Are the stings in string theory, considered to be matter?

[lightarrow]

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The equation you keep using is a statement about the energy value equivalence of a massed object, it is not a physics equivalence.

When you compute the four-momentum square modulus of a particle, for example, you say that what you get is not mass because it's just mathematics? Weird

 

[per.sundqvist]

It may be classical, but it is correct. F/a is a perfectly valid measure of mass, where abstract equations become an experimental science, as you can actually F/a.



As you've noted, Newtonian gravity may predict the deflection of a photon, but it predicts it incorrectly. So, it lends no supporting evidence to photon mass, one way or the other.

In the case of General relativity, the particle or photon appearing deflected by the influence of a planet is not a result of the curvature of spacetime about the object by the object, but the curvature of spacetime by the planet. Massive and massless objects behave in the same way; following geodesics. Again, no evidence for or against. The difference in the case of gravity is that light follows "null geodesics," but this is the same in Minkowski space.

Here the planet or sun have a huge mass comparable to the object (photon). I can think of an experiment where you have a gamma-ray photon package (Gaussian like blob), like 1Gev which is hitted closely by a photon of visible light 1eV. Would that photon bend in presence of the other? If yes -> photon has mass since it CAUSE gravity. If not not m=E/c^2 is wrong. But deflection is so ultra small and I guess impossible to measure even if you could calculate it, so ...

Also, do you septics believe Rindler was wrong in the statement: "All forms of energy has mass"? Also where origin the mass when you create a electron-positron pair? You can't use E=mc^2 because its just mathematics?