Science Friction_ Where the Known Meets the Unknown - Michael Shermer [33]
Because these cosmological heresies are still in their borderland stages we must be cautious in our evaluation of them. The mathematics may be “beautiful” and the theories “elegant,” as cosmologists like to say, but we need more than that for science. We need empirical tests. Still, the history of science compels me to embrace the multiverse concept for the simple reason that this is the next natural stage in our scientific development. We went from the solar system being all there is, to the galaxy being all there is, to the universe being all there is. Like unsheathing Russian nested dolls, there is no reason to think that there is not another cosmic shell to pull off, and thus I give this heresy a fuzzy factor of .7.
Heresy 2. Time Travel Is Possible
Although time travel is the staple of science fiction writers, most physicists and cosmologists agree that time travel is impossible. Not only does it violate numerous physical laws, there are fundamental problems of causality. The most prominent is the “matricide paradox” in which you travel back in time and kill your mother before she had you, which means you could not have been born to then travel back in time to kill your mother. In Back to the Future, Marty McFly faces a related but opposite dilemma in which he must arrange for his parents to meet in order to ensure his conception. In the original Star Trek series Dr. McCoy falls through a time portal and changes the past in a way that erases the Enterprise and her crew, with the exception of Kirk and Spock, who must travel back to fix what McCoy has undone.
One way around such paradoxes can be found in extremely sophisticated virtual reality machines (think of Star Trek’s holodeck machine), programmed to replicate a past time and place in such detail that it would be nearly indistinguishable from the real past. Another theory involves the parallel universes model of the multiverse in which you travel back in time to a different universe from your own, although you would select one very similar so as to experience a past very much like that of our own universe. This was the plot line in Michael Crichton’s science fiction novel Time Line, in which the characters journeyed back to medieval Europe in a closely parallel universe, without concern for mucking up their own time line.
The fundamental shortcoming for both of these time travel scenarios is that it isn’t really your past. A virtual reality is simply a museum writ large, and transporting to some other universe’s past would be like going back and meeting your mother only to witness her marry someone other than your father, thus eliminating you from that past—surely a less appealing trip than one in your own time line. To do that you need the time machine of the California Institute of Technology cosmologist Kip Thorne, who had his interest in time travel piqued when he received a phone call one day from the Cornell University astronomer Carl Sagan, who was looking for a way to get the heroine of his novel Contact—Eleanor Arroway (played by Jodie Foster in the film version)—to the star Vega twenty-six light-years away.
The problem Sagan faced, as all science fiction writers do in such situations, is that at the speed of spacecraft today it would take over 300,000 years to get to Vega. That’s a long time to sit, even if you are in first class with your seat back and tray table down. Thome’s solution, adopted by Sagan, was to send Ellie through a wormhole—a hypothetical space warp similar to a black hole in which you enter the mouth and fall through a short tube in hyperspace that leads to an exit hole somewhere else in the universe (think of a tube running through the middle of a basketball—instead of going all the way around the surface to get to the other side, you take a short cut through the middle). Thome’s calculations showed that it was theoretically possible for Ellie to travel just one kilometer down the wormhole