Time Travel

Have you ever dreamt of travelling through time? I'm sure we all have. Maybe you want to go back to the past to see how things were or even change something. Or would you prefer to go into the future to see how things turn out? Time travel is a mainstay of science fiction, with books and movies imagining the benefits and risks of such an ability. But is time travel actually possible? And if so, what do we need to be able to do it?

Understanding Time

To understand how we might go about travelling through time, we must first understand what time is. Classical physics saw the concept of time as something that exists for everyone, everywhere in the universe. It is independent of anyone who perceives it and progresses at the same pace for everyone. This means that an effect always follows a cause, never the other way around, something that the universe's structure relies upon.

However, the problem with this understanding of time is that it doesn't hold true in all circumstances. That is why Einstein's theory of relativity is seen as one of the most important scientific breakthroughs ever because it explains the changing nature of time. The theory of relativity sees time as one element of four-dimensional space-time and can be influenced by other factors. For example, objects moving at high-speed experience time much slower than those moving with less velocity. There is a similar effect for objects held within gravitational fields.

Relativity and Time Dilation

On a human level, this means that an astronaut orbiting the Earth will age slower than those of us who remain on the planet. But there are far more unexpected consequences of this. Take black holes, for example. They exert the most excellent gravitational pulls of any known object in the universe. They are so strong that light cannot escape, and they also cause time to slow down to an extreme level. If you were to pull a Matthew McConaughey and fall into a black hole while looking out into the rest of the universe, you would theoretically witness hundreds of millions of years' worth of events before ultimately succumbing to your inevitable fate.

Speed of Light and Time

Another quirk of time occurs with the speed of light. As you get faster and faster, time slows down for you, and this continues until you reach the theoretical maximum speed that anything can go: the speed of light. At this speed, time has slowed to such an extent that things seemingly happen instantaneously. Imagine, for example, a photon of light emitted by a star on the other side of the universe. Even at its incredible speed, it will take many millions of years to reach us on Earth and be seen by our eyes as a twinkle in the sky. For the photon, though, the journey is instantaneous; it is created, and then it reaches us in the same instant. When travelling at the speed of light, time is neutral; it travels neither forward nor backwards.

Traveling Forward in Time

So, if the faster you go, the slower time appears for you compared to everything else, this is a potential route to travelling forward. You could speed away from Earth and return; many years will have passed without you getting much older.

Traveling Backward in Time

The challenging part, of course, is going backwards in time. If time is stagnant at the speed of light, does that mean that if you travelled faster than the speed of light, time would work in reverse? Many researchers think so, and there is a theory that a subatomic particle does precisely this, known as a tachyon. These particles are theoretical and have never been observed, partly because if the theory is true, you would never be able to see them coming towards you as this event would be occurring in the future. The ideas of cause and effect would work in reverse for tachyons, but some believe that harnessing them could be the best route to learning how to travel through time.

Wormholes and Other Theories

Another theory is that of wormholes. These act as tunnels through the fabric of space-time and could create a path between any two places at any given time. The theory of relativity allows for wormholes to exist. Still, it states that the energy levels required to create one would be astronomical and could result in the formation of a black hole. Stephen Hawking believed that radiation feedback, which works similarly to sound feedback, would make wormholes inherently unstable and unable to last long enough to be used as a time machine.

Other researchers have suggested a number of ways in which space-time could be harnessed to allow time travel. Perhaps lasers could be used to create extreme levels of gravity. Quantum physics may allow for the formation of a so-called quantum tunnel between universes, and perhaps string theory might lead to revelations of how cosmic strings and black holes could intertwine to warp space-time enough to travel back through time.

Closing

In conclusion, the notion of time travel has long been of interest to researchers and all of us at some point or another. For a long time, it was thought to be completely impossible. With advances in our understanding of the universe in the last century, it's no longer seen as completely impossible, but it's still an ability that lies well beyond our current capabilities. The laws of physics do allow for it to happen, and it could very well, in the future, become more of a fact than fiction.

But let me know what you guys think. Do you believe time travel has already been invented, and are there now time travelers among us?