- #1

- 165

- 1

## Main Question or Discussion Point

I was reading Spacetime and Geometry by Caroll and I came across this notion:

I have never understood this and I was wondering if someone could enlighten me.In special relativity there is no absolute notion of "all of space at one

moment in time." Instead, there is a rule that particles always travel at less than or equal to the

speed of light. We can therefore define light cones at every event, which locally describe

the set of allowed trajectories. For two events that are outside each others' light cones,

there is no universal notion of which event occurred earlier in time.