How did I lose my passport? I apparently leave it in a photocopy machine. I tried
to copy it yesterday. Because of this, I had to postpone my trip.
Well, if photon has energy (E=hf, as you said), then the fact that it is massless
perhaps because its mass is converted into energy. But, do photon really have
energy? How to measure its energy? To measure energy is not as simple as
to measure mass.
Oops... it safe though, to get your passport back i mean? That's a real bitch!
The idea that energy has an energy, derives from the work of Newton (i think). For a photon to have a work, there must be some kind of energy attributed to it for it to do work. Even a potential to do work, must have a potential energy for it to do work.