Ben Crowell's answer contained a very good estimate of the order of magnitude of the stress on bone. From the comments and answers, I gathered that the effect of inflation on bound quantum systems (like the hydrogen atom) was the underlying basis of my question. I did some more hunting around and discovered many astronomers and physicists (like Schrodinger) have pondered this question in the past. I found 2 interesting papers on the topic:

http://arxiv.org/pdf/astro-ph/0411299.pdf (which mainly discusses the loss of energy in bound quantum systems)

http://link.springer.com/content/pdf/10.1007%2FBF02721588.pdf (which mainly discusses the Dirac equation in the FLRW metric, although a few assumptions have been taken in some places)

I would like to quote some sections of the first paper:

**Assumption A:**
*"that metric expansion
proceeds at all gravitationally
classical scale lengths — is not contradicted by available physical evidence, and it is consistent
with the standard general relativistic interpretation of the metric."*

I believe the above applies to anything above Planck Length scales.

**Assumption B:**
*"That bound systems contract in the comoving frame to counter
the expansion
of space follows naturally from assumption (A) and is consistent with observational evidence
such as the recent investigations of the value of the fine structure constant in distant galaxies
[10]. The contraction of bound systems (such as hydrogen atoms) proceeds in such a way that
fundamental energy levels of quantum systems are unchanged over measurable time-averaged
periods. Thus, the energy structure of the systems appears unaffected, in agreement with observation
fundamental energy levels of quantum systems are unchanged over measurable time-averaged
periods. Thus, the energy structure of the systems appears unaffected, in agreement with observation"*

**Assumption C:** *"In contrast to classical systems, quantum systems radiate energy intermittently and discontinuously, and they do not exhibit inertial follow-through
. As a result, unlike classical systems,
we posit that they can follow the expansion of the comoving metric during time intervals be-
tween radiating (Assumption A). If they expand along with the comoving metric between emission, but intermittently collapse back to their original fix
ed proper sizes, then they should emit
MCE, analogously to classical systems (
e.g.
, gas clouds) and more typical quantum systems
(
e.g.
, hydrogen atoms). We emphasize that quantum MCE emission is
not due to change in
quantum number, but is due to change in spatial scale only. Emission should continue as long
as they are embedded in an expanding spacetime metric, but emission rate clearly depends on
the metric expansion rate [12]. Assumption C is consistent with the standard physical interpretation of energy release by classical and quantum systems. I
t presumes, of course, the validity
of Assumptions A and B."*

The paper claims that there is evidence in favor of this MCE and the assumptions. One could say, in a sense, that there is an effect on quantum bound systems on the atomic scale and above, but it is **REALLY** tiny. However John Rennie has pointed out that if a Big Rip like event occurred, these bound states might certainly destabilize, thus shattering bone.

This post imported from StackExchange Physics at 2014-05-08 05:11 (UCT), posted by SE-user dj_mummy