👯 Twin Paradox
One twin rockets away at near-light speed; the other stays home. When the rocket twin returns, less time has elapsed for them — they are younger. Adjust β and trip distance to see the age gap from Lorentz time dilation.
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The Twin Paradox
The paradox: if motion is relative, why isn't each twin younger than the other? The answer is that the rocket twin accelerates — they change inertial frames at the turnaround point. This breaks the symmetry. The rocket twin truly ages less by a factor of γ.
Earth elapsed time: T = 2d/(βc). Rocket proper time: τ = T/γ = T√(1−β²). Age difference: T−τ = T·(1−1/γ). At β = 0.8, γ ≈ 1.667, so the rocket twin ages only 60% as much.