Today is Pretend to be a Time Traveller Day. 10 things you might not know about time travel.
- Actually, we’re all time travellers. We do it all the time, moving through time at a rate of one second per second.
- However, the term “time travel” usually refers to the concept that people travel much faster or slower than that, and end up in another time entirely, possibly using a time machine. H.G. Wells's 1895 novel The Time Machine popularised this idea. Fast forward (see what I did there?) to the modern age and you get devices like Doctor Who’s TARDIS.
- H.G. Wells wasn’t the first author to dabble in the realms of time travel, though. In 1881 Edward Page Mitchell published a story in the New York Sun called The Clock that Went Backward, in which a Clock takes people backwards in time when they wind it. Mitchell doesn’t explain how this actually works, so the story tends to be classified as fantasy rather than science fiction. Even if you decide that a fantasy about a clock doesn’t count there is still someone who beat H.G. Wells to it – Enrique Gaspar y Rimbau, who wrote a story featuring a time machine in 1887 – El Anacronópete.
- Even these are not the first tales about travelling in time. Time travel stories date back to ancient myths. A Japanese myth tells of a fisherman named Urashima-no-ko, who visits and undersea world for three days, but when he returns home, 300 years have passed. In Hindu mythology, the Mahabharata tells the story of King Raivata Kakudmi, who travels to heaven to meet the creator Brahma, and when he returns to Earth many ages have passed. In Buddhism, Kumara Kassapa, a disciple of the Buddha, explains that time in the heavens passes at a different rate to that on Earth.
- You could argue that the Hindus and the Buddhists aren’t far wrong. Einstein’s theory of relativity says pretty much the same thing. Space and time are linked and gravity slows time down. Scientists know this is true and that clocks on satellites orbiting the Earth do run slightly faster than the ones on the ground. It might not seem like a big deal, but if the scientists didn’t account for this in their calculations, GPS satellites would be worse than useless as the time differences would add up and the satellites would have no idea where they, or you, actually are.
- Another mechanism myths and writers use to make their characters travel in time is to have them fall asleep and wake up many years in the future. In Jewish tradition, the 1st-century BC scholar Honi ha-M'agel is said to have fallen asleep and slept for seventy years. L'An 2440, rêve s'il en fût jamais (1770) by Louis-Sébastien Mercier, Rip Van Winkle (1819) by Washington Irving, Looking Backward (1888) by Edward Bellamy, and When the Sleeper Awakes (1899) by H.G. Wells are all examples of this idea.
- Travelling backwards in time potentially causes a whole raft of problems. Could a time traveller change history, for example, by killing Hitler before he became a power hungry dictator? This gives rise to the famous “grandfather paradox” where a time traveller kills his or her grandfather (or grandmother) before his father (or mother) is conceived, thereby making it impossible for the time traveller to exist. If he or she doesn’t exist, they never go back in time to kill anyone. And if people could travel back in time to witness historic events, those events could have much bigger audiences and there’d be more unexplained appearances of items from the future in old images. Like the woman pictured during the Kennedy Assassination who appeared to be talking into a mobile phone.
- There are two main theories which deal with time travel paradoxes. One is called the Novikov self-consistency principle, which asserts that a time travel mission to kill Hitler or your grandfather is doomed to failure. It simply cannot happen. Or perhaps the time traveller’s intervention is what causes history to unfold the way it did, for example, an attempt on Hitler’s life when he was a young man is what sends him on the path to megalomania. The other theory is that if a time traveller does something to change history then a new timeline is created, running parallel to the old one. So there would be an alternate timeline in which WWII never happened.
- Another theme in time travel stories is the "time loop" or "temporal loop" where a period of time repeats itself endlessly until the protagonist figures out what they need to do to end it. The most famous example of this plot device is probably the movie Groundhog Day.
- While travelling back in time in a time machine may not be possible, we can look back in time. Einstein said nothing can travel faster than the speed of light (186,000 miles per second). The universe is so vast that light from distant galaxies takes centuries or even millennia to get to us even at that speed. So when the light reaches Earth, what we are seeing is what the distant galaxy looked like a long time ago.
Want to read some stories with time travel and wormholes and paradoxes in?
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