This Board is an educational one, no doubt about it. I’ve learned several things on it over the years, esp. about physics.
Nevertheless, a lot of the argument about “real” vs. “virtual” particles strikes me as more philosophy and verbal sleight-of-hand than reality (an understandable confusion at the quantum level). From this site:
So the particles can’t be observed because if you do so they change the outcome. But if you don’t insist on the outcome being unchanged, and merely observe the situation, and the particles do interact, then you can observe the ouitcome, and say that real particles interacted. So the particles are observable. They don’t obey the energy law because the amount of energy they have violates the energy balance by the amount allowed by the uncertainty relation. But if you observe it after the interaction everything seems to balance perfectly, provided you don’t insist that everything happen the way it would have if the interaction wasn’t observed.
Yes, that’s the whole point. You can change the experiment, but when you do you are no longer attempting to observe virtual particles. You’re now observing real particles. Virtual particles can never be detected.
Particle interactions are described in terms of quantum fields. Virtual particles are a sometimes-convenient way of talking about those fields. They do things real particles can’t do, like traveling faster than light (at times). You can never catch them in the act (unless you add enough energy to promote them to real particles, as Ring said).
