The Virtue of Being Virtual
The photon that left your computer screen and just hit your retina now certainly was a ‘real’ photon. Right? Well, not so fast. Sketch the Feynman diagram for the process. The photon was emitted by an atom in the screen, and absorbed by an atom in your retina. The diagram is indistinguishable from that for a virtual process- it’s all a matter of scale. (more…)