3 ms·
The way to really think about this is that there really isn't any objective thing except proper time and the manifold of the spacetime you're interested in. The
by nathan_compton 3y ago
The way to really think about this is that there really isn't any objective thing except proper time and the manifold of the spacetime you're interested in. The idea of things taking an objective amount of time as seen by all observers is only an approximation valid at low speeds and low curvature in a small area. The only objective thing is the causal structure.
- raattgift 3y agoThere's an awful lot of matter which seems pretty objective, at least to me. There's also a lot of electromagnetic radiation around, and you can't calculate a proper time for that. Likewise gravitational waves and gluons. Surely the causal structure depends in part on matter? Future null cones of time-orientable flat Minkowski spacetime narrow in the presence of mass; matter is also relevant in null cones on general curved Lorentzian spacetimes.
- nathan_compton 3y agoI only mean with respect to the coordinates we use to talk about the world. It is tempting to believe you can give an objective description of the state of the universe using a 4d vector space but this isn't true - the universe fundamentally has less structure than a vector space description suggests. And in GR it has structure which the vector space simply cannot capture.