I am currently learning QFT and there is always a question to haunt me.
As I know, virtual particles represent those propagators in the Feynman diagram which could be off-shell. My understanding is that, the concept of virtual particles is artificially given by theoretical physicist to describe physical processes more visually.
My question is that, does it mean that though we are using the description like exchange virtual particle to describe the interaction process, currently we do not know what is actually happening when interaction happened in QFT. Even though the result by using Feynman rule is consistent with experiment data, maybe what we have is just a black box and the actual nature is still unknown.
If you are not clear about what I mean. The comments below could help you to better understand.