Liz, I don't know how you are getting so sidetracked here. p. 718 clearly applies to the areas of the universe that are NOT homogeneous. Otherwise there wouldn't be any of the effect they are describing...
While the universe may be roughly homogeneous at the largest scales, it most certainly is NOT homogeneous at galactic scales which is the scale of dark matter effects. Edgar On Thursday, January 23, 2014 5:03:23 PM UTC-5, Liz R wrote: > > On 24 January 2014 02:34, Edgar L. Owen <[email protected] <javascript:>>wrote: > >> Liz, >> >> Close but not quite correct. It's not a matter of whether the universe is >> isotropic or homogeneous that's important, its what its local mass energy >> content is that determines whether that locality expands with the Hubble >> expansion or not. >> > > If it's homogeneous and isotropic, the "local mass energy content" is > identical at all points in space. So there is nothing to make one region > behave differently from any other region, indeed there are no "regions" - > the universe would in this case contain a uniform, idealised gas (in which > the only bound systems were atoms, hence my caveat to that effect). I > believe on p718 M, W & T were dealing with this idealised case, but I don't > have my copy of "Gravitation" with me at work, so I can't be sure. I'd be > surprised if they weren't, however, most solutions to GR make this > assumption (except when they're dealing with gravitational collapse, in > which case they generally assume a uniform sphere). > > > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
