224
PHVSICS OF THE IMPOSSIBLE
last only a brief period.) Gott says, "A collapsing loop of string large
enough to allow you to circle it once and go back in time a year would
have to have more than half the mass-energy of an entire galaxy."
But the most promising design for a time machine is the "transversable wormhole," mentioned in the last chapter, a hole in spacetime in which a person could freely walk back and forth in time. On
paper, transversable wormholes can provide not only faster-than-light
travel, but also travel in time. The key to transversable wormholes is
negative energy.
A transversable wormhole time machine would consist of two
chambers. Each chamber would consist of two concentric spheres,
which would be separated by a tiny distance. By imploding the outer
sphere, the two spheres would create a Casimir effect and hence negative energy. Assume that a Type III civilization is able to string a
wormhole between these two chambers (possibly extracting one from
the space-time foam). Next, take the first chamber and send it into
space at near light-speed velocities. Time slows down in that chamber,
so the two clocks are no longer in synchronization. Time beats at different rates inside the two chambers, which are connected by a wormhole.
If you are in the second chamber, you can instantly pass through
the wormhole to the first chamber, which exists at an earlier time.
Thus you have gone backward in time.
There are formidable problems facing this design. The wormhole
may be quite tiny, much smaller than an atom. And the plates may
have to be squeezed down to Planck-length distances to create enough
negative energy. Lastly, you would be able to go back in time only to
the point when the time machines were built. Before then, time in the
two chambers would be beating at the same rate.
PARADOXES AND TIME
CONUNDRUMS
Time travel poses all sorts of problems, both technical as well as social.
The moral, legal, and ethical issues are raised by Larry Dwyer, who
PHVSICS OF THE IMPOSSIBLE
last only a brief period.) Gott says, "A collapsing loop of string large
enough to allow you to circle it once and go back in time a year would
have to have more than half the mass-energy of an entire galaxy."
But the most promising design for a time machine is the "transversable wormhole," mentioned in the last chapter, a hole in spacetime in which a person could freely walk back and forth in time. On
paper, transversable wormholes can provide not only faster-than-light
travel, but also travel in time. The key to transversable wormholes is
negative energy.
A transversable wormhole time machine would consist of two
chambers. Each chamber would consist of two concentric spheres,
which would be separated by a tiny distance. By imploding the outer
sphere, the two spheres would create a Casimir effect and hence negative energy. Assume that a Type III civilization is able to string a
wormhole between these two chambers (possibly extracting one from
the space-time foam). Next, take the first chamber and send it into
space at near light-speed velocities. Time slows down in that chamber,
so the two clocks are no longer in synchronization. Time beats at different rates inside the two chambers, which are connected by a wormhole.
If you are in the second chamber, you can instantly pass through
the wormhole to the first chamber, which exists at an earlier time.
Thus you have gone backward in time.
There are formidable problems facing this design. The wormhole
may be quite tiny, much smaller than an atom. And the plates may
have to be squeezed down to Planck-length distances to create enough
negative energy. Lastly, you would be able to go back in time only to
the point when the time machines were built. Before then, time in the
two chambers would be beating at the same rate.
PARADOXES AND TIME
CONUNDRUMS
Time travel poses all sorts of problems, both technical as well as social.
The moral, legal, and ethical issues are raised by Larry Dwyer, who