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time machine tales the science fiction adventures and philosophical puzzles of time travel pdf

For example, while both groups talk of the grandfather paradox, the philosophers worry
in particular about motivation (why the murderous mission?), while physicists have
never to my knowledge asked themselves that question4 (other than to figure out
how to avoid it!). After all, philosophers talk of flesh-and-blood humans as time
travelers, while the physicists send only billiard balls (with no personal identities or
memories) on time trips into the past for the expressed purpose of avoiding the
messy human issues of ‘motivation’ and free will.

This approach by physicists isn’t because they are cold and emotionless. It is a useful strategy because, if it can be shown that a mere billiard ball can travel into the past then, as one philosopher
pointed out long ago, “It is implausible that it should be possible for some physical systems to travel back in time, and not others. Thus, if we suppose that simple objects can time-travel … then we must suppose that more complicated systems, e.g., human beings, can also time-travel.”5

For the most part, philosophers and physicists have worked at the extreme,
opposite points of the time travel spectrum. Much better, I think, would be to
adopt the following, more balanced position advocated recently: “The study of time
machines is a good opportunity for forging a partnership between philosophy and
physics. Of course, philosophers have to recognize that in this particular instance
the partnership is necessarily an unequal one since the mathematical physicists have
to do the heavy lifting. But it seems clear that a little more cooperation with
philosophers of science in attending to the analysis of what it takes to be a time
machine could have led to some helpful clarifications in the physics literature.”6

In the past, philosophers gained a reputation for being just a bit too ‘unconstrained by the facts’ for scientific tastes—as the English mathematician Augustus De Morgan (1806–1871) wrote in an 1842 letter, “There are no writers who give us so much must with so little why, as the metaphysicians”7 —but I do think today’s physicists would do well to reexamine that harsh opinion.