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I have seen the classical twin paradox before. It uses a twin stationary on Earth and the other traveling away and back. I have seen many contradictory solutions for it, some use general relativity, others use special relativity, either way, I have never been satisfied with what I've read. They always try to break the symmetry through the traveling twin's acceleration and deceleration, but never quite succeed.
So, let's do away with the classical twin paradox and let's explain a much simpler, perfectly symmetrical version of it where both twins are moving towards each other.
So imagine we have Twin A in a spaceship, and Twin B in another. They are both traveling at the same speed towards each other.
If I understand relativity properly:
- From Twin A's frame of reference, he's stationary and Twin B is moving at a constant speed towards him, therefore, Twin B is aging slower.
- From Twin B's frame of reference, he's stationary and Twin A is moving at a constant speed towards him, therefore, Twin A is aging slower.
When they both finally meet, they both think that the other is younger. Which one of them is right?