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Comment by kmoser | Hacker News Reader

Dumber question: would a galaxy that appears to spin clockwise appear to spin counter-clockwise when viewed from the other side? Does this imply that the real question is why galaxies' relative orientations seem to favor more spinning in one direction than the other?

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Yes, that's it exactly. There's a net asymmetry in the distribution of galaxy axes. "Clockwise" by itself is a relative term. This seems to be the paper in question: https://academic.oup.com/mnras/article/538/1/76/8019798

That said: I'd wait a bit here. This is a single-author paper by a non-astronomer (he's a CS professor). The sample size seems small (N=263), and the measurement coarse (he's just bucketing galaxies into "rotating in the same/different direction as the Milky Way"). And the technique may be too novel for its own good. The gold standard here would be to look at differential redshift, but all he's doing is applying a ML filter to detect the "twirl" direction in the image of the spiral galaxy. Which... might be amazingly effective or might fall on its face because of bugs in the filter.

But the signal seems strong, though (158 vs. 105 galaxies in each direction).

Basically, I'd wait a bit for someone to try to replicate with more data and more conventional measurements.

Wouldn't it be biased towards nearby galaxies? A net rotation of the local cluster would be reasonable. But it would be very wrong to extrapolate that to the whole universe.

Look, if the visible universe is expanding, as we think it is, that is already a direction. Viewing galaxies “from the other side” is not the same in an expanding bubble. It’s like being surprised that many things are redshifted no matter where you look. As for rotations — you could perhaps have some local coriolis force.

The visible universe is redshifted and galaxies are getting further and further away. So jumping straight to “we are in a black hole” is weird

It is far more plausible that there is some coriolis like spinning effect in a higher dimension, even if the universe is flat it could have similar effects to how the earth’s spin makes cyclones all spin in the same direction.

Problem solved. Next?

> Look, if the visible universe is expanding, as we think it is, that is already a direction.

Could you point in that direction?

> when viewed from the other side?

Nobody has done it so far. We have only theories and hypothesis.

I'm not sure I understand this response -- basically all of cosmology involves theories based only on somewhat subjective interpretations of sensor data targeting far-off objects. So I don't necessarily disagree.

But what could possibly happen other than they act like all other physical objects do? It boggles the mind to think how broken physics would have to be to accommodate a second correspondence principle for the big-but-not-too-big scale...

I feel like maybe I'm misunderstanding your sentiment, because this seems like a basic shared fact: a clock anywhere in the universe is still a clock.

Except most theory can be observed where this one can’t until we find a wormhole to travel through or break c

I guess I'm saying that we also can't observe any proof for the theory that anything exists beyond the solar system instead of a giant screen run by aliens built to trick us. I appreciate the empirical mindset, but taking it this far is not leaving room for the usual amount of parsimony-based reasoning!

This is exactly the dumb question I came here to ask. So now I wait with you for a less dumb person to reply.

My clock certainly seems to tick in the opposite direction when I look at it from behind.

Answering to your and original question above: there are no poles (or axes of rotation) in the Universe. On large scales (think distances to include thousands and millions of galaxies each with billions of stars with even more planets) the Universe is uniform - isotropic and homogeneous [1]. It is expanding with acceleration in all direction in each and every point of its space, so there is no preferred direction thus in average we should have 50% of clockwise and 50% of counter-clockwise galaxies since orientation of those should also be absolutely random in average, unless something when the Universe was being created or evolving affected that balance.

1. https://en.wikipedia.org/wiki/Cosmological_principle

So it makes about as much sense to ask why 2/3rds of the galaxies are "upside-down" from our vantage point, because there's no clear reason it should be something other than 50% in a sample size this large?

Correct. On the largest scales it should be 50-50.

If it's not that would add a significant term to the Big Bang that nobody had previously expected. It would be a rather big deal... if it holds up.

Dumb question time continues: The majority of the solar planets rotate in the same way, and the majority of the large moons rotate in the same direction as their planets. I assume this is influenced by the rotation of the relevant accretion disks. And I assume this is common for stars within a galaxy?

I don't think the universe is considered to have any significant rotation, however. Is this due to scale for us to measure, and/or having nothing external to compare against?

That's exactly it. Solar systems and galaxies have net rotation, and maybe even galactic clusters.

But there is no reason to think that the universe has a net rotation. It could have one; you don't need a frame of reference to detect rotation. (The same way you feel centrifugal force.)

It would be huge if it were shown to have a net rotation. So huge that I take this claim with skepticism until heavily confirmed.

Hemispherical Power Asymmetry (HPA) observed in the Cosmic Microwave Background (CMB) temperature fluctuations [1]

"We conclude that the hemispherical power asymmetry still remains as a challenge to the standard model." [1]

1. https://arxiv.org/abs/2411.15786

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