# Re: Another stab at the universal present moment - a gedanken..

```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
>
> 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 <edga...@att.net> 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
>
>
>
> 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
>
>
> 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 <liz...@gmail.com> 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 <jason...@gmail.com> wrote:
>
>
>
>
> On Thu, Jan 2, 2014 at 8:57 PM, Edgar L. Owen <edga...@att.net> 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).
>
> SpecRel/Flash/LengthContract.html for a good explanation.
>
> <blockquote style="margin:0px 0px 0px
>
> ...

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