I must admit that i've always been confused by virtual particles. Are virtual particles "real"? Is the notion of virtual particles scientific? I am most certainly way off here but here are some questions I have:
1. What foundation is there for speaking about virtual particles? That is, in quantum field theory/second quantization states are equipped with creation/annihilation operators, however these creation/annihilation operators don't exist in relation to the internal lines of feynman diagrams, so what is the underlying formalism ?
2. In what sense can the intermediate terms of a series be said to be "real"? One needs to renormalize just to get an actual physical quantity to be measured at which point the terms corresponding to these supposed "virtual particles" no longer exist, no?
3. According to this thread non-perturbative approaches to qft such as lattice gauge theory don't give rise to virtual particles. Why do physicists say that these virtual particles have an independent existence if they can only be spoken about if one is using a perturbative approach to calculating scattering?
4. If virtual particles can come into existence due to the uncertainty principle(leaving aside the question as to whether time can be introduced as an operator in quantum mechanics and the fact that there is a ground state) then they are by definition not observable/measurable, in which case how can descriptions of them be scientific?
I have a few other questions about virtual particles but these are the ones i'm having the most difficulty understanding.
Hi!
ReplyDeleteI think this post paints a nice picture of what's going on https://profmattstrassler.com/.../virtual-particles-what.../
Me, I usually just think of them as the internal lines of the Feynman diagram expansion of the S matrix elements. It's perturbation theory anyway, so I tend not to worry if my interpretation of each term is not that solid.
I recommend this intro to QFT http://physics.ucsd.edu/~mcgreevy/s14/239a-lectures.pdf if you're ready to jump in. (It shows my bias towards condensed matter theory)
Thank you for the comment. Prof. Strassler's explanation and the following comments were very enlightening. It seems part of the difficulty about this topic is that there are so many varying opinions; I tend to resort to just considering them as metaphorical.
ReplyDeleteThank you also for the link to those lectures, I will certainly take a look at them.