Time-reversed twin paradox This started with wondering about the nature of certain physical quantities under time-reversal - chiefly, that acceleration retains its magnitude and direction at a given time regardless of the 'direction of time' used; this is different to say momentum, which may be reversed under time-reversal (in the sense that we are integrating forward in time from our perspective, along the backward direction in time).
There may be already agreed-upon conventions I'm not aware of regarding which quantities would be reversed, but the essence of the idea is that some quantities or some combinations of quantities need to be reversed, while others (such as acceleration) don't.
With respect to the twin paradox, this got me wondering if it works under non-trivial time reversal regarding the acceleration periods of the paradox. That is, suppose it isn't enough to simply reverse the order of events; if we assume everything runs in reverse, could we start off with two people of different ages, and due to relative reverse motion cause one twin to 'catch up' in 'getting younger' such that at some future (ie their past) they are of the same age?
-PS
To put the question more simply:
Given that acceleration retains direction going forward and backward in time while velocity (or momentum) may not, do the relativistic effects remain the same (and do they make physical sense) from the perspective of a forward-time observer watching events unfold in reverse?
More generally:
By virtue of acceleration having the same magnitude in both directions of time, does it mean it is impossible to discern a direction of time from any measurable acceleration alone? (further questions tempt relevance)
 A: You can have a situation where two people start out next to each other with different ages, then move apart and reunite later so that they are the same age when they meet, with the one that started out younger moving inertially between meetings and the one that started out older accelerating during the journey. If they carried clocks that showed, say "100 years minus my current age", then if you played the movie of this backwards, you would have a situation where their clocks initially show the same reading, then both clocks tick "forward" as the movie continues to play backwards, with the inertial twin's clock showing a greater reading when the twins are again next to each other at the end of the time-reversed movie. So just looking at their clocks, this would look just like a movie of the standard twin paradox scenario, and if the movie showed the rate each clock was ticking in some inertial frame at each point in the journey, this rate would be $\sqrt{1 - v^2/c^2}$ slower than a clock at rest in this inertial frame, just like in the standard twin paradox. If the movie didn't show any thermodynamically irreversible processes (or any of the rare particle interactions that violate T-symmetry), there would be no way of knowing you were watching a movie being played backwards.
