Beaconator
Valued Senior Member
They share the same destination
And, as I've described before, she can set up a grid of clocks, stationary wrt her, and synchronized via light signals, with each clock manned by a helper observer (always having her same age) who can send her a message giving that helper's age and the other twin's age when the other twin goes flying by that helper. That message she receives will always agree with what the TDE equation told her when she asked the question.
OK. Now you have specified that he has accelerated (with a Dirac delta acceleration that instantaneously reduces his speed relative to her to zero). So now you DO have to specify which simultaneity method you want to use. You can't say anything now about simultaneity until you've chosen a simultaneity method. From your conclusions about what happens at that instant (when he changes their relative speed to zero), you have clearly chosen the CMIF (Co-Moving Inertial Frames) simultaneity method. The defining assumption of the CMIF method is that the observer ALWAYS agrees with the perpetually-inertial observer (the PIO) with whom he is currently co-stationary and co-located at that instant. The PIO says that she is 40 at that instant (when he is 20).
He doesn't abandon his prior belief. I.e., he doesn't say "I must have been wrong before". What he says is that she instantaneously aged by 30 years, from 10 years old to 40 years old. (And if, instead of changing their relative speed to zero, he had instantaneously increased his speed, the CMIF method would say that her age had instantaneously DECREASED by some amount ... i.e., she had instantaneously gotten YOUNGER).
But if, instead of choosing the CMIF simultaneity method to get your answer, you had chosen my simultaneity method, then he would NOT conclude that her age changed instantaneously when he changed their relative speed to zero. He would NOT agree with the PIO for some (determinable) time after his speed change. That amount of time in his life when he disagrees with the PIO is called the Disagreement Interval (DI). The magnitude of the disagreement is largest immediately after his speed change, and decreases after that until it reaches zero at the end of the DI...
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Let T- denote the instant (in his life) infinitesimally before his speed change, and let T+ denote the instant immediately after his speed change. There is only an infinitesimal time difference between those two instants.
With the CMIF method, at T-, he tells PIO_A that A's array of clocks are all perfectly synchronized, and he tells PIO_B that B's array of clocks are terribly synchronized.
It seems to me that my method comes out of that comparison looking pretty good. In both methods, clocks that were perfectly synchronized become terribly synchronized, and vice versa. But in my method, the changes in the degree of synchronization are gradual, not abrupt as in the CMIF method. That could be considered to be a good thing.
I don't find your argument compelling. Deciding that a line of clocks, which were perfectly synchronized an instant ago, are now suddenly very unsynchronized seems more bizarre to me than a line of clocks which gradually become unsynchronized.
I am, at the moment, much more interested in your reaction to my possible proof, in the other thread, that negative ageing doesn't occur in the CMIF simultaneity method.
I like the simplicity of CMIF, and I have no problem with negative ageing. What bothers me is to not KNOW what the correct simultaneity-at-a-distance for an accelerating observer IS. I'm convinced that there IS a correct simultaneity-at-a-distance for an accelerating observer, and I want to know what it is.
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You are still ignoring the really important question: "Is my proof, that negative ageing doesn't occur, valid?" If my proof IS valid, then CMIF simultaneity ISN'T valid.
You don't think it is invalid that all of the perpetually inertial people who are stationary wrt the home frame say that "she" is 40 years old when the home-grid synchronised clocks display 40 years. So to PROVE that it would be invalid for "him" to use CMIF simultaneity after he has stopped moving and become stationary with respect to her, you would have to prove the following:
1. All of the perpetually inertial people who are stationary wrt the home frame are CORRECT when they say that "she" is 40 years old when the home-grid synchronised clocks display 40 years, but...
2. The one person "he" who is stationary wrt the home frame who has not been perpetually inertial is INCORRECT if he says that "she" is 40 years old when the home-grid synchronised clocks display 40 years.
Go ahead, I'll wait.