Albert Einstein’s vs. Newton: General Theory of Relativity

Albert Einstein, most famously known as a physicist, was a contributor to the scientific world with his many known researches and humanitarian work. As a Nobel Prize Winner in 1921, his chronicled and more important works include Special Theory of Relativity (1905), Relativity (English Translation, 1920 and 1950), General Theory of Relativity (1916), Investigations on Theory of Brownian Movement (1926), and The Evolution of Physics (1938). (Nobel Prize Foundation, 1921) In all his important works, Einstein’s Theory of Relativity has lead the way for how science currently views time, space, energy, and gravity. Relativity, which all motion must be defined relative to a frame of reference and that space and time are relative, rather than absolute concepts, consists of two principal parts: The theory dealing with uniform motion, or the Special Theory of Relativity (1905) and the theory dealing with gravity, or the General Theory of Relativity (1916). (dictionary. com, pars. 2) Einstein’s Special Theory of Relativity is the physical theory of measurement in inertial frames of reference. Although Einstein’s Special Theory of Relativity was â€Å"special† because it dealt only with inertial reference frames; his General Theory of Relativity accounts not only for these, but also for bodies that accelerate and are based on the postulate that the local effects of a gravitational field and of acceleration of an inertial system are identical. (dictionary. com, pars. 2) An example of Einstein’s Special Relativity: One of the peculiar aspects of Einstein's theory of special relativity is that the length of objects moving at relativistic speeds undergo a contraction along the dimension of motion. An observer at rest (relative to the moving object) would observe the moving object to be shorter in length. General relativity or the general theory of relativity (GR) in whole is the geometric theory of gravitation. It is what we currently define as gravity in modern physics. GR integrates with special relativity in relatively, but GR consists of Newton’s law of universal gravitation and describes gravity as a property of the geometry of space and time. Even though special relativity intertwines a lot with general relativity, these two viewpoints are really what GR is about and relate greatly to each other. In the first viewpoint of GR, it is a theory of the behavior of space and time. Before the 20th century, all physics theorists assumed space and time to be absolutes, or separated from each other. Now called spacetime, together space and time formed a background within which matter moved. (Felder, pars. 4-5) In Einstein’s theory of GR, this physical theory was to describe how different kinds of matter would interact with each other and predict their motions. The theories of space and time greatly changed after the development of the Special Relativity Theory and shortly later the General Relativity Theory by Einstein. This results that space and time came to be viewed as the important variables in physics, which are capable of being changed by the mater within them and in turn changing the way that matter behaves. (Felder, pars. 5) Spacetime is an important factor in GR. In Newton’s world and before the 20th century, physics space and time again were viewed completely separately. In relativity theory, time is the fourth dimension our world has instead of the three one would think there is. It is hard to picture a 4D world, so to make things simpler let’s picture a 2D world. As shown in diagram 1, we can view spacetime as a 2D surface where the horizontal direction is space and the vertical direction is time. The diagram below shows the world line of an object in a one-dimensional space (Felder, pars. 7): (Diagram 1) A spacetime diagram like this is very critical to help in understanding relativity. It answers questions like: What’s the world line of a particle at rest? What the world line of a particle moving with constant speed in one direction? How would you describe the motion of a particle with the world line shown below? Viewing spacetime this way allows us to formulate physics in new ways. It is a similar way in getting Newton’s first law of motion, which states that an object with no force acting on it will move in a straight line at a constant and we can just say that the world line of a free object (one with no forces on it) is a straight line. speed (Harrison, pars. 6) Comparing to Newton’s laws, spacetime are considered two separate things, while in relativity, both in special and general theory, it is necessary to view spacetime as one. In GR this team of spacetime is curved by the effects of gravity. Now in GR, curved space often refers to a spatial geometry, which is not â€Å"flat. † Spacetime becomes curved in the response to the effects of matter and there is no gravitational force deflecting objects from their natural, straight paths. This puts gravity to correspond to changes in the properties of space and time, which in turn changes the straightest-possible paths that objects will naturally follow. So the act of curving is caused by the energy-momentum of matter and affects matters behaviors. In Newton’s first law of motion, it states that, where an object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. In a curved spacetime what used to be straight lines are now twisted and bent, and particles with no forces acting on them are seen to move along curved paths. (Physics Classroom, pars. 1) John Archibald Wheeler, an American theoretical physicist, paraphrases, â€Å"Spacetime tells matter how to move; matter tells spacetime how to curve. † (Britannica Encyclopedia, pars. ) To explain curved space in an example, suppose there are two people. Each person stands two feet apart from each other facing the same direction and