johnnymckiernan

You are correct(in my opinion).The photon has a very definate energy (for the laser E=hc/lambda.....lambda is very precisely known(same with c). but dE*dt >h.......By Heisenberg so dt, the time for transition, is large. It is not absorbed in an instant but over a minimum time given above (if it encounters another He atom). Photons a readily absorbed by matter. If the photon has the same energy as a transition excited state of an atom then the photon will be absorbed.The speed of the electron in the atom is a few percent of c from the 1st Heisenberg Eqn viz dx*Dp>h Where dx is the diameter of the atom.kinetic energy=p^2/2*m where m=10^-30kg for the electron. This means that the speed of the electron is not precisely know nor its direction within an atom.In such cases it is better to assign a probability distribution to it.

Yes, a photon has a physical size. It carries a tiny amount of energy but that doesnt mean it's tiny. A laser has a very well defined wavelength,lambda;(633nm).It ,therefore, has a very well defined momentum,p=h/lamda.h=Plank's constant=6.6*10^-34Js. Dp*Dx>h from Heisenberg So Dx = 0.2m i.e about 20cm (..... the diameter of the beam is about 2mm) How big is a photon? Answer: I make it about 20cm long for a laser.