Bruno, You say of the present moment "Yes, it's not a clock time." I agree, then what is the present moment if it isn't a clock time?
Edgar On Sunday, January 5, 2014 3:07:10 AM UTC-5, Bruno Marchal wrote: > > > On 04 Jan 2014, at 19:32, Edgar L. Owen wrote: > > Jason, > > If you don't agree with my theory of the Present moment, then what is your > theory of this present moment we all experience our existence and all our > actions within? > > > Before I read Jason answer, let me tell you in three words: the indexical > theory. "present" is an indexical, and can be defined by using the > arithmetical theory of indexicals, or self-reference theory. It helps to > define all indexicals the 1-I, the 3-I, the now, this and that , etc... > Each machine lives his state as belonging to the present moment. > > > > It clearly is not a clock time simultaneity since Pam and Sam shake hands > and compare watches in the same present moment and their clock times are > not simultaneous. > > > Yes, it is not a clock time. > > Bruno > > > > This question is the key to the whole issue. Be interested to hear your > answer... > > Edgar > > On Friday, January 3, 2014 11:51:53 AM UTC-5, Jason wrote: > > > > > On Fri, Jan 3, 2014 at 11:10 AM, Edgar L. Owen <[email protected]> wrote: > > Jason, > > Thanks for your several posts and charts. You really made me think and I > like that! > > > Thanks, I am glad to hear it. :-) > > > I'm combining my responses to your multiple recent posts here. > > First though there are two ways to analyze it, GR acceleration, as opposed > to SR world lines, is the most useful because it makes the following > argument re present time easier to understand. > > > In my example, acceleration effects can account for no more than 4 minutes > worth of age difference, since they spend no more than 4 minutes > accelerating. How do we explain the other 3 years, 355 days, 23 hours and > 56 minutes that are missing from Pam's memory? > > > > Imagine a new experiment in which Pam is completely still relative to Sam > but somewhere way off in the universe and in a gravitational field of > exactly the same strength. In this case both Pam's and Sam's clock times > run at exactly the same rates and both agree to this. Therefore it is clear > they inhabit the exact same present moment even by your arguments, and > their identical clock times correlate to this. > > Now assume Pam's gravitational field increases to the point where her > clock time runs half as fast as Sam's. Again there is no relative motion so > again both agree that Pam's clock time is running half as fast as Sam's. > And again both exist in the exact same present moment, it's just that Sam's > clock time is running twice as fast through that common present moment. > Again clock time correlates with present moment time... > > > I think we should resolve the apparent problems P-time has with SR before > trying to tackle GR... > > > This gravitational time slowing is a GR, not SR effect, and GR effects are > absolute in the sense that they are permanent real effects that all > observers agree upon. They must be distinguished from SR effects which make > the situation more difficult to understand in terms of a present moment. > > > You may be right that P-time has no difficulties with GR, but it seems to > have some with SR so let us focus on solving that. > > > An acceleration equivalent to the gravitational field would produce the > exact same GR effect, but also introduces an SR relative velocity effect. > > Now consider an pure SR effect in which Pam and Sam are traveling past > each other at relativistic speeds but there is no acceleration. Velocity is > relative, as opposed to acceleration which is absolute, therefore both > observers think the other is moving relative to them, and both views are > equally true. Now because of this relativity of velocity both observers see > the clock of the other observer slow and by equal amounts. But the > absolutely crucial thing to understand here is that this SR form of time > dilation is not permanent and absolute like GR time dilation is. It > vanishes as soon as the relative motion stops, > > > That is not true, the the effects of dilation in SR remain as well. Let's > say James was born on a space ship at Proxima Cenauri travelling at 80% c > toward Earth. It takes 5 years to get to Earth at this speed, but when we > see baby James on board as he whizzes by he is only 3 years old. If the > ship stops (or not), James is still 3 years old. GR never was a factor in > James's reduced age. > > > whereas GR time differences are absolute and persist even after the > acceleration stops. > > This is why the SR versus GR model is more useful in understanding what is > going on particularly with respect to the common present moment. > > > SR and GR are not two ways of looking at the same phenomenon, but two ways > of explaining two different phenomena. > > > > So during relative motion between Pam and Sam there most certainly is a > common present moment, but trying to figure out what clock times of Pam and > Sam correspond to that present moment leads to a contradiction (as you > quite rightly pointed out with your diagrams) because Pam and Sam see clock > time differently and do not agree on it. They did agree on their GR > relativistic time differences and thus knowing which of their clock times > corresponded to the same present moment was easy. With SR, equal and > opposite, time dilation it is impossible to correlate both observers' clock > times to the same present moment. Nevertheless that's just an artifact of > SR clock time which doesn't falsify a common present moment. A common > present moment exists, it just isn't correlated with clock times the same > way by both observers. > > > Gabriel offered a clear example that I think falsifies the notion of a > single consistent present moment, and his point has not yet been adequately > addressed. > > > > All the nice chart examples you took the time to produce demonstrate this. > They are trying to assign an agreed upon clock time to the common present > moment time during SR relative velocities and thus they correctly lead to > the contradiction you pointed out. > > However once you understand how this works > > > Do you currently understand how this works or are you also still trying to > figure it out? > > > you understand that fact doesn't falsify a common present moment as you > implied. > > > Why doesn't it? I am not seeing it or you haven't explained it clearly > enough for me to get it. > > > Now