But there is NO "inertial frame that is not (presumably you meant 'in which 
THEY are not') moving relative to one another" for the twins during the 
trip. If you think there is then what is it and how is it defined?

One twin is accelerating and the other isn't for goodness sakes. There 
simply is no common 'frame' in the sense of something measurable by a clock.

There is however a common present moment of p-time in which the twins 
always exist. Perhaps that is what the notion of 'coordinate time' is 
grappling with?

If coordinate time posits that the 'REAL' spacetime coordinates of the 
twins are the same prior to, during, and after the trip, but these 
coordinates CAN'T be actually measured then it's just trying to explain the 
present moment of p-time without understanding what it actually is, that 
it's a real observable present moment which is basic to all existence.

If that's true then coordinate time is just a feeble half-hearted shot at 
P-time without understanding it's an entirely separate kind of time that is 
actually real (and the fundamental observable phenomenon of our existence) 
and in which clock time runs at different rates.

So (if I'm correct) then if you believe in coordinate time you are actually 
arguing FOR p-time and must accept p-time.



On Friday, January 17, 2014 8:00:20 PM UTC-5, Brent wrote:
>  On 1/17/2014 10:07 AM, Edgar L. Owen wrote:
> No. If you think so called 'coordinate time' is a real kind of time then 
> how do you measure it? 
> You measure it by using clocks in an inertial frame that are not moving 
> relative to one another.  That's exactly how Einstein thought of it.
> How do you measure p-time?
> Brent

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