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Author Topic: Is there a 'net angular momentum' of the universe?  (Read 9109 times)

Offline Arthur Lubenfeld

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Arthur Lubenfeld asked the Naked Scientists:

There are many objects in the universe. They all seem to have some spin (angular momentum). Presumably, this occurs by a slightly off centre collision. This collision would leave the total angular momentum as zero.

My question is: has anyone actually added up the total angular momentum of the universe. If not how might it be done. If so, does it come to zero, or is there a net "universal" spin.

What do you think?


 

Offline lightarrow

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Is there a 'net angular momentum' of the universe?
« Reply #1 on: 13/06/2008 19:57:20 »
According to the present data, there is no spin, otherwise we would observe a difference of recession speed between the galaxies along a plane and those on the axis orthogonal to that plane.
 

lyner

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Is there a 'net angular momentum' of the universe?
« Reply #2 on: 13/06/2008 21:29:36 »
That's what I heard.
The other evidence / argument is that, if there was a measurable angular velocity now, it would imply a simply huge angular velocity when it had a small initial diameter. This would have had a significant contribution to the expansion rate.
 

Offline LeeE

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Is there a 'net angular momentum' of the universe?
« Reply #3 on: 14/06/2008 13:44:42 »
Very good point.
 

Offline Arthur Lubenfeld

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Is there a 'net angular momentum' of the universe?
« Reply #4 on: 20/06/2008 05:18:20 »
I am not sure if I understand the answers given as I was not asking about the spin of the universe but the components within. I.e. could you add up the individual angular momentums (momenta) (or linear for that matter) of all objects in our universe, and get to zero. Perhaps this is the same question. If it is indeed the same question then may I ask a supplementary one: Black Holes spin when looked at from outside. If you were born inside one, you would have no knowledge of the outside world. Time and space would be self-contained as the event horizon would drag time and space along with it. If this were true then light and gravity would have to follow. If this were true, what reference frame could you use to convince yourself that your universe was, or was not, spinning. Perhaps I have made a mistake in the logic flow, but I need someone with more knowledge to tell me where it is, because if there is no flaw here, then we really do not know if our universe is spinning (when seen from outside). This is, as far as I can see, the same type of problem as being in a sealed elevator and trying to tell the difference between gravity and acceleration.
 

lyner

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Is there a 'net angular momentum' of the universe?
« Reply #5 on: 20/06/2008 10:01:28 »
Any angular momentum in the Universe, at least by classical argument, would be the same now as at the start of things. This is one of the 'Conservation Laws' which is pretty much obeyed in all observations, so far.
Angular momentum of a mass around a point depends upon the mass and the separation and the angular velocity. The ice skater can increase angular velocity by bringing her arms in close to her body and reduce it by stretching them.
My view is the following.
Taking all the bits of the Universe, all their angular momentum (about a 'centre' and about each other) would have to add up to zero. If it were not Zero, then when the Universe had a very small diameter, it would have had the same total angular momentum. Consequently its angular velocity would have had to be ENORMOUS. This would have affected the rate at which it expanded around its axis of rotation compared with along the axis. That effect should still be detectable today.
 

Offline lightarrow

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Is there a 'net angular momentum' of the universe?
« Reply #6 on: 20/06/2008 12:37:40 »
Anyway, I admit not to understand very much most of the speculations about the entire universe or about its beginning. For example: how we know the total mass of the universe? We cannot see objects out of the visibility horizon; on the other hand, the total mass should be taken in account to compute all the forces present at its beginning. Second: what physical meaning would have the "angular momentum of the universe"? It would rotate with respect to what?
 

lyner

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Is there a 'net angular momentum' of the universe?
« Reply #7 on: 20/06/2008 13:02:33 »
Imagine you were drifting in space in a ship with no windows. If you were spinning, then you would be aware of a centrifugal force and a coriolis force, if you tried to move. You wouldn't need to refer to any other objects around you to know whether you had angular momentum. You would also know its axes.
Perhaps the concept of 'no angular momentum' would have to depend upon the absence of either of these forces, or possibly their Integral over the region of interest. This would tie in with experience - when discussing the angular momentum of an object (classically) we are including the sums of all of the spins of, components, particles and rotations of any gas molecules inside.
But I agree, the idea of all mass and space rotating is a bit meaningless so, perhaps zero angular momentum of the Universe is a given. Angular Momentum is, perhaps, something which only relates to some sort of local region and tends to zero as you include more and more of the Universe.
Someone could probably do a clever, Maxwell-style vector equation which says sopmething like
 Integral over all space (Curl(Momentum)) = 0

The evidence seems to support this, too, as there have been nothing to indicate it, even at the limit of our observations.
Locally, in our Galaxy, however, there seems to be a definite overall value of angular momentum; most of it seems to be going 'anticlockwise looking down on it'.
 

Offline lightarrow

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Is there a 'net angular momentum' of the universe?
« Reply #8 on: 20/06/2008 17:55:50 »
Imagine you were drifting in space in a ship with no windows. If you were spinning, then you would be aware of a centrifugal force and a coriolis force, if you tried to move. You wouldn't need to refer to any other objects around you to know whether you had angular momentum. You would also know its axes
I don't agree. Mach's principle forbids it. If the universe were your ship only, there were no way to say if you're spinning or not, that is, those forces wouldn't exist. In our universe those forces should arise from the fact that the ship is spinning with respect to all the other (far away) masses present in the universe.

