1. The problem statement, all variables and given/known data 2. Relevant equations spacetime interval ##Δs^2=-Δt^2+Δx^2+Δy^2+Δz^2## 3. The attempt at a solution We know that the straight path in spacetime diagram is the one with maximum proper time, however we get the same value after going around the universe and this is not consistent of my understanding of Lorentz invariance. I just want to know if my understanding is right or not. Any comment would be appreciated, Regards.