In a recent question on superpositions of different quarks it was explained, that the superpositions of different electric charged particles cannot exist, in contrast to strangeness quantum number. It was reasoned that this is because of decoherence that comes from the QED vacuum - the photon interacts ("measures") with charged particles -> thus their charge is known -> destroys decoherence.

But of course, double slit experiments with single electrons have been performed already in the 70s.

My questions:

Why do virtual photons not cause decoherence of the spatial coherence of single electrons?

If they would cause decoherence, it would result in reduction of the contrast in single electron double-slit experiments.

  • $\begingroup$ Virtual photons are mathematical, not physical objects (and real photons aren't physical objects, either, they are properties). That electric charge is conserved is a symmetry property and does not depend on measurement. Why nature should care about some folks making tiny slits into metal foils is philosophically as questionable as it's physically irrelevant. $\endgroup$
    – CuriousOne
    Jun 11 '16 at 20:05
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    $\begingroup$ @CuriousOne Your comment on virtual photons seem to ignore things like Casimir effect, Zitterbewegung etcetcetc. Your second sentence, thanks - that was indeed misleading, which I corrected now. Your 3rd sentense seem very dubious, you say that the electron-double-slit experiment is physically irrelevant (even though it has been elected as "the most beautiful experiment" in physics?). I guess/hope i misinterpret what you are saying, could you please clarify? And why did you downvote? $\endgroup$ Jun 11 '16 at 20:23
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    $\begingroup$ It may be worth noting that the usual electron one experiments with (i.e. the one that has a mass of $m_e \approx 511\,\mathrm{keV/c^2} \approx 9.11 \times 10^{-31}\,\mathrm{kg}$ and a g-factor of $−2.00231930436182 \pm 0.00000000000052$) is 'dressed'. That is, it already has the effects of the QED vacuum folded in. No one has even gotten to play with the hypothetical, pristine, unicorn-attracting, 'bare' electron. $\endgroup$ Jun 11 '16 at 21:35
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    $\begingroup$ @NiceDean These two answers are both connected to your question. Also read the comments on the first one. $\endgroup$ Jun 12 '16 at 14:01
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    $\begingroup$ Who are the people who vote to close a question like this? There seems to be a cohort on this site, whose response to a question with slightly mistaken premises, is to just close the question! It's the only way I can understand some of the closures that occur. $\endgroup$ Jun 12 '16 at 19:43

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