TIME TRAVEL 223
mentioned in the previous chapter, passing through the wormhole at
the center of a black hole is a one-way trip. As physicist Richard Gott
has said, "I don't think there's any question that a person could travel
back in time while in a black hole. The question is whether he could
ever emerge to brag about it."
Another time machine involves a spinning universe. In 1949 mathematician Kurt Gôdel found the first solution of Einstein's equations
involving time travel. If the universe spins, then, if you traveled around
the universe fast enough, you might find yourself in the past and arrive
before you left. A trip around the universe is therefore also a trip into
the past. When astronomers would visit the Institute for Advanced
Study, Gôdel would often ask them if they ever found evidence that the
universe was spinning. He was disappointed when they told him that
there was clearly evidence that the universe expanded, but the net spin
of the universe was probably zero. (Otherwise, time travel might be
commonplace, and history as we know it would collapse.)
Third, if you walk around an infinitely long, rotating cylinder, you
also might arrive before you left. (This solution was found by W. J. van
Stockum in 1936, before Gôdel's time traveling solution, but van
Stockum was apparently unaware that his solution allowed for time
travel.) In this case, if you danced around a spinning May Pole on May
Day, you might find yourself in the month of April. (The problem with
this design, however, is that the cylinder must be infinite in length and
spin so fast that most materials would fly apart.)
The most recent example of time travel was found by Richard Gott
of Princeton in 1991. His solution was based on finding gigantic cosmic
strings (which may be leftovers from the original big bang). He assumed that two large cosmic strings were about to collide. If you
quickly traveled around these colliding cosmic strings, you would
travel back in time. The advantage of this type of time machine is that
you would not need infinite spinning cylinders, spinning universes, or
black holes. (The problem with this design, however, is that you must
first find huge cosmic strings floating in space and then make them collide in a precise fashion. And the possibility of going back in time would
mentioned in the previous chapter, passing through the wormhole at
the center of a black hole is a one-way trip. As physicist Richard Gott
has said, "I don't think there's any question that a person could travel
back in time while in a black hole. The question is whether he could
ever emerge to brag about it."
Another time machine involves a spinning universe. In 1949 mathematician Kurt Gôdel found the first solution of Einstein's equations
involving time travel. If the universe spins, then, if you traveled around
the universe fast enough, you might find yourself in the past and arrive
before you left. A trip around the universe is therefore also a trip into
the past. When astronomers would visit the Institute for Advanced
Study, Gôdel would often ask them if they ever found evidence that the
universe was spinning. He was disappointed when they told him that
there was clearly evidence that the universe expanded, but the net spin
of the universe was probably zero. (Otherwise, time travel might be
commonplace, and history as we know it would collapse.)
Third, if you walk around an infinitely long, rotating cylinder, you
also might arrive before you left. (This solution was found by W. J. van
Stockum in 1936, before Gôdel's time traveling solution, but van
Stockum was apparently unaware that his solution allowed for time
travel.) In this case, if you danced around a spinning May Pole on May
Day, you might find yourself in the month of April. (The problem with
this design, however, is that the cylinder must be infinite in length and
spin so fast that most materials would fly apart.)
The most recent example of time travel was found by Richard Gott
of Princeton in 1991. His solution was based on finding gigantic cosmic
strings (which may be leftovers from the original big bang). He assumed that two large cosmic strings were about to collide. If you
quickly traveled around these colliding cosmic strings, you would
travel back in time. The advantage of this type of time machine is that
you would not need infinite spinning cylinders, spinning universes, or
black holes. (The problem with this design, however, is that you must
first find huge cosmic strings floating in space and then make them collide in a precise fashion. And the possibility of going back in time would