Guess Who’s Coming to Dinner dvd What If Tourists From The Future Could Visit Us? If time machines are possible, it is likely that someone in the future will already have constructed one. After all, in the future there is time to complete even the largest engineering project! Even if humans are not up to the task, creatures from other planets may try.
So why are we not overrun by visitors from the future? This is the argument used by the famous English physicist Stephen Hawking in what he called his “chronology protection conjecture.” Like many other scientists, Hawking is troubled by the weird paradoxes of time travel. He argues that the universe simply couldn’t allow time travel to happen, because its evolution since the Big Bang cannot be reversed. If the universe were to contract instead of expanding, asks Hawking, would human beings “unevolve” in the same way they have evolved over millions of years?
A second explanation for the absence of visitors from the future is that none of the time machines envisaged so far lets the voyager go back before the moment the machine was first constructed. So relax. Since no one has built a time machine yet, out-of-time tourists are not a problem!
Technical limitations aside, the “many worlds” theory also solves most of the paradoxes of time travel. According to this theory, an infinity of universes is constantly being created. In quantum physics, when subatomic particles have a “choice” of options (such as going through one hole or another in a screen), they select one at random. The “many worlds” theory says that there is a universe for each possible choice made by the particle.
“Many worlds” solves another of the famous time travel paradoxes. Say you went back in time and shot your grandfather before he met your grandmother. Would you never have been born? If not, you could never have traveled back in time and shot your grandfather. Which means that you “were” born, so you “could” have gone back… According to “many worlds,” when you go back in time you actually emerge in another universe that develops in parallel to our own. But with an infinity of universes to choose from, how can time travelers ever hope to find their way back to the one they started out from?