# Individual Protons Are Zero Mass Particles. Is Zero Mass Defined By This?

## Main Question or Discussion Point

Individual Photons Are Zero Mass Particles. Is Zero Mass Defined By This?

Is zero mass as we know declaired because photons are theorisized to be true "weightless" and massless, or could it be a case that we do not have sensitive enough instrements and limited in our detection? Or on the other hand is their solid science backing up the theory?

Remember that E=MC^2, so that in theory in order to obtain any mass you need energy, even if it is individual 'energy bits' combined in a way beyond our understanding

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You typed proton in the title, though I am sure you meant photon. E=mc^2 is rest mass, but because photons are never at rest, that equation does not apply.

A photon is not a defining zero mass particle, it just happens to be one which has, to our best measurement, zero mass (An upper limit is Mass m < 10^-18 eV, which is ~10^-45) - http://pdg.lbl.gov/2009/tables/rpp2009-sum-gauge-higgs-bosons.pdf

Yes, Thank you. Another classic example of my mind moving faster then I can type. So as far as scientists have established, do particles have more "motion energy" then neutral or negatives 'free' elementry particles? I'm leaning towrds no but I'm not certian.

You mean kinetic energy?

Actually, the rest energy is usually way higher than kinetic energy. The c^2 in mc^2 is a large number.

For SR, KE = (γ - 1)mc^2, where rest energy is mc^2. So unless gamma is equal to or greater than 2, the rest energy will be greater.