Which of us hasn’t idly wondered about what it would be like if we could play with time instead of time playing with us? If we could go back and change the past or leap forward and live in a world beyond our fantasies!

Time travel may be considered the epitome of science-fiction and an enthralling fantasy to entertain, but its principle is rooted in possibility, if not plausibility.

If we were to conceptualise our current take on time, we could imagine it as a unidirectional line, extending towards the future. In this scenario, there is no provision for reversing the direction or changing our speed, and we all must plunder along as time ploughs through the past and into the future.

Now let’s consider some very real (albeit, so far, theoretical) possibilities backed by physics. Einstein was a precocious genius, brilliant beyond his time, and his theories are still being unravelled to this day. One of those was the Special Theory of Relativity; something even those not interested in science might have caught a glimpse of in Interstellar. One of the postulates provides that the speed of an object is inversely tied down with the ‘speed’ of the time experienced by it. Simply put, the faster you go, the slower time goes for you!

For reference, the speed of light, which is the fastest ‘thing’ in the entire universe, is 3*10⁸ m/s. Now imagine if you boarded a spacecraft going at 99% of that speed at the age of 25, and spent 5 years in it. By the time you’re rejuvenated and geared up to go home to your girlfriend, she’ll be a ripe 62 years old. You might be perplexed as to how that happened. While you were on your 5-year space-exploration, back on Earth it seemed like 37 years, and not just because your girlfriend was missing you.

Time dilation, as it is called, will occur at any speed. So, even while a speedy run might put you ahead of others, the difference won’t be appreciable.

Another possibility to leap forward in time is by making use of Einstein’s General Theory of Relativity, which was developed to take into account the eccentricities of gravity. One of these eccentricities is that the larger the gravitational field in which an object is, the slower time passes for them. So, if the idea of travelling near light-speed makes you dizzy, you could hole up on a celestial object that has significantly higher gravity than that of Earth, where loitering for mere hours could signal decades having passed back on Earth.

The only hassle in these possibilities is that they are a one-way ticket. Once you speed up right into the future, you can’t simply speed down into the past because of the linearity of time.

Travelling to the past is a little trickier, but in a way we’ve been doing it all our lives, and no, not metaphorically by ”living in the past” or through memories, but literally.  Everything we see emits or reflects light, which is why we can see it. And this light takes some time to cover the distance to reach us; thus, everything we see, we see in the past, as at the very moment we perceive it, it has moved forward in time from when we saw it. Quite a head-scratcher? Maybe an illustration will help.

Take the sun, for example. It is a giant ball of helium and hydrogen, giving off intense heat and light. This light takes about 8.5 minutes to reach us on Earth, so the sun we see is not as it is now, but as it was 8.5 minutes ago. If the sun were to suddenly die out (not something we have to worry about for the next 5 billion years), we would not even realise it until about 10 minutes after the fact!

It might be mind-boggling to think that if an alien situated on a planet 70 million light years away from us would look at Earth through an ultra-powerful telescope right now, it wouldn’t see you reading this post, but a T-Rex stomping the ground in search of prey. Dinosaurs may have been decimated, but they’re living on in the past that’s still being broadcast to the universe.

However, this might not be the kind of time travel to the past you had in mind. To physically alter the linearity of time to go backwards, ideas can be foraged once again from the General Theory of Relativity, which depicts gravity as being a dip in the fabric of space-time. It has been hypothesised that this fabric can be warped enough to create a wormhole. The warping can lead to the formation of CTCs or closed time-like curves. Going through these time loops could provide an opportunity to afford as much multi-directional freedom along the path of time as a physical path would. This possibility has been given weightage by scientists like Stephen Hawking and Kip Thorne.

Needless to say, travelling through time would not be a pleasant journey, but fraught with complications and paradoxes. It would pose a multitude of conundrums and predicaments.

An illustrious example would be the Grandfather Paradox. If you travelled to the past and killed your grandfather, would you still be born in the ‘future’? If you were never born, how did you go back in time to kill your grandfather?

How about if you copied Einstein’s Theory of Relativity and went back in time to 1905, just before he published it, and allowed him to publish it? What is the origin of the theory?

There is an almost certain possibility that it could be misused by everyone from the governments to petty criminals, and throw the world as we know it in a state of upset.

The idea of time travel is as staggering as it is riveting. What has always been considered a fantastic element of science-fiction may well be fact. After all, if time travel ever exists in the future, it already exists now.