Part 6/10:
Because the traveling twin’s motion isn’t uniform—due to acceleration and deceleration—the effects on aging are asymmetrical. When considering the entire journey, including the turnaround, the traveling twin will indeed be younger upon reunion, having experienced less elapsed time.
The Light Experiment: Visualizing the Journey
To understand this better, imagine both twins sending beams of light to each other at regular intervals—each marking a year in their own frame of reference. For the stationary twin on Earth, the light beams travel straightforward paths, marking years consistently.