Time Travel. A History

“For what is and what has come about, then, it is necessary that affirmation, or negation, should be true or false,” Aristotle said. In other words, statements about the present and statements about the past are either true or false. Consider the proposition There was a sea battle yesterday. True or false. There is nothing in between. So it is natural to consider whether this applies to statements about the future. There will be a sea battle tomorrow. By Saturday this will be true or false, but must it be either true or false now? Put in terms of language and logic, these propositions look identical, so the same rules should apply. There will be a sea battle tomorrow. If it’s not true or false, what else is there?

Aristotle remained unconvinced. He carved out an exception for propositions about the future. Where the future is concerned, he felt logic needed room for another state of things: call it indeterminate, contingent, unfixed, unknown, up for grabs…The modern philosopher finds this clumsy.

By the weekend, there will have been a sea battle. Not every language has a future perfect progressive tense built in; when your language does, it tends to feel natural. Either there will have been a sea battle or there won’t. When the time comes, we’ll know which. It will seem to have been inevitable. In this way, language and logic tend to suggest an eternalist view, the Universe Rigid, the view that gained solidity with the arrival of clockwork physical laws as revealed by Newton and Laplace. The block-universe package was wrapped and sealed, seemingly, in the four-dimensional space-time continuum. The new physics profoundly influenced philosophers, whether they acknowledged it or not. It freed them from the common intuitive sensation that past and future are quite different. It freed philosophers, that is, while imprisoning the rest of us. “Past and future must be acknowledged to be as real as the present,” wrote Bertrand Russell in 1926, “and a certain emancipation from slavery to time is essential to philosophic thought.”^*2 A fatalist says: Everything that happens had to happen. Q.E.D.

Donald C. Williams, a realist from California, picked up that thread at midcentury with a paper on “The Sea Fight Tomorrow.” His brand of realism was four-dimensional—fully modern, in other words. He asserted “the view of the world, or the manner of speaking about it” (a nice distinction, so easily forgotten),

which treats the totality of being, of facts, or of events as spread out eternally in the dimension of time as well as the dimension of space. Future events and past events are by no means present events, but in a clear and important sense they do exist, now and forever, as rounded and definite articles of the world’s furniture.

In the 1960s, the sea battle of tomorrow got a new life in the journals of philosophy. An argument raged over the logic of fatalism, and a milestone in the debate was the essay “Fatalism” by Richard Taylor, a metaphysician and beekeeper at Brown University. “A fatalist,” he wrote, “thinks of the future in the manner in which we all think of the past.” Fatalists take both past and future as given, and equally so. They may get this view from religion or, lately, from science:

Without bringing God into the picture, one might suppose that everything happens in accordance with invariable laws, that whatever happens in the world at any future time is the only thing that can then happen, given that certain other things were happening just before, and that these, in turn, are the only things that can happen at that time, given the total state of the world just before then, and so on, so that again, there is nothing left for us to do about it.

Taylor proposed to prove fatalism entirely by philosophical reasoning, “without recourse to any theology or physics.” He used symbolic logic, representing the various statements about the sea battle in terms of P and P′ and Q and Q′. All he needed were “certain presuppositions made almost universally in contemporary philosophy.” Something had to give: either fatalism or the rules of logic. A philosophy battle ensued. One of Taylor’s presuppositions was not as evident to everyone else: “that time is not by itself ‘efficacious’; that is, that the mere passage of time does not augment or diminish the capacities of anything.” In other words, time itself is not an agent of change; more of an innocent bystander. Time doesn’t do anything. (“What is a mere passage of time” retorted one of his critics. “Could time possibly pass without something, somewhere, changing—without the tick of a clock, the movement of a planet, the twitch of a muscle, or the sight of a flash?”)