Richard Gott's Time Machine

Richard Gott's Time Machine 

by : Aria Ratmandanu 

     In 1991, J. Richard Gott of Princeton University proposed yet another solution to Einstein’s equations which allowed for time travel. His approach was interesting because he started from an entirely fresh approach, abandoning spinning objects, wormholes, and negative energy entirely.

        Gott was born in Louisville, Kentucky, in 1947, and he still speaks in a gentle southern accent that seems a bit exotic in the rarefied, rough-and-tumble world of theoretical physics. He got his start in science as a child when he joined an amateur astronomy club and enjoyed stargazing.

       While in high school, he won the prestigious Westinghouse Science Talent Search contest and has been associated with that contest ever since, acting as chairman of the judges for many years. After graduating from Harvard in mathematics, he went to Princeton, where he still works.

       While doing research in cosmology, he became interested in “cosmic strings,” a relic of the big bang that is predicted by many theories. Cosmic strings may have a width thinner than an atomic nucleus, but their mass may be stellar and they may extend for millions of light-years in space. Gott first found a solution to Einstein’s equations which allowed for cosmic strings. But then he noticed something unusual about these cosmic strings. If you take two cosmic strings and send them toward each other, then, just before they collide, it is possible to use this as a time machine. First, he found that if you made the round-trip around the colliding cosmic strings, space was contracted, giving it strange properties. We know that if we move around a table, for example, and return to where we started, we have traveled 360 degrees. But when a rocket travels around the two cosmic strings as they pass each other, it actually travels through less than 360 degrees, because space has shrunk. (This has the topology of a cone. If we move completely around a cone, we also find that we travel less than 360 degrees.) Thus, by going rapidly around both strings, you could actually exceed the speed of light (as seen by a distant observer) since the total distance was less than expected. This does not violate special relativity, however, because in your own frame of reference your rocket never exceeds light speed.

       But this also means that if you travel around the colliding cosmic strings, you can take a trip to the past. Gott recalls, “When I found this solution, I was quite excited. The solution used only positive- density matter, moving at speeds slower than the speed of light. By contrast, wormhole solutions require more exotic negative-energy-density material (stuff that weighs less than nothing)."

       But the energy necessary for a time machine is enormous. “To allow time travel to the past, cosmic strings with a mass-per-unit length of about 10 million billion tons per centimeter must each move in opposite directions at speeds of at least 99.999999996 percent of the speed of light. We have observed high-energy protons in the universe moving at least this fast, so such speeds are possible,” he observes.

       Some critics have pointed out that cosmic strings are rare, if they exist at all, and colliding cosmic strings are even rarer. So Gott proposed the following. An advanced civilization may find a single cosmic string in outer space. Using gigantic spaceships and huge tools, they might reshape the string into a rectangular loop that is slightly bent (resembling the shape of a reclining chair). The loop, he hypothesized, might collapse under its own gravity, so that two straight pieces of the cosmic string might fly past each other near the speed of light, briefly creating a time machine. Nevertheless, Gott admits, “A collapsing loop of string large enough to allow you to circle it once and go back in time a year would have to be more than half the mass-energy of an entire galaxy.