Re: m_photon = 0


Peter Christensen wrote:
I've just been involved in a discussion about this, and I would like to
get a strictly correct answer on this question. How are masses defined
today, when we do not use m=E_0/c^2 (Einstein) or F=m*a (Newton)?

Is it just by using m^2*c^4 = E^2 - p^2*c^2?

PC

Not sure what you mean by a *definition*. Yes, this is the definition
for invariant mass of all particles, massive and massless.

How is the value of it determined experimentally? Well, usually not by
measuring E and p and doing the math above. There are other signals
which are dependent on the value of the photon mass as well, such as
frequency-dependent dispersion, and this is what is more customarily
associated with a measurement of m.

PD

.