On Wed, Feb 12, 2014 at 8:28 AM, Edgar L. Owen <edgaro...@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 twins moving towards each other at some nonzero >> velocity, and they pass right next to each other without either one >> accelerating. Relativity can be used to predict their respective ages at >> the moment they pass (if we idealize them as pointlike observers, the >> "moment they pass" can refer to their worldlines passing through precisely >> the same position and time coordinates). To use my usual numbers, >> relativity might say that twin A is turning 30 and twin B is turning 40 at >> the moment they pass. In terms of my operational definition, if A was >> sending a continual stream of light signals to B and seeing how long it >> took to receive the reflected signal, the time interval on A's clock >> between sending a signal and receiving the reflection would approach zero >> as his own age clock approached 30, and the age he would see on B's age >> clock in the reflected light would approach 40 as he approached 30. >> Likewise, if there was a camera at the point in space they passed, and it >> took a photo just as they passed, the photo would show A's age clock >> reading 30 and B's age clock reading 40. And if A had a bomb that would >> destroy anything in his immediate local vicinity but would leave anything >> at a distance from him unharmed, then if A set it to go off when he turned >> 30, B would be killed at age 40, but if A set it to go off at any other >> age, B would survive unharmed. >> >> Given that relativity would predict all these things, are you saying >> these predictions could all be correct, but that A turning 30 and B turning >> 40 would *not* be simultaneous in p-time, not even approximately so? Or are >> you actually saying relativity would be *wrong* in the predictions above >> when it predicts the event of A turning 30 will have the same x,y,z,t >> coordinates as the event of B turning 40? Or did you just misunderstand >> what I meant when I said "two clocks meet at a single point in spacetime, >> their two readings at that point [A turning 30 and B turning 40 in this >> example] must be simultaneous in p-time"? Or would you say "none of the >> above"? Please give a clear answer to this question. >> >> >> >> >> The method is trivially simple. I'll give two approaches: >> >> >> 1. Instantaneously pause all relativistic effects at any time t on A's >> clock and read the time t' on B's clock. These clock times are a point when >> A and B were/are in the same p-time current moment. >> >> >> >> "Instantaneously pause" has no frame-independent meaning in relativity, >> do you disagree? If A and B are in relative motion, and unlike my example >> above, B is *not* at the same point in spacetime as A when A turns some age >> (say 60), then different frames disagree on what age B is "at the same >> instant" that B turns 60. So if one frame said B was 48 at the same instant >> A turned 50, and another frame said B was 75 at the same instant A turned >> 50, then at what age should B's motion relative to A be "paused"? We don't >> have an "objective instantaneous pause machine" that can settle the >> question empirically, it has to be *our choice* when to subject B to a >> sudden acceleration to instantaneously bring him to rest relative to A. >> Again, do you disagree? >> >> Since the whole rest of your explanation depends on this notion of an >> "instantaneous pause", I'll await a response to this question before >> dealing with the rest of your discussion of your "method". >> >> Jesse >> >> >> >> >> 2. Do the same thing for any t you wish. The t' that corresponds will be >> the clock time in the same present moment of p-time as the t you paused at. >> >> 3. In general if you want to know what clock time t' of B occurred in the >> same p-time as any time t on A's clock, all you have to do is pause the >> experiment at t so that all relative motion ceases and just read t' on B's >> clock. >> >> Because this can be done at any point t on A's clock we can always >> determine what t' on B's clock occurred in the same p-time as that t simply >> by reading B's clock. >> >> Note this is exactly what happens when the twins meet up in the same >> p-time present moment and read each other's clocks to determine what clock >> times occurred at the same p-time, in that same common present moment. >> >> >> You can also do this with a calculation as well as by pausing the >> experiment. >> >> 1. Note there are two classes of relativistic effects in the general case: >> a. Reciprocal temporary effects of relative motion in which A and B >> each see the other's clock slow by the same amount. These effects vanish >> when relative motion ceases and A and B do NOT agree on these effects >> because they are equal and opposite. No permanent actual age differences >> are produced by this type of effect. >> b. Persistent and agreed effects of acceleration and gravitation in >> which one clock slows permanently relative to the other and both A and B >> agree on the amount of slowing. These effects persist after the >> relativistic differences vanish. They are permanent. And both A and B agree >> on these effects. These effects manifest as real permanent age differences. >> >> 2. At any desired time t on A's clock, identify, calculate and discard >> the effects of relative motion of type a. so that the only effects between >> A and B left are of type b., the actual real actual age differences up to >> point t on A's clock. We keep only the effects that would be/are permanent >> (type b. above) and disregard those that are not (type a. above). >> >> This is effectively the same as pausing the experiment at >> >> ... > > -- > 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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