# Space-time puzzle

## Main Question or Discussion Point

Why is it possible that an object can be found in the same place in different times but can not be found at the same time in different places?

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Dale
Mentor
Because an object's worldline is always timelike.

JesseM
Yes, if you could have a faster-than-light particle with a spacelike worldline, then according to the definition of "same time" used by inertial frames in relativity, there would be at least some frames where the particle would be at different places at the same time.

Yes, if you could have a faster-than-light particle with a spacelike worldline, then according to the definition of "same time" used by inertial frames in relativity, there would be at least some frames where the particle would be at different places at the same time.
This means that if you could have a faster-than-light particle then even the existance of a particle is relative because diffirent place at the same time means another particle

Dale
Mentor
This means that if you could have a faster-than-light particle then even the existance of a particle is relative because diffirent place at the same time means another particle
Classically we have no difficulty in identifying a given timelike particle now and earlier as the same particle provided the worldline is continuous. I would think that we would similarly have no conceptual difficulty in identifying a given spacelike particle here and there as the same particle provided the worldline is continuous.

Classically we have no difficulty in identifying a given timelike particle now and earlier as the same particle provided the worldline is continuous. I would think that we would similarly have no conceptual difficulty in identifying a given spacelike particle here and there as the same particle provided the worldline is continuous.