Originally posted by Royce
Quote originally by Alexander from religion forum.
"Don't you know that photons are MATTER? Being bosons they obey different statistics than fermions (electrons, protons), rather than that have same properties other particles have - they are wavy (as all particles), have spin, momentum, energy. What makes you think that photons are not matter?
By the way, if you place about 3x10^35 of green photons in a massless box, the box will acquire mass 1 kg. (Both inertial mass and gravitational mass)."
Is this true? The last that I read from books published as late as 2002, photons were still considered quantum packets of energy with zero rest mass and traveled at the speed of light, not matter which has mass and therefore cannot travel at the speed of light.
Part of the discussion is simply about how contemporary scientists use words. ("matter"(nonzero rest mass) vs. "electromagnetic radiation"(zero rest mass) "mass"(inertia at rest))
Part of the discussion is substantitive, not merely semantic.
As mainstream physicists talk (Tom confirmed this in another thread) "mass" means rest mass. Photons do not have mass. They are not ordinarily described as matter. Alexander is using words in an eccentric personal way if he calls them matter.
On the other hand putting energy into a box certainly increases its inertia! A good deal of the inertia of the sun, for example, is due to the radiation energy in it and the kinetic energy----beyond what you would get if you took all the particles out and weighed them separately.
This is an unintuitive kink in physicists language. A photon has zero mass, but if you put it in a box the box will then have more mass. There is an intuitive failure of the "additivity" picture. that is just how it is---how conventional physics language has evolved.
If you focus on energy, everything will be all right verbally. The equation E = mc^2 only applies to bodies at rest (as Tom's recommended Special Relativity text states very clearly).
You can add the energy of the light to the energy of the box and get a new energy for the box and since the box is at rest you can measure its inertia and also use E = mc^2 to calculate its new inertia and get the right answer.
You just can't add inertias (as if the light were a material) because then you get the wrong answer.
Now there is the substantive question. It would be good to check Alexander's statement that the inertia conferred by
3E35 green photons is a kilo. (they don't have inertia but putting them in the box, which is at rest, gives the box that much)
In natural units (to make calculating quick) the typical energy for green photons is 2E-28
so the energy of 3E35 photons would be 6E7, or 60E6
This is 60 x 22 grams or 1300 grams. So if Alexander said that
2E35 green photons contribute 1000 grams to the box then he is to be congratulated! He is only a bit on the low side----just fine for back of envelope.
Maybe his greens are less energetic and more yellowish than
the ones I am thinking of!
The substantitive question is probably more important than the verbal one. If he wants to call light a form of matter (which ordinary working physicists would not) then just let him---he probably doesn't do any harm by having his own verbal habits.