Is the Universe rotating?

  1. Since everything in the Universe seems to be rotating, be it atoms or planets or stars or galaxies, and since the Universe consists of everything, shouldn't the Universe also be rotating? And if it is rotating, what is its axis?
  2. jcsd
  3. wolram

    wolram 3,552
    Gold Member

    I think the answer will be , rotating in reference to what.
  4. Garth

    Garth 3,537
    Science Advisor
    Gold Member

    Well, that is the question, rather than an answer!

    As a Machian asking this question I would say that the universe as a whole cannot be rotating, but I am willing to be proved wrong.

  5. wolram

    wolram 3,552
    Gold Member

    I have noticed that no machine with many moving parts is entirely static, may be the universe is in some perfect balance, but would that not be an exception?
  6. I'm sorry if I'm being unclear, but I don't know how else to phrase it. My thought is this. If the Universe is expanding from the central point of the Big Bang, would not the Universe also be rotating around that point, so that a galaxy at the edge of the Universe would complete an orbit every gazillion years or so?
  7. cristo

    cristo 8,387
    Staff Emeritus
    Science Advisor

    According to the current cosmological model, there is no centre of the universe. If there were, then this would mean that there is a special reference frame in the universe, which contradicts the cosmological principle. I think your misconceptions come about from thinking of the big bang as an explosion in the usual sense of the word, which one should avoid. See here for more of a discussion.
  8. wolram

    wolram 3,552
    Gold Member

    You are quite clear utek1, i asked this question myself some time ago, the point is if the universe is rotating or not there is no way for any one to observe it, as the universe is every thing there is.
    And people on this board will also tell you the universe is not expanding from a central point
    rather space is expanding at every point, so there is no center.

  9. Hello! This is a very interesting question! I remember that during my cosmology course I wondered if the Hubble flow could be alternatively explained by a rotating Universe theory based on some sort of centrifugal force! That would be amazing! However, a centrifugal force implies a centre, and, actually, there is no one as wolram has just written!
    The Big Bang is not a point around which the Universe expands, but it is the Universe "concentrated" in one point (the so-called singularity). Therefore, the Big bang was everywhere (in fact the expansion due to the Hubble flow is identical in every directions and every points of the space)! For the same reason, I think that a rotation around the Big Bang is not possible!
  10. wolram

    wolram 3,552
    Gold Member

    I an not sure, it seems cosmology is telling us that that on large scales things can only move in a prefer ed direction, and that there can be no large scale coupling, i may have this wrong but if frame dragging is a reality why is it not possible for some sort of coupling on the scale of the universe
  11. wolram

    wolram 3,552
    Gold Member

    As an aside to this question is there a prefer ed direction of rotation for galaxies referenced from our only observation point.
  12. Standard cosmology is based on the Robertson-Walker metric, which stems from the cosmological principle and is not rotating because of the homogeneity and isotropy. The cosmological principle seems to be true only on very large scales (over than 200 Mpc). So in this framework rotations are not allowed because they would identify a preferred dierction (that of the rotation axis). But this just a model. Let's think, for example, to the Kerr metric, which indeed is a rotating one! It is a vacuum solution, but perhaps a similar solution of Einstein equations, in presence of a non-zero stress-energy tensor, could exist which could properly describe our Universe.
  13. It may be very simple. Any collection of objects has a centre of mass, by definition. Gravity everywhere in the universe should average to point roughly to the centre of mass.

    Therefore everything should tend to follow orbits around this centre. Just like if you throw lots of particles in a simulator, gravitationally attracted they tend to form rotating patterns.

    (I have to admit though I have not understood some of what has been written, apologies if what I am saying has been said already or proven wrong).
    Last edited: Feb 26, 2008
  14. Here's a "universe" of particles in a simulator. No surprise the end up as a rotating galaxy.

    For rotation to be prevented, everything should move in a straight line from the centre, which of course is not the case in the observed universe.
    Last edited: Feb 26, 2008
  15. Wallace

    Wallace 1,251
    Science Advisor

    As has been said, there is no centre of the Universe and hence no centre of mass. This is an important but hard to grasp concept. The simulation you link to has a bunch of particles in a spherical cloud surrounded by empty space hence there is a net attraction due to gravity in towards the centre of the cloud. Think of a particle on the edge of the cloud, it has a pull on one side due to the rest of the cloud but no pull on the other side, since there is empty space.

    The Universe on the other hand consists of space that is full of roughly the same density of material everywhere, there is no edge beyond which there is empty space, so there is no centre to which everything is attracted.
  16. If there was no empty space around the cloud, but there was nothingness, no space, then would the law of gravity not apply between the particles? The simulation shows the law of gravity internally only, the interaction does not change whether there is empty space or "nothingness" around the cloud.

    There's got to be an edge of space, with space on one side, and nothingness on the other, if you follow the big-bang theory.

    Of course the big-bang theory is only a theory, theories come and go, so maybe in the future we will be told that the universe is infinite and swelling/contracting only locally in places.
  17. Here's the paper:

  18. cristo

    cristo 8,387
    Staff Emeritus
    Science Advisor

    But "nothingness" does not exist. It seems that you are confusing your term "nothingness" with empty space. Whether the universe is finite or not, there is nothing beyond it; that is, by definition, the universe is everything, be it stars, planets, or even spacetime itself. It makes no sense to talk about what is "beyond" the universe

    This does not follow. Why do you think the big-bang theory implies this? It seems like you are still thinking of the big-bang as a conventional explosion: this is not the case!!

    Indeed the big-bang theory is only a theory, but it's a pretty good one, that agrees with many observations. However, we are not in a position to speculate about what may or may not be discovered in the future here.
  19. That does not seem at all from what I wrote: "if there was no empty space around the cloud, but there was nothingness, no space", which implies one of two cases:

    1. Either there is empty space around the cloud

    2. Or there is "true nothingness" around the cloud, ie the extent of the spacetime continuum is entirely occupied by the cloud.

    You've just done it though:

    Hey, no offense, I know what you mean.

    Alright, it does not follow that the extent of spacetime has an edge. But it does follow that the cloud of mass has an "edge". As the cloud is expanding under the limitation of the speed of light, at the present time in its history.

    Surely the beginning was not like a conventional explosion, the laws of physics are believed by many people to not apply in the early universe, that was expanding faster than light, and both matter and spacetime were probably expanding, etc etc.

    But in the present time, expansion follows the familiar laws. Anything that does not move right, they associate it with the presence of "dark mass". Or they change the law of gravity from the familiar inverse square to slight modifications to match the observations.

    I agree, I take it back. But this is not because we're stupid or ignorant, it's because this place is for teaching wide-spread and practically useful models (like Newtonian physics or other well-established ideas), not for research.

    Before you tell me research should only be done by "professionals", may I remind you that Einstein's revolutionary paper on relativity:

    1. did not give a single reference,
    2. was not reviewed at all,
    3. was not by an academic, and
    4. was 100% right (in its range of applicability of course).
    Last edited: Feb 26, 2008
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