Okay, smart people I respect believe this acausal trade business so I've been hesitant to dismiss it and have tried to wrap my head around why I should give a damn about people in parallel universes.. The best I could do is that acausal decision theory is either...

a) Acausal trade is what you end up believing in if you assign a non negligible likelihood to the simulation hypothesis

b) Acausal trade is an attempt to put a rational grounding underneath some types of kindness and altruism

I'm probably wrong about this. If somebody would please explain to me like I'm a five year old what it is I'm missing (without relying on omniscient beings or simulations or other speculative stuff), I would be in that person's debt.

>how do we test this

Curious what definition of parallel universes you are thinking of @JacyAnthis ? The types I think of (multiverse, many-worlds) do not support meaningful interaction between parallel universes almost by definition.

@jack May be referring to acausal trade with them, which wouldn't require communication.

@IsaacKing Hmm, I suppose that could potentially work, true.

@IsaacKing I often make acausal trades with alternate mes produced through intentional splitting using the "Universe Splitter" app, which uses the results of single-photon interference events to split the universe.