According to the theory of special relativity, if twins A and B depart from triplet X in opposite directions, traveling at the same speed, and eventually meet up again after their respective journeys, they will experience time dilation relative to each other.
From the perspective of observer X, who remains at the original location, both A and B will appear to be moving away from X at the same speed. Therefore, from X's perspective, the clocks of A and B will both appear to run slower than X's own clock due to time dilation.
However, from the perspective of A, who is in motion relative to X, B is also in motion. According to special relativity, A will observe B's clock running slower than their own clock. Similarly, from the perspective of B, who is also in motion relative to X, A is in motion, and B will observe A's clock running slower than their own clock.
This phenomenon is known as time dilation, where time appears to move slower for objects in motion relative to an observer. It is a consequence of the constancy of the speed of light and the relativistic effects of spacetime.
Therefore, according to special relativity, A's clock will appear to run slower than B's clock from B's perspective, and vice versa. When they reunite, the difference in the elapsed times on their clocks will demonstrate the time dilation effect.