Time and Distance in Special Relativity
Most recent answer: 03/18/2019
- Jacqueline Georges (age 35)
Millbury, MA, USA
On the first part about going around the earth, actually everybody will agree about how many times the train (or, realistically, satellite) has gone around. An earth observer and a somebody going around just have to count how many times they wave as they go past each other, and they'll get the same count.
On your second question, the key point is that there is no such thing as one true answer to "how fast is it going?" Velocity depends on the reference frame, an the same laws of physics work in frames that are in motion with respect to each other. So there is no way to pick one answer as the right one. Different frames not only assign different time intervals to events but also different length intervals. They don't agree on which events are simultaneous, unless the events also happen at the same place. Basically they all agree on when things bump into each other, but use different coordinates to describe other pairs of events.
Mike W.
(published on 03/18/2019)