Jesse, Depends on what you REALLY mean by the same point in spacetime.
If you mean the same point in spaceCLOCKtime, then no, because the twins are NOT at the same point in clock time, though they are at the same point in space, and are the same point in p-time. But if you define same point in spacetime by your reflected light test then yes they are at the same point in p-time. But they still have different ages, different clock times. As for the rest of your post you have a remarkable ability to move the goal posts during the game! The whole point of assuming an INSTANTANEOUS acceleration to stop the relative motion is that instantaneous acceleration produces NO actual physical effect. It obviously can't because instantaneous acceleration is IMPOSSIBLE. It's a thought experiment device designed NOT to produce any effect, so that only the effect of the relative motion can be studied. It's functionally the same as my magical stopping of relative motion. So, given that, my analysis is correct, and yours is wrong, because you seem to think a physically impossible acceleration is producing some actual acceleration effect which is not possible. Edgar On Wednesday, February 12, 2014 8:59:43 AM UTC-5, jessem wrote: > > > > On Wed, Feb 12, 2014 at 8:28 AM, Edgar L. Owen <[email protected]<javascript:> > > wrote: > > Jesse, > > Not at all. I pointed out maybe a week ago with examples why your notion > of "a same point in SPACEtime" is not the same as a same point in p-TIME. > They are the same is true only when A and B are at the same point in SPACE, > > > Ah, it's clear you've misunderstood me then. My definition of "same point > in spacetime" ALWAYS means that the events happen at the same point in > space, no exceptions. Not sure how you could possibly imagine otherwise > given my operational definition(s), and given that I specifically explained > that all spatial coordinates of the two events are the same as well as > their time coordinates if they occur at the same point in spacetime. But > now that I've made that clear, do you agree that events that occur at the > same point in spacetime must occur at the same point in p-time? > > > > > but every observer is ALWAYS at the same point in p-TIME because there is > ONLY one current point in p-time across the entire universe. > > > I never talked about whether "observers" are at the same point in p-time, > only "events". And as I've told you before, I'm asking about deciding in > retrospect whether two events occurred at the same point in p-time, so I'm > not just talking about currently happening events (which are the only ones > you'd say actually "exist" I assume). > > > > > Also you have a basic misunderstanding of relativity theory in your > example. In NON-accelerated relative motion there is no actual age > difference or time dilation between the comoving (OWN) clocks of the two > observers. A's OWN clock and B's OWN clock both read exactly the same t > values. A's t = B's t', and there are no actual age differences. > > > > No relativity textbook will agree with you on that, time dilation is > perfectly well-defined for purely inertial observers. And the phrase > "actual age difference" is just meaningless unless the observers get > together and compare clocks at the same point in spacetime--for observers > separated in space there *is* no "actual" age difference in relativity > theory, only the age difference as judged in different frames, which use > different definitions of simultaneity. You seem to be confusing your own > theories about p-time for mainstream relativity theory. > > > > This is basic relativity theory. It is only the OTHER clock that APPEARS > to be running slow to both A and B, but their own clocks are running at the > exact same rate. > > > In each one's rest frame the other is running slow, and neither frame is > more correct than the other. But there is no objective truth that the are > "running at the exact same rate", nor is there any objective truth that > they "run at different rates" in examples involving acceleration; a > comparison of "rates" is simply an intrinsically frame-dependent notion, > there is no well-defined way to define a frame-independent truth of the > matter in relativity theory. > > > > > This other clock view is an illusion of relative motion that ceases with > the relative motion with NO actual age differences. > > > Huh? If two twins are moving apart inertially, then if either twin > accelerates instantaneously to instantly come to rest relative to the other > twin, there WILL be an age difference in the frame where the two twins are > now at rest. For example, if twin B is moving apart from twin A at 0.8c, > and twin B suddenly comes to rest with respect to twin A when twin B's > clock shows 6 years have passed since departure, then immediately > afterwards in the frame where they are now both at rest, twin B's clock > will show 6 years have passed since departure while twin A's clock will > show 10 years have passed since departure. These two readings were > simultaneous in A's rest frame immediately before B accelerated, and B's > instantaneous acceleration doesn't cause any sudden change in B's clock > reading in this frame, so they are still simultaneous immediately after B > comes to rest in this frame. > > Also, if A was the one who accelerated to come to rest relative to B, and > A did this when her own clock showed 6 years since departure, the situation > would be exactly reversed; in their new mutual rest frame immediately after > the acceleration, A's clock would show 6 years since departure, while B's > would show 10 years departure. So there is a symmetry in the sense that > either one can do the sudden acceleration to come to rest relative to the > other, and that will be the one who will have aged less in their new mutual > rest frame after the acceleration. > > If you disagree with my numbers above, you are misunderstanding something > really basic about elementary SR calculations. I can try to find some > similar textbook examples like this if you don't believe me, or you could > ask about this specific scenario (twins moving apart inertially, one twin > makes an instantaneous acceleration to come to rest relative to the other, > immediately after coming to rest their ages are compared in their mutual > rest frame) in the physics forum at > http://www.physicsforums.com/forumdisplay.php?f=70 which contains a lot > of grad students and Ph.D.s and stuff, I'm sure they'd all confirm what I > say about the different ages (if you do go to that forum make sure to stick > to asking about mainstream relativity and not try to talk about your own > non-mainstream ideas, since they don't allow that over there). You could > also ask Brent, who's a physicist, I'm sure he would agree too. > > Jesse > > > > > > On Tuesday, February 11, 2014 7:46:30 PM UTC-5, jessem wrote: > > > > On Tue, Feb 11, 2014 at 7:08 PM, Edgar L. Owen <[email protected]> wrote: > > Jesse, > > Your example does NOT establish any inconsistency. I NEVER said "I'm > pretty sure you've said before that you agree that if SR predicts two > clocks meet at a single point in spacetime, their two readings at that > point must be simultaneous in p-time)." That is NOT true. Only if there is > no relative motion or acceleration is it true. I really wish you could just > get the basics of the theory straight. > > > I thought you agreed on my operational definition of "same point in > spacetime", and that events that satisfied this definition would also occur > at the same point in p-time. I wonder if you actually are correctly > understanding what I say in the quoted sentence, because I find it hard to > believe you would deny it if you understood it correctly. > > Let's say we have two > > ... -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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