[Universe Rotation : Red/Blue Shift]

[hypergreatthing]

can someone explain to me why a universe can't be in a state of rotation, similar to that of planetary bodies in a solar system? It would seem to me with red shifted galaxies and blue shifted ones, we are approaching and departing both at the same time.

[pzkpfw]

Question moved from here: http://www.bautforum.com/showthread....-not-expanding!

(My title, not hypergreatthings'.)

[Hornblower]

can someone explain to me why a universe can't be in a state of rotation, similar to that of planetary bodies in a solar system? It would seem to me with red shifted galaxies and blue shifted ones, we are approaching and departing both at the same time.

No cosmic-scale rotation is needed for this. A few nearby galaxies, such as M31, are moving toward us. Their local irregular motions overwhelm the cosmic expansion tendency which is slight at these relatively short distances. Over truly vast expanses of the cosmos the expansion is dominant, so the overwhelming majority of observable galaxies are receding.

[Jens]

can someone explain to me why a universe can't be in a state of rotation, similar to that of planetary bodies in a solar system? It would seem to me with red shifted galaxies and blue shifted ones, we are approaching and departing both at the same time.

What exactly would you mean by rotation? Rotating around what? A problem with that is that it seems to assume that there is a center to the universe and that everything is rotating around that point. Is that what you are thinking of? And as a clarification, are you thinking of the matter in the universe rotating around a center, or are you thinking of the space itself rotating? These may be important distinctions.

[noncryptic]

It would seem to me with red shifted galaxies and blue shifted ones, we are approaching and departing both at the same time.

There are many more red shifted galaxies than blue shifted galaxies (and they are more red shifted the dimmer/further away they are), so there's a lot more departing than approaching.

[Strange]

As well as the problem of "rotating about what" (and the fact that we don't see a similar number of red and blue shifted galaxies) your suggestion would imply that the universe was rotating but we were stationary (in order for everything to move relative to us). Seems pretty implausible.

[neilzero]

If the universe was shaped like an eliptical galaxy, then rotating would be likely. The part we can see is a sphere with us in the center, and little or no evidence of rotation. We may be considerably off center including the part we can't see, which may have a shape other than spherical, or be without any boundaries as we typically think of boundaries. Neil

[hypergreatthing]

What exactly would you mean by rotation? Rotating around what? A problem with that is that it seems to assume that there is a center to the universe and that everything is rotating around that point. Is that what you are thinking of? And as a clarification, are you thinking of the matter in the universe rotating around a center, or are you thinking of the space itself rotating? These may be important distinctions.

hmm...
Here's my idea and please correct me if i'm wrong.
The big bang created an initial shell, which forms the cosmic background radiation we detect.
Inside of that shell, the first forms of matter which were cooled down nanoseconds (or less) started to condense un-uniformly. These caused matter to form galaxies instead of being uniformly distributed (I'm sure there are many theories on this but lets not get hung up on this part). Gravity from galaxies affect nearby galaxies (as we can see from local galaxies like Andromeda and others who are blue shifted/approaching us). The movement of these galaxies closer to one another has an effect (but at a much lesser amount) to the further galaxies which are attracted to their nearby cousins. A sort of galactic interaction between other galaxies form and they end up rotating around each other in a sort of unstable way (were there are collisions and others are flung out).

So no, it wouldn't be rotation from a conventional standpoint where there's a center and everything rotates around it, it would be more like a complex shell, or more like fluid dynamics where the elements inside the shell rotate around each other.

My other question is would there ever be a state in which the rotation around other galaxies could become stable and rotate around each other? Like a binary star system. Or will expansion eventually lead to collapse?

[Strange]

From http://www.physlink.com/education/askexperts/ae384.cfm

Almost all the galaxies are red shifted; they are moving away from us, due to the Hubble expansion of the Universe. There are a handful of the nearby galaxies that are blue shifted.
...
There are about 100 known galaxies with blueshifts out of the billions of galaxies in the observable universe. Most of these galaxies are in our own local group, and are all in orbit about each other. Most are dwarf galaxies among them include the Andromeda Galaxy, M31, etc.

Which would seem to answer both your questions. Red shift is evidence for the expansion of the universe. Locally, galaxies can orbit and we can see blue shift.