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Light cones and causality
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Only events inside the cone can influence each other.
The light cone from an event separates the future, past and elsewhere; only events inside can be causally connected. It guarantees effects follow causes in all frames.
The Sun's current state can't affect you for 8 minutes.
Faster-than-light signals would break causality.
In more detail
A light cone separates events into those that can influence an event (its past), those it can influence (its future), and those that are unreachable (elsewhere). Causality is preserved within these cones.
Real-world uses
- Light cones define what information can travel between events.
- They are key to understanding causality in relativity.
- Physicists use light cones to decide which events can affect each other and which cannot.
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Frequently asked questions
Can anything travel outside the cone?
No. Nothing can travel faster than light, so the cone bounds all causal influence.
What is elsewhere?
Events outside the light cones, which are not causally connected to the origin.
Can anything go outside the light cone?
No. Causal influence cannot travel faster than light, so only events inside the cone can be connected by a signal.
Related topics in Relativity
Twin paradox · Spacetime diagrams · Spacetime interval · Proper time · Relativistic momentum · Relativistic energy