Saw this as an answer to another question and can’t wrap my head around the logic. What? How? Why??
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Causality sounds like a big scary word but it’s actually an incredibly simple concept that we all intuitively understand – it’s just cause and effect. Some event occurs and effects something else. You drop the plate you’re holding, and the plate hits the floor and breaks. Super easy – you dropped the plate (cause) and it broke (effect). That’s all causality is.
Now the universe has a maximum speed limit, which “happens” to be the speed light travels at in a vacuum (it’s not a coincidence, more on that in a moment) – just under 300,000 kilometers per second. Nothing can travel faster than this, and light travels at exactly this speed. In fact, all massless particles *have* to travel at exactly this speed. This is the speed of causality. It’s no coincidence that light and other massless particles travel at this speed, and the source of this speed limit comes not from the fact that light travels at the speed, but from the fact that it’s a the fundamental speed limit of the universe for *everything.* In other words, light obeys the speed limit of causality, not the other way around.
Because of that speed limit, it takes time for distant events to have a causal relationship. Let’s say you press a button (cause) and it makes bell ring (effect). The fastest that information can travel from the button to the bell is the speed of light, so if you’re 300,000k away from the bell (the distance light travels in one second),it can’t ring sooner than 1 second after you sent it. If the bell rings sooner than 1 second, it couldn’t have been you that caused it because it takes the bell a full second to “know” that you pushed the button. In other words, those 2 events are not causally related. There’s no way for the button to have an effect on the bell because not enough time has passed for the cause to reach the effect.
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