On Thu, Feb 13, 2014 at 1:47 PM, Edgar L. Owen <edgaro...@att.net> wrote:
> 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. > I mean same point in spacetime in terms of the coordinate times and positions assigned by a background grid of coordinate clocks and rulers of the type I have discussed with you many times before. And in SR, when two observers' worldlines converge the same position and time coordinate in any coordinate system, this IMPLIES that they must also satisfy the operational definition I gave (if you disagree, and think it is possible in SR for two worldlines to cross through the same position and time coordinate but NOT to satisfy the operational definition I gave, please elaborate). In my Alice/Bob/Arlene/Bart example at https://groups.google.com/d/msg/everything-list/jFX-wTm_E_Q/pxg0VAAHJRQJthat demonstrates a contradiction in your ideas about p-time, take "same point in spacetime" in either of the above senses, since they are physically equivalent. Points 2 and 4 are based on the idea that if two clock readings happen at the "same point in spacetime" in these senses, they must be at the same moment of p-time. For example, in point 4, the event of Bart's clock reading T=0 happens at coordinates x=25 light years, t=20 years in the single coordinate system I am using to describe events, and likewise the event of Bob's clock reading T=20 happens at coordinates x=25 light years and t=20 years in this coordinate system. If there was a coordinate clock at the x=25 marking on a ruler, then when that clock read t=20, both Bart and Bob would be right next to the clock at that moment, with Bart's clock reading T=0 and Bob's reading T=20. Since these readings all happen at the same point in space, naturally if Bob and Bart were bouncing light signals off each other they would satisfy the operational definition I gave too. So, can you please over the example and tell me if you disagree with any aspect of it (either my predictions for what readings should occur when and where according to SR, or my conclusions about what this implies for p-time simultaneity), or simply find some aspect confusing or in need of clarification? Since as I've said, I'm convinced this example shows a basic contradiction in your assumptions about how p-time works, it really would be helpful if you would address it. > > > 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. > Are you saying that a difference in readings is an "effect" while identical readings is "no effect", so the mere fact that instantaneous acceleration should produce "no effect" implies the readings should be identical afterwards? If so this is just a confused argument-by-word-definitions, one could just as easily (and just as incorrectly) define a spatial separation to be an "effect" and no spatial separation to be "no effect", and therefore conclude that if Bob instantaneously accelerates when he is 200 light years away from Alice, he should suddenly find himself back at the same position as Alice with zero spatial separation. In any case, instantaneous acceleration isn't just a meaningless "impossible" scenario, it's actually used all the time in relativity textbooks to simplify calculations (for example, see http://books.google.com/books?id=vDWvUBiNgNkC&pg=PA180&dq=%22instantaneous+acceleration%22+%22twin+paradox%22&hl=en&sa=X&ei=GB_9Uq-ELfTEsAScgYGIBw&ved=0CEMQ6AEwBA#v=onepage&q=%22instantaneous%20acceleration%22%20%22twin%20paradox%22&f=false). You can understand it as a shorthand way of talking about a LIMIT (in the calculus sense) of a series of cases where the acceleration is made briefer and briefer, but where the final relative velocity after acceleration (zero, in this example) is the same in each case. Or you can just consider it as an approximation--if the example deals with scales of years and light-years, then if the acceleration only lasts a few seconds it'll be a perfectly good approximation to treat it as instantaneous. Either way, relativity does tell us what the ages would be in their mutual rest frame after the "instantaneous" acceleration, and they would NOT be identical. Jesse > > 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 <edga...@att.net> 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 <edga...@att.net> 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. > To unsubscribe from this group and stop receiving emails from it, send an > email to everything-list+unsubscr...@googlegroups.com. > To post to this group, send email to everything-list@googlegroups.com. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/groups/opt_out. > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. 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