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There is many ways to think about virtual particles. From a particle point of view one can think of it as quantum mechanics allowing you to create a high energy

There is many ways to think about virtual particles. From a particle point of view one can think of it as quantum mechanics allowing you to create a high energy particle for a short amount of time, even if that would not be allowed classically. From a field theory point of view, you can have excitations in the fields that are not sufficient to be a particle, but can still interact locally.

gpsx 10y ago
I was looking for an explanation of why the lines of a Feynman diagram are called virtual particles when they are really particles in the unperterbed (or free) model. So why do you think of this as creation of a particle for a short amount of time?
- KenoFischer 10y ago
  Generally if you look at the Feynman diagram for an interaction, you'll have some number of external legs which one thinks of as physical particles, as well as a number of interactions. The lines between the interactions may be particles whose mass exceeds the total amount of energy of the incoming particles, so they obviously can't be real. They are thus generally called virtual (or off-shell particles). How one can think of this is what I tried to address in the original response.
  - gpsx 10y ago
    I appreciate you saying the external legs can be thought of as physical particles, since they are not technically physical particles. The renormalization groups tells us that those look like physical particles. Internally to the interaction this is not true, which is why they would be called virtual particles. But I see them as a pure mathematical relic of the perturbation calculation. Perhaps I am just not able to extend my intuition here. And likely a more depth description from you or someone else is not really practical here. I just come back to the fact that in the end, particles are just different excitation states of the system. There is a vacuum state, a bunch of states we would consider one particle states, a bunch more we would consider two particle state, and so on. Doesn't this cover all configurations of the system and there are no "in-between" or what you would call off-shell states? I think these only make sense when we are making an approximation around the non-interactive model.

gpsx 10y ago

I was looking for an explanation of why the lines of a Feynman diagram are called virtual particles when they are really particles in the unperterbed (or free) model. So why do you think of this as creation of a particle for a short amount of time?

KenoFischer 10y ago
Generally if you look at the Feynman diagram for an interaction, you'll have some number of external legs which one thinks of as physical particles, as well as a number of interactions. The lines between the interactions may be particles whose mass exceeds the total amount of energy of the incoming particles, so they obviously can't be real. They are thus generally called virtual (or off-shell particles). How one can think of this is what I tried to address in the original response.
- gpsx 10y ago
  I appreciate you saying the external legs can be thought of as physical particles, since they are not technically physical particles. The renormalization groups tells us that those look like physical particles. Internally to the interaction this is not true, which is why they would be called virtual particles. But I see them as a pure mathematical relic of the perturbation calculation. Perhaps I am just not able to extend my intuition here. And likely a more depth description from you or someone else is not really practical here. I just come back to the fact that in the end, particles are just different excitation states of the system. There is a vacuum state, a bunch of states we would consider one particle states, a bunch more we would consider two particle state, and so on. Doesn't this cover all configurations of the system and there are no "in-between" or what you would call off-shell states? I think these only make sense when we are making an approximation around the non-interactive model.