Some open future views rely on the concept of a nomically possible branch—a complete sequence of how things might go given the laws of nature.
The problem with the concept is this. A nomically possible branch seems to be something like an exhaustive collection of propositions about all times, specifying precisely what happens at all times, with the collection as a whole compatible with the laws of nature. But now consider a world where indeterminism never gives out on any branch: no matter how things go, at every time there will still be more branching. (Our world may well be like that.) Then on an open future view, the propositions making up a branch cannot be all true together—for at no time t can the exhaustive propositions about t’s future be true, as that would violate open futurism given that branching never gives out.
For a while I thought that a decent solution to this is to say that a branch only needs to satisfy the weaker condition that for every time t, all the propositions in the branch about times up to t can be true together with the laws of nature.
But my recent example of random transtemporal causation is problematic for this solution. Suppose that today an indeterministic event E causes a green flash of light to happen on a random future day, and that the laws guarantee that no green flashes happen for any other reason. Then a branch that contains E but no green flashes of light satisfies the weaker possibility condition: for at every time t, all the propositions in the branch about times up to t can be true together with the laws of nature, since E does not causally guarantee that a green flash will happen at or before t, but only that a green flash will happen at some time or other.
Probably the best move for the open futurist is to deny causation across temporal gaps or any other mechanism that nomically guarantees that some event will happen without guaranteeing a time by which it will happen.
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