Avengers endgame, while most of us have been fanatic about the characters so many of us have been crazy fans of its action, concept and the thrill of knowing the practical applications of unknown and then comes THANOS, the greatest evil of the Avengers world who was destroyed by IRON MAN, our beloved billionaire physicist, by traveling back in time, yes but what if I tell you our actual physicists believed that THANOS couldn’t be killed. So here I introduce to you all to what we call the Grandfather paradox.
It is a paradox because it introduces to us a contradictory concept. Imagine you go in your past and kill your grandfather that would mean your father wasn’t born and so weren’t you but you are alive and breathing. That is why it is called what it is the Grandfather paradox.
Before I begin to tell you the solutions to this paradox let’s dive into time travel. While most of the scientists believe that time travel is possible albeit it still remains a question. Albert Einstein’s Special Theory of Relativity stated that time and space are linked together as space-time curves and nothing can travel faster than light. Space-time forms a curved coordinate and gravity is nothing but a dimple in it.
But if we travel with a speed faster than that of light which is 3×108 m/s, we might be able to travel back to our past and see someone we have never met before. But it cannot be that easy right? First achieving the speed of light is a challenge in and of itself and then the human body cannot endure that speed, at this speed mass will become zero. Stephen Hawking during an interview said ‘time-traveling is very serious question’ and it can be approached scientifically, as an optimist, I will take yes for an answer.
I certainly believe that after getting to know about time travel we can get devoured in the solutions of Grandfather Paradox. Most scientists have the theory that if you or I travel back into our past and kill our grandfather, we will create a parallel universe where our grandfather no more exists but in real-world everything will carry on just the same and there are sufficient scientific papers for us to know about a parallel universe.
Stephen Hawking, in his last research paper, discussed the multiverse, this term was first coined by Hugh Everett in the theory Many-Worlds Interpretations, the former scientist proposed the theory that there can be the infinite universe and with it an infinite possibility, for instance, some planets like our own, some creatures like on earth or our doppelgangers.
What is it? And why am I introducing you to it? It was given by Novikov, according to it if we went back in time a physical barrier would prevent us from killing our grandfather i.e it is impossible to create grandfather paradox.
Physical barriers such as, if you want to poison your grandfather, it is possible that somehow you spill it or due to moral infliction you will no longer be willing to kill him, or your eyesight would get damaged and you can no longer put it in the right vessel these are the kind of obstacles we are talking about. Although it provides a good solution, it requires some additional mechanisms for the principle to work and therefore it is in question.
CTC: closed time-like curves
In the search for our solution I came across a term CTC, closed time-like curves. What is the proof of their existence? So, according to Einstein, space-time exhibits closed paths in space-time, and a quantum particle travels through a wormhole back in time and returns to the same position in space and time i.e. closed time-like curves are created so now it is clear that the probability of the existence of CTCs provides a means to travel back to time but how do they give us the solution?
Well, if CTC is used to travel to our past that would mean that we, who are time travelers here have always been part of the curve and thus past and so leading us to the solution of our dilemma ‘we can change nothing in our past’. Albeit many scientists like Stephen Hawking thinks the CTC is an awful concept but many like Novikov believe these curves would be the very reason we can meet our grandfather in the past.