May it not be that our inability to leap into the fiftieth century, A.D., seems impossible to us, merely because of certain prejudices we entertain or certain facts and tricks of which we are still hopelessly ignorant? Assuredly, this is not a foolish query. Its answer, whatever that may be, carries immeasurable consequences for metaphysics.” —a scholar wonders62 A thought-provoking possibility for explaining the scarcity of certified time travelers is the central thesis of a fascinating paper in the philosophical literature.
The author of that paper argues (note 13) that nobody would believe a time traveler even if he willingly confessed and revealed his knowledge of the future, or even gave the details of his time machine. He goes on to make the astonishing assertion that even the time traveler himself would have doubts! This perhaps shocking suggestion deserves some elaboration, especially because it invokes the authority of the patron saint of skeptics for support, the Scot David Hume (1711–1776). The crucial point to keep in mind is explicitly stated in the argument:
The key question will not be ‘Is time travel possible?’ We shall instead ask whether it is possible to justify a belief in a report of time travel.” This gets to the real heart of Clarke’s puzzle from the previous section. Much of the resistance to the idea of time travel lies in sheer skepticism. For many, time travel (to the past, in particular) is simply too much out of the ordinary to be taken seriously. For many, time travel would literally be miraculous.
Hume’s great work, An Enquiry Concerning Human Understanding, 63 contains a section on how a rational person should react to a claim that a miracle has occurred. Hume proclaimed that a miracle by definition violates scientific law and that, because such laws are rooted in “firm and unalterable experience,” any violation of one or more of these laws immediately provides a refutation of the report of a miracle. In Hume’s own words:
Nothing is esteemed a miracle, if it ever happened in the common course of nature. It is no miracle that a man, seemingly in good health, should die on a sudden; because such a kind of death, though more unusual than any other, has yet been frequently observed to happen. But it is a miracle, that a dead man should come to life; because that has never been 62W. B. Pitkin,
Time and Pure Activity,” Journal of Philosophy, Psychology and Scientific Methods, August 27, 1914, pp. 521–526. Pitkin’s essay was a critique of time travel as presented in Wells’ The Time Machine, which Pitkin called “one of the wildest flights of literary fancy.” 63Making its first appearance in 1748, Enquiry has been reprinted numerous times since. I used the 1963 edition published by Open Court.