Saw this as an answer to another question and can’t wrap my head around the logic. What? How? Why??
In: 56
The speed of causality is roughly 3×10^8 m/s, which is to say, the speed that light just happens to go at.
More conceptually, the speed of causality puts a limit on what events can be causally related.
For instance, the Moon is roughly 1 light second away from the Earth. No events happening on the Moon for the next second can in any way depend on events happening on *Earth* for the next second. Events happening on the Earth for the next second can only possibly effect events on the Moon that happen *more* than a second in the future. There is simply no avenue for information about an event on Earth to reach the Moon in less than a second.
Why does this concept exist? Well that’s a bit tricky. To some degree, the laws of physics simply exist, and we just have to accept them. We can sometimes say “this law of physics has to work in this way because these *other* laws of physics work in *that* way”, but then you’re just pushing the question back to those other laws of physics.
So for instance, we could look at Albert Einstein’s Special Theory of Relativity. One of the consequences of Special Relativity is that there is *no such thing* as an objective “present”. In one frame of reference Event A might happen prior to Event B, while in another frame of reference, Event B might happen prior to Event A. There might then be other frames of reference in which Events A and B occur simultaneously.
Now rather critically, the degree to which events can be moved around in relative time is dependent on how far apart the events are. If Event A takes place on Earth at time 0s, and Event B takes place on the Moon at time 0.5s (in the reference frame of the Earth), then there will exist other reference frames in which Event *B* takes place at time 0s, while Event *A* takes place at time 0.5s – in that light second of spacial distance, we get a second of “wiggle room” on the ordering of events.
If there weren’t a finite speed of causality, this could cause problems for us. For instance, if A could *cause* B, then we’re going to have reference frames in which the *effect* (B) happens *earlier in time* than the cause (A). Now maybe the universe would be perfectly fine with something like this happening, but at the very least, it’s not something that our limited human brains know how to deal with.
But because there *is* a finite speed of causality, we know for a fact that event A could *never* be a cause of event B, and therefore it doesn’t matter if we swap the ordering around.
But of course, this still really just pushes the question back. The questions then become, *why is special relativity true?* and *why is it important for causes to precede effects?* And yeah, maybe we can come up with answers to those questions, but said answers will just raise more questions of their own.
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