The Rocket Twin is Younger!
Answer: The rocket twin returns younger! But why? Why can’t we use principle of relativity to say they are the same age?
The key is: The Rocket Twin accelerated while the Earth Twin didn’t! The acceleration distinguishes the two twins and prevents us from applying the principle of relativity.
The Calculation: Identify 3 Events:
- The Rocket Twin measures proper time for both time intervals: 1-2 and 2-3. Therefore the Rocket Twin measures the smallest time interval from 1-3!