In MLE today we discussed Boris Kment’s ‘Counterfactuals and Explanation’. See here for the details of the discussion, handout, etc. I really liked the view of this paper, and found myself wondering how to carry it over to my own view.
According to Everettian Modal Realism, all worlds share the same fundamental laws. So criterion 1) of Kment’s theory of closeness gets explained by EMR, rather than stipulated.
Of course, EMR can’t appeal to the notion of impossible worlds to explain counterfactuals with necessarily false antecedents. So we have two options here – either take all such counterfactuals to be trivially true, and explain their assertibility or lack thereof in pragmatic terms, or give an alternative metalinguistic account of their truth-conditions. I prefer the former option, as explained here. This might look like a disadvantage of EMR, but only if you’re comfortable with ersatz linguistic possible worlds – for those of us persuaded by Lewis’ criticisms of such worlds, impossible worlds just make no sense at all.
Kment’s account also involves worlds featuring violations of laws of nature, which looks incompatible with EMR. But if we restrict the exceptions used in the analysis to apply only to non-fundamental laws, like the laws of statistical mechanics or economics, then Kment’s account of closeness can be retained for all ordinary counterfactuals. The only problematic cases will be counterfactuals explicitly about fundamental physics.
Consider two cases:
1) If the electron was now here rather than there, the entire history of the world would have been different.
2) If there were now no electrons within a million miles of here, the entire history of the world would be different.
Even on EMR, 1) comes out as false, because the closest worlds with an electron in a slightly different position are worlds which diverged quite recently, due to indeterministic evolution. Since on EMR determinism is not even a metaphysical possibility, the burden on Kment’s account to deal with deterministic worlds is lifted, and cases like 1) present no real problem.
Cases like 2) are a bit harder. The indeterministic evolution required to get rid of all electrons within a million miles from here in the relatively recent past is a phenomenally unlikely event – so unlikely, I think, that it counts as a ‘big violation of law’ in Kment’s terms (although the only laws violated are special-scientific laws, like classical electrodynamical laws.) What seems to matter is that very low-probability events would have to occur to get rid of the electrons in the recent past, while courses of events starting much longer ago which would have led to a lack of electrons round here are much higher-probability.
So I think a defender of EMR should adopt the following criteria of closeness:
– avoid very low-probability events.
– achieve match in matters of particular fact, where the facts have the same explanation in each world.
These are the only two criteria we need; and the trade-off between them will be non-trivial. However, we have a good enough intuitive grasp on the trade-off – it seems plausible that the spontaneous disappearance of all the electrons within a million miles is low-enough probability to cancel out billions of years of match in matters of particular fact, whereas the spontaneous movement of one electron across a micrometre or so of space is not low-enough probability to cancel out more than a few seconds of match in matters of particular fact.