Pass me the flux capacitor!
“One day, if somebody knocks on your door and claims to be your great-great-great-great-great-granddaughter a thousand years into the future, don’t slam the door! Because maybe your descendant got into a time machine to visit her ancestor.”
- Michio Kaku, theoretical physicist
Time, by definition, is an illusion. Well, almost all of us think of time as just a medium on which we record a sequence of events. More accurately, we just keep our definition of time to the classical level that is “the indefinite continued progress of existence and events in the past, present, and future regarded as a whole” (Oxford English Dictionary). But the question is, how can you find a medium to sequence events unless you believe that no events occurred before the Big Bang and no events will occur after a certain point (that is, fixing two end points between which the medium lays)? Philosophers have long held the view that time, motion, and change are all mere illusions. Science, on the other hand, has significantly neglected the seriousness of time as a subject. This is precisely why we still don’t have an answer to the question: what is time?
Ever since science began the quest to explore time, it has been apparent that the subject is too complex even for some of the great minds. The first person to bring time into the limelight in the world of physics was Albert Einstein. Einstein realized that time is like a river that meanders its way through stars, as opposed to Newton who believed that time was like an arrow – once you fired it, it never deviated. Einstein’s new views regarding time opened a whole new collection of theoretical possibilities, especially the ones regarding time travel. Newton’s arrow could never deviate so time travel was impossible, but the river of time Einstein proposed could bend around; therefore, time travel was possible. But there was more to time travel than just Einstein’s views.
In the beginning of the 20th century, physics was seeing heights never before achieved. Einstein had presented his ideas of general and special relativity, and it seemed that the physical universe was about to be explained by just a handful of equations. Mathematics seemed to govern the universe as its deepest enigmas began to unravel through elegant mathematical equations. In fact, Kurt Gödel, one of the greatest mathematicians of the 20th century, found a solution to Einstein’s equation that allowed for time travel. Gödel suggested that if the universe was rotating and an object goes round the universe, it would end up returning back to its original point before its starting time. Einstein was not worried about Gödel’s solution because the universe isn’t rotating, it’s expanding. However, since then we have found hundreds of solutions to Einstein’s equations that perfectly allow for time travel. Moreover, these solutions do not require the universe to be rotating either.
To date, there is no law of physics that does not allow for time travel. Theoretical possibilities of time travel are materializing at laboratories of scientists who have been engaged in this study. Popular theories include faster-than-light travel and wormholes. Wormholes, short cuts through space and time formed by the bending of space time by super-massive black holes, are certainly the most famous science fiction method of time travel. However, there is not much evidence to support the presence of wormholes in inter celestial space. The most famous theories of time travel are merely theoretical, and are based upon solutions of Einstein’s general relativity equations with different geometries of space time.
Time travel, apart from bringing a truly different and perhaps a more interesting colour to physics, has also brought problems and paradoxes that seem to have endless implications, some of which are very amusing. The most famous irony associated with travelling in time is the ‘grandfather paradox’. Suppose a person goes back in time and kills his grandfather before he has met his grandmother; the person’s father and the person himself will never be born. Stephen Hawking has suggested the absence of visitors from the future is a definite argument against time travel.
Travelling in time has always been one of man’s greatest longings, but every time man has hoped to achieve it, the illusion of time has eluded him. So one day if you come across a stranger who claims to be from the future, I strongly advise you – don’t slam the door!