A proton and a neutron interact via the strong nuclear force. Their interaction is mediated by a meson, much like the interaction between charged particles is mediated by photons-the particles ol the electromagnetic field.
a) Perform a rough estimate of the mass of the meson from the uncertainty principle and the known dimensions of a nucleus (~10-15 m). Assume that the meson travels at relativistic speed.
b) Use a line of reasoning similar to that in part (a) to prove that the theoretically expected rest mass of the photon is zero.