In a message dated 13/12/2009 18:52:37 GMT Standard Time, charles_steinm...@lavabit.com writes:
Volts and yards, at least, are also not absolute measurements in the same sense that measurements of time are not absolute. Volts express the difference in electrical potential, and yards the physical separation, between two spatial points. But two points in space just define a spatial interval, precisely analogously to two points in time specifying a temporal interval (more below). ----------------------- But that is no different than the other three dimensions of spacetime -- measuring intervals is all we have there, too. "One kilometer" is no different from "one second" in this regard -- in both cases, it is one unit *between* two places (we usually call places in time "events," but it's the same thing). If general relativity ("GR") is correct (and we have every reason to believe that it is), time is no different than space, although we perceive it quite differently. For example, in order to move about in the space dimensions we think we need to "do something," while we need to do nothing to move about in the usual way in the time dimension (and, indeed, have not figured out how to move differently in time or to stay in one place). But note that we are really hurtling through space at a good clip, without it being apparent to our natural senses -- and in comparison to this, we really haven't much power to move about in space, either. So, we could say that we have an initial velocity through both space and time when we are born, and our initial velocity through time is more apparent to our natural senses than our initial velocity through space -- but in reality, there is no difference between them. ---------------------- In my view, these are all questions, not about time, but rather about our perception of time. At the end of the day, we have every reason to believe that GR is correct and, consequently, that spacetime is the fabric of the universe. Space and time are both altered, in complementary ways, by the great forces of the universe (gravity and acceleration -- time will tell whether the nuclear forces do so, as well, and there is some evidence to date that they may), implying that there is a conservation relationship that applies to the four dimensions collectively. But there is no difference in terms of the spatial dimensions being "absolute" and the temporal dimension not being "absolute" -- all of our measurements of the four spacetime dimensions are relative and "not absolute" in the sense you mean (although, as I've pointed out, by refering both back to the origin of this universe, which we have good reason to believe was a mathematical and physical point where this universe began, we could in principle at least have a master datum for all four dimensions, providing a form of absolutism). The puzzle is why we perceive the spatial dimensions so differently from the temporal dimension. It is a fascinating question, but may not be fundamentally a question of the physics of spacetime. --------------- Hi Charles Many thanks for your reply, but I'm not so sure anymore that spatial and temporal intervals really are quite the same. It deserves more thought. The spatial intervals have the property of persistence until "time" becomes involved, whereas temporal intervals really have the property of decay regardless. Whether or not "we" have an initial velocity in any reference frame is not so much the issue as to what was the reference to start with. We are indeed hurtling through space "at a good clip" but where exactly does that lead us? Mr Flat_Earth mentioned the "arrow of time", without any due consideration to the fact that one doesn't need to invoke the second law of thermodynamics, or anything else for that matter, if time is merely an artefact of universal expansion. Should the universe eventually begin to contract it's then we should consider it, time reversal might just be inevitable after all. The puzzle may be one one of perception, but perhaps perception should not always be ignored. I begin to think that we perceive spatial dimensions so differently from the temporal because there might just be a difference. Perhaps not, but at least the mind is open and thinking:-) regards Nigel GM8PZR _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.