Hello all, I am asking this question in the context of general relativity. In general relativity the stress-energy tensor is related to the spacetime metric through the Einstein field equations. The production of a curved spacetime is what creates what we call gravitation. For example a single particle with mass creates a spacetime which can be described by the schwarzschild metric (among others). Now electromagnetic fields have a well known stress energy tensor, and of course photons are an electromagnetic phenomena. So photons seem like they would produce gravitational effects. But would they be identical to a particle with equivalent energy? Could the spacetime around a photon be described with the schwarzschild metric? I know that for a massive particle, the mass shows up in the schwarzschild metric, but that mass is of course an experimentally determined thing. If the photon set up a schwarzschild spacetime, we could experimentally assign it a "mass". So any thoughts? Do photons curve spacetime? What makes them different from what we typically call massive particles? This is a speculative matter, not an experimental one obviously.