Physics 197 Lecture 28: The Cosmic Speed Limit
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Physics 197 Full Course Notes
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Nothing can travel faster than the speed of light in a vacuum. Causal in uence: any effect (particle, object, wave, or message) produced by one event that can cause another. The speed of light is the real cosmic speed limit. Timelike: when (cid:791)s^2 > 0: we can nd an inertial frame where the events occur at the same place, we then measure (cid:791)s with the frame"s clock at that location. These categories are frame-independent, since the value of (cid:791)s^2 is frame- independent. Events separated by a spacelike interval cannot be causally connected, since the causal in uence would have to travel faster than the speed of light. Since the categories of spacetime interval are frame-independent, all observers will agree about: which events have a timelike (or lightlike) interval with a given event p and occur after it in all frames.