This effect was put in a semiquantitative form by Dennis Sciama: postulating the existence of a gravitational force which, in analogy with the EM force produced by accelerated charges, is generated by accelerated masses and depends on distance as 1/r:

F = (GMm/c2)*a/r

F = force made on an object of mass m from an object of mass M and acceleration a
r = distance between the two objects

he integrates on all the visible universe's volume, using the present values for Hubble's constant H (the integration upper limit is taken as c/H) and the average density of matter, and he computes, approximately, the inertial force experienced by an object in an accelerated frame of reference, and the result is of the order of magnitude of the real value. (I consider this fact as really impressive!).

http://en.wikipedia.org/wiki/Mach's_principle
« Last Edit: 20/06/2008 18:03:31 by lightarrow »
 

lyner

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Is there a 'net angular momentum' of the universe?
« Reply #9 on: 20/06/2008 19:05:20 »
Quote
I don't agree.
Well how does the wind know which way to blow? It can't look at the stars to tell the Earth is spinning and it definitely gets a hint of Coriolis force.
So it happens locally and can be measured- all I'm saying is that, as you include more and more of the Universe in your 'ship', these (effective) forces will get smaller and smaller (integrate to zero).

This was my first reaction but I am not sure what you are 'not agreeing' with. You can't mean that the Coriolis force doesn't occur for a spinning object so, what are you actually not agreeing with?
 

Offline Soul Surfer

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Is there a 'net angular momentum' of the universe?
« Reply #10 on: 20/06/2008 19:28:16 »
My guess is that the universe probably does have some net angular momentum and that this is equal to or less than the maximum angular momentum that a black hole with the total mass and energy of the whole universe can have but as the universe has clearly expanded vastly since the earliest phases of the big bang that this angular momentum is now so small as to be virtually undetectable in any observations except possibly the cosmic microwave background.  Careful observations are being made of this and these will be improved soon when new detectors are used.  Some hints of structure have been seen but it is not yet clear how these may be interpreted.
 

Offline lightarrow

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Is there a 'net angular momentum' of the universe?
« Reply #11 on: 21/06/2008 10:42:32 »
Quote
I don't agree.
Well how does the wind know which way to blow? It can't look at the stars to tell the Earth is spinning and it definitely gets a hint of Coriolis force.
So it happens locally and can be measured- all I'm saying is that, as you include more and more of the Universe in your 'ship', these (effective) forces will get smaller and smaller (integrate to zero).

This was my first reaction but I am not sure what you are 'not agreeing' with. You can't mean that the Coriolis force doesn't occur for a spinning object so, what are you actually not agreeing with?

You wrote:

"Imagine you were drifting in space in a ship with no windows. If you were spinning, then you would be aware of a centrifugal force and a coriolis force, if you tried to move. You wouldn't need to refer to any other objects around you to know whether you had angular momentum."

What I coloured in blue is true only inside our universe, which already has massive (even if they were only distant) objects. In a universe consisting of a starship only, without any other massive object in it, you would have no way to say if the ship were spinning or not, because of Mach's principle. Since we are talking about the entire universe's spin, the same reasoning applies to it: to say if it's spinning, there should exist other massive objects to which refer the spinning (given, of course, the law of physics we already know).
Don't know if you agree with it or not; in case you do, forgive me.  :)
« Last Edit: 21/06/2008 10:51:33 by lightarrow »
 

lyner

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Is there a 'net angular momentum' of the universe?
« Reply #12 on: 21/06/2008 11:52:19 »
No. That's fine. :)
 

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Offline Pmb

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Re: Is there a 'net angular momentum' of the universe?
« Reply #13 on: 21/04/2012 19:42:50 »
Shrunk
When I was studying this subject when I opened the hood and someone mentioned from the class I was sitting in. They told me that this girl had opened the set realizing that she was still alive and anxious to get back to get back to work.

Orange - She wanted an to start reading in opneing to start to an opening at a buisness open buisness so that I know how to grow oranges. It took off from there.
 

Offline yor_on

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Re: Is there a 'net angular momentum' of the universe?
« Reply #14 on: 22/04/2012 18:18:17 »
Expressed another way, is spin a 'relative motion'?

If it would need to be relative something then there can't be a 'spin' without needing a external reference frame from where to define it. Against it you have the definition of a 'spin' as a acceleration, presenting us with a local 'gravity' :)

First you just need to define the geometry for it :)
Closed or open?
 

Offline yor_on

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Re: Is there a 'net angular momentum' of the universe?
« Reply #15 on: 22/04/2012 18:22:51 »
Although?

A spin inside of some object inside our universe, presenting us with a local gravity, as some hollow tube. Wouldn't that too then need another 'frame of reference' to create this Gravity/framedragging?

Ouch.
=

That one was tricky.
« Last Edit: 22/04/2012 18:24:22 by yor_on »
 

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Re: Is there a 'net angular momentum' of the universe?
« Reply #15 on: 22/04/2012 18:22:51 »

 

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