🚀 go-pugleaf

I'm cross-posting to sci.astro in the hope that some cosmologist who's
more up-to-date on the current literature can help out.  The question
being discussed in sci.physics --- surely a FAQ somewhere ---  is 
whether a small gravitationally bound system experiences the expansion 
of the universe.

In article <Sep.29.16.54.08.1992.28530@ruhets.rutgers.edu> bweiner@ruhets.rutgers.edu (Benjamin Weiner) writes:
>ynecgan@cid.aes.doe.CA writes:
>[...]
>I think a usual rule of thumb is that if a system is [in the Newtonian
>gravitational approximation] gravitationally bound, it's not
>correct to apply the simple expansion-of-space rule to it.

I've heard this rule of thumb, but my impression is that there are still
some open questions.  My reference is Ellis and Stoeger, "The 'fitting
problem' in cosmology" (Class. Quantum Gravity 4 (1987) 1697).  The
problem their title refers to is that of fitting together a small scale,
"lumpy" solution of the field equations of general relativity and a
large scale, smooth cosmological solution.  The have a section that
specifically discusses the effect of cosmological expansion on local
physics, and basically answer, "we don't know."  (In their approximation,
there is an effect, but they cite other authors with different
approximations and different results.)  The issue is confusing because
you have to separate out real physics from coordinate-dependent effects,
but there are certainly invariant questions that can be asked (e.g., do
circular orbits close?)

My reference is five years old, though, and I imagine there has been more
recent work.  I know that Ellis and Stoeger have written papers on their
program since then, but it's outside my field, and I haven't kept up.
Does anyone have more recent results?

Steve Carlip
carlip@dirac.ucdavis.edu