Albert Einsteins Theory of Relativity - Essay Example

RELATIVITY THEORY Introduction Albert Einstein’s Theory of Relativity has baffled many scientists and some of its theoretical underpinnings have been tested by modern scientists who feel that these theoretical postulates have a remarkable practical value in them. To put it succinctly, general relativity (1907-1915) refers to a body of theory in which Einstein first hypothesized that under the so called ‘equivalence principle’ two physically identical states – one of accelerated motion of a body through space and the other of a corresponding static body caught up in a gravitational field (e.g. earth-bound existence) – can be regarded as tenable. This gave rise to a controversy because in classical mechanics a free fall in a non-gravitational field is known as ‘inertial motion’, i.e. there is no external force applied on the object. But gravity is a force. Therefore, classical mechanics holds the view that ‘inertial objects moving through space cannot accelerate with respect to each other’. Now we come to the crux of the problem – how to reconcile the two seemingly incompatible theoretical postulates? Einstein next proposed an alternative theory in which he argued that the space-time continuum is curved. His subsequent field equations relate the curvature of space-time to the mass, energy and the momentum within it. Hence his famous equation: E = MC2 Where E = energy, M = mass and C = the speed of light in a vacuum. The corpus of arguments Now I will come to the point in the article. So called “Grandfather paradox” is directly related to the same “traveler-homebody” paradox here. Since space-time curvature as suggested by Einstein would allow us to solve the seemingly irreconcilable twin paradox presented in this article, it might be pertinent here to examine all probabilities of the theory. According to the Grandfather paradox a time traveler who goes back in time will be able to kill his biological grandfather before the latter meets the time traveler’s grandmother so that one of his parents might not be conceived. Logically, this means that he himself might not be born. Now comes the real paradox. Since the time traveler did not go back in time, his grandfather was not killed. Therefore one of his parents was born thus enabling him or her to meet the other. Finally, the time traveler was born. Now I am coming to the gist of the argument presented in the article: The traveler uses the length-contraction equation of special relativity to measure distance. So the star six light years away to the homebody appears to be only 4.8 light years away to the time traveler who goes at a speed of 0.6c. Therefore to the traveler the trip to the star takes only eight years (4.8/0.6) whereas the homebody calculates it as taking ten years (6.0/0.6). The homebody finds out to his amazement that his brother is now four years younger than him. The logical sequence of events should provide an equally logical outcome. Now let’s look at what the Doppler effect has to offer us by way of an explanation. According to the Doppler effect “waves that propagate in a medium such as sound waves, the velocity of the observer and the source are relative to the medium in which the waves are transmitted”. Naturally this leads us to the conclusion that the sum of the Doppler effect must hold that motion of the source, motion of the observer or motion of the medium will influence the outcome, irrespective of any other interference. As we are aware there are those waves which do not need a medium to propagate such as light or gravity. For example according to special relativity, we have to take into consideration only the relative difference in velocity between the observer and the source. When we extend this principle to the above mentioned twin paradox we have a partial solution to the problem. The homebody is a static observer on the earth while the time traveler is in motion. The relationship between the observer and the traveler and that between the observer and the medium determine the outcome. In this instance the outcome is the paradoxical change in ages. The Doppler effect is not so simplistic. In fact it has much more in it than we can explain by using simple hypotheses. For instance the Doppler effect is present whenever the source of waves is moving with respect to an observer. The Doppler effect can be described as “the effect produced by a moving source of waves in which we can notice an upward shift in frequency for those observers towards whom the source is approaching but on the other hand a downward shift for those observers from whom the source is receding”. It is very significant here to note that this effect does not result from an actual change in the frequency of the source. The theory of special relativity is connected with this phenomenon to describe the twin paradox. For example Halliday et al in their book “Fundamentals of Physics” (2004), argue that special relativity theory is capable of explaining seemingly paradoxical situations that defy ordinary laws of physics. Both the traveler and homebody set their clocks at zero when the traveler leaves earth for the star (event 1). When the traveler reaches the star (event 2) his clock reads 8 years. However when the homebody sees the traveler reach the star, the homebody’s clock reads 16 years. Why 16 years? Because to the homebody the craft takes 10 years to make it to the star and light 6 additional years to come back to the earth showing the traveler at the star. So to the homebody the traveler’s clock appears to be running at half the speed of his clock (8/16). Doppler effect can be applied to solve this paradox now, though still there may be some inexplicable physical properties such as the presence of multiple and parallel dimensions. When Einstein resolved the paradox by referring to the space-time curvature it did not look so convincing to the scientific community to hypothesize on the existence of time curves that were subject gravity. Though Newton’s theory of universal gravitation was superseded by Einstein’s theory of general relativity, it has some special applicatory value in respect of the gravitational fields. By extension this principle cannot be ignored when one considers the impact of gravity on time and light. Einstein dwelt on it at length to reconcile his original theory with what classical mechanics presented by way of inertial motion. Conclusion I have been highly enthralled by what Paul Davies says in his best seller “How to Build A Time Machine”. Davies uses simple examples in this book to illustrate how physical perception of time as against its psychological perception, must be treated. It is all about measurable time differences however insignificantly smaller they may be. He sets out with an illustration of Einstein’s theory of relativity and takes us on a journey not only through outer space but even through well known physical landmarks such as Manchester and Heathrow airports. Davies has been engaged in research in his pet subject “field theory in curved space-time” for a long time. As I have already demonstrated it is this particular theory that Einstein was trying to develop and that every space scientist and physicist wants to master. Let’s look at what he has got to say about time in his masterpiece: Time is elastic? It can be stretched and shrunk. How? By simply moving very fast. What precisely do I mean by stretching time? Let me state it more carefully. According to the theory of relativity, the exact duration between two specified events will depend on how the observer is moving. The interval between successive chimes on my clock might be one hour when I am sitting still in my room but it will be less than one hour if I spend that time moving about (Davies, 2002, pp.9-10). Here the author refers to paradox of time as the most important aspect in understanding the relationship between two events. From the view point of the homebody it is painfully prolonged while to the mobile traveler it is something of a dynamic pleasant experience. Davies has pointed out in his book that this must not be regarded as something psychological but a physical perception of time by the individuals involved. Further, such experiences on the earth can have a very insignificant time differential but on a universal scale it is much bigger. In fact, his theoretical arguments are well reinforced by simple examples throughout the book. Finally let me conclude by saying that what seemed to be a paradox at the beginning of the 20th century has become a reality at a little distance or to put it another way a seeming probability right now. Therefore it is not far-fetched to conclude by saying that though time-travel proper may not be possible it is possible to construct identical scenarios based on new findings. References 1. Davies, P(2002), How to Build A Time Machine, London, Penguin Books Ltd. 2. Halliday, D, Resnick, R and Walker J (2004), Fundamentals of Physics (7th Ed.), New Jersey, John Wiley & Sons. Read More