If you had a 2-sphere universe, would things flying around on the 2D surface cause a forcing outwards on this hyperthetical universe? ie would it expand, if things were moving around in it?

I just wondered, if this could apply to a hypersphere.

I thought that it would be an interesting explination, but with the 2D model, the objects would have zero mass in the 3D world, so maybe there would be no Centrifugal force.

Why would they have zero mass?.
Your centrifugal force idea sounds right to me.

Can either of you show us, in some mathematical detail, how such an idea compares with the standard model?

You are just making work for us.
YOU show us the mathematical detail of the standard model.
Not much work for you ,just copy and paste what you think is relevant.
Will it explain anything in the real world?.
Can it explain my centrifugal spin drier?.

Are you thinking of something like marbles on a turntable?
When the turntable spins the marbles fly outward with ever increasing velocity each experiencing more acceleration the further it is from the center.
Your question of weather a 2D object could have mass is irrelevant as it is the space-time which is moving so in fact though they occupy no volume they still have a presence and should therefore be affected.

Isn't rotation inherently non-isotropic? (And, yes, a hypersphere is a topological oddity, but even so I would have thought that a cosmological rotation implied some sort of distinguishable direction.)

well, it wouldn't be the balloon(or hypersphere) that was spinning, imagine lots of cars moving around on the inside of the balloon; that would force it to expand wouldn't it?

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Like the motorbikes inside the "globe of death" at the funfair.If they stick to the walls even upside down then the force acting away from the center must be more than 1 G.That is plenty to expand the walls if they were not made of steel.
A million tiny motorbikes moving at random inside an elastic globe would make the globe expand more or less evenly.Each would also make its own dent under its wheels into which others may move because of the dent.They would appear to attract each other.(does that sound familiar).

What does "hyperthetical" mean? Is it "hypothetical," or "hyper-somethingotherical?"

hypothetical.

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Then I'd have to ask more about your hypothetical 2-sphere universe.

Decided to remove this post until a Moderator gives a nod to the draft.
But I think it is an interesting idea; perhaps an SO4 rotation non-passive.

The Nod:

This ties in with my ATM idea here.

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"You can't talk to a brick wall but you can do Graffiti"

Are you proposing that our universe is imbedded in, and spinning in, a 4-space? And this causes the expansion of the universe? If so, an interesting idea, but not a Q&A subject. As an ATM idea, though, it would be fun to pick apart (there's no evidence of other dimensions, the expansion doesn't take place in bound systems, the rotation would be detectable, and on and on . . . ).

Regards, John M.

If the universe is finite (who knows?), then, spacially, it's surely going be a "finite but unbounded" manifold, locally three dimensional. S3 (the hypersphere) is a strong candidate (but I suppose a hypertorus, a projective space, and some other oddities cannot be ruled out).

S3 is special, and (I'm guessing) could perhaps "rotate" along a set of Clifford parallels without the axis of rotation that an S2 sphere (or for that matter a simple infinite Euclidian three dimensional space) would entail.

And what if this 'bound' system is made of plasticine? Bound at any instant but not bound in time? As for anisotropy if we try to think in 4D and we have the axis of rotation approximate to the time axis then as we look towards the axis (look into the past) we see part of some smaller 'revolutions' (a smaller universe, or denser) and as we look further and further away from the axis (towards the present) we see a larger radius to the 'revolutions' (a larger or less dense universe). I mean like the view of the angular speed we would get if we were inside a hollow Earth and looking from one of the poles to the equator.

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"You can't talk to a brick wall but you can do Graffiti"

'Bound' here refers to gravitationally bound systems, which extend out to galaxy cluster size. Due to GR costraints, the expansion of the universe does not occur in such bound systems.

Expansion is only in the 'empty' spaces . . . now isn't that something to think about!

Regards, John M.

What- That the expansion is phenomenally wimpier than the wimpiest of forces?

the rotation would be detectable, and on and on . . . ).

Yes but on what time scale?.
Earth rotation can be detected by gyroscope or pendulum in a few hours,taking a few percent of a rotation.The same thing for the universe may take 10^6 years.

A STILL picture of the Earth (from space) shows clouds moving in vortexes
due to the corriolis effect.Earth spin is confirmed ,direction can be worked out simply.
A STILL picture of the universe may show corriolis effects if we look in the right direction.
I say STILL picture because a 10^6 year movie would be very expensive , boring and not needed.
I want to know NOW.