On Sat, Oct 13, 2012 at 12:05 PM, James Cloos <cloos@jhcloos.com> wrote:
"MS" == Mike Stay <metaweta@gmail.com> writes:
MS> E = mc^2 only holds for objects at rest. The more general statement is MS> E^2 = (mc^2)^2 + (pc)^2
But momentum is mass * velocity, so cannot be +ve if mass == 0, so a
Only for non-relativistic particles.
massless particle is still energy-less. And all photons have energy.
The energy of a photon is given by E = hf, where h is Planck's constant and f is the frequency.
(Or is there a concept of non-finite wavelenght?)
No.
Put another way, since velocity increases the mass-energy of a particle, a photon would have to have zero mass-energy at rest also to have it at any non-zero speed, including at c.
There is no rest frame for a photon. -- Mike Stay - metaweta@gmail.com http://www.cs.auckland.ac.nz/~mike http://reperiendi.wordpress.com