Can rotation solve the Hubble Puzzle?

https://academic.oup.com/mnras/article/538/4/3038/8090496?login=false

45•toss1•3d ago

Comments

hoseja•6h ago

Wait did nobody seriously consider rotation yet? Everything is rotating. Angular momentum is conserved.

jvanderbot•6h ago

Isotropy is a fundamental assumption that is very hard to let go of.

exe34•5h ago

Where would the axis of rotation be?

nodfyr•4h ago

That would imply a preferred direction in the universe (the axis of rotation) and thus anisotropy.

There are stringent constraints on anisotropy from the cosmic microwave background.

In particular, one can use the Doppler effect to check whether the CMB dipole is compatible with our velocity with respect to the CMB frame.

lumost•4h ago

Rotation implies a great many observables and properties of the universe. There would be a cosmic axis, which implies a cosmic center and a cosmic north. Both concepts that are problematic in an infinite universe. If the universe is in fact inside of a black hole of a different universe - some of these problems go away as the Hubble volume would be the finite boundary of the universe.

exe34•4h ago

and we would be at the center?

theoreticalmal•4h ago

My dog is quite sure she’s at the center, if we’re trying to be specific

shermantanktop•2h ago

Main Character Energy? My cat has that too.

AnimalMuppet•4h ago

Are we in an infinite universe? I thought the current thinking was that it was finite but unbounded; that is, that it curved back on itself.

jl6•4h ago

That’s one speculative possibility, but we don’t know. It could be infinite, or finite with a boundary just out of sight (beyond the edge of the observable universe), or some other more exotic geometry. There’s no solid evidence either way.

My money’s on non-infinite, just because I’m not sure infinity is a well-defined concept outside of mathematics. We’ve certainly never observed any other infinite phenomena.

XorNot•4h ago

Except plenty exist - every electron is an infinite phenomena. They're point-like particles made up of no constituents. You can get infinitely close to an electron and still get closer to it.

Infinity extends both upwards and downwards in scale.

lambdaone•4h ago

Below the Planck distance, "closer" ceases to be a meaningful concept. Similarly, distances larger than the size of the observable universe may also be meaningless.

hnuser123456•3h ago

The co-moving radius of the universe is about 3x larger than the observable universe, but I don't think there's any practical measurements larger than that. We don't know how much is beyond that because potentially a large chunk of the universe is already forever outside our past and future light cone.

kstrauser•3h ago

Why is that? I've heard this before but don't understand what it actually implies. Like, why can't 2 things meaningfully be half a Planck distance apart?

Nevermark•3h ago

Imagine that at some small distance, space itself is quantum, so quantized. I.e. at the bottom, space is a discrete graph with incredibly small edges. Possibly very tangled and not even layed out in obvious dimensions over short distances.

We don’t know if that is the case. That is only one possibility.

But it seems very clear that whatever happens at the Planck distance or lower isn’t simple smooth space as we model it for larger scales.

AnimalMuppet•3h ago

Imagine the universe is made out of graph paper, with only the points of intersection of the lines being actually "real". That is, space is actually discrete. If that is true, then you cannot meaningfully talk about things being "half a square" apart.

People (some people) think that the universe really is that way, at the Planck distance. Actual experimental confirmation is somewhat lacking at this time...

daxfohl•2h ago

The only reason I've heard that isn't super handwavy is that measuring it would require a wavelength with enough energy to create a black hole. IDK if that's true or not, and IDK if that also means the distance doesn't exist or if it's just not measurable.

I've also heard that there's nothing special about planck length other than it being universal constant that we and any conceivable aliens would agree on as a standard of measure. So, idk.

griffzhowl•2h ago

It's just that it's physically impossible to measure such small scales. To probe a smaller scale you have to put more energy into a volume (roughly, because you have to force particles closer together), and at some point you have to put so much energy into such a small volume that it becomes a black hole, then any more energy you put in will just make the black hole bigger. So there seems to be a fundamental limit to how short a scale we can probe, and therefore we can't give a physical meaning to smaller scales. Nima Arkani-Hamed talks about htis in a few lectures online.

This is just according to our current theories, and you don't need any speculative ideas about granularity of space. Mathematically, there's no problem in considering arbitrarily small length scales, because current theories are based on continuous space and time dimensions, but since we can't give physical meaning to small length scales, that's a clue that a more fundamental theory will somehow not be based on continuous space and time

AnimalMuppet•3h ago

That's only if you view the electron classically, which is an inadequate picture.

voidUpdate•4h ago

It's only been a finite time since the universe was very small, so unless it's expanding infinitely fast, I don't see how it could be infinite

immibis•4h ago

Was the universe infinitely small or was it just extremely or infinitely dense?

