Time travel has always been a thing of the imagination, encouraged by hundreds upon thousands of science fiction TV shows, movies and books. But what is time travel? Surely everyone is travelling through time, just at the same linear rate, with everyone else. What people want is the time travel that Doctor Who and Star Trek exhibit: the almost instant change of time, on a select object, both backwards and forwards on the timeline.
Travelling backwards in time has always been a conundrum for theoretical physicists; it creates paradoxes. The best example for this is the Grandfather Paradox, where you travel back in time and murder your grandfather before he meets your grandmother. Then, since one of your parents are not born neither are you. You would never have existed to create the time machine, so your grandfather lives which means you murder him and the cycle repeats – creating a paradox. This renders the possibility of time travel to the past impossible; or rather not impossible, it would just end the universe, time, and space. There are theories that once the time traveller murders his grandfather he joins a parallel timeline, or an alternate universe, of which he was never born. Other paradoxes such as the autoinfanticide paradox (travelling back in time and murdering oneself as an infant) present the same message: travelling backwards in time is unachievable.
Going forward in time is easily achievable, because everyone is doing it. Going faster than everyone else, however, is slightly more difficult, but possible. According to Einstein’s theory of general relativity, gravity, affects both space and time. This means mass drags on time, slowing time down. Artificial satellites prove this, where they gain one-third-of-a-billionth of a second every day, compared to Earth. This is due to their distance away from a large mass, thus gravity does not drag on time as much on them. To the theory into practise, the largest known mass in the Milky Way is the centre black hole Sagittarius A. It has the mass of four million suns in one dense point. If a spacecraft had the ability to orbit this supermassive black hole, it would experience half as much time as on Earth. So if you had trillions of dollars to spend and a death wish, you could visit this Sagittarius A for five years and ten years would have passed on Earth. So travelling faster in time is possible, it just takes a lot of time.
A much more efficient way of travelling faster in time is to go at almost the speed of light. Reaching the speed of light is impossible, as shown by Einstein, and, because of this, strange anomalies occur when you get close to 300 million m/s, such as the slowing down of time. If, somehow, a train was built to circle the Earth, and get 99.999% of light speed, it would slow down. The train’s speed wouldn’t slow, but time would, meaning everyone on board would be going slower than everyone outside the train. The passengers wouldn’t notice a difference, but if they were on that train for 1 year, 223 years would have passed for everyone else on Earth. However, the implications of living on a train moving at near-light speed for 1 year are a much larger problem. Food and water would quickly run out, and ordering at a McDonald’s Drive-Thru isn’t capable at 299 million m/s.
Jumping through time is a different problem all together. There is only one real possibility of time jumping being attainable, and this is the Einstein-Rosen Bridge; a wormhole. Imagine space as a sine wave. Time and space travels the curve, take the long route. Wormholes open up a possibility of going straight through the wave taking a much shorter route. The only way to penetrate through the metaphorical sine wave is when two incredibly large masses push against it, such as the case of a supermassive black hole. Theoretically, if anything would be enter this black hole, it would go through each point, and come out of the other side. It would have travelled though time and space.Although not seen before by astrophysicists, the equations of the theory of general relativity have valid solutions that contain wormholes, so they are a possibility. One theory by Stephen Hawking is that these wormholes exist in quantum foam, the smallest environment in the universe.In the simplest of terms, quantum foam is the foundation of the fabric of the Universe, smaller than anything else known to man. These tiny wormholes flash in and out of existence, but momentarily link separate places and times in the universe. As theorised by Stephen Hawking, if it was possible to control and enlarge these wormholes, humans would be able to travel though space and time.
In reality, these are only dreams. Any possibility of these theories being tested in the next century, let alone in out lifetime, remain simply as hopes. However, no one knows when a breakthrough may occur like harnessing the energy to control wormholes, or when the answers suddenly become clear. The great thing about time is that, however permanent the past may be, the future is open to anything.