Natural Science Forum / Physics / Research / November 2004

I don't remember the value off-hand, but you can probably find it on the
Particle Data Group's Web site:

http://pdg.lbl.gov/

Tu et al, "The mass of the photon", Rep. Prog. Phys. 68, 77-130 (2005)
[currently on the IOP "free for 30 days" recent papers list]

Extra-terrestrial observation, perhaps somewhat speculative in some cases,
gives a lowest upper limit of 3 x 10^(-63) kg. The official "safe" figure
these days looks to be 4 x 10^(-52) kg; a more recent 1 x 10^(-52) kg was
reported earlier this year.

When a gas is excited the mass of the photon emitted is related to the
states momenta.  And to limit the photon mass is to recognize the
maximum state size.  And so to postulate the largist mass of state
ever found is your question.  On the open air electron beam
experiments of the Advanced Test Accelerator the air state exceeded a
milligram. A 50 Mev and many thousands of amps beam. Or one nanosecond
pulse width and a millicoulomb per pulse.

A space charge was found and the electron spectra reversed. It was an
artifical nebula for real. A milligram might be postulated for a
single quanta deexcitation of the nebula. Highly unlikely, but
possible.

Making the theoretical limit astronomical. Except the large natural
nebula quanta never get to earth and interact on the way here.

Eagleson- Gaithersburg, MD USA