Thursday, December 12, 2013

Non-local theories violate causality

A new paper by Egg and Esfeld has this abstract:
The paper argues that a causal explanation of the correlated outcomes of EPR-type experiments is desirable and possible. It shows how Bohmian mechanics and the GRW mass density theory offer such an explanation in terms of a non-local common cause.
This is nonsense. A non-local theory is not a causal explanation of anything.

An explanation of how an event A causes an event B means that there is a continuous chain of causes from A to B moving forward in time. A non-local theory is just the opposite, as it posits some sort of action-at-a-distance.

The article says:
There are two principled ways of causally explaining correlations between two distinct events: one can either postulate a direct causal influence of one event on the other or one can suppose that a common cause of the two events accounts for the correlation. In everyday contexts, this distinction is crucial, because it has consequences for the kinds of manipulations that we can perform. If there is a direct causal link from event A to event B, then we can (in principle) bring about changes in B by intervening on A, whereas this is not possible if A and B are only connected via a common cause. In the context of quantum mechanics, however, the distinction between a direct cause (DC) and a common cause (CC) is much more elusive, since we cannot control the outcomes of quantum measurements in the right way to perform the intervention on A that is necessary to distinguish between these two causal structures.

Bohmian mechanics is thus not committed to superluminal causation in an operational sense, but it is so committed in a metaphysical sense: given any initial particle configuration, the theory supports counterfactual claims of the type: “If Alice had chosen a different setting, Bob would have obtained a different outcome”. This might sound like a kind of action at a distance that should be understood in terms of a DC model (see section 2), rather than as the manifestation of a common cause.
I am not why anyone likes a silly theory like Bohmian mechanics, but some people mistakenly believe that it gives a causal interpretation to quantum mechanics. It does not. The ordinarly Copenhagen interpretation is much more compatible with causality than Bohmian mechanics.

1 comment:

  1. Physics is truly about describing how objects interact...interaction is not possible without causation involving objects. Modern physics is philosophically destitute, delights in illogic, and can not discern an object from a concept. Squishy definitions lead to pathetic fudges and bad English papers, not good physics. As for the Copenhagen interpretation, why anyone would be impressed with an interpretation of a 'mechanism' that requires one to confuse the concepts of 'and' with 'or', and require a suspension of rationality or visualization is beyond me.
    If your theory can embrace a mechanism without an actual physical mechanism, declare that no further understanding is possible, and declare 'non-local theory' a suitable explanation of physical process without a cause, why not dispense with any pretense of logical rigor whatsoever and just take up metaphysics?