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A spinning universe

  1. Feb 18, 2010 #1
    Hey,

    I was reading a book about dark matter and how it could be the cause of our universe to be expanding. However, from what I understand dark matter has not been "discovered" yet. Well I was thinking if our universe was spinning then could the centripetal acceleration caused by the spinning, be the reason for the universe to expand at an accelerating rate?
     
  2. jcsd
  3. Feb 18, 2010 #2
    That's an interesting idea, but as far as anyone can tell our universe is not rotating. I believe you're also confusing Dark Energy with Dark Matter. The source of DE is probably fluctuation in the quantum vacuum.

    Even if the universe WERE spinning, this would not cause a uniform acceleration as you seem to believe. The effect would be more subtle. I don't know what book this is, but if it's attributing a repulsive force to dark matter... put down the book... walk away... and read these forums more. :wink:
     
  4. Feb 18, 2010 #3
    For something to spin implies that whatever spins has a centre. The universe has no centre.

    If your assumption were true, we could look at equidistant galaxies in any direction and the accelaration of them from us would be different in each direction. This is not the case.
     
  5. Feb 18, 2010 #4
    I have thought about this problem with the universe having no center. Now what I imagine is that right now we experience 4 dimensions. So the universe might not be spinning in these dimensions but maybe the universe is spinning in a higher dimension by which the only effect we feel is a uniform acceleration.

    Now i am only using my imagination here, i don't have a very strong background in higher level physics. Yet :) .
     
  6. Feb 19, 2010 #5

    Mentz114

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    There is a general relativistic space-time ( the Godel metric ) that describes a rotating universe. It is not physically realizable.

    see for instance http://en.wikipedia.org/wiki/Gödel_metric

    This is the same Godel of undecidability fame. He was at the Princetown institute at the same time as Einstein and used to walk and talk with him.
     
  7. Feb 19, 2010 #6
    The difference between Einsteinian and Newtonian understanding of gravity is vast. When you learn about the Einsteinian model of gravity (general relativity, usually a third/fourth year undergrad or masters level of physics study), it is vital in the understanding of the current universe model.
     
  8. Feb 20, 2010 #7
    Whether spinning is right or wrong fys - and maybe its wrong - it is still an interesting idea to explore.

    I'm just wondering...
    In a steady expanding universe one place looks the same as the next in terms of expansion rate.
    I'm wondering if in a spinning anything this would hold true as well.

    I'm guessing that if you had a plate of marbles some in the middle and others on the outside edge and spun the plate with the marbles locked in place and then released all the marbles at once; the marble in the middle would stay put and depending upon where the marbles are radius-wise will determine their speed of departure.
    There direction of departure will always be perpendicular to the radius.

    So if we take 3 marbles side by side on a radius line they will all travel in the same direction as each other. But the inner marble will move slower than the middle marble which will move slower than the outer one.

    So they will still move apart but in the same initial apparent trajectory.
    The relative speed of the 3 marbles is dependent on the rpm (revolutions per minute) of the plate and their distance from the centre which determines the circumference at that point and therefore the distance traveled per revolution and therefore that speed.

    C = 2 pi r, which shows that there is a linear increase of distance travelled per revolution, and therefore also speed, with radial distance.

    What this means is that the inner marble will move away from the centre marble at the same rate that the centre marble moves from the outer marble.

    Despite the initial spin it can be seen that the relative inertial speed remains constant between these three.

    So others will have to tell me here whether those calculations are correct.
    So I am basically asking just as much as you are.
    Wouldn't the marbles move apart at a constant speed even if the universe were 'spinning'?

    Or is the substance of the OP's idea different to what I am talking about?
    Are they looking at something other than Newtonian initial spin math?
    I'm interested to know...
     
