Let's say I have an electron traveling alone in the vacuum, when a vacuum disturbance (fluctuation) occurs nearby. If the disturbance has the correct form, say, an electron-position pair, could the positron annihilate with the original electron? (leaving the remaining electron) The positron would have to have negative mass to ensure conservation of mass/energy.

So, the overall question, could something like the above occur? I've been careful to specifically stay away from the term virtual particle.


1 Answer 1


Yes, the "virtual" positron will annihilate with the original electron, leaving the remaining electron. This permanently occurs, and thus has to be accounting for when summing all possible events occuring between target initial and final states. See also Feynman diagrams , and possibly, renormalization . (Indeed, "virtual" is a bad name for these particles).

  • $\begingroup$ "particle" is also a bad name for "virtual particles" because these things only happen in the mathematics of perturbation series. Just like an exponential function is NOT the same thing as its Taylor series (not even for the mathematicians), the perturbative expansion of a physical process is NOT the same thing as the process itself. Even Feynman has pointed this out to prevent people from believing in the "reality" of Feynman diagrams. $\endgroup$
    – CuriousOne
    Oct 25, 2015 at 15:46
  • $\begingroup$ Yep. But field theory is kind of a big cake to eat ;-) . BTW you could say the same thing for any "real" particle, isn't it ? Wouldn't you say that (at least far from high energy) the particle interpretation is a working one (giving right intuitions and calculus - up to the usual limits of duality of course). Casimir effect, vacuum polarisation effects, Hawking radiation, even the concept of Fermi sea or accurate interation with atom nucleus, I guess all these don't consider it would be invalid to think in term of particles (including virtuals), is it ? $\endgroup$ Oct 25, 2015 at 16:42
  • $\begingroup$ I am saying the same thing about real particles. There is plenty of evidence that they don't "exist" as physical objects. "Particles" are completely indistinguishable, their number varies and it is, in many cases, not even defined. That's not a good start for something that supposedly "exists" in some philosophically well defined sense. What does exist is ONE field (or, depending on the description we chose, a number of distinguishable fields) which interact(s) exclusively by exchange of quanta, which are well defined, but only as configuration changes of one object. That works all the time. $\endgroup$
    – CuriousOne
    Oct 25, 2015 at 19:14
  • $\begingroup$ I would say science is not about ontology (let this to philosophs :-) ), but about proposing models that account for facts given a context made of a range of questions and configurations. Classical mecanics is a very useful model for plenty of situations, then more convenient to manipulate and understand than quantum or relativistic. I think it's the same about particles. It is just important to keep in mind that all these are models, ie, with limits of validity. The mind needs projections to learn and manipulate. Let start first by easy ones, especially when they have some range of validity. $\endgroup$ Oct 25, 2015 at 21:49
  • $\begingroup$ For the same reason, I guess it's better to teach integers first for pupil math classes, then floats to teenagers and adults (if only they could use them...) rather than to start directly with Lie groups :-D $\endgroup$ Oct 25, 2015 at 21:53

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