The physical meaning of expansion in cosmology

[zankaon]

The "space that expands" is that described by the FRW metric - yes it does require a smattering of GR and also the interpretation of the observation of Hubble red shift, marcus has clearly defined it and distinguished it from 'ordinary space'.

Garth

Perhaps one simplistic model, might be to think of a manifold (i.e. continuum) being stretched uniformly for a given stage of universe (i.e. for given value of Hubble parameter). Then concomitantly (i.e. for given value of Hubble parameter), one also has local depressions forming (i.e. indentations i.e. curvature), representing local gravitational aggregation.

 

[oldman]

Such as "cosmological space"??

Garth

Yes. This is well defined. Just 'space' --- so often used --- is much too vague for informed discussions.

 

[Hurkyl]

This post is admittedly vague---it is merely meant to convey my attitude about GR. Briefly, my attitude is don't live in a straight-jacket of Greek expectations about geometry.

I feel I should point out that even the Greeks were capable of imagining non-Euclidean phenomena; e.g. that a pair of lines, in defiance of the Parallel postulate, could be in a situation where the interior angles add up to less than 180°, but the lines merely tended towards each other indefinitely without crossing. And, of course, they had all those lively debates about our notions of space.