### 9 Answers

- Anonymous8 months agoFavourite answer
There is no such proof because there's proof of the opposite. Light particles (i.e., photons) have been proven to have mass (an extremely small amount of mass) by observing how it bends towards gravity, like when passing a star. Light particles having mass is also what makes black holes black -- the gravity is so intense that light particles, because of their mass, cannot escape.

- oldprofLv 78 months ago
Neb...you must have loved the answers in this group....argh.

So, goring, from special relativity we can derive the total energy equation (TE)^2 = (Mc^2)^2 = (mc^2)^2 + (Mvc)^2; where M = m/sqrt(1 - (v/c)^2) = relativistic inertia of a particle with rest mass m going v speed. Mvc = kinetic energy of that particle going v speed, mc^2 is the rest mass equivalent energy and Mc^2 is the total energy.

If we can agree that photons travel at the speed of light, then we can set v = c in the total energy equation. So that becomes (Mc^2)^2 = (mc^2)^2 + (Mcc)^2 = (mc^2)^2 + (Mc^2)^2; so we have (Mc^2)^2 - (Mc^2)^2 = 0 =(mc^2)^2.

And there we are. (mc^2)^2 = 0 reduces to mc^2 = 0. And since c > 0 that means that m must = 0. The rest mast of a photon must be zero if it's going light speed. QED.

- ...Show all comments
Goring, that's the point of setting v = c in the proof. We assume that light travels at v = c the speed of light in a vacuum. And in that assumption we find that m = 0 is a must; a photon cannot have rest mast.

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- D gLv 78 months ago
photons have NO REST MASS

they are born moving at the speed of light and never go at 0 m/s relative to anything..

they do have RELATIVISTIC MASS ... that is because the light is moving at a velocity

it comes from the energy formulas for light in quantum physics

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- Jeffrey KLv 68 months ago
Photons move at the speed of light. Nothing with mass can do that.

Photons are bosons, so many can be in the same place at the same time. Nothing with mass can do that.

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- Andrew SmithLv 78 months ago
In science there is never proof. There are philosophical positions at work. During my time light was assigned a mass called a "relativistic mass" which was the mass of the energy contained. Using E = mc^2

But such a view would also mean that the mass of a particle that had kinetic energy would vary from one frame of reference to another.

So that if mass is to be an invariant property of an object we cannot consider that the mass energy is part of its mass.

Which leads to many other philosophical points.

Basically we redefined mass, energy and momentum to fit this model.

Remembering that the only real test of a model is if it works and if it makes valid predictions. If this model works then it is as good a model as any other. Perhaps better than some. Yet it remains a model and that may be torn down in the future with some other model that is "better".

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- daniel gLv 78 months ago
You are talking photons, a sub atomic energy front. A wave front and narrow part of the EM spectrum.

There is no evidence to show they are totally without mass, but Crooks radiometer would suggest the do have some level of mass in order to exert force.

Gravity can bend the path of photons also suggesting a mass. Very small, albeit, but not massless.

No, no, no Daniel. Photons carry momentum which can be transferred to exert a force. Mass is not required for something to be affected by gravity. Photons can generate a gravitational field simply through energy density and momentum. You haven’t got past Newton.

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Dr Zorro is correct. This answer is completely wrong.