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| Tags: examined, general, relativity |
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#2
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Eunitno07 wrote:
General Relativity Examined See: "Was Einstein Right?" by Clifford M. Will "Quasars. Cosmic fireball radiation. Pulsars. Black holes. Gravitational lenses. What do these things have in common? "First, they were all discovered after 1960, during a period of unparalleled advances in the technology of scientific investigation, especially in astronomy. "Second, they have attracted intense popular interest. Just look at the success in recent years of the books (THE FIRST THREE MINUTES). Movies (THE BLACK HOLE), and television productions ("COSMOS") that have presented them to the general public, to say nothing of wris****ches (Pulsar) and television sets (Quasar) that carry some of their names. "Third, Their existence makes us ask the question, "Was Einstein right?" Every item in the preceding list involves Einstein's general theory of relativity in a crucial way. Black holes, the remains of dead, collapsed stars, are an important prediction of the theory; a black hole is thought to be responsible for the astronomical X-ray source Cygnus X1, and they are believed by many to power quasars, the incredibly luminous beacons that we can see almost to the edge of the visible universe. The cosmic fireball radiation is most likely the afterglow of the big bang that began the universe, an event whose understanding requires the theory of relativity. The structure of pulsers, believed to be rapidly spinning neutron stars, is strongly influenced by super-strong general relativistic gravitational forces. Finally, the recently discovered gravitational lenses are galaxies that bend and focus passing light by means of the general relativistic warping of space-time around them. "Modern day astronomers and astrophysicists must use general relativity as a tool in their attempts to comprehend these phenomena. If the theory