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 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 any t, because > that is just a simpler method of eliminating effects of type a. > > Again all we have to do now is compare t and t' to see what t' of B > occurred at the same p-time as t on A's clock. This will be the real age B > is when A is t years old, which is the test of the same p-time. Both A and > B agree on this age difference because it is real and persistent after all > relativistic effects cease. > > 3. This can be done either in A's frame for any t, or in B's frame for any > t'. > > 4. This process is transitive between any number of arbitrary observers in > any relativistic situation. We can always find the clock time t-values of > each that occurred in the same p-time, the same present moment of p-time. > > Edgar > > > On Tuesday, February 11, 2014 2:00:23 PM UTC-5, jessem wrote: >> >> >> >> On Tue, Feb 11, 2014 at 1:13 PM, Edgar L. Owen <[email protected]> wrote: >> >>> Jesse, >>> >>> Your condition C. was not example dependent. You just need to rephrase >>> your condition C. as two observers with no relative motion AND in identical >>> gravitational fields. Then it does hold and is consistent with conditions A >>> and B. I already gave several examples. >>> >> >> But I gave a different example where it leads to inconsistent >> conclusions, are you going to address that? In my example, Alice and Bob >> have no relative motion and are both in identical gravitational fields >> (zero gravitational fields, since this is an SR flat spacetime example). >> Likewise, Arlene and Bart have no relative motion and are both in identical >> gravitational fields (again, zero). The only comparisons I made between >> members of different pairs were ones that involved their passing next to >> each other and comparing clock readings at the same point in spacetime, so >> their relative motion shouldn't be an issue (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). >> >> Please just look over the Alice/Bob/Arlene/Bart example I gave at >> https://groups.google.com/d/msg/everything-list/jFX-wTm_E_Q/pxg0VAAHJRQJand >> tell me if you disagree with any of the numbered conclusions about >> p-time simultaneity 1-4. >> >> Jesse >> >> -- > 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 [email protected]. > To post to this group, send email to [email protected]. > 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. 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