The History of Classical Gravitational Theory and General Relativity In the beginning scientists and religious men of their era tried to explain the universe both biblically and scientifically. One of the foremost Greek scientists was Aristotle; taught by Plato, that the circle and sphere are the two most perfect shapes in a 2 and 3 dimensional universe, Aristotelian system placed Earth at the center of the universe; and all other heavenly bodies revolved around the earth in crystalline orbitals. Another Greek Mathematician, Aristarchus theorized that the sun was the center of the universe and that the Earth revolved around it.
His simple reasoning was constituted purely by the fact that the Earth is a much smaller body than the sun, and the smaller should orbit the greater. By the 2nd century CE it became more and more apparent that the simplistic models derived nearly 2000 years before, were flawed. Kepler, a Scientist of the early 1600s concluded not only that the previously stated purely circular orbitals around the sun were in fact ellipses, and that planets travel faster when near the sun, and slower when farther from the sun, and lastly he found that the mathematical relationship between the orbital period, and the orbital radius of any given planet.
While Kepler was creating a new model of the universe Galileo Galilei was tearing apart the out dated Aristotelian system. Conceiving the theory of inertia, disproving the concept that all planets orbited the Earth (essentially providing the proof Aristarchus’s theory lacked) disproving the Catholic church’s geocentric model that had become so fundamental to its dogma, and lastly left a major concept of physics unexplained, to an influential scientist, that was born the year Galileo died.
Isaac Newton the man that finally unified Earth and the heavens discovered the weakest force in our universe; gravity. Having inherited all the works of physicists previous to his time, Newton deduced that there was a force that pulled matter towards it. He concluded that the same force that pulls an apple to the Earth also holds the planets and moons in orbit. Prior to Newton no one had considered that the Earths gravity extended into the heavens above, much less that solar gravity bound the planets to their orbits around the sun. By using Kepler’s laws, geometry, algebra, and his ew laws of motion he was able to pull everything together to explain the universe in a very basic way; the law of universal gravitation. This law states that the attraction between any two bodies in the universe is directly proportional to the product of their masses, as well as inversely proportional to the distance between them squared. Or… FG = GMm/R2 “Newton’s work in mechanics was accepted at once in Britain, and universally after half a century. Since then it has been ranked among humanity’s greatest achievements in abstract thought.
It was extended and perfected by others, notably Pierre Simon de Laplace, without changing its basis and it survived into the late 19th century before it began to show signs of failing. ” (http://www. newton. ac. uk/newtlife. html) As well as the Law Of Universal Gravitation, Newton also began to calculate and explain the aspects of motion that had so eluded physicsits before. Newtons first law of motion states that an object in motion stays in motion unless acted on by an outside force and therfore an object at rest will stay at rest unless acted on by outside force.
This law allows for equilibrium of soliditary objects and in objects in motion that are not in acceleration. Our universe as we know consits of 4 fundamental forces: 1. electromagnetic force 2. nuclear forces 3. “ ” 4. gravity-holding it all together. The problem is, all the other forces seem to be ballanced; equaling each othre out. Gravity on the other hand doesn’t want to cooperate. Gravity is an extremely weak force. Physiscits around the world try to explain this phenomenom. In their quest, they discover some miraculous things…
Born on October 10, 1731 in Nice, France; Henry Cavendish was an English Physicist and Chemist. “The English physicist and chemist Henry Cavendish determined the value of the universal constant of gravitation, made noteworthy electrical studies, and is credited with the discovery of hydrogen and the composition of water. “ (http://www. notablebiographies. com/Ca-Ch/Cavendish-Henry. html) The Cavendish Experiment was the first exerpiment to calculate the earths gravitational constant. His experiment resulted in the following conclusion
Or that the gravitational Constant of Earth = Acceleration of gravity at the surface of the Earth times the Earth’s Radius squared over its mass = 3 times Acceleration of gravity at the surface of the Earth over 4 pi times the radius of the Earth times its density. One hundred years ago Albert Einstein published a theory so monumental and eventually leading to the creation of the Nuclear Bomb, satellite technology, space travel, and a better understanding of the universe. Einstein soon became the most famous physicist in history, by publishing his most profound theory, the Theory of General Relativity.
General relativity states that energy is equal to mass times the speed of light squared or … E=MC2 This equation proves that a small amount of matter can emit a huge amount of energy. The equation also explains why the sun shines, the big bang theory, and further clarifies the speed of light to be 3×108 m/s. but his theory also lead to the creation of the worlds most deadly weapon; the Nuclear bomb. Inertia and gravitational properties of mass also play key roles in the Theory of General Relativity. The equivalence principle is a key component to his theory.
The equivalence principal means that a gravitational field can be produced either by mass or by acceleration. So for instance; “A person in a free-falling elevator experiences weightlessness, and objects either float motionless or drift at constant speed. Since everything in the elevator is falling together, no gravitational effect can be observed. In this way, the experiences of an observer in free fall are indistinguishable from those of an observer in deep space, far from any significant source of gravity.
Such observers are the privileged (“inertial”) observers Einstein described in his theory of special relativity: observers for whom light travels along straight lines at constant speed.  Einstein hypothesized that the similar experiences of weightless observers and inertial observers in special relativity represented a fundamental property of gravity, and he made this the cornerstone of his theory of general relativity, formalized in his equivalence principle. Roughly speaking, the principle states that a person in a free-falling elevator cannot tell that he is in free fall.
Every experiment in such a free-falling environment has the same results as it would for an observer at rest or moving uniformly in deep space, far from all sources of gravity. ” The Space Time fabric can be described by using a 2 demensional analogy where space and time are distorted by mass. Matter changes the geometry of the space time fabric. The more mass an object has, the more distortion there is. All things considered, most celestial bodies are spherical in one way or another; this being said the curved distortion in the fabric of space time is gravity’s pull.
