On Wed, Feb 26, 2014 at 6:46 PM, Edgar L. Owen <edgaro...@att.net> wrote:

> Jesse,
>
> O, for God's sakes. Just take a SINGLE INERTIAL coordinate system centered
> at some point in deep space from which they both depart, travel
> symmetrically away from RELATIVE TO THAT SINGLE COORDINATE SYSTEM and then
> meet back up at. That addresses all your concerns.
>
> The whole trip is symmetric, the twins' proper times will be in a 1:1
> correlation at all times from beginning to end. Both twins agree their
> proper clocks run at the exact same rates, not because they observe them
> but because they understand relativity.
>
> Do you agree? Of course not....
>

I agree that there is a 1:1 correlation between their proper times RELATIVE
TO THAT INERTIAL COORDINATE SYSTEM (in this case, the correlation is such
that a given proper time time T of one is correlated with the SAME proper
time T of the other, according to that coordinate system's definition of
simultaneity). Likewise, their proper clocks "run at the exact same rates"
RELATIVE TO THAT INERTIAL COORDINATE SYSTEM (i.e. both have the same
function for proper time as a function of coordinate time). But so what?
Their proper times have a different 1:1 correlation relative to some other
inertial coordinate system (in which the proper time T for one is
correlated with a DIFFERENT proper time T' for the other--this is still a
1:1 correlation in the sense that a specific proper time for one is
correlated to a specific proper time of the other), and their proper clocks
run at different rates relative to this other coordinate system (they have
different functions for proper time as a function of coordinate time). So
this is of no help in deciding which of the VARIOUS possible 1:1
correlations in their proper times represent the proper times that share
the same frame-independent "present moment", even if such a thing exists
(as you know I am skeptical about such a thing, but I don't totally rule it
out as a possibility).

Please tell me if you agree or disagree that all statements about 1:1
correlations of proper times and ratios of "rates" only have meaning
RELATIVE TO SOME COORDINATE SYSTEM (in mainstream relativity theory anyway,
leaving aside ideas which aren't part of relativity like p-time), and that
all inertial coordinate systems are considered equally valid in special
relativity.

If you continue to ask me "Do you agree?" type questions while ignoring the
similar questions I ask you, I guess I'll have to take that as a sign of
contempt, in which case as I said I won't be responding to further posts of
yours. Any response is better than just completely ignoring questions, even
if it's something like "I find your questions ambiguous" or "you've asked
too many questions and I don't have time for them all right now, please
narrow it down to one per post".

Jesse



>
> Nevertheless, it's correct and the rest of what I said follows...
>
> Edgar
>
>
>
>
>
> On Wednesday, February 26, 2014 3:40:36 PM UTC-5, jessem wrote:
>>
>>
>>
>> On Wed, Feb 26, 2014 at 2:31 PM, Edgar L. Owen <edga...@att.net> wrote:
>>
>> Jesse,
>>
>> You continue to quibble over terminology to avoid engaging the real
>> issues. Of course by 'view' I DO mean the actual equations in terms of a
>> coordinate system with origin at a particular observer. There is OF COURSE
>> a single set of equations that describes that view.
>>
>>
>> There are a single set of equations for any particular coordinate system,
>> but my point is that for non-inertial observers or observers in curved
>> spacetime, talking about an observer's "view" is ill-defined because there
>> is no convention about which coordinate system to label as the "view" of a
>> given observer. Even if you specify that you want a "coordinate system with
>> origin at a particular observer", there are an infinite number of DIFFERENT
>> non-inertial coordinate systems you could come up with that would have the
>> property that the observer is always at the origin, each with a different
>> set of equations. I asked about this issue specifically in the second
>> question from my last post, which you didn't answer:
>>
>> '--If you don't disagree with the statement above, do you disagree with
>> my statement that there's no specific coordinate system that is understood
>> by physicists to represent a particular observer's "view" or "perspective"
>> in general relativity, so that if you just talk about equations "used by"
>> observer A without specifying a coordinate system, physicists wouldn't know
>> what you were talking about?'
>>
>> Could you please just just quote my questions and answer them
>> specifically in turn, as I always do with yours, rather than just sort of
>> summarizing what you think my main points are and addressing them in a
>> broad manner?
>>
>>
>> Answers to your next question:
>>
>> Yes, of course the OBSERVABLES are based on some coordinate system, but
>> you can't seem to get it through your head that any observer A who observes
>> another observer B can also know the equations governing how that observer
>> B observes A himself.
>>
>>
>> I'm not sure which question you are responding to here, you say "next
>> question" but it seems like this is actually a response to my FIRST
>> question (with no response given to any of the others), namely:
>>
>> '--Do you disagree that equations that observer A uses to "calculate the
>> observables of any other observer B" are always based on A using some
>> particular coordinate system? (if so, can you give an example of an
>> equation that could be used to make such a calculation which would not
>> depend on any specific coordinate system, but which would still be
>> observer-dependent in some sense, so it would still be meaningful to
>> identify this equation specifically with observer A?) '
>>
>> You didn't really respond to any of the subsequent three questions with
>> dashes before them, as far as I can see, although you did respond to the
>> question in my last paragraph. Can you please go back and respond to the
>> middle 3 questions?
>>
>>
>>
>> Do you deny that?
>>
>>
>> I deny that there is any single set of "equations governing how observer
>> B observes A himself", if B is not an inertial observer in flat spacetime.
>> If he's not, then as I said, there's no convention in relativity that says
>> that any particular coordinate system should be interpreted as "belonging"
>> to B. If you specify in detail what coordinate systems you want A and B to
>> use to perform calculations (or if both of them are inertial in flat
>> spacetime, so it's taken as read that they each use their own rest frame),
>> then of course A can figure out what B would calculate and B could figure
>> out what A would calculate.
>>
>> Also, do you understand that even for inertial observers, the idea that
>> an observer's own rest frame can be labeled "his view" or taken to describe
>> "his observations" is PURELY A MATTER OF CONVENTION, not something that is
>> forced on us by the laws of nature? Physicists just don't want to have to
>> write out "in the observer's comoving inertial frame" all the time, so they
>> just adopt a linguistic convention that lets them write simpler things like
>> "from this observer's perspective" or "in his frame" as a shorthand for the
>> observer's comoving inertial frame. Physically there is no reason an
>> observer can't assign coordinates to events using rulers and clocks that
>> are moving relative to himself though, lots of real-world experiments
>> involve measuring-instruments that move relative to the people carrying out
>> the experiment.
>>
>>
>>
>>
>> I'll skip now to the point you make in your last paragraph responding to
>> my symmetric trip case:
>>
>> Your comments
>>
>> ...
>
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