I think an observer is a quantum process interacting with another quantum process. Photons are fundamentally different from particles with mass - and they inter

I think an observer is a quantum process interacting with another quantum process. Photons are fundamentally different from particles with mass - and they interact differently. Two photons interact like waves at the surface of an ocean - amplitudes and phases changing, for instance. But photons interact with particles with mass by either being absorbed and, later, re-emitted by the other particle or being completely absorbed and altering the particle with mass' state in some way (speed/momentum). I remember reading somewhere about a geometry which described photons' existences as fundamentally different from particles with mass. Particles with mass have lifelines that change over the course of time. Particles without mass, such as photons, don't experience time and never change themselves. Photons etch out a straight line in this geometry from fixed points to other fixed points. The fixed points represent particles with mass. (something like that)