What hold galaxies together?

Only if you are in America!
The rest of the world doesn't give a damn about Thanksgiving.
And we, even in Australia, are being bombarded by Black Friday sales....what blatant and unconscionable commercialism! Pah!

 

It's all that American TV.

-Will

 

No, it is not. Acceleration is a mathematical tool to calculate the effects of gravity.

 

Yes, it is. Acceleration is the measure of the effect of gravity.

 

The SF author James Blish, addressed the issue of gravity & the expanding universe in his "Cities in Flight" series. The final volume "A Clash of Cymbals"postulated that the cosmic expansion would eventually cease.
Cities in Flight - Wikipedia https://en.wikipedia.org/wiki/Cities_in_Flight#A_Clash_of_Cymbals/The_Triumph_of_Time

Below is the final paragraph of another Wikipedia article about the subject.

"Paul Davies considered a scenario in which the Big Crunch happens about 100 billion years from the present. In his model, the contracting universe would evolve roughly like the expanding phase in reverse. First, galaxy clusters, and then galaxies, would merge, and the temperature of the cosmic microwave background (CMB) would begin to rise as CMB photons get blueshifted. Stars would eventually become so close together that they begin to collide with each other. Once the CMB becomes hotter than M-type stars (about 500,000 years before the Big Crunch in Davies' model), they would no longer be able to radiate away their heat and would cook themselves until they evaporate; this continues for successively hotter stars until O-type stars boil away about 100,000 years before the Big Crunch. In the last minutes, the temperature of the universe would be so great that atoms and atomic nuclei would break up and get sucked up into already coalescing black holes. At the time of the Big Crunch, all the matter in the universe would be crushed into an infinitely hot, infinitely dense singularity similar to the Big Bang.[12] The Big Crunch may be followed by another Big Bang, creating a new universe."
Big Crunch - Wikipedia https://en.wikipedia.org/wiki/Big_Crunch

Having turned 80 yesterday, it now occurs to me that most of you are all too young to have immersed yourselves in the SF of the 1940s & 1950s. The SF writers back then, predicted many things we take for granted now. Issac Asimov wrote "The Last Question", which first appeared in the November 1956 issue of Science Fiction Quarterly. I think it was his best work. https://physics.princeton.edu/ph115/LQ.pdf

 

As a fellow fourth quartile centurion ( centarian?), I also was an avid follower of Asimov and his ilk. The genre has gone downhill since Dune.

 

There is maybe Liu Cixin, "The Three Body Problem" ''(2015) , first of a trilogy in the vein of Arthur C.Clark. Since Pierre Bordage, "Warriors of silence" (1994), Liu Cixin is, in my opinion, one of the latest authors who add to the SF's standards, like Asimov in his time.
I've read all the Jules Vernes (several times), about whom it has been said that he had forseen a high number of the XX's technologies. The most famous could be his explanation of the mechanical principle of a rocket that can fly to the moon.

These authors have for certain the ability to dig the roots of our culture and express in some trully fascinating manners our desires for the future.

 

The definition of acceleration is a change of velocity with respect to time. You keep on repeating the same thing as a petulant child instead of providing any well thought argument.

 

No need for ad hominem, it only encourages a return in kind.

-Will

 

You are right.

 

More evidence of a spinning Universe.

Asymmetry Detected in the Distribution of Galaxies | Quanta Magazine https://www.quantamagazine.org/asymmetry-detected-in-the-distribution-of-galaxies-20221205/

At least locally. It's not like anything can spin in both directions at once. Of course, we could have spin on multiple axis (axies, axi?), but one direction at a time.

 

The universe is the universe. How can it be spinning? Relative to what? Something outside of the universe? That's impossible. Items may be spinning within the universe and giving the illusion of a spinning universe but that is only an illusion.

 

Everything spins around the sun?

Or everything is spinning around our galactic center?

Or Something was trying to diffuse the Big Bang when it went off?

Progress!

 

I used to sit in on Asimov’s lectures at MIT on occasion, and rather liked his idea of psychohistory, so much that I included it’s precepts in a final in Bernard Bailyn’s course on Early American History at dear old Harvard. Bailyn promptly flunked me. Weeping bitter tears, I appeared at Bailyn’s office to beseech him the answer to ‘why’?

So Bailyn hears me out, picks up the phone, calls Asimov, and basically cusses him out, telling him to leave his (Bailyn’s) undergraduate students the **** alone, because it wasn’t history. I wasn’t quite sure of all what Asimov said, but it was loud, and included the phrase ‘get your head out of your ***’ and look what’s going on at Berkeley’. Bailyn slams the phone down, looks at me in the eye, and says, ‘ “you took your chances and got what you deserved.” I was pretty shaken up, and wobbled out of his office, certain that my future was dark indeed. Luckily, it was a pass/fail course, and didn’t mess with my rank.

Later I discovered Greenblatt’s work on Self Fashioning during Shakespeare’s era, and understood a bit of what was going on in academia in the early 70’s, which, as much as I loved academia, started jettisoning me on to other things.

As much as I liked Asimov, there was a resurgence of SciFi during the late 80’s on that has been remarkable, ‘The Three Body Problem’ (thanks, Alan) being a fairly recent bright light. Cyberpunk, Gibson, Chiang, Egan (from your neck of the woods), Hamilton, Stross, Kress, and many others have done amazing work, at least the equal of Asimov’s Nightvision, which is my favorite of his. As far as MIT is concerned ‘The Forever War’ from 1974 (although I think it presaged the 90’s) is burned my brain. If you haven’t already, I’d suggest short story anthologies, which seem to be the center of SciFi right now.

 

Not so. Angular motion (spinning) is the one, non-relative motion, because it is in constant acceleration and it makes no difference as to how that acceleration is applied to the body in motion. It will always be perceptible.

Think about it. Imagine two rings of a space station with astronauts inside, turning one ring against the other. If the two rings rotate equally, one clockwise, the other counter-clockwise. Both astronauts will feel an equal force from the power wall holding them against the rim. They will watch the other astronaut pass them at twice their rotational speed, but the centripetal force the experience will only be felt as if each astronaut was only traveling at half the angular velocity (their actual rate of rotation).

If, one were to stop one of the rings from spinning, but allow the other ring to continue, relative to the other ring, the two astronauts would experience very different result even if the saw no change in their relative velocities. The astronaut in the stopped ring would lose all force pressing against the outer rim, while the other astronaut would find that force had doubled. Their relative motion to the other ring would make no difference to their absolute rotation. It wouldn't matter if the universe were spinning around them. The force the would experience is going to be completely dependent upon an absolute rate of rotation relative to nothing.

If the universe were spinning, even an imperceptibly slow one, it could conceivably have a very perceptible affect on the rotation of other things within it, but it would not change the sense of force provided by centripetal force.