How Can We Understand the Possibility of Time Travel in Relativity?

[shyamalshukla]

Special theory of relativity says that in the absence of an absolute reference, different observers may disagree on the time at which a particular event happened.

With this knowledge, how do i explain time travelling? Every observer should be witnessing the same set of events (though their watches may disagree on the time of observation). How can someone see an event B happening at point P when a different observer is seeing event A happenning at the same point, which i suppose is what most of us refer to as time travelling

 

[Doc Al]

Every observer should be witnessing the same set of events (though their watches may disagree on the time of observation).

Events are things that happen at a particular place and time. Example: Lightning strikes a rock at point P at 1 pm.

How can someone see an event B happening at point P when a different observer is seeing event A happenning at the same point,

Maybe they happen at different times? If they didn't, then they would be occurring at the same place and time and both observers will see it.

which i suppose is what most of us refer to as time travelling

Not really.

 

[bcrowell]

There are two different things you have to distinguish here.

In special relativity, different observers disagree on which events are simultaneous. However, they always agree on the time-ordering of events that have a cause-and-effect relationship, and they can always sort out a chain of such events in linear order.

In general relativity, which is the extension of special relativity to describe gravity, there are hypothetical situations in which you can have a chain of cause and effect that is circular. This is referred to as a closed timelike curve (CTC). The chronology protection conjecture is the hypothesis that CTCs will not arise under realistic conditions in our universe.

A good book on this subject is Time Travel in Einstein's Universe, by Gott.