Mindscape #124
How Time Travel Could and Should Work
Alas, Sean Carroll doesn’t pull any punches in his realistic assessment of the kinds of
time travel that are or may be possible under the laws of physics as we know them in our
universe. Or, as Professor Carroll himself puts it: “
. . .
podcasting isn’t for the squeamish.” In my layman’s understand of his most
excellent explication, time travel aficionados have two physical phenomena on which to
hang their
Hat Things:
- Time Dilation: Under the laws of Einstein’s special relativity, a
fast traveler who leaves the Earth, zooming around for a while at near light speed before
returning, will experience less passage of time than those who stay in the more-or-less
fixed reference frame of Earth. How cool is that? Yes, you can travel as far into
the future as you like, so long as you have a means of zooming up to a high enough speed
and returning. (And according to general relativity, time dilation also occurs inside a
high gravitational field, although I didn’t notice a discussion of this sort of time
dilation in the podcast.)
- Closed Timelike Curves: The
second hope for time travelers are certain distributions of matter that (according to
Einstein’s equations of general relativity) result in directed paths through spacetime
in which a traveler along the path is always moving forward through time—and yet
completing a full circuit of the path returns the traveler to the starting point in both
space and time. That’s the good news. The bad news is that such paths, called
closed timelike curves, might only be possible in the presense of infinitely long
rotating cylinders or other physical conditions that may be impossible to
engineer.
Up in the ITTDB Citadel, many of us found ourselves in a disquieted
state at this point in Professor Carroll’s podcast (roughly the two-hour mark). Some
went to bed early in a kind of daze; others decided it was time for a long walk through
the lonely ice paths that surround the Citdel. But for those with the fortitude to keep
their ears glued to the pod, there was a great reward. Carroll had already waded through
the swift, waist-high currents of causality, predeterminism, free will, the A Theory of
Time, the B Theory of time, and more. But now he was ready to dive into deep, uncharted
waters. Yes, now he was ready to leave known physics behind, to talk about branching time
that went beyond the Everettian Many Worlds of Schrödinger’s equation, and to consider
what kind of a world would be needed to allow stories such as
Back to
the Future and
Looper to consistently hold together.
With this in mind, he devices a four-pronged theory that concludes with what he calls
Narrative Time. For me, narrative time shares some features with the
time model of
Asimov’s
The End of
Eternity (a model that we call
Hypertime in our
story-tagging system), but it goes far beyond that.
Suffice it to
say that when all the Librarians up in the Citadel woke from their sleeps and returned
from their treks, we had a celebration that was strident enough to raise Lazurus Long himself from the dead (if he is dead, that is).
— Michael Main
I think that if we really try hard, we can make sense of this. But there’s a rule in
physics or whatever that the more surprising and weird the phenomenon is, the more
you’re gonna have to work to introduce some weird elements into your theory to explain
it. That’s not surprising, right? So we’re gonna need some leaps of faith here, but I
think I can come up with the scheme that involves four ingredients on the basis of which
we can actually make sense of
Back to the Future, Looper, and other similar
movies.
