Title: What is the relative mass of a proton? - Quora
Headings: What is the relative mass of a proton?
What is the relative mass of a proton?
Jeremy Fry

Content: This does not mean that photons accelerate or decelerate; this is just gravity causing clocks to run slower and rulers to shrink. The problem here comes from the fact that speed is a coordinate-dependent quantity, and is therefore somewhat ambiguous. To determine speed (distance moved/time taken) you must first choose some standards of distance and time, and different choices can give different answers. This is already true in special relativity: if you measure the speed of light in an accelerating reference frame, the answer will, in general, differ from c. Based on the Schwarzschild solution of the Einstein’s equation of gravitational field, it is proved that the speed of light would change and the isotropy of light’s speed would be violated in gravitational field with spherical symmetry. Above description is compatible with point-like concept of quantum mechanics, but is incompatible with new approaches and evidences. In quantum mechanics, the concept of a point-like particle is complicated by the Heisenberg uncertainty principle, because even an elementary particle, with no internal structure, occupies a nonzero volume. According to the quantum mechanics that photon and electron are unstructured particle, we cannot answer the unanswered questions. With all the effort that was undertaken in recent decades on QED, there is a fundamental question that has never been raised or if it has raised (we have not seen) is ignored.