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There are many discussions on this site about the nature and reality of vacuum fluctuations. The general consensus seems to be that this it falls into the Lie-to-Laymen category. On the other hand, there are simulations like the ones by Derek Leinweber that visualize the nontrivial QCD ground state structure, which he explains as follows

Contrary to the concept of an empty vacuum, QCD induces chromo-electric and chromo-magnetic fields throughout space-time in its lowest energy state. After a few sweeps of smoothing the gluon field (50 sweeps of APE smearing), a lumpy structure reminiscent of a lava lamp is revealed. (The animation was featured in Prof. Frank Wilczek's 2004 Nobel Prize Lecture.)

enter image description here

This clearly seems to suggest that some kind of fluctuation is going on. While it's certainly problematic to speak of particle-antiparticle pairs that pop in and out of existence, I'm wondering if there is nevertheless at least some truth to the fluctuating ground state picture?

jak
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  • I can't speak for others, but I find frantic animations in the middle of text to be very distracting, with the invariable result that I don't bother reading it. – D. Halsey Nov 21 '19 at 14:31
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    I like the frantic animation for what it's worth. Do you know what a path integral is? That's what's going on behind the animation – octonion Nov 21 '19 at 14:44
  • @octonion yes, of course! – jak Nov 21 '19 at 14:50
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    I think that it is simpler to consider QED to speak about vacuum fluctuations. For me, screening of electric charge due to the vacuum polarization and corrections to Coulomb law is pretty well description of vacuum fluctuations. In addition, fo course, Casimir effect. Then, you can try to read about Unruh effect & Sokolov-Ternov effect. It seems that they are close to vacuum fluctuations. I just emphasize that QCD vacuum is much more complicated. – Artem Alexandrov Nov 24 '19 at 10:33
  • The frantic animation is ok, as long as you don't forget that a vacuum state is stationary. – PM 2Ring Nov 24 '19 at 14:11
  • @PM2Ring Can you elaborate or provide a reference? Moreover, as far as I understand it stationary does not mean that there are no fluctuations, right? – jak Nov 24 '19 at 14:34
  • Yes, there are fluctuations. However, as the Wikipedia link says: "[...] the system remains in the same state as time elapses, in every observable way. [...] The wavefunction itself is not stationary: It continually changes its overall complex phase factor, so as to form a standing wave. [...] However, all observable properties of the state are in fact constant in time." Also see https://en.wikipedia.org/wiki/Quantum_fluctuation but unfortunately that article does not stress that a vacuum state is stationary. – PM 2Ring Nov 24 '19 at 14:53
  • @PM2Ring Thanks! This is an extremely subtle terrain. If we measure the field value in the ground state at three different times, we measure, in general, three different values. This is what a nonzero VEV, for example, means. But of course, the state is in any case the ground state which is stationary although it fluctuates. – jak Nov 24 '19 at 15:24
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    Well yes, it is subtle. And it tends to get mangled a bit when we try to express it in words, rather than in mathematics. ;) – PM 2Ring Nov 24 '19 at 15:29
  • @PM2Ring It looks like you should make an answer. – BioPhysicist Nov 24 '19 at 17:32
  • @Aaron I was hoping someone with a bit more expertise in the topic would write a proper answer. I just quoted some stuff off Wikipedia... – PM 2Ring Nov 24 '19 at 18:02

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