Exchange
Particles
When
interaction between particles occurs there is a change in the energy state
of each particle eg. one gains energy the other loses it. We know that
mass and energy are interchangeable, we can therefore consider an 'exchange
particle' going from one to the other.
When we detect a particle
it interacts with our detector! Therefore if we detected the exchange
particle it would not be acting as an exchange particle any more but have
come out of the system..that is why we can call exchange particles virtual..if
they did more than exchange energy/mass/charge they would not be exchange particles
at all.
Click here to see an animation of this.