13 Oct
2012
13 Oct
'12
1:42 p.m.
On 10/13/2012 12:05 PM, James Cloos 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,
Only in the non-relativistic approximation. Brent
so cannot be +ve if mass == 0, so a massless particle is still energy-less. And all photons have energy. (Or is there a concept of non-finite wavelenght?)
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.
-JimC