begins walking straight. Even though one might think the two people are walking in parallel lines (since they are walking only in a straight line), is one will stand behind them in between them, he/she will notice that those two people will start to drift apart. In awhile the two people will become four feet apart instead of the 2 feet that they started on and both are not pointed in exactly the same direction as they started on. One might assume it’s because one is not going in a â€Å"straight† line. (Picture of Geodesics) Although, what is a â€Å"straight† line? One assumes that a straight line means being parallel or that a straight line is the shortest distance between two points. But in curved space path that stay parallel to each other are not paths of minimal distance and vice-versa, there is no path in space that fits a â€Å"straight† line being parallel or the shortest distance. In space, a straight line is curved and the shortest path between two points is called a geodesic. The second viewpoint of general relativity is described as a theory of gravity. In Newton’s second law of motion, that states that the acceleration of an object is dependent upon two variables – the net force acting upon the object and the mass of the object. (Physics classroom, pars. 2) In other words, getting two massive bodies like the Earth and Newton’s â€Å"famous† apple are going to pull each other because of the law of gravity. To explain further, if an apple started out at rest and when it just breaks off from a tree, gravity would make it move towards the Earth until it collided with it. Newton’s curiosity of a fallen apple not only explains his law of gravity and the falling of apples, but also the orbit of the moon about the Earth, the motions or the planets about the sun, and much more. Einstein’s theory of GR relates to this because it explains all of Newton’s laws, but in a very different way. In GR, a massive body like the sun causes the spacetime around it to curve and this act of curving in turn affects the motion of the planets, causing them to orbit around the sun. In Newton’s second law of motion, these objects (i. e. the earth and the apple) will have a gravitational attraction, causing them to accelerate towards each other until they eventually collide. In GR, the same effect will happen, but the description is different because gravity is not a force in GR. Objects neither exert nor feel any-non-gravitational forces, so basically the objects should act like free particles moving alone geodesics. (Felder, pars. 5) In a flat spacetime, which has no gravity, the geodesics would be in straight lines. Since objects started out at rest, their world lines would be vertical lines, this means that they would always stay the same distance from each other. However, in the effects of gravity, we know that the objects will have spacetime around it. In a curved space, parallel lines do not always stay parallel. The geodesics in this curved spacetime start out parallel but over time it doesn’t. This results in the objects colliding. Einstein shows that although Newton’s theory of two objects colliding is predicted, the underlying description of the curved space is different. To show an example about gravity and curved space with a couple of geodesics, here is another graph (Felder, pars. 14): To explain the graph in more detail, the yellow rectangle is the sun (and the space around the sun is really three-dimensional), the spatial axis is â€Å"r† (radius) instead of x, and â€Å"t† (time) instead of y. The geodesic lines (red ; blue, respectively) are the particles moving directly towards or away from the sun. The red geodesic shows that an object initially at rest will curve towards the sun. Even an object moving away from the sun could fall back in if it were moving slowly. While the blue geodesics, is for the particle starting out at the same place but with an initial outward velocity large enough that I will never fall back, objects that have an escape velocity. Explaining the basis of GR helps form a stepping stone to Einstein’s more complicated theories and consequences, along with some knowledge of the General Theory of Relativity. In this very complicated version by Einstein of Newton’s laws of motion, it in fact shows not that Einstein just complicated Newton’s theories, but showed that results are not the same. The result in fact that objects collide are there and come out slightly the same, but the behavior is different. Spacetime is therefore â€Å"curved† as a straight line. The theory of GR has brought the science world to a dramatic position of understanding the universe. Space and time, in which were two separate things are now explained as one union with each other. In GR gravity is not only viewed as a force but now as a description of the geometry of the universe. This helps scientists envision the universe in a more dramatic and insightful way. As Albert Einstein was forced to summarize the general theory of relativity in one sentence, he quoted: â€Å"Time and space and gravitation have no separate existence from matter. † Works Cited â€Å"Albert Einstein† Pac Bell. ; http://home. pacbell. net/kidwell5/aebio. html; â€Å"Albert Einstein†, Colliers Encyclopedia, (MacMillan, 1985) Volume 8, pg. 684-685 â€Å"Albert Einstein†, World Book, (World Book Inc. , 1999) Volume 6, pg. 146-147 â€Å"Albert Einstein†, Encyclopedia Britanica, ( Encyclopedia Britanica Inc. , 1997) Volume 4, pg. 403 â€Å"Albert Einstein†, Current Biography Who's News and Why, (H. W. Wilson Co. , 1953) Volume 1953, pg. 178-180 â€Å"Albert Einstein†, Current Biography Who's News and Why, (H. W. Wilson Co. , 1955) Volume 1955, pg. 177-178 â€Å"Albert Einstein†, The Biographical Dictionary of Scientists, (Oxford University Press, 1994) Second Edition, pg. 206-208 Felder, Gary. 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