It is possible that certain other conceptions of free will may be under threat by certain metaphysics of time. For example, when agents make decisions, they typically suppose that there is some sense in which the future is open to possibilities. Libertarian free will (the ability to do otherwise) requires an agent to have (at the moment of choice) multiple alternate possibilities from which to choose. But if eternalism (or the B-theory of time) is true, then it would seem, at least prima facie, that the future is not open to possibilities. Eternalism, after all, is the thesis that all events (including past and future events) are equally real. Future events are just as real as past and present events according to this theory of time. This could imply that the future is metaphysically closed and fixed. To the libertarian, this may mean that the only choice available to any agent is the one that is already part of the actual future. One can thus believe that eternalism is incompatible with libertarian free will.

As Niall Shanks (1994) argued, libertarian free will seems to be incompatible with such a theory of time. To Shanks, a theory of time in which future events and objects are ontologically equal to past and present ones is inhospitable to libertarian free will. He claimed that one of the reasons for this is because the agent lacks existential control: the ability to bring events and objects into existence.