  9. Feb 20, 2010 #8

    bcrowell

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    I don't think this is correct. A spacetime in GR can be either static or not static. Static is a specific technical term that means that clock synchronization is transitive (if A is synchronized with B, and B with C, then C is synchronized with A). Non-static spacetimes are typically described as rotating. There are spacetimes in GR that are non-static, and yet have no center of rotation. One that I know of is the Petrov metric http://arxiv.org/abs/0802.4082
     
  10. Feb 21, 2010 #9
    @gongegahgah: Among other things, the procession of galaxies would be altered in a fairly obvious manner. Bcrowell already really answered your question by pointing out that a rotating spacetime in GR isn't described in the same manner as the newtonian view.

    Think of this: You place marbles on a flat plate. You slowly rotate the plate. From WITHIN the bounds of the plate, relative to each other, no point is changing; no marble moves (ignoring shakey hands, etc). Only a pseudo-force acts on the marbles, which is a function of relative frames, and doesn't necessarily apply to a rotating spacetime.

    In short, a rotating universe is NOT analogues to a rotating record on a static base; rather it is more like a record that is rotating along with the ENTIRE player.

    That's not all of course, as galaxies (like the marbles) WOULD change their motion, but not because of a centrifugal 'force' when the entire frame of reference rotates Relativistically.
     
  11. Feb 21, 2010 #10
    Cool. I was wondering then if frame dragging were involved? Or is it still different again to that?
     
  12. Feb 21, 2010 #11

    Dale

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    Why not?
     
  13. Feb 21, 2010 #12
    I don't believe that would be a factor. If the universe as a whole rotated, all inertial frames would be equally involved. Rotational Frame Dragging is really an Relativistic effect around rotating massive bodies. Wikipedia has a decent intro for it, but really drops the ball on Linear FD.

    http://en.wikipedia.org/wiki/Frame-dragging
     
  14. Feb 21, 2010 #13
    I would like to read more about linear frame dragging. Can you recommend any references? Thanks. Ciufolini and Wheeler in their book "Gravitation and Inertia" briefly mention linear frame dragging but spend almost the whole book on rotational dragging.
     
  15. Feb 21, 2010 #14
    I hate to say that I really know very little about Linear Frame Dragging. I'm not sure that it's as prominant an effect as the rotational variety, and after all, the extremes of RFD can be found in the Ergoregion of a Kerr Black Hole. For the linear variety of a similar magnitude I believe you'd need a cosmic string.

    I'll do a little research, and if I find anything respectable I'll post it here or pm you. For myself, if one of the advisors or staff has a good place to look, I wouldn't say no to a good source of info myself.
     
  16. Feb 21, 2010 #15

    bcrowell

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    If it were, then it would be a counterexample to the chronology protection conjecture, because it has CTCs.

    In some cases, one can prove explicitly that there is no way to bring about a particular solution that has CTCs, starting from realistic initial conditions in our universe. Here's an example of such a result: http://arxiv.org/abs/0802.4082
     
  17. Feb 21, 2010 #16
    To be fair, it could be physically realized at some future point, just at no point in this universe's history, as with any model that includes CTCs.
     
  18. Feb 21, 2010 #17

    Dale

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    I don't think that the mere existence of CTCs in a solution is sufficient to say that it is not physically realizable. However, it is clear that it does not model this universe, and in some sense it is rather silly to say that something is "physically realizable" but not in this universe.
     
  19. Feb 21, 2010 #18

    bcrowell

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    That's what the chronology protection conjecture states. Nobody has been able to prove the chronology protection conjecture. On the other hand, if you could come up with an elementary counterexample, you'd get the Nobel Prize.
     
  20. Feb 21, 2010 #19
    Would that be the equivalent of stating that a nonstatic spacetime undergoes nonhomogenous relatavistic effects? (multiple inertial frames)

    AS I understood it, the OP was applying the sphere/disc centripetal force mechanicss to the notion of space duplication.

    I think relativity (and most physics/science in general) needs to take a restraining order out on semantics.
     
  21. Feb 21, 2010 #20
    The problem is that we're discussing concepts that we can't visualize as we could an everyday object, in a subject where there is always a translation from the math. Semantic clarity may seem annoying, but it's actually the shortcut here. The alternative is usually lengthy and heated misunderstanding.

    As for your understanding of the OP's view, you'd seem to be right. The rest has been a correction of that assumption and related tangents. :smile:
     
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