“Causality” Addendum
Nobody has ever directly observed “causation”. What is observed is correlation and sequence: B reliably follows A. Causality is the interpretation we lay on top of that pattern.
David Hume made this exact point in the 1740s: all we ever actually perceive is one event followed by another, over and over. We never perceive the necessary connection between them, that’s something the mind supplies, a habit of expectation built from repetition, not a thing we directly detect in nature. He called it one of philosophy’s genuine open wounds, and it still is. Kant’s response was to argue causality isn’t something we find in the world at all, it’s a structure our minds impose on experience in order to have coherent experience in the first place, more like a pair of glasses we can’t take off (or a VR headset) than a fact we’re discovering.
So in that sense: causality was never “a theory” in the way, say, general relativity is a theory, a specific falsifiable mathematical model. It’s more like a precondition other theories are built on top of. Every physical theory including entanglement assumes some notion of causal structure to even be formulated.
Where physics actually does treat it formally: In relativity, causality gets a precise technical meaning, it’s encoded in the light-cone structure of spacetime. “A can cause B” is defined as “A lies in B’s past light cone,” i.e., a signal traveling at or below light speed could get from A to B. This is the actual load-bearing reason entanglement is such a puzzle: the correlations show up outside each other’s light cones, which is exactly why physicists were so careful to prove no usable signal (no causal influence in the relativistic sense) is transmitted. If it were, you’d get closed causal loops, effects preceding causes in some reference frames, actual paradoxes. So relativistic causality is a hard constraint physicists build their theories to respect, precisely because they’re not fully certain why it must hold, only that every observation says it does.
If ER/EPR-style ideas are right and spacetime itself is built out of entanglement, then causal structure (which depends on spacetime’s light cones) would be derived from entanglement rather than the thing entanglement has to obey. That would flip the whole hierarchy; causality stops being bedrock and becomes emergent, same as distance. Physicist want formulas before they decide its true. I’ve already decided it is.