Any science fiction aficionado has seen it all before: beaming through walls, riding in starships that move faster than light, or traveling instantly to distant places in space and time. These ideas aren’t just creative fantasies, though; they emerge from theoretical physics, especially the work of Albert Einstein, whose vision included a universe that curves back on itself in three dimensions of space and a fourth, invisible dimension of time. If Einstein’s version of the universe is correct—and experiments done over the last century suggest that essentially it is—then the fictionalized feats based on his theories might be possible as well. The potential has become so tantalizing that serious physicists now regularly comment on Einstein-based technologies in the most august journals of their field.
One of the most insightful of such speculators is Michio Kaku, a physicist at the City University of New York. Einstein’s scientific legacy, Kaku points out, has already formed the basis of many incredible inventions, including the laser and the global positioning system. But what would it take to reach the next level, developing such extrapolations of Einstein’s genius as the means to journey through wormholes, teleport through space, or travel back and forth in time? Scientists have already begun the work, and Kaku reports on their progress here.
ANOTHER LOOKING GLASS In science fiction movies like Stargate and Contact, wormholes connect distant points in the universe, allowing people to travel from one spot to another in far less time than the hundreds or millions of years required to make the trip at the speed of light, the greatest conventional velocity. Einstein’s general theory of relativity suggests the possibility of wormholes—literal shortcuts through space-time caused by the curvature of the universe itself. But do wormholes really exist, or are they figments of mathematics?
There are several major problems to face. Many solutions result in “nontraversable wormholes.” As with a black hole, once you pass the event horizon of such a wormhole, you can never leave it. In 1988, Kip Thorne and his colleagues at Caltech found a possible way out: a traversable wormhole, one through which you could pass freely back and forth. In fact, for one solution, the trip through a wormhole would be no worse than riding in a plane.
There was a catch, though, that made such a wormhole impractical. Gravity would crush the throat of the wormhole, destroying any travelers trying to reach the other side. To stabilize the throat of the wormhole, scientists would need the repulsive force of perhaps the most exotic and speculative entities in the universe: negative mass and negative energy. Conceivably, using either could keep the throat open sufficiently long to allow astronauts a clear passage.
Scientists have looked for negative matter in nature, so far without success. One should note here that antimatter and negative matter are two entirely different things. The first exists and has positive energy but reversed charge. Negative matter has not been proved to exist. Negative matter is quite peculiar because it is lighter than nothing. In fact, it floats. Unlike meteors that come crashing into planets, drawn by the planets’ gravity, negative matter would shun large bodies like stars and planets. It would be repelled, not attracted. Hence, although negative matter might exist, we’d expect to find it only in deep space, certainly not on Earth.
Even if we could locate or create negative energy or matter, there is still a big problem: getting and manipulating enough of the stuff. Matthew Visser of Victoria University in Wellington, New Zealand, estimates that the amount of negative energy needed to open up a one-meter-wide wormhole would be comparable to the mass of Jupiter, except that it would be negative. He says, “You need about minus-one Jupiter mass to do the job. Just manipulating a positive Jupiter mass of energy is already pretty freaky, well beyond our capabilities into the foreseeable future.” It might be millennia before we can even think about harnessing power on this scale.
Yet, if we ever do create them, wormholes could open the door to traveling not just in space but in time as well.