How many times have you wanted to go back to a moment in your life and smack a hand across your mouth before you utter something stupid and inappropriate in public? How many times have you longed to travel back and re-live a moment in your life? How many times have you wished you could alter the course of your life?

We’ve seen it in science fiction, we’ve dreamed of it often, but can it really happen? Can we really step back in time, which only seems to flow forwards?

The question that plagues us for personal reasons, plagues the greatest thinkers of our generation due to academic curiosity. So what are drawbacks and counters that physicists in the field are discussing today regarding backwards time travel?

One of the simplest, yet blatantly discounting questions posed against backwards time travel is how to account for the absence of time travel. Surely, if we had ever succeeded in accomplishing time travel, we would’ve first returned back in time to visit ourselves. Why is it we do not see inter-temporal visitors amidst us today?

Another highly popular paradox posed is the ‘grandfather paradox’. This paradox says if one was to go back in time and stop his grandfather from ever meeting his grandmother, he effectively severs the bloodline that would have culminated in him and his siblings. Thus, he essentially prevents his own existence. But, if he were never to have existed, then nobody could have prevented his grandparents from meeting each other, thus his existence is assured again. What this paradox essentially says is that a change in the past eventually boils down into a change in the future that can affect the event which sparked the initial alteration in the best. And in some cases, as this one, contradict both events: both being dependent on the other.

The paradoxes and drawbacks against time travel are not struck without retaliation from believers of time travel. Counters for these challenges are along the following lines of thought:

The first drawback is based on two assumptions. One, that travelers from the future would be any different from us in contemporary times. They might be from the future and yet could blend in perfectly in our society. For all we know, Lady Gaga might be a time traveler and her eccentric dressing sense might be the global fad centuries from now [or she’s just eccentric or attention-seeking].

Second, we assume that people from the future would be inclined to meet us ‘past peasants’. Perhaps they find us borderline stupid, as we perhaps regard farmers and Neanderthals who existed millennia ago.
We assume that future travelers will be willing to spend time and resources into returning back in time to where we are now. There is no guarantee for this, and hence this drawback is inadequate to rule out the possibility of time travel.

The counter to the grandfather paradox is also simple, but a little tougher to understand. This counter follows the idea of the multiverse theory. In very brief, this theory states that there are infinite universes present parallel to ours, each of which differs from the other, some are quite similar, some drastically different.

According to this counter, both the events (the grandparents meeting and the grandparents never meeting) occur, but happen in parallel universes. So in one universe, there is a scenario where the grandparents never met hence wiping out the existence of the individual, while in a parallel universe, the grandparents meet and the individual very much exists.

When discussing time travel, one cannot ignore time dilation. What time dilation essentially states is that there is a definite lag between the elapsed time when a body is near another body of great gravitational mass. In short, the cosmic web of space-time is stretched near a body of great gravitational density (like the sun, or the most extreme case, a black hole) than it would be around a lesser dense body (a spacecraft or a planet).

What does this mean?

This implies if we were to go near a body like the sun from the earth, the time we spend near the sun would be lesser than the time elapsed in the same span on the earth. And by the time we would have returned to the earth, we would have essentially traveled into the future. (This by the way is the science behind Christopher Nolan’s Interstellar).
This is a simple debate for forwards time travel (which is considered as an active possibility by researchers). However, it does not hint at backward time travel.

These are but a few basic paradoxes and counters posed for and against backwards time travel. The human mind can come up with any number of drawbacks and challenges as presented here, yet the possibility of time travel will only be verified with the advancement of science and technology.

Perhaps one day, we shall transcend higher from the 3 dimensional world we live in – where time flows unilaterally [All hail, Christopher Nolan]. Perhaps one day, we too shall engage in active time travel as an independent, scientifically oriented community. Perhaps one day; perhaps soon, you can travel back in time to stop yourself from making stupid mistakes. Until then, think twice before you speak.

Check out the trailer of the recently released movie Interstellar that used time-travel as part of its plot. Also, take a look at the director of the movie, Chris Nolan, explain the science behind the movie.

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