
#1
Aug2711, 12:17 AM

P: 43

Hi
If two events are separated by a timelike interval, then all inertial reference frames will agree on the order of the two events. For example, if event A occurred before event B in one inertial reference frame, then event A occurred before event B in all inertial reference frames. The invariant interval, given by I = (c[itex]\Delta[/itex]t)^{2}+([itex]\Delta[/itex]x)^{2}+([itex]\Delta[/itex]y)^{2}+([itex]\Delta[/itex]z)^{2}, for two events separated by a timelike interval is always less than 0. My question is, for two events that are causally connected, can the invariant interval be less than or equal to 0? Or does I have to be strictly less than 0 for such events? I'm not sure because as far as I'm aware, there can only be a causal connection between two events if it is possible for a signal to travel between the two events, so that means that two events can be causally connected if they are separated by a lightlike interval too, ie, I = 0. But if this is the case, then in the reference frame of the light, doesn't event A and event B occur at the same time then, in which case there isn't any causal connection between event A and event B? Thanks 



#2
Aug2711, 12:58 AM

Physics
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P: 5,510

http://physicsforums.com/showthread.php?t=511170 


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