Time travel : is it possible ?

Time travel : is it possible ?

Submitted by Editor on Mon, 2016-04-18 18:33 After a mugger kills Emma, his fiancee, Dr. Alexander Hartdegen, a young inventor who teaches at Columbia University in New York City, devotes himself to building a time machine that will allow him to travel back in time and save her. When he completes the machine four years later, he travels back in time and prevents her murder, only to see her killed by a horse and buggy. This is not a real story, but the plot of a movie called the “Time Machine” made in 1960. Of course, the original idea of time travel came from H G Wells’ famous book, ‘The Time Machine’, published way back in 1895. The story poses two questions. Whether time travel is possible and whether you can influence events in the past or future? When I was a child, I was fascinated by comic heroes like Phantom and Mandrake. I still remember how much I enjoyed reading them. Fantasy is an essential element of human experience. However, when you ask a scientist if time travel really possible, one is asking a question of its feasibility in reality. For a scientist, framing a question is most important, more important than the answer. For example, when a question is properly framed, it could also reveal a possibility of it not having an answer within the realm of science. Scientists often reframe a question to decide whether the question is meaningful or not. One could always ask any random question. However, whether it is meaningful or addressable within the purview of science is itself another question. You could ask a question like: “Is fish really fish?” The question would not make any sense because you are contradicting yourself through such a question. Therefore, before we look for an answer to a question, it is essential to ascertain the validity of the question and understand its meaning in an unambiguous way. So let us examine the question: Is time travel possible? What makes me think that I can answer this question? If someone asks me a question: “How much wood do you need to make an arm chair? “ I would simply say I do not know for I am not a carpenter. I first of all need to determine whether I am qualified enough to answer a question. Examining the question further might reveal an answer to this. Let us try to reframe the question as follows: Is there any scientific law which says time travel is not possible? This question is something I could attempt to answer. We need to ask now a second question: What is meant by the phrase “time travel”?  The logic hidden in the idea of time travel seems to be that the observer can be isolated from the observed, which I would call the hypothesis of an “isolated observer”. This is what is assumed by the person who is asking this question. And the following are further assumed: there is something called past (observed) and there is someone who is a traveler (observer) and he or she is isolated from the observed. By isolated, we mean the “observer” is not a part of the “observed”. Only then he can observe something. In Order to observe the past, you should not become the past yourself! Then you would be violating your own definition of time travel! Therefore, if the observer becomes a part of the observed, the concept of time travel collapses. The movie The Time Machine, however, does not assume that the observer is isolated. It simply suggests in a naive way that one cannot mess around with one's past, but that time travel without having the ability to alter past is still possible. Often the idea that you cannot influence the past is illustrated by a “thought experiment” called “killing your own grandfather”.Suppose you travel backwards in time and kill your own grandfather before he was married, you land up in a situation that you won’t be existing. But you do exist, which is what made your time travel possible in the first place. This is called a paradox. The point is, if your idea is logical, then you would not end up in a paradox. Conversely, if you end up in a paradox, then your idea cannot be logical. This is an interesting way to figure out whether an idea is logical or not. The movie tries to convey this. I am going to a level more subtler than that. Now let me ask the question a little more technically: Can you be an isolated observer when you travel in time? By isolated, I mean you not only don’t get to mess with the observed quantity, but you have no influence whatsoever on it. To make it even more precise, I say, you cannot even interact with it. However, the point that I would like to make is, according to science, observation itself is an interaction. When you either see something or use a camera to record an event, light is needed for the observation. Here, I elaborate. What is seeing? Seeing requires light. When light is incident on an object and gets reflected from the object, reaches the eye (or camera), seeing happens. This is what we call an observation. The object, the eye and light: all the three are necessary to make an observation complete. Without any one of them the observation does not happen. Light itself is an object and in science they are called “photons”, meaning particles of light. Let us formulate and examine the idea with little more clarity. Let us call the system being observed as system A, and observer as system B. The question now boils down to this: Is system B isolated from system A? System A and B cannot be isolated as they are interacting! As I stated above, photons belonging to the the observed (System A) interacts with the eye of the observer (System B). This makes these two systems -another single system, and not two isolated systems! Therefore, the idea of the isolated observer has broken down. Based on this I say “time travel” is not possible. The catch is, the moment you time travel and go to the past, you are interacting with the observed quantity. So when light enters your eye, it is interacting with you. This means you are not an isolated observer anymore, thereby violating your own definition of time travel. You might get around this by saying you travel back in time, but you do not observe anything. Then you are not violating anything. Hold on, if you do not observe anything how do you know that you have time traveled ? Oops !!! There seems to be no way around it. It is very easy to see that there would be a number of more serious objections to time travel if you go on these lines. One of them is, when you travel back in time and watch something, where do you position yourself? To be present there, you need some empty space. There is no empty space anywhere, by standing there you are replacing millions of atoms that were present in the space before you travelled there. Which means you are seriously messing around with the past, from a physicist's perspective! Though I am not against the possibility of time travel through some mechanism  which is currently unavailable to the scrutiny of science, I would conclude that a closer look at the question shows a paradox at its heart from the point of view of the present understanding of “observation”, as defined by science.(The Author is a Physicist and a Teacher. He is presently working as an Assistant Professor of Physics at Amrita Vishwa Vidyapeetham, Coimbatore, Tamil Nadu. His doctoral work is in the field of atomic physics and he continues to do research in the same area. He also holds interest in Adventure Sports, Psychology, Literature and Music.)