Time Travel: An Inventor’s Fantasy?
Storytellers have used the idea of time travel as a fictional device for hundreds of years. But some scientists and inventors have taken the concept a stage further. They have speculated whether the laws of physics are able to allow time travel to happen. Some have even proposed machines that could exploit these laws and make journeys to the past or the future a reality.
LiteratureThe Time Machine is perhaps the most famous example of a time travel story. The author H. G. Wells successfully combined adventure and scientific conjecture in a novel that has been in print since 1895.
Other less scientific stories about time travel abound. One of the earliest is from eighth century Japan. A fisherman discovers an underwater palace and remains there for three days. When he returns to his village, he is horrified to find his house ruined and his family dead. During his three-day absence, three hundred years have passed.
The FutureThe story of the fisherman is about time travel into the future. Physicists have suggested various ways in which such travel may be possible, although they believe there are limits.
Relativistic velocity is one option. An astronaut leaves Earth and travels slightly less than the speed of light. The astronaut then returns at the same speed.
The journey may last a few years. But travelling at a relativistic velocity means that hundreds and perhaps thousands of years may have passed on Earth by the time the astronaut arrives home.
A similar concept relies on Albert Einstein’s general and special theories of relativity. According to the theories, time slows down for anyone who moves faster than a given object or person. A watch that travels almost at the speed of light, for example, slows down relative to an observer on Earth.
Inventors have proposed a time machine based on Einstein’s relativity theories. The machine would be a sphere, five metres in diameter. It would need the mass, however, of the planet Jupiter.
Such a mass would enable the sphere to take advantage of Einstein’s theories. But the mass is equivalent to two and a half times that of every other planet in the solar system combined. Nonetheless, assuming that someone could produce such a sphere, the occupants could move forward in time four times faster than normal time on Earth.
The PastGoing forward in time is all very well, but most travellers may wish to return to the era they come from. They might also prefer to travel into the past rather than the future.
Scientists and inventors are becoming more confident about the theory and practice of time travel into the past. They generally subscribe to one of a number of possibilities such as black holes, wormholes and cosmic strings.
According to Einstein’s general relativity theory, a dense mass can distort spacetime. This distortion would create a black hole. Such a hole in space absorbs light and everything else near it. The theory is that entering a black hole may allow a time traveller to visit the past.
A wormhole is a variation on the time travelling theory of a black hole. A wormhole is a route through spacetime from one black hole to another. By entering one black hole, a time traveller may be able to exit the second hole in another era. The difference between this and the black hole theory above is control. If scientists can control the wormhole by adjusting its velocity, they may be able to send a time traveller to the past and then bring the traveller back.
Cosmic strings are another time travelling possibility. But unlike black holes and wormholes, cosmic strings are one dimensional, hypothetical and don’t rely on the accepted theories of general relativity. The use of cosmic strings for time travel is therefore highly speculative.
ParadoxThe practice of travelling back in time raises a paradox, however. What would happen, for instance, if someone goes back in time and alters history? More specifically, what if a time traveller adjusts his or her own personal history?
The often-quoted example is the grandfather paradox. A time traveller goes back in time and meets his young grandfather. The traveller then interferes with his or her grandfather’s life. As a result, the grandfather never meets the time traveller’s grandmother. If this happens, one of the time traveller’s parents would not have been born. The time traveller would therefore not exist. Therefore, the traveller could not have gone back in time in the first place.
Some scientists and inventors have answered this by suggesting that a traveller who goes back in time enters a parallel universe. Any action the traveller takes in this universe will not affect the events of the traveller’s own universe.
Professor Ronald MallettThis is a theory to which Professor Ronald Mallet, of the University of Connecticut, subscribes. He has an idea for a time machine. And he believes that if he can raise the money he needs to build the machine, he’ll be able to travel backwards and forwards in time within the next few years.
The machine uses Einstein’s relativity theories. But Professor Mallet has sidestepped the need for a dense mass. His idea is to use lasers that distort space and consequently distort time. A time traveller can enter the distortion and go into the future or the past.
If Professor Mallett is right, the ultimate form of travel may soon begin.