This is related to another question I asked. Might we actually be observing dark energy when we do experiments that verify the Casimir effect?
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asked Oct 4, 2015 at 18:03
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There are two problems that arise here. One obvious problem is that the Casimir effect is attractive1, while dark energy is repulsive. The other problem is one of scale.
Casimir (1948) shows that, between two particles (instead of the oft-cited case of two plates) $$\delta E \propto R^{-7}$$ That's an enormous drop-off. On large scales, this should be negligible. Dark energy, however, is clearly non-negligible on these scales, while its effects are unobservable on small scales.
The Casimir effect is certainly one manifestation of vacuum energy, which may also be the cause of dark energy (in some theories), but that doesn't mean that dark energy is an example of the Casimir effect, or vice versa.
1 There are exceptions, as pointed out by Stan Liou, which arise under certain conditions, but they wouldn't play a part here.
answered Oct 4, 2015 at 18:55
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2$\begingroup$ Casimir force can be repulsive (Casimir-Lifshitz in that case), but yeah, fundamentally it's a van der Waals force between polarizable things with electric charge, so linking it to dark energy is dubious from the start. Moreover, only energy differences are measurable in QED, so no measurement of the Casimir effect (nor any QED effect) could detect an an absolute energy density of the set by gravity. $\endgroup$ Oct 4, 2015 at 19:27
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$\begingroup$ @StanLiou Thanks for the mentioning the first point; I should add that in. I had considered mentioning in the can der Waals connection, especially as it features prominently in Casimir's original derivation, but I figured that might complicated the answer a bit much. $\endgroup$– HDE 226868 ♦Oct 4, 2015 at 19:31