Now thanks to Newton we know that the more mass you have, the stroger gravity’s pull is on you. So in effect, if we took a large sheet of thin rubber (here representing the space time fabric), stretched it out tight, and place 3 different balls all of different masses (here representing different hevenly bodies) on the rubber sheet, we could see were the balls curved the rubber downwards. The largest ball would have the largest gravitational pull because it has the most mass and therfore the most gravity, because it creates the most distortion of the space time fabric. 916 German astronomer Karl Schrarzchild found a solution to Eistines’s theory of relativity. He showed that if mass of a star is concentrated in a small engough region, the gravitational field at the surface of the star becomes so strong that even light can no longer escape. This is what is called a black hole, a region of spacetime bounded by a so called event horizon from which it is impossible for anything including light to escape. When a star runs out of fuel or any heavenly body collapses on its self all of its mass becomes concentrated in one point and its gravitational pull becomes emensly massive.
Black holes have, in fact, have had their exsistance proven; scientists have recently noticed that there were planets spiriling inwards to an invisible anomalie with a very powerful gravitational pull. After many test and studies, they came to conclude that these anomolies were in fact black holes thus proving their exsistance. The radius of the black hole’s event horizon is calculated by Schwarzchild’s equation (thus the reason for calling it the schwarzchild radius). R=2GM/c2 Or that the Radius = 2 times Newton’s Constant x the Mass divided by the speed of light squared.
So for exapmle, a black hole with the mass of our sun, would only have a radius of 2 miles! “According to Einstein’s General Relativity Theory, light will be affected in the same way matter is affected by gravity. This is because under this theory, we should think of gravity not in terms of vector like forces, but as a consequence of the “shape” of the universe. ” Because light has momentum, any object or energy that has momentum is affected by the warping of space time, or gravity. “Imagine a bright object such as a star, a galaxy, or a quasar, that is very far away from Earth (say… 0 billion light years). For our discussion, let us imagine we have a quasar. If there is nothing between it and us, we see one image of the quasar. Yet, if a massive galaxy (or cluster of galaxies) is blocking the direct view to the quasar, the light will be bent by the gravitational field around the galaxy. This is called “gravitational lensing,” since the gravity of the intervening galaxy acts like a lens to redirect the light rays. But rather than creating a single image of the quasar, the gravitational lens creates multiple images. ”
Wormholes are like intergalatic short cuts. A wormhole is a hypothetical topological feature of spacetime that would be, fundamentally, a “shortcut” through spacetime. For a simple visual explanation of a wormhole, consider spacetime visualized as a two-dimensional (2D) surface (see illustration, right). If this surface is folded along a third dimension, it allows one to picture a wormhole “bridge”. ”al though there is no proof what so ever that wormholes exsist they are essentially a secret passage, a tunnel, with the two ends at different ends of the spacetime fabric. In other words if you went in one you never know where or when you would come out. therefor it is important to dress accoringly. ) the problem is no one really knows if they exsist or not. The real question is; Has all this been tested? The answer is yes, Eistein’s theory of General relativity has been tested… numerous times. “…it was not until a program of precision tests was started in 1959 that the various predictions of general relativity were tested to any further degree of accuracy in the weak gravitational field limit… Beginning in 1974, Hulse, Taylor and others have studied the behaviour of binary pulsars experiencing much stronger gravitational fields than found in our solar system.
Both in the weak field limit (as in our solar system) and with the stronger fields present in systems of binary pulsars the predictions of general relativity have been extremely well tested locally. ” General Relativity has been tested and many predictions have been made. General relativity and classical relativity, define physics as we know it today. Not only physics, but every science and our world and universe as we see it. We may not fully comprehend the vastness and complexity of our universe today; but over time humanity will gradually develop theories that prove and disprove the ones before them. Further expanding our knowledge of the universe as we know it. We still don’t completely understand how gravity works; but we will… eventually.
Works Cited Berry, A. J. Henry Cavendish. London: Hutchinson, 1960. Jungnickel, Christa. Cavendish: The Experimental Life. Lewisburg, PA: Bucknell University Press, 1999. Henry Cavendish Biography – life, history, son, information, born, time http://www. notablebiographies. com/Ca-Ch/Cavendish-Henry. html#ixzz15OD7AuBj http://en. wikipedia. org/wiki/Cavendish_experiment Cavendish, Henry (1798). Experiments to Determine the Density of the Earth”. In MacKenzie, A. S.. Scientific Memoirs Vol. 9: The Laws of Gravitation. American Book Co.. 1900. pp. 59–105. http://books. google. com/? id=O58mAAAAMAAJ&pg=PA59 Online copy of Cavendish’s 1798 paper, and other early measurements of gravitational constant. http://en. wikipedia. org/wiki/Introduction_to_general_relativity Ehlers, Jurgen; Rindler, Wolfgang (1997), “Local and Global Light Bending in Einstein’s and other Gravitational Theories”, General Relativity and Gravitation 29: 519–529, doi:10. 023/A:1018843001842 http://www. physlink. com/education/askexperts/ae661. cfm http://imagine. gsfc. nasa. gov/docs/features/news/grav_lens. html http://en. wikipedia. org/wiki/Wormhole http://en. wikipedia. org/wiki/Tests_of_general_relativity C. M. Will, The Confrontation between General Relativity and Experiment, Living Reviews in Relativity (2006). An online, technical review, covering much of the material in Theory and experiment in gravitational physics. It is less comprehensive but more up to date. (and my dad was a BIG help)