Expert: Philip A. Stahl - 11/18/2007

Question
Greetings .!!!
Ive derived the equation for da mass of photon .. just wnted to make sure that is it correct!!

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p = E/C (Momentum of Photon) (E = hxfrequency)
i.e 6.34x10^-34 x 7000 = 4.438x10^-30

p is also equal to mv(classical physics)
hence
m x v = 4.438x10^-30/C
m = 4.438x10^-30 / 3x10^8 x 3 x 10^8
m = 4.438x10^-30 / 9x10^16

Mp = 4.931 x 10^-47

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Answer
Hello,


While you are correct that the mass of the photon is non-zero - you're own estimate of it is evidently too large by more than ten orders of magnitude.

In the reference 'Gravitation and spacetime', Ruffini and O'Hanian (2nd ed.) the UPPER limit of the mass is given as:

m(p)  <   10^-59 g

This is based on possible deviations from Maxwell's equations.

You can see other limits - derived from experimental and galactic magnetic data here:

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photonMass.html

The limit of (7 x 10^-17 eV) cited in one experiment (by Roderic Lakes in 1998) is actually about 7 orders of magnitude larger than the limit set by Ruffini and O'Hanian. However, it is much smaller than the 3 x 10^-27 eV limit)

Bear in mind here: 1 eV = 1.6 x 10^-19 J.

So it seems that the Ruffini & O'Hanian value is probably a reasonable limit from a number of perspectives.