Proper time is only defined along a timelike world line, e.g. the timeline of a specific reference point / object. It’s “objective” in the sense that is true for the reference point, but other reference points may (for example) perceive distant events in a different order
Proper time is only defined along a timelike world line, e.g. the timeline of a specific reference point / object. It’s “objective” in the sense that is true for the reference point, but other reference points may (for example) perceive distant events in a different order