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Big Bang and rotational energy.

  1. Aug 26, 2006 #1
    Looking up at night I see the galaxy, stars and planets all rotating happily along and wondered, as to the source of rotational energy.
    As I understand there can be only one source, the Big Bang event.

    Can I conclude then, that the singularity was rotating at the time of Big Bang ? :confused:

    If so, can I go like: kinetic energy E= ½ I w^2 where E is likely to be a constant? :eek:

    The implications gives me a headace, so help me out here.
  2. jcsd
  3. Aug 26, 2006 #2


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    By "rotating happily along”, do you mean that you see the objects rotate around Earth? If so, you are observing the Earth's rotation, not the rotation of the Cosmos!

    If you mean that all objects are rotating around their centers of mass, you are still not observing a rotation of the universe. As far as I know, observations indicate that the universe as a whole is not rotating – maybe our PF specialists can enlighten us on this.
  4. Aug 27, 2006 #3
    I don't think he means that. He means that evrything is in relative motion, what the enregy source of that motion?

    Well energy is convertible. Energy released during the bang bang is converted into gravitional energy and that is why we see evrything moving
  5. Aug 27, 2006 #4
    Thanks for the replys.

    Sorry for not being proberly specific.
    It's the source of the rotational energy that puzzels me. By this I mean the energy bound in the rotation around center mass.
    Why is the sun (or everthing else for that matter) rotating?

    As I understand, a hypothetic hydrogen cloud with a center mass and a totaly random distribution of partikels still could contract into a star, but it would not be rotating. So I conclude that there must be rotational energy in cosmos and that it must have a source.

    I agree that it's energy from big bang thats the source, I only conclude that this must include rotational energy.

    As for the rotation of cosmos, if this in any way could be observed it would also indicate that the singularity was rotating.

    So, how about it?
    Can I conclude that the singularity was rotating at the time of Big Bang ?
  6. Aug 28, 2006 #5


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    From NASA's 'Ask an Astrophysicist':
    Hope it helps
  7. Aug 29, 2006 #6
    I suspect the answers they will give may involve the Cosmic Microwave Background as a universal and ubiquitous reference frame against which all observers can decide whether they are moving, accelerating or rotating. Shades of Mach and Einstein!

    I find that such questions are of the deep -- now you see it, now you don't -- kind that give me headaches. I live far from drug stores or chemists and I've run out of Grandpa Headache Powders. So I'll join you in hoping that "our PF specialists can enlighten us on this".
    Last edited: Aug 29, 2006
  8. Aug 29, 2006 #7


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    Jorries references provide a very adequate, albeit elementary explanation. It is pretty simple to explain why planets, stars and galaxies rotate. Fluid dynamics is the short answer. Pull the plug on a bathtub full of water and observe the motion of the water as it drains.

    Explaining how we know[?] why the universe does not rotate is a bit more complicated. We know from observation that the motions of galaxies in the universe are not detectably aligned in any preferred direction. Neither their axes or direction of rotation exhibit non-random distributions [i.e., a preferred direction]. The CMB is also a good example, but the technical details are a bit complex. In a nutshell, polarization of the CMB would be very pronounced in a 'rotating universe'. That is not observed.
    Last edited: Aug 29, 2006
  9. Aug 29, 2006 #8
    Thanks for answering my stupid questions. I didn't realize how elementary my question
    about the rotation of a star was, before Chronos examplefied it by fluid dynamics.
    I feel my headace easying up already, man I love this forum. :smile:
  10. Aug 29, 2006 #9
    "all right"-"imagime this. Right You get this bath. Right. A large round bath. And it's made of ebony"
    "doesn't matter...!"
    "So you keep saying."
    "listen. You get this bath, see...? Imagine you've got this bath. And it's ebony. And it's conical."
    "Shhh!. It's conical. So what you do is, you see, you fill it with fine white sand, all right? Or sugar. Fine white sand, and/or sugar. Anything. Doesn't matter. Sugar's fine. And when it's full you pull the plug out, are you listening?"
    "I'm listening"
    "You pull the plug out and it just twirls away, twirls away you see, out of the plughole."
    " I see"
    "You don't see, you don't see at all. I haven't got to te celver bit yet. You want to hear the clever bit?"
    "Tell me the clever bit"
    "I'll tell you the clever bit. The clever bit is this. YOu film it happening."
    "you get a movie camera and you film it happening"
    "thet's not the clever bit. This is the clever bit, I remember now that this is the clever bit. The clever bit is that you then thread the film in the projector... backwards!"
    "Yes. Threading it backwards is definately the clever bit. So then, you sit and watch it, and everything just appears to spiral upwards out of the plughole and fill the bath. See?

    "And thet's how the universe began, is it?"

    "no. But it's a marvellous way to relax."

    gosn. Prdzadza
  11. Aug 30, 2006 #10


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    It was a very good question and not at all naive. Stars begin as a gas cloud, very much like water in the bath tub. The gas flow acquires angular momentum as it falls into the gravitational well. Galaxies are merely very large bath tubs where stars represent knots formed by micro turbulence in the flow. This is a very instructive example of how different branches of science are self reinforcing on large and small scales.
  12. Aug 30, 2006 #11


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    The universe can have zero net angular momentum and still contain rotating objects. Remember, angular momentum is a pseudovector with both magnitude and direction.

    Here's a thread on the origin of rotation in galaxies and planetary systems:


    As for the universe as a whole, our best measurements so far indicate that it is not rotating (in any sense of the word or about any axis).
    Last edited by a moderator: Apr 22, 2017
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