# I Angular momentum of the Universe

1. Oct 26, 2017

### rootone

It explains very well many aspects of the Universe.
Why should there be any angular momentum though?
The idea that the Universe is itself intrisically rotating doesn't make sense.

2. Oct 27, 2017

### phinds

Right. Because it isn't. What made you think it is? If it were rotating then it would have a center and thus a preferred frame of reference. You are certainly right that this doesn't make sense (goes against evidence)

3. Oct 27, 2017

### Staff: Mentor

Where did you encounter this idea?

4. Oct 27, 2017

### rootone

Tbh, I don't recall where I first heard of the notation that the Universe as a whole has angular momentum.
It isn't something I made up though, and I rejected that for the same reasons as pointed out by Phinds.
It might have been better not to have mentioned a proposal I had already dismissed.

However having dismissed that, the question still remains.
Why does rotation of massive bodies exist at all?, and not just exist but is a fundamental feature of massive bodies.
Isn't the implication of this that at a very early time the evolution of the Universe would have to be asymmetric,
(As in being not isotropic)

Edit: (So you know I didn't pull the idea of thin air before rejecting it)
Here is a reference to a rotating universe model, though it isn't where I heard of the idea originally.
https://arxiv.org/ftp/astro-ph/papers/0601/0601659.pdf

Last edited: Oct 27, 2017
5. Oct 27, 2017

### Staff: Mentor

No. Individual systems within the universe can have nonzero angular momentum even if the total angular momentum of the universe is zero. (More precisely, the concept of "total angular momentum of the universe" isn't even well-defined, but heuristically, the angular momenta of all the individual systems should "average out" to zero in some suitable sense.)

6. Oct 27, 2017

### Staff: Mentor

I know it's on arxiv, but there is no sign that it's been looked at by anyone except the author. I haven't had time to read through the paper in detail, and I'm not sure it's worth it; I would just point out that whatever model is described in the paper might not be a valid one, and I would not rely on it as a source.

7. Oct 27, 2017

### jerromyjon

I have heard of this as well, not that my two cents is worth much, but I have read that it has been constrained to a small amount of rotation. As per arXiv:1207.6640v1
I would think it is about as important as redshift, since if everything is rotating as the metric is expanding... I imagine you get my drift.

Small edit to clarify what is quoted.

Last edited by a moderator: Oct 27, 2017
8. Oct 28, 2017

### Laurie K

Regarding validity, any model that produces similar results to Lambda CDM, where the ratio of all universal matter to ordinary universal matter is 2 * Pi +/- 1%, can be considered just as valid as the Lambda CDM model.

9. Oct 28, 2017

### Staff: Mentor

I don't know what you mean by "all universal matter" and "ordinary universal matter". Nor do I know where you're getting the ratio of $2 \pi$ from.

In any case, a model can be considered "just as valid" as the Lambda CDM model only if it matches all of the confirmed predictions of the Lamda CDM model, which predicts a lot more than just the ratios of dark energy/dark matter/ordinary matter. If you know of such a model, please give a reference.

10. Oct 30, 2017

### rootone

So far so good, I think we mostly agree that the idea of the Universe as a whole having angular momentum doesn't make sense.
I do appreciate the math efforts of those who think it could be possible though, it's well above my level of math.
OK, so if the Universe after the big bang event is perfectly isotropic, then why do things rotate, they shouldn't do that.

11. Oct 30, 2017

### Staff: Mentor

It isn't. Perfect isotropy is an idealization.

12. Oct 30, 2017

### rootone

Aha!, quantum scale randomness then?
Brownion motion?

13. Oct 31, 2017

### Staff: Mentor

In inflationary cosmology, the deviations from perfect isotropy in the early universe are ultimately due to quantum fluctuations being amplified during the inflationary era. But perfect isotropy is an idealization in any context, just from ordinary classical randomness.