I'm an engineer and I've never studied particle physics, but I like it, and I like to see Feynman diagrams and try to understand as much as I can. Looking for a Feyman diagram involving the Higgs boson, I found the following picture which can be found in this pdf file https://cds.cern.ch/record/2759490/files/Feynman%20Diagrams%20-%20ATLAS%20Cheat%20Sheet.pdf):

enter image description here

According to what I understand (of course, I may be wrong), the interaction between the two gluons in the left side is performed by exchanging a virtual top quark, and this top quark disintegrates into a top-antitop pair (also virtual). What I don't understand is how this top-antitop pair is generated at the same time from two different locations and from the same particle. Can anyone explain this to me? Understand that I don't have any background in particle physics, all I know is what I have learnt in Internet.

Something I have thought about this is that the first virtual top is travelling vertically, so it does not spend time in arriving from one gluon to the other, so this may explain how the top-antitop is generated at the same time from two different locations.

  • $\begingroup$ Careful, you're going to summon a horde of commenters with very strong opinions on whether virtual particles are to be interpreted as actual particles or not (most commenters on this site are very fundamentalist on the POV that they're not) $\endgroup$ Apr 21, 2023 at 7:01
  • $\begingroup$ @AwkwardWhale What's wrong with telling him that he can find "virtual states" already in non-relativistic quantum mechanics? He can decide for himself whether these mathematical terms in perturbation theory are physically real in his mind or not. In my mind not even "real particles" exist. There are only reversible and irreversible processes and the reversible ones can often be written in terms of virtual states. Not even that is correct in all generality if I understand the theory correctly. There are plenty of phenomena that require non-perturbative calculations, aren't there? $\endgroup$ Apr 21, 2023 at 7:11
  • $\begingroup$ I think the decide for yourself part is important here, imo questions like "are virtual particles real" are purely philosophical and therefore largely a matter of opinion. $\endgroup$ Apr 21, 2023 at 7:20
  • $\begingroup$ On virtual particles & Feynman diagrams: physics.stackexchange.com/a/275099/123208 $\endgroup$
    – PM 2Ring
    Apr 21, 2023 at 7:43
  • $\begingroup$ @AwkwardWhale Are imaginary numbers real? :) $\endgroup$
    – Avantgarde
    Apr 21, 2023 at 8:07

1 Answer 1


Feynman diagrams are meant to be pictorial shorthand for integrals. Those positions are chosen for artistic beauty. After the diagrams are converted back into integrals, those positions are integrated over all spacetime. i.e. a particle is integrated both propagating forwards and backwards. "Different place at the same time" is a special case

The top quark is really just going in a loop, a part of the trajectory thus needs to be going backwards in time. You can think of it as being punched by an interaction so hard that it went backwards in time, which is what we interpret as the anti-top.


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