Anyway, we don't actually know that, since we do not have a time machine. The theory that the universe used to be much smaller is something we infer based on the snapshot we see today, just like we infer rotation based on the snapshot we see today. Either one could yet be proven wrong.

ben_w•2h ago

It's (mathematically) allowed for it to have always been infinite, and still grow.

If you take the number like and apply f(x) = 2x, it was infinite before and after.

voidUpdate•2h ago

yes but if x is finite, any f(x) will still be finite. So the universe has either always been finite, or always been infinite, and given that it started out being very small in a big bang, it would imply the former

lumost•2h ago

not if x is the set of all Real numbers. All points could have been infinitely close to each other at the big bang, and the universe could still have been infinite in size.

ben_w•2h ago

> yes but if x is finite, any f(x) will still be finite.

The number line is not finite, even though every value on it is. The universe may be like the number line.

> and given that it started out being very small in a big bang, it would imply the former

The universe started out denser, which is not quite the same as "small" when talking about infinities. The currently visible universe gets both things at the same time, but only because the visible bit is finite.

Apply f(x) = x * 1e-60 to the number line, and things which were previously spaced out every integer, are now much more densely packed, but the number line as a whole is still the same size — infinite.

AnimalMuppet•1h ago

f(x) = tan(x)

f(x) = 1/(1-x)

So if x is finite, f(x) can still be infinite.

pfdietz•4h ago

It's so close to flat that we can't tell.

Galatians4_16•3h ago

>If the universe is in fact inside of a black hole of a different universe

The observation could also be due to an area of relatively high density inside an area of relatively no density.

TheRealPomax•1h ago

Except why would there only be one axis?

est31•5h ago

> All objects within our universe rotate, including planets, stars, solar systems, galaxies, and galaxy clusters. Moreover, black holes, spherically symmetric objects with horizons, display near maximal rotation as presented by Daly (2019). The idea that everything revolves [...] naturally extends to the whole universe, as hinted by recent claims of anisotropic Hubble expansion in X-ray observations by Migkas et al. (2021). Furthermore, a plausible syllogism is that the universe has near-maximal rotation, motivated by cosmologies where the universe is the interior of a black hole (Pathria 1972).

BigParm•2h ago

If spacetime rotates, does that imply there being a centre of the universe?

irrational•2h ago

And an axis.

layer8•1m ago

Or an axis.

pmontra•2h ago

Wouldn't the center be the Big Bang and the 3D Universe at the current time (if Relativity lets me write about a current time) be the 3D surface of the 4D sphere (or spheroid) that the Big Bang is creating by keeping to expand?

layer8•3m ago

If the universe is the interior of a black hole, one would assume so.

bostonwalker•5h ago

I seem to recall there was an article posted here recently which noted that galaxies have a preferred direction of rotation. Seems like the universe itself rotating could be a reason why?

dkural•3h ago

That article is by a crank. People pointed out that he cherry-picked the galaxies, and no one else who looked at the data objectively saw any evidence of preference for a rotation direction.

ziddoap•3h ago

I looked around (Smithsonian, space.com, astronomy.com, etc.), but nowhere has any mention of people disputing the findings, do you have a link? Who is "people" in this case?

(I was/am skeptical just because it's a single-author study with pretty spectacular results, and have been keeping an eye out for any followups, but must have missed them)

iainmerrick•3h ago

This comment has a good summary of the debunking: https://news.ycombinator.com/item?id=43540635

It's unfortunately rare for this kind of straightforward falsification to make it into publications aimed at the general reader. "A lie is halfway round the world before the truth has got its boots on," as they say.

ziddoap•3h ago

Thanks.

I was hoping for something a bit more authoritative than a reddit comment being copy/pasted to HN (e.g. an actual retraction, or a paper directly disputing the findings), but I'm guessing most of the community just ignored the paper due to the history of the author.

roarkeful•2h ago

The universe being a giant toilet in the process of flushing is delightfully Doug Adams inspired.

BurningFrog•3h ago

If I understand what I skimmed, the idea is that space-time itself rotates, not all the collective matter in it?

daxfohl•2h ago

ICYMI: a slick link from the article with a video that demonstrates how closed timelike curves work in Godel's time traversal solution to Einstein's field equations. https://iopscience.iop.org/article/10.1088/1367-2630/15/1/01...

WhitneyLand•1h ago

“We show that a Gödel inspired slowly rotating dark-fluid variant of the concordance model resolves this tension…”

Gödel wait what? I thought of him as “only” the logician who killed Hiblert’s dreams and caused people to question the very foundations of mathematics.

Dude then took up physics as a hobby and trolled Einstein by discovering closed time-like curves?

TheRealPomax•1h ago

If your paper has a question title, it should be sent back to you with the note "change the title to summarize the paper".

jinwoo68•1h ago

Universe is called universe because it is the only one. Everything that exists should be part of the universe. When we say the universe rotates, what does it mean? Rotate relative to what? Does it mean that there's a larger "universe" that contains ours?

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