rather what conditions need to be satisfied in order to have a viable theory of our universe. Ie, the model would need to explain how our universe could be expanding... anything like that.
    Last edited: Jul 15, 2004
  2. jcsd
  3. Jul 17, 2004 #2
    I think that means you'd like to know how space-time came to be in the first place and how particles formed within that space, right?
  4. Jul 19, 2004 #3


    User Avatar

    Staff: Mentor

    Well, as always, you start with observations: Galaxies, red-shift, background radiation, etc. I'm not sure thats what you're looking for though... can you elaborate?
  5. Jul 19, 2004 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The shape of the observable universe is spherical, of course. The observable universe is the region of space from which light has had time to reach us. The universe is too young for light from more distant objects to have reached us yet.

    We cannot even speculate about the "shape" of the entire universe. More useful than "shape," however, is topology. Is the universe smooth and locally flat like the surface of a balloon? Does the universe have lots of holes in it, like a doughnut? Does the universe wrap back around on itself, or does it continue infinitely in every direction?

    - Warren
  6. Jul 19, 2004 #5
    The shape of the universe

    The universe has glass sides with air holes poked into the top.

    Like language, geometry is made in the mind of man. There is no "shape" to the universe as a whole. There is no geometry to the universe. The universe is dimensionless in both time and space though some might argue current theory on this. Chroot touches on this when he talks of topography rather than shape.
    If this helps at all, Stephan Hawkins says in his book, "A Brief History of Time" that the universe is probably finite but unbounded. Like the suraface of the Earth, you can drive around and around it forever and eventually you come back to the same place you started. This is not implying that the universe is the shape of a sphere, Hawking only used the surface of the Earth as an analogy.
    Last edited: Jul 19, 2004
  7. Jul 19, 2004 #6
    IN the beginning there was nothing, and God said: "Let there be light"
    And still there was nothing, but you could see it.

    We do not have a good model of the universe - we do not know why the so called constants have the value they do, and we do not know why the universe is expanding - the fun is in the pursuit of the answers - how boring it would be if all the mysteries were solved.
  8. Jul 20, 2004 #7
    To Yogi


    I like your editting of Genesis. Very clever and truthful
  9. Jul 21, 2004 #8
    My question is wouldn't the universe have to start out with dimensions that all circle back on themselves. Would this be called a closed universe - like in a closed surface without boundary? If so, then how does the universe then acquire dimensions that are flat or even hyperbolic?
  10. Jul 21, 2004 #9
    Mike 2 - perhaps the universe is only asympotically flat - if so it falls within the math frame work applicable to closed universes. Infinite universes pose conceptual problems - in theory there would be an infinite number of identical earths and so on - the notion of a hyperbolic universe, while a mathematical possibility based upon the assumptions used by Robertson and Walker to derive the metric, probably can't represent reality.

    To Gale 17, I would suggest the book "Cosmology" by Ed Harrison. It discusses many of these interesting questions in an unbiased and easy to understand manner.
  11. Jul 22, 2004 #10
    say theoretically, the universe is spherical and therefore has boundaries.
    What would happen if you would reach the boundary, and touch it.
    This already suggests it's an object (touch), what would happen.
    An arm just dissapear?
    What would the result be of contact with the boiundary of the universe.
    (if such a thing ofcourse exists)
    A Q thats been haunting my mind for some years now, and i can't realy picture it.
  12. Jul 22, 2004 #11


    User Avatar

    You may not be alone in not being able to picture it.
    Perhaps it is where sanity and insanity merge or perhaps you cannot put your arm through it, or perhaps your arm would dissappear when you did.
    Perhaps there is no boundary or multiple Universes exist side by side with boundaries that cannot be seen but are nonetheless there. Or perhaps there is one finite Universe, or perhaps the Universe is not there. Or anything really.
    If all the theories of the nature of the Universe were written down, it could be that the actual answer wasn't in the list.
    Last edited: Jul 22, 2004
  13. Jul 22, 2004 #12


    User Avatar
    Science Advisor
    Gold Member

    You mean spherical as in the area bounded by a 3 dimensional sphere?

    The problem is that ther is no useful description for that situation as it is one that is newither predicted by theory nor supported by observation. There is no physicasol theory that can describe the situation.
  14. Jul 22, 2004 #13
    Maybe if we adjust our thinking like Kaku did, looking at the carp, looking at the surface of the water?

    It would be a good exercise in looking at surface orientation recogizing this ability to see a surface in two possible ways.

    Omega would have conclude a critical density and a relationship. Curvature parameters of Friedmann.

    Maybe we are in a bubble? We would have to look for tell tale signs from the edge?
  15. Jul 22, 2004 #14
    If you're thinking that the boundary is all one connected hypersurface, then doesn't that imply some pre-existing background dimensions which would enable you to say, "this is the inside, and this is the outside"? There would then be dimensions other than defined by the existing universe, dimension "outside" it, beyond its boundary, where all dimensions of reality are suppose to exist. There is not supposed to be anything (including dimensions) outside the universe.

    But have you thought about the possibility that particles are bits and pieces of a boundary that has broken up into smaller parts? string theory and M-theory would then be taking different slices of these boundary particles.
  16. Aug 7, 2004 #15
    um, on a different note, i was reading an astronomy book the other day, actually it was a few weeks ago so i may have remembered this wrong... but it was saying something about the edge of the universe also being the big bang, or the edge if time. the center would therefore be the present. i think i'll go back and reread it, but it did show a picture with the big bang being the edge of the circle, and then showing the different stages of the universe as it grew progressively inward. not sure if i got that right, someone want to help clarify what that was about for me?
  17. Aug 8, 2004 #16
    Most think that the big bang originated from a singularity, a single point. It would be hard to imagine a single point qualifying as a boundary of some sort.

    Is that a picture of you under your login name? My, you're quite a pretty girl, Gale17.
  18. Aug 9, 2004 #17
    In the book "Faster Than The Speek of Light" Joao Magueijo describes the universe as being a hypersphere where-as the universe is the inverse of a sphere. This would result in the universe being infinite and looking like a saddle at every point.
  19. Aug 9, 2004 #18


    User Avatar
    Homework Helper

    The big bang is not believed to have originated from a point.

    Eg: The Cosmologically flat universe:
    Try to imagine all the matter around you being alot closer billions of years ago. There was still an infinite expanse of universe back then, just as expansive as now. The difference is how much "empty" space there was and how much universe could be seen. Going back to a very short time after the big bang, things were quite crowded, but the universe was still infinite in expanse. Also, if you would look out through a telescope, you would see a rather pronounced opaque "wall," not too far away, surrounding you in the shape of a spherical shell, with yourself at the center. We now see this wall billions of lightyears away, and it is the source of the CMBR. This is the wall of observation, or the edge of the observable universe, and it represents almost the beginning of time. Light emitted by this wall takes on the order of the same amount of time to reach our detectors as the age of the universe. So, the spherical shell surrounding us represents the oldest observations that we have made, and thus the earliest phenomena we have observed. The phenomenon we call the big bang is actually believed to be "hiding just behind this wall."
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook