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In "The Great Soviet Encyclopedia", 3rd Edition from 1970-1979, (evidently an old book), some V. I. Grigor’ev has a well-written little note on microcausality. Towards the end he states an experimental bound on the vialotation of microcausality. According to that ancient encyclopedia article, if such violation occurs at all then it must be on scales smaller than $10^{-15} cm$.

I don't see a citation for that number in his text (I don't have the original book in my hand though, to be frank) and I am wondering which experiment Grigor’ev might have been thinking of.

And: if there are decent such experiments indeed, then probably there are more recent numbers on whatever that experiment actually measured.

My question is if anyone might be able to help me with finding whatever useful there might be to say about experimental bounds of the kind Grigor’ev seems to be referring to, or anything similar.

Maybe I should say that I am not trying to find such violations. Rather, I am in some discussion with some mathematicians interested in axiomatic QFT, and I'd find it entertaining to be able to accompany the statement of the microcausality axiom (or a similar axiom) with something substantial that has the word "experiment" in it.

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    $\begingroup$ This is very interesting, I am curious to see answers too :-). BTW maybe you are interested in this too? $\endgroup$
    – Dilaton
    Commented Aug 22, 2013 at 9:07
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    $\begingroup$ Referring specifically to QED, he gives the time scale $10^{-25}$ s, which corresponds to an energy of about 40 GeV. He may simply be saying that at that time, QED had been tested up to that energy scale. Any violation of microcausality would presumably cause some kind of disagreement with the predictions of QED, which assumes microcausality. $\endgroup$
    – user4552
    Commented Aug 22, 2013 at 14:08
  • $\begingroup$ I found this little old paper, but don't know if it is really relevant (maybe references given at the end?) $\endgroup$
    – Trimok
    Commented Aug 22, 2013 at 15:52
  • $\begingroup$ @Ben, that's of course a good point. Somehow I was hoping for something fancier, but I guess you must be right. $\endgroup$
    – Urs Schreiber
    Commented Aug 22, 2013 at 22:30

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The text you refer to is vintage but not ancient as there are many who still remember their own work from those times. As far as I know the experimental data you seek was not the result of a laboratory experiment specifically designed to test the limits of microcausality but were rigorous thought experiments using the physical data and mathematics available at the time. As no violations could be found, predicted or inferred within the precision of data at the time, it was concluded any violation must be on scales smaller than $10^{−15}$ cm. You need not, however, feel bound by these vintage results as we no doubt have better tools and ideas to address the question now.

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