According to this article,
the universe may be spinning. Spinning with respect to what? It doesn’t seem there would be anything to measure the spin relative to so the only thing I can think of is there’s evidence of some kind of centrifugal force (which I can see might affect the measured Hubble constant). But how do you separate the notion of spin from the notion of a variable Hubble constant?
To itself. Rather, rotation is about how the components of the rotating object - stars and galaxies rather than atoms, in this case - move relative to each other.
And given that the entire universe is almost certainly larger than the observable universe we can actually see, the answer might be “relative to the rest of the universe”
Not true because we don’t feel the rotation.
-Flat Earther
Is it possible this is localize to, say, the observable universe? Like how galaxies spin.
Unless I’m missing some subtle nuance, this sounds totally silly to me. Anything that’s spinning must, by definition, be rotating around some central point. But the whole premise of the Big Bang theory is that the universe has no center. Galaxies spin, sure, but they spin around a distinct center point that usually (always?) contains a supermassive black hole. What center point is the universe spinning around?
I don’t know, I feel dizzy all the time. I think this might be why.
I may be wrong, but I got the impression from another article on this topic that, it is the objects in the universe (galaxies etc) that are tending to rotate in the same direction. If not then yes, I agree it does not seem to make sense that the universe as a whole is rotating.
This statement is only true for a single solid body. Rotation is more complicated for a set of solids or fluids in general. A simple example: imagine a room full of spinning tops. Each top is spinning at some particular speed, either clockwise or not, but not moving otherwise. The total angular momentum of the tops is unlikely to be zero. Thus the total spin of the set of tops is not zero, yet there is no central axis.
I just skimmed through the actual paper Can rotation solve the Hubble Puzzle? and it looks like they’re using fluid models to estimate the angular momentum of the observable universe. It’s not zero.
Yep.
Thank you to both of the above for the clarification. So to summarize my understanding:
Q: Is the universe spinning?
A: No. The concept makes no sense, and the headline in Popular Science is stupid.
Q: Does the universe possess an angular momentum?
A: Maybe.
Didn’t Gödel prove that a universe with a net nonzero angular momentum contains closed timelike curves? I.e., time travel?
Just what I was going to mention
Gödel metric - Wikipedia
My understanding is that it can contain closed timelike curves but they aren’t necessarily there,
From the paper linked in my post:
The required a minimal rotation is an order of magnitude larger than the maximal rotation avoiding closed time-like loops within the horizon.
So the authors believe their estimated rotation is too low to permit timelike curves.
Edit: I may be misreading them. Please don’t take my interpretation without confirming.
A spinning object implies that a point on the surface or volume orbits/rotates around some central point…which violates our current understanding of cosmology according to our present understanding of physics.
But let us put that aside for the time.
Rotating non-solid objects tend to have inner and outer layers rotate at different velocities, such as a gas giant planet, or a galaxy.
The only cosmic-scale motion I’m aware of is the accelerating expansion of our observable portion of the universe.
(Galactic-scale motion CAN have galaxies collide…but that is kind of like Brownian Motion in the greater order of things 
)
The hypothesized “Dark Flow” is another example of cosmic scale motion.
At any rate the observable universe is probably only a small portion of the entire universe, and it rotating around a center wouldn’t make that center point the center of the universe; just of the part we can see. We’d just be like tiny fish trapped in a whirlpool who can’t see outside of it and assuming the whole universe is spinning.
I’m wondering if there was in the early-ish days of the Universe that there were mega superclusters of galaxies that picked up some spin when the clusters were much closer. Such motion, as viewed today, might explain some of the peculiar velocities of clusters, the apparent great attractors and possibly even the spins seen in this new study.
This doesn’t mean that all such mega superclusters spin the same way.