consider the twins from the original example. In this case there is > both lots of relative velocity SR effects between both twins, and there is > the absolute GR acceleration effect on Pam only. > > Now the SR effects persist only during relative motion and when the twins > meet up again that leaves ONLY the GR acceleration effect which is the only > cause of the twins' clock time difference. > > > If Pam were under acceleration for just a few minutes it could not explain > an age difference of years. If you put Pam under the gravity of a black > hole for 4 minutes, she would not age much during those 4 minutes, and so > when you took the black hole away you would find her 4 minutes younger. In > the experiment I described, the acceleration, which you compare to gravity, > only lasts a few minutes. It is the time dilation of special relativity > that accumulates over the years, and remains to explain the bulk of their > age difference. > > > All SR relative velocity effects must vanish when the relative velocities > cease. Otherwise we would have Pam and Sam meeting up again with each > claiming the other's clock time was going slower than theirs. That is > impossible. > > > It is possible when you consider the geometry of the situation, as Brent's > nice charts further clarify. (What software did you use to make them Brent?) > > > At rest in the same present moment all observers must be able to agree on > their clock time differences. Both agree Pam's clock time passed more > slowly than Sam's and both agree as to the amount, based ONLY on GR > (acceleration) effects. > > > Not true. > > > Assume again the twins passing each other at a constant (no acceleration) > velocity. Both see the other's time passing slower than theirs and thus > both see each other at an earlier clock time date than themselves. This is > contradictory > > > It is not contradictory, it is because their paths are at an angle to each > other through space time. If both of our paths are at 22.5 degrees toward > each other, either of us can consistently say "the other is at a 45 degree > angle toward me." This is not inconsistency, only relativity. > > > and cannot last when they meet. It is the acceleration that brings the > relative velocities to zero that produces the only absolute persistent time > effect and when, and only when, that happens will the twins agree as to > their time differences, as always in a shared universal present moment. > > > In my "James example", there is no acceleration on James but he ages only > 3 years in his 5 year journey. > > > This is why is is possible to correlated clock times to present moment > time for GR acceleration time dilation, but NOT for SR relative velocity > time dilation. > > Hope this is clear. It may be a little difficult... > > > > I don't think we've yet addressed the core issues between SR and P-time. > Also, you have not said what use P-time has beyond SR. What can it explain > that SR cannot? In other words, when would it make a prediction that > differs from SR? > > Jason > > > > > On Thursday, January 2, 2014 9:52:54 PM UTC-5, Jason wrote: > > > > > On Thu, Jan 2, 2014 at 9:31 PM, LizR <[email protected]> wrote: > > Jason, > > You may be missing the fact that the acceleration of the space traveller > is what causes the twin paradox. > > > I would say it is not so much the acceleration that explains the paradox, > but the fact that no matter how you rotate the paths, you always see a kink > in the path Pam takes. So even if we start in Pam's reference frame where > she is still, she has to stop (putting her back in the reference frame > where Sam is 5 (not 1.8), then accelerate to 0.8 c back toward Earth, which > she will see as length contracted to 2.4 ly again, and she will experience > as taking 3 years, but in this frame, of heading back toward Earth at 0.8 > c, Sam is not 5, but 7, so when she gets there after 3 years, Sam is (as > she expects) 10 years old. > > It isn't the acceleration which causes her age to suddenly change, but > rather, her changing frames of reference (present moments), that causes her > perspective of Sam to radically change, depending on her velocity. > > > As Edgar pointed out, time dilation is mutual, but only while velocities > are constant. > > > Their relative velocity in relation to each other, and therefore their > relative time dilations and length contractions, are always the same. > > > Your diagram demonstrated that the straight line parts of Pam's movement > could be mapped either way onto Sam's (just tilt the diagram. But you can't > may the entire trajectory onto Earth time by tilting the diagram. > > > I'm not sure what you mean by this.. > > > > Apologies if I'm teaching my gradnmother to suck eggs. > > > No worries. Let me know if my example or explanation still does not make > sense. :-) > > Jason > > > > > On 3 January 2014 15:25, Jason Resch <[email protected]> wrote: > > > > > On Thu, Jan 2, 2014 at 8:57 PM, Edgar L. Owen <[email protected]> wrote: > > Jason, > > An excellent question. First of all let's stick with the actual example of > only Sam and Pam. Now how do you know all this stuff about who is doing > what when? > > > I calculate it from the parameters of the experiment as I described it. > The different answers depend on different reference frames, which you can > consider as straight lines dividing the past and future (but at different > angles depending on one's velocity through space). > > [image: Inline image 1] > > If you consider the gold and purple stars as two different events, the > person moving to the right sees the present as all events on the blue line, > and so they see the purple star happen before the yellow star, and vice > versa for the observer moving to the left, whose present is represented by > the red line. They see the yellow star come before the purple star. > > > How are you measuring it to know it's true? > > > 4 light years away, at 80% the speed of light. It is no different than > figuring out how long it takes to travel 4 miles at 0.8 miles per year. > However, when travelling at these speeds, you have to contend with length > contraction and time dilation (which are two aspects of the same phenomenon > seen from two different perspectives). > > See: http://faraday.physics.utoronto.ca/PVB/Harrison/ > SpecRel/Flash/LengthContract.html for a good explanation. > > <blockquote style="margin:0px 0px 0px > 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1 > > ... -- 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.
