Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Grimbo1 on 15/11/2013 19:25:23
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Why does everything in the universe rotate ?
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Why does everything in the universe rotate ?
That depends upon your definition of "rotate". Remember that all motion in the universe is relative to one's frame of reference. Consider the moon for one example. One side of the moon is always facing the earth so in one respect, it doesn't appear to be rotating. However, it does circle the earth so in another respect, it does.
Rotation is caused by energy imparted to a body or system. In the cosmic realm, rotation is usually caused by gravitational energies. In the quantum realm, rotation can look very different and unusual to us. In this micro realm, these rotations are imparted, in large part, thru heat energy and charge differentials.
It all boils down to different energies applied to material objects.
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A perfectly uniform arrangement of matter is required to avoid rotation.
The random chaotic (http://en.wikipedia.org/wiki/Chaos_theory) nature of nature means such uniformity generally does not occur, so rotation is the norm.
e.g. formation of a rotating of protoplanetary disc from a cloud ...
Protostars typically form from molecular clouds consisting primarily of molecular hydrogen. When a portion of a molecular cloud reaches a critical size, mass, or density, it begins to collapse under its own gravity. As this collapsing cloud, called a solar nebula, becomes denser, random gas motions originally present in the cloud average out in favor of the direction of the nebula's net angular momentum. Conservation of angular momentum causes the rotation to increase as the nebula radius decreases. This rotation causes the cloud to flatten out—much like forming a flat pizza out of dough—and take the form of a disk.
http://en.wikipedia.org/wiki/Protoplanetary_disk#Formation
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If the moon didn't rotate, we should find it rotating, as is moves around Earth :)
But it doesn't. So, it does :)
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Grimbo The answer to your question is simple. The universe was very smooth and flowing evenly in the early stages of its existence as shown in the cosmic microwave background signal. However radiation and stellar winds from stars together with many explosions of supernovae have created turbulence in the flow of gases etc throughout the universe when these are created they do not generate any overall angular momentum (rotation) for the universe but they do generate rotation in all sorts of different directions that balances out to zero overall. When bodies contract under gravity to form stars and galaxies there is always a small imbalance in this rotation in some "random" direction. As the collapse progresses this rotation speeds up and becomes more visible and so all collapsed bodies rotate to a certain extent but some more than others.
Surveys have been taken of the net speed and direction of rotation of galaxies and clusters of galaxies and currently there appears to be no clearly favoured direction overall although there are slight hints that there may be one.
It is also important to note that black holes because they are so tiny. A black hole with the mass of the sun is one million times smaller than the sun at around one mile across! Almost all black holes must be rotating at the absolute maximum speed allowed
There is an upper limit to the amount of angular momentum energy (rotation) that a black hole of given mass can contain. Any particle that attempts to exceed this limit will not fall into it but just "bounce off" and not cross the event horizon!
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Soulsurfer, I agree with all you wrote there, but there's one thing I wonder about. Is there any mathematical or physical proof guaranteeing that the rotations take them self out? Or is it a reasonable assumption?
Conservation laws? Or is it symmetry?
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Eh, one more thing though. Sort of missed "There is an upper limit to the amount of angular momentum energy (rotation) that a black hole of given mass can contain. Any particle that attempts to exceed this limit will not fall into it but just "bounce off" and not cross the event horizon!"
That one was new to me, is that your own, or do you have a link for it?
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Rotating masses have angular momentum. Angular momentum is a vector; the total angular momentum of a system is the vector sum of the angular momenta of its parts. By definition, that vector points in the direction of your right thumb when the fingers of your right hand indicate the motion of the surface. If a body appears to rotate clockwise from your point of view, then the its angular-momentum vector points away from you. Identical masses rotating in opposite directions have a net angular momentum of zero. As far as we know, the total angular momentum of the universe is zero.
A body with zero net angular momentum can break into two or more parts, each of which has non-zero angular momentum; but the vector sum of angular momenta of the parts must be the same as the original angular momentum of the parent body.
At the quantum scale, particles have a property called "spin", but this may or may not relate to rotation of the particle's constituent parts, which in many cases are not observable or even hypothesized. In some cases, it is not known if that spin implies the existence of angular momentum. If a particle has non-zero angular momentum and zero diameter (perpendicular to its spin axis), then it's rotation rate, if it has one, is either infinite or undefined.
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I remember reading in one of Michio Kaku's books that a rotating universe would violate causality for some reason, therefore the sum angular momentum of the universe is zero.
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A rotating universe is equivalent to one with closed time like curves I think? Meaning that it allows for 'time travels'. And there is some vague memory of some whispering that there seemed to be evidence for the universe rotating, looking at the universe from astronomical photos, but another memory insists that this was debunked later.
If you have time travels causality will be violated, as any other idea in where you can get a cause to appear, before the effect leading to it.
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Closed timelike curves and causality violation. (http://arxiv.org/abs/1008.1127)
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btw: it won't help to 'split' universes as one goes 'back in time', assuming the one you come to, to be a 'new version' of your old at a equivalent time and place. Not as long as it includes you too, because now you will have two versions of yourself in it, and that should violate causality too. To me this reasoning seem to lead to a necklace of 'time travels', in where there is no end to it, to give it a balance. If you imagine yourself as consisting of an amount of energy 'time travels' also seem to violate the conservation laws, assuming a arrow of time. Only if ignoring that arrow, and taking a measure of a whole SpaceTime under all of its existence can you argue a equilibrium to exist. So it seems to demand the arrow to be a illusion as well, to exist.
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Has the “gravastar” proposed by Mazur and Chapline been debunked yet?
The name is derived from the words Gravitational Vacuum Star. My, possibly very over-simplified, understanding is that a gravastar is a black hole within which not everything is crushed into an infinitely small space, or even into a super-heavyweight micro-speck. In a nutshell, a gravastar, according to Mazur and Chapline, is formed when an exceptionally large star nears the end of its life and starts to collapse under its own gravity. During this process it reaches a critical density at which its matter is converted into energy which gives rise to a fiery boundary layer. This is the gravastar. From outside its appearance will be that of an enormous star. Further collapse will be prevented because, the authors state, the gravity of spacetime inside the boundary will be repulsive. All cannot remain in a state of equilibrium, however, because some of the energy at the boundary will be converted back into particles of matter.
Such particles that form on the inside of the boundary layer will be accelerated away from one another by the repulsive gravity mentioned above. This scenario, in which every particle of matter is rushing away from every other particle, bears a striking similarity to the Big Bang scenario. A major difference, however, is that the original star in this model will have been spinning, (everything in the observable Universe spins, so there is no reason to suppose that this particular star would not do so) and this spin will be conserved in the gravastar. Mazur and Chapline reason that this spin will manifest itself as vortices forming near the boundary, but being left behind as the boundary moves outward. These vortices will influence the movement of matter particles, giving rise to the formation of stars and galaxies. Although the vortices, and subsequent structures to which they give rise, may have been left behind by the spreading boundary, they will not be stationary, but will continue to recede from one another in precisely the manner described for the expanding Universe which we observe around us. The boundary will be racing away from the vortices nearest to it in the same way that the vortices and galaxies continue to recede from one another. Obviously, the flatness and temperature problems will not arise in this model, as there will have been plenty of time, during the lifetime of the original star, for every part to have had contact with every other part.
Whether or not this idea still has commands any credence, I would be glad of comments, just to test my own understanding.
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I don't know, it seems to be allowed by GR:s equations? Then again, I'm not happy about 'negative' gravity, or repulsive? Saw someone else describe it as "The gravastar theory claims that the "springy space" is a result of gravitic distortion of quantum fluctuations in space, leading to a phase change, similar to a Bose-Einstein Condensate. The springy space is thus a condensate bubble surrounded by a shell of gravitational energy." In that case it seems really close to the idea of 'virtual particles' and then the claim becomes, what? I'm not following it any further than that? That virtual particles contribute to a gravity? Or that a condensate somehow allow them to be long lived?
All gravity I ever have heard of is connected to mass, or (uniform constant) accelerations, but as far as I know gravity has only one sign. Doesn't matter how you look at it, it's of one sign.
No plus and minus to it.
So if you're right in that it can be seen to have a 'repulsive gravity', then that one needs to be experimentally defined. I can't see gravity taking out gravity? If we on the other hand define a 'empty shell' of some immense density? I don't know?
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Think of a empty shell of a immense density, imagine yourself inside it. Will there exist geodesics? It must. Everywhere you can imagine, a geodesic should be possible. So whatever gravity is, it's on one hand acting on you, you acting on it, everywhere. On the other hand geodesics without 'friction/resistance' also exists, everywhere.
Nah: if it was this one http://www.eurekalert.org/pub_releases/2006-03/ns-tce030806.php ??
I don't think so.
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I think the dark energy star was a later development from the gravastar. Obviously that was still going a few years ago.
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Bill
WMAP is quite clear that stars are repelling each other and rotating in galaxies. So would your dark energy star do the same?? Dark energy should better be re-defined as the dark force that is making stars repel each other.
That repelling force may well be electrical and thus would be massless.
CliveS