time machine tales the science fiction adventures and philosophical puzzles of time travel pdf
In 1993 the first edition of my book Time Machines was published by the Press of
the American Institute of Physics. In 1999, after Springer acquired AIP Press, the
second edition of that book appeared. So, is this the third edition? Well, yes and
It is because large chunks of the 1999 edition are still here, along with new
discussions of the advances by physicists and philosophers that have appeared in
the intervening 18 years. The prime example of that centers on the time travel
paradoxes. Those discussions contain mostly what is in the second edition, but they
have also been brought up to date with the latest thinking on the paradoxes, by
physicists and philosophers.
And yet this book is not quite the third edition because the emphasis is now on
the philosophical and on science fiction, rather than on physics as it was when
written for AIP Press. In that spirit there are, for example, no Tech Notes filled with
algebra, integrals, and differential equations, as there are in the first and second
editions of Time Machines. That’s because I wish to avoid having this book seem to
be simply a long physics treatise.
I have, in fact, some sympathy with the following
views, expressed by two philosophers:
“There is one metaphor in the physicist’s account of space-time which one
would expect anyone to recognize as such, for metaphor is here strained far beyond
the breaking point, i.e., when it is said that time is ‘at right angles to each of the other three dimensions.’ Can anyone really attach any meaning to this—except as a
recipe for drawing diagrams?”1
This is from the outset a study in descriptive metaphysics. In consequence, I
shall have nothing to say about twice-differentiable Lorentzian manifolds,
Minkowski diagrams, world-lines, time-like separations, space-time worms
[a ‘thick’ world-line], or temporal parts.”2
I don’t completely endorse these sentiments, however, and so please understand
that I am not denying the ultimate importance of physics when it comes to achieving
a deep understanding of time travel. To quote yet another philosopher,
“Arm chair reflections on the concept of causation [are] not going to yield new
The grandfather paradox is simply a way of pointing to the fact that if the usual laws of physics are supposed to hold true in a chronology violating spacetime, then consistency constraints emerge. [To understand these constraints] involves solving problems in physics, not armchair philosophical reflections [my emphasis].”3
I could not agree more. So, in Time Machine Tales you will find some physics. In support of time travel to the future (and in how to make a wormhole time machine for travel into the past), for example, I’ll show you a high school level derivation of the famous time dilation formula from special relativity. There are some spacetime diagrams, some simple algebraic manipulations, and here and there just a touch of freshman calculus; even the metric tensor gets a few words, too. But it is, admittedly, pretty light weight stuff.
So, while certainly saluting the premier position of physics, Time Machine Tales is not a scholarly, in-depth treatment of time travel physics. Rather, it is an examination of how science fiction writers (and many philosophers, too) have viewed time travel. (Even in the physics discussions, science fiction will regularly appear.) Those views, by their very nature, are far more romantic than are those of hardcore theoretical physicists.
History has shown, of course, that the results of the work of theoretical physicists may, in the end, prove to actually be far more astonishing than anything fiction writers cook-up—and if there is any scientific subject for which that may again prove to be true it’s time travel—but for us, here, it
will be the fiction writer who has center stage.
The philosophers will be only slightly less important in this book. While much of the early philosophical literature on time travel and backwards causation reads like imaginative fairy tales spun out of vacuous vapors (more on this soon), many modern philosophers have shown themselves to be quite sophisticated. What they have written deserves serious consideration by anyone interested in time travel, and that includes physicists. However, while the time travel interests of philosophers and physicists have a lot of overlap, those interests are not in total agreement.