Any one of us can work out x by x plus y by y plus z by z less c by t by t where x and y and z and t are each part of how to get from one "here and now" to a 2n

Any one of us can work out x by x plus y by y plus z by z less c by t by t where x and y and z and t are each part of how to get from one "here and now" to a 2nd "here and now". I can try to tell you what c is or we can just say that it is one (i.e. c by t by t is just t by t). And the math that we do will work out the same if I work it out from what I see or if you work it out from what you see, even if I do not move at the same rate as you.