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.
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. This is not directly observable but is the only
logical conclusion based on their starting and ending at a shared present
moment and both their spacetime travels being continuous with no breaks in
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. 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.
Thus the only possible conclusion is that there is a common universal
shared present moment time which is completely different from clock time.
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.
> > wrote:
>> On Wed, Jan 1, 2014 at 8:41 AM, Russell Standish
>> > wrote:
>>> 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 not
>>> > 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
>>> University of New South Wales http://www.hpcoders.com.au
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