On Thu, Jan 2, 2014 at 8:50 AM, Edgar L. Owen <edgaro...@att.net> wrote:
> Hi Jason,
> No, sadly you haven't quite gotten it yet but you are getting closer it
> First the twins do NOT have the same (x,y,z,t) coordinate times (that
> would be true of an SR constant velocity example, but not the twins' GR
> acceleration based example). Their watches show they don't, and when they
> compare watches both twins agree with the readings on both watches. Not
> only do the twins have different ages but their clocks accurate show that
> age difference. Both twins agree that the traveling twin aged less because
> comparing their clocks both mechanical and biological confirms that.
> Thus they have different (x,y,z,t) coordinates yet they DO interact. Why?
> Only because they share the exact same present moment which is the only
> place interactions can occur whether clock times are the same or not. And
> that present moment P-time is a completely independent kind of time from
> clock time. There is simply no way around this.
You are describing coordinate time.
> Yes, you are correct the twins shaking hands and comparing watches
> confirms a shared present moment by direct experiment if the (x,y,z)
> coordinates are the same but not they they different. However the argument
> to deduce a common present moment when (x,y,z) coordinates are different is
> simple and clear. I've already posted it a couple of times but will
> summarize it again.
> The twins start and end at the same (x,y,z) coordinates. At both times we
> agree they share the same present moment. Their passages from point A to
> point B must both be represented by continuous lines, one curved, one
> straight. During every point during that passage both twins continuously
> experience their own present moment time without interruption and those
> present times are the same when they start and when they meet up again.
> Thus we must logically conclude that at every present time moment for
> either observer there absolutely must have been a corresponding present
> time moment for the other.
You have demonstrated it for two observers at the same x,y,z, but it does
not logically follow for different x,y,z's.
> This is not directly observable
So we should maintain some doubt..
> but is the only logical conclusion
SR shows there is another possible conclusion.
> based on their starting and ending at a shared present moment and both
> their spacetime travels being continuous with no breaks in between.
This can also be explained by a an (approximately) continuous,
four-dimensional reality, in which all events are embedded.
> The easy way to understand this is that every present moment for either
> twin, the other twin must actually exist and be doing something too.
In some relativistic frames, with separated twins might be considered dead,
and the other still alive, while in another frame, the former twin is still
and the other is dead. The only sense in which the other is guaranteed to
exist and be doing something is that both twin's "world tubes" exist and
are eternally embedded in the four dimensional reality.
> There is absolutely no way around that! Thus they must share a common
> present moment in which they are existing and doing something even when
> they are separated spatially. Clearly this cannot be experimentally
> confirmed (measured) but it is the only tenable logical conclusion unless
> you think things pop in and out of existence which they don't.
Now again for the nth time. don't try to analyze this by relativistic clock
> time theory. That correctly describes how clock times change during the
> trip but has no relevance to present time whatsoever! Two completely
> different kinds of time.
I fail to see how this is any different from coordinate time vs. proper
time in SR.
> Thus the only possible conclusion is that there is a common universal
> shared present moment time which is completely different from clock time.
Why doesn't four dimensionalism work?
> On Wednesday, January 1, 2014 3:15:27 PM UTC-5, Jason wrote:
>> I believe I may understand your point about a universal present, but it
>> is something relativity handles, as far as I can see, without having to
>> postulate anything new. Anything having the same (x, y, z, t) coordinates
>> can interact, where t is coordinate time. It seems like you believe that
>> because the twins are different ages (in different proper times), that they
>> cannot interact. But they can, because each has traced exactly 10 light
>> years through space-time (their coordinate times are the same).
>> So you might say everything with the same coordinate time, at the same
>> place (x, y, z) the same, shares a present moment. But you cannot use this
>> fact to extrapolate to spatially separated things sharing a present. For
>> this, the definition of a present (what things exist having the same
>> coordinate times) differs in different reference frames.
>> On Wed, Jan 1, 2014 at 3:01 PM, Jason Resch <jason...@gmail.com> wrote:
>>> On Wed, Jan 1, 2014 at 8:41 AM, Russell Standish
>>>> On Mon, Dec 30, 2013 at 01:20:35AM -0800, Edgar L. Owen wrote:
>>>> > Jason,
>>>> > That's a totally off the wall answer. When the two shake hands it's
>>>> > just photons that are interacting, it's the electrons, protons and
>>>> > of the matter of their hands which don't travel at the speed of light.
>>>> > Goodness gracious!
>>>> > Edgar
>>>> Jason is correct - electron-electron and electron-proton interactions
>>>> are mediated by photons. Only nucleon-nucleon interactions are
>>>> mediated by different stuff (gluons in that case), but for all
>>>> practical purposes, the strong force is irrelevant to the phenomenon
>>>> of handshaking.
>>> And if it were, say in some particle accelerator, the gluons also travel
>>> at the speed of light and their present is spread across all proper times.
>>>> Which gets us to the more important point. You idealise a handshake as
>>>> instantaneous as a demonstration of your "present moment", but in fact
>>>> those interactions Jason was alluding to are smeared out over a
>>>> temporal duration of the order of a few picoseconds (a duration well
>>>> measurable by current day technology - my laptop's CPU clock cycles on
>>>> a sub-picosecond timescale, for example).
>>> You must have a VERY fast laptop! :-)
>>>> This doesn't matter much for human affairs, but becomes quite
>>>> significant when extrapolating over cosmological scales.
>>>> Prof Russell Standish Phone 0425 253119 (mobile)
>>>> Principal, High Performance Coders
>>>> Visiting Professor of Mathematics hpc...@hpcoders.com.au
>>>> University of New South Wales http://www.hpcoders.com.au
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