The Possibility of Time Travel Essay Example

The Possibility of Time Travel Essay Example The Possibility of Time Travel Essay The Possibility of Time Travel Essay Essay Topic: The Time Machine The possibility of time travel Introduction Although the study of time travel is a fairly new topic of scientific and philosophical investigation, it is so well-known because of different literature, films and stories in our daily life. It is believe that most locals have got access to at least one such production related to time travel. Yet, the possibility of time travel is still a question mark to them. Is it possible to have a time travel? The answer is definitely yes. Although not every scientist agrees with the answer, supporters of relativity would also be supporters of time travel. Moreover, some scientists or philosophers give explanations to the paradoxes and make the answer almost certain. In this article, we give a clear explanation to some kinds of time travel with high possibility such as time travel to the future. For time travel to the past, we discuss the possibility and point out the impossibility of some counter arguments as well as the contradiction of some ‘paradoxes’. Definition Among lots of definitions of time travel, David Lewis’s version is easy for everyone to understand. An object time travels if and only if the difference between its departure and arrival times in the surrounding world does not equal the duration of the journey undergone by the object (1). Although the definition of the phrase ‘surrounding world’ is indefinite, we give such definition: the environment at sea level on the Earth. Yet, things are not clear. What is time? Philosophers offer a few explanations such as eternalism, possibilism, and presentism(2). Eternalism and possibilism give same explanation for the past and present The eternalist thinks that time, correctly understood, is a fourth dimension essentially constitutive of reality together with space. All times, past, present and future, are actual times just like all points distributed in space are actual points in space, while possibilism suggests that future is the only possible. They are in fact the determinism and indeterminism version of the similar theories. The presentist thinks that only temporally present objects are real. Whatever is, exists now. The past was, but exists no longer; the future will be, but does not exist yet. ’(3) Therefore, the past does not exist and we cannot travel to the past. We would put presentist aside and consider eternalism (or possibly possibilism). The above gives the concept of time-flow. Yet, the time-flow of a person might not be the same with the others. Time could distinguish from physical time or external time (which we defi ne as the time at the surrounding world) and personal time or inner time. Put this into the definition of time travel, we could get the combination: An object time travels if and only if the inner time during the journey is different from the external time(4). To be more detail, if the inner time is longer than the external time, we call it ‘time travel to the past’, while we called it ‘time travel to the future’ for the opposite. Relativity and time travel It is important to understand general relativity before studying this issue. In Newtonian gravity, which we usually learn in high school, the source of gravity is mass(5). In special relativity, we replace the term mass with more accurate terms, including energy, momentum densities, pressure and shear, called energy-momentum tensor(6). Using the equivalence principle, this tensor could curve space-time since time and distance are not the invariance but the speed of light is. This breaks many people’s common sense. The distance and time are not fixed but variable when under different gravitational force or experiencing different ‘speed’. The theory shows that if the gravitational force and the speed change, the inner time could also change and the way of time travel is to change the force and the speed(7). This is explained in later chapter. Real case of relativity in daily life Do you believe that we could have time travel by a bus? It is possible. Assuming the bus is moving at 70km/h and by definition the speed of light is constant, the inertial frame of the bus passenger is moving relative to a standing pedestrian acting as a stationary inertia frame. Put it in this way. The lights observed by the pedestrian on the road and from the bus are all at speed c. The lights observed by the passenger from the bus are also at speed c. Yet, we must not forget the fact that the passenger is at 70km/h going at the same way of the light from the bus. By common sense, the passenger should observe the light going at speed (c-70km/h) but he does not. Who takes this 70km/h away? In fact, no one take it. That’s because the passenger is experiencing a time travel, which is called ‘time dilation’ by Einstein (8). That the time on the bus is a bit slower than the time of a person in stationary inertia makes two people see the same speed of light. After a trip from Lingnan University to my home, I should be a few picoseconds (1nanosecond=1000picoseconds) younger than I should have. Moreover, such daily usage of time differences happen everyday. For example, the clock on GPS satellites is affected by both different speed and gravitational force relative to the clock at sea level in stationary state. By special relativity, it experiences a future time travel of 7. 2 microseconds per day according to its high rotational speed. By general relativity, it experiences a past time travel of 45. 9microseconds per day according to its ‘lost’ of gravitational force because of its high altitude. Therefore, the clock of the satellites should be 38. microseconds slower than a normal clock per day(9). ‘Real’ time travel to the future Although the above cases are real cases in most senses, people would argue that it’s not the ‘real’ time travel as they cannot observe the case obviously. ‘Can I jump into a machine for a while and the external time goes fast forward for several years? ’ This is people’s imaginatio n. Since we have the empirical prove from the GPS satellites, the problem is not the possibility but the degree of the travel. In my, as an art student’s, erspective, the easiest way would be using an extraordinarily extremely fast space shuttle to move toward a remote planet with an extraordinarily extremely strong gravitational force, rotate around it and move back to the Earth. After a yearly trip, he would probably saw his granddaughter breathing her last after aging. ‘Real’ time travel to the past This is a bit harder for we human being. Same as above, the question ‘can I jump into a machine for a while and the external time goes fast backward for several years’ could be asked. It is suggested that we could do it in some ways, which all of them are only hypothetically applicable. First, we could use a moving machine which could move faster than light. According to special relativity, if an object or information could move from one point to another faster than light, it could have moved backward in time(10). Second, we could use wormholes(11). The theories behide are out of a philosophy student’s handle. Yet, it is proved by Einstein field equations of general relativity and openly discussed by some professionals such as Stephen Hawking. The limitation is that we could only go back to the day the time machine built(12). Time travel and Philosophy While the possibility of time travel is proven by physical theories, what is related to philosophy? Although scientists have spotted out the physics theories behind, something is still unable to explain by science. For example, presentism (which we put aside before and probably after this sentence) suggest that we could not travel to a destination which does not exist. Moreover, if I can prove myself exist, who can prove the existence of the future me standing in front of me? At the same time, the physics affects some definition of philosophical theories. According to possibilism, our past and present are actual times but our future is the only possible. Says that 07:00 of 07/07/2007 an object was disturbed at a particular position, would a time travel to past before 07:00 of 07/07/2007, says 06:00 of 06/06/2006 of one make the time 07:00 of 07/07/2007 become possible from actual for him? In another word, change the history? Even if determinism exists, if an object is determined to go back to some time before, would it replace or affect the before it? Since questions arose in many senses, paradoxes appeared. The grandfather paradox(13) and similar The paradox is this: suppose a man travelled back in time and killed his biological grandfather before the latter met the travelers grandmother. As a result, one of the travelers parents (and by extension the traveller himself) would never have been conceived. This would imply that he could not have travelled back in time after all, which means the grandfather would still be alive, and the traveller would have been conceived allowing him to travel back in time and kill his grandfather. Thus each possibility seems to imply its own negation. Similar paradoxes came out like bamboo shoots after a spring rain. The simplest one is that one goes back to the past and kill the past him. Will he exist anymore? Philosopher Bradley Dowden even makes his argument with these paradoxes(14). He wrote that: â€Å"Nobody has ever built a time machine that could take a person back to an earlier time. Nobody should be seriously trying to build one, either, because a good argument exists for why the machine can never be built. The argument goes like this: suppose you did have a time machine right now, and you could step into it and travel back to some earlier time. Your actions in that time might then prevent your grandparents from ever having met one another. This would make you not born, and thus not step into the time machine. So, the claim that there could be a time machine is self-contradictory. † The solution of this paradox could simply ask a local kid as the cartoon ‘Doreamon’ is so popular among kids. â€Å"If you use the ‘If Telephone’ to change the world, the world could return to normal if and only if you use the telephone again in the same (parallel) world(15). † answered by a kid in the local playground. The parallel universe is a new topic to scientists but an old topic for fiction and animation. Let’s put it this way: Assume there is a person Tom. The present Tom is the real Tom in the present world, named world A. Since time is irreversible, Tom’s grandfather has met Tom’s grandmother and so on. It is an actual case happened in this world A. If you go back to a place where that particular case would still be a possible future, that particular world must not be world A but a parallel world, named world B. Even if Tom kill that ‘grandfather’ before he would have met his wife, Tom would only prevent the existence of Tom in that parallel world B but not the Tom in the original world A. Existence of parallel universe One may question: does parallel universe exist? No matter it exists or not, the grandfather paradox is still meaningless if we are clear-headed. Assume that it exists; it is obviously no more a paradox. If it does not exist, Tom could never go back to a time before he could be since by something past is actual and irreversible by definition. The past cannot be changed by definition since no parallel world could be changed by him. He will never succeed and therefore it is no more a paradox. The only ‘change’ (would it still called a change? could be done by a ‘future object’ must have been past and become an actual time just like everything is determined and becomes a history, while some people would still called it a paradox named Predestination paradox but it is something determinism could explain. Conclusion Although the paper does not mention some related theories, it included most physical and philosophical theories needed to cover this topic generally. In this topic, physicists and philosophers affect each other and new ideas spark every moment. The philosophical theories give idea to physicists and hysics theories change the mind of philosophers. In conclude, a time travel to the future is possible. Similar events occur everyday. A time travel to the past is partially possible. For those who is just travel relatively past to the external time but still future comparing with the time of depart, such time travel is possible. Similar events happen occur everyday. For those travel which the arriving destination is before the departure time, a parallel universe should be exist or the ‘past’ should already be determined. Otherwise, such travel may not exist. References 1: Lewis, David. 1976. The paradoxes of time travel. American Philosophical Quarterly. 2: Hunter, Joel. 2004. Time Travel. Philosophy of Science ( iep. utm. edu/category/s-l-m/science/) 3: ^[2] 4: ^[3] 5: Arnold, V. I. 1989, Mathematical Methods of Classical Mechanics, Springer, Chapter 1. 6: Gott, J. Richard. 2001. Time Travel in Einstein’s Universe: The Physical Possibilities of Travel Through Time. Houghton Mifflin. 7: ^[6] 8: Einstein, Albert. 2004. Relativity : the Special and General Theory by Albert Einstein. Project Gutenberg ( gutenberg. org/etext/5001) 9: Rizos, Chris. 1999. GPS Satellite Signals. University of New South Wales. 10: ^ a b Jarrell, Mark. 2006. The Special Theory of Relativity: ( physics. uc. edu/~jarrell/COURSES/ELECTRODYNAMICS/Chap11/chap11. pdf) 11: Thorne, Kip S. 1994. Black Holes and Time Warps. W. W. Norton. 12: ^[11] 13: ^ Barjavel, Rene. 1943. Le voyageur imprudent (The Imprudent Traveller). 14: Bradley Dowden. 1993. Logical Reasoning. International Thomson Publishing 15: . F.. 1984. 5 .