An Essay on Time Travel
Time travel has been a phenomenon of science fiction since the very first days of the genre. Man has been fascinated with the possibility of manipulating one of nature s most divine traits. Recently the question of the possibility of time travel has crossed over from the world of fantasy to serious science. It is no longer a question left just to the authors of sci-fi stories. Thus now more than ever it is imperative to investigate whether the idea of time travel is even meaningful. To explore this question it is necessary to first clearly understand time and subsequently the concept of time travel. Time has always been considered to be an intrinsic part of our environment. It is so fundamental to our thought processes that it is always taken to be an absolute. Only recently did modern physics begin to study the nature of time and how it relates to space. Together space and time constitute the very fabric of reality known as space-time. We now take it for granted that space- time is a real entity which is independent of our existence. The problem lies not in this assumption but in how it is applied to the nature of time. It maybe true that time is a state variable of the universe but there are definite indications that our view of it is either incorrect or incomplete. Time is always discussed as if it were a fluid. We seem to think it flows and has a direction or an arrow.
Another underlying every day assumption is that time is absolute for everyone. On the other hand the physics of relativity tells us that time is a dimension and there is no such thing as absolute time. This information causes many people to prophesize that we should be able to move just as freely through the fourth dimension as we do through the other three spatial dimensions. Here is where the discrepancy lies, in the connection between the dimensional nature of time and the classical fluid view of time. In our attempt to reconcile the intuitive view of time with the physics of relativity, we try to join the two in such a way that is still acceptable to our common sense. However the recent past has shown that as physics gets closer to describing the very nature of the universe, it gets further away from current day common sense and intuition. The best example of such a branch of physics is quantum mechanics. Quantum mechanics has time and time again held up to experimental evidence and yet its basic tenet of probability/uncertainty is highly unsettling to most people. If we are to embrace the relativistic and dimensional nature of time, then we must abandon the one stemming from the idea that it is fluid. We must also accept that as beings who exist physically in three dimensions it will be extremely difficult to visualize how exactly a fourth dimension fits into our existence. A limited analogy of a two-dimensional being having difficulty grasping the third dimension may be used. The only problem with that analogy is that time, if it is indeed a dimension, is very different from the three spatial dimensions we perceive. Thus if we begin to accept the idea that time is purely dimensional and we have a somewhat limited perception of it, the concepts of past present and future take on new meaning. They all coexist.
A world line isn t created as one move forward through time; it is always there in its entirety. However we will never be able to see this because our brains are not equipped to deal with such information. The complexity of our neural net at our current stage of evolution does not meet the standards to comprehend time in its true form. One of the most important methods of information organization that the brain uses is sequencing. Our memories are temporally ordered to a large extent. Time is the main associative operator in the thought process. As the brain gets new information from the five senses, it is time stamped and goes into memory. Imagine the information overload and chaos that would occur if we began to see past, present and future all at once. One would go completely insane. An analogy to the situation would be a dam breaking. A dam allows small amounts of water to flow consistently and calmly. If the dam were to break the sudden onrush of water would destroy everything in its path. Thus it can be seen that there maybe a profound difference between the real nature of time and time as perceived by the human psyche. This is the handicap we have in coming to grips with time as it really is.
In a nutshell this could mean that time is the dimension in which the other three spatial dimensions exist. Our 3D world is a level curve of a surface in 4D. We cannot experience the whole surface at once. But by moving through that surface we can experience it piece by piece. This is the current state of things. Since space itself is expanding through time, we are forced to move through it as well and feel the passage of time and its arrow. Equipped with the new idea of time as a dimension we are closer to its real nature. Thus the question of time travel can now be better tackled. The idea of time travel must first clearly be defined. Obviously it does not refer to the normal ticking of the clock we experience due to the expansion of space. It refers to a movement through time not caused by the expansion of space. This leaves two possibilities. Relativistic time dilation and discrete jumps through time. Time dilation can be implemented to create, in effect, time travel to the future. Since it is a one way trip no paradoxes arise. All you are simply doing is slowing down the rate at which you move through time compared with normal space. It is done by moving at speeds close to that of light. When you slow down enough to once again move through time at the same rate as which space is, you will have arrived in your future faster than you normally would have.
The extreme case analogy would be suspended animation. No paradoxes arise because one does not disappear from space (violating the
conventional concept of the conservation of mass-energy). You simply move through space at such a velocity that you begin to run into its dimensional boundary that is expanding in time. This causes your rate of passage through time to be different from that of space. There is no example that could sufficiently illustrate this mechanism but consider the metaphor ramming into space itself a starting point. It is the second concept of jumping through different points in time that is problematic. It is still unclear as to whether the laws of current physics or even future physics will allow such a thing and even if it did, some very unsettling paradoxes arise when considering time travel of this sort. They arise because of the psychological view of time. However assuming that physics does not have a problem with such a mode of temporal travel the paradoxes can be dealt with if we use the dimensional viewpoint of time.
One of the paradoxes that arise is the grandmother paradox. In essence it states that if one were to go back in time and kill his or her grandmother, then their mother would never be born and she would never give birth to the time traveler. Of course then the question arises how did he/she travel back in time in the first place? The idea gnaws deeply at the notion of cause and effect. But what if cause and effect were an illusion? The connection our thought processes make between two occurrences need not necessarily exist outside of our head. If the past and future exist at the same instant then so would cause and effect. They need not be in any order. The order we perceive is a creation of the mind. They are just there, always. Subsequently if a being free to move through time was to interact in what they thought were the past, the future need not change. The idea may be very unsettling at first but then so was Einstein s introduction of time dilation. The second paradox of free will is more metaphysical in its nature. A thorough examination of it is beyond the scope of this paper. However it can be briefly examined in its relation to the passage of time. One of the questions concerning time is whether the future is open or not. From the dimensional point of view of the conclusion leans towards a closed future since it already coexists with the past and present.
On the surface this appears to have deep implications about free will. Are we truly free to choose as we do? This is an ambiguous question. From the point of view of an omnipotent being who can see entire world lines the answer would be no. However from our point of view, even if we knew that the future was closed, we cannot know what that future is. Therefore free will seems to hold. The counter argument to this reasoning is that no matter what decision you make, that was the decision you were destined to make. This argument is circular and highly flawed. If any decision is predestined, then predestination really has no effect on the decision making process. Once again this is related to how one defines free will.A third oddity that usually surrounds time travel of this sort is the violation of the conservation of mass- energy. An example is if one time travel back a few minutes and meets the former self and then both time travel to the future to meet another and so on, matter will be created out of nothing. This argument could be falsified if it is shown that the amount of mass-energy is constant not only in space but also through time. Since three dimensional space is enclosed in the fourth dimension of time, it is really the time-mass-energy that has to be conserved. All of the energy and mass of the past, present, and future coexist in time and together they are conserved over time.
In examining the nature of time and subsequently the question of time travel, hopefully the most popular arguments concerning the two topics have been addressed. This is not to say that the point of view presented in this paper is necessarily the correct one. That is left to the future physicists and philosophers to ponder over. However it does appear to shed light on an exit out of the hall of paradoxes that are usually associated with the subject matter. Whenever a theory can explain all the same concepts as the theory it is superseding, and more, it usually is accepted in the scientific world. Many scientists agree with this point of view of time and hopefully as more come to accept it, we will make further inroads into its understanding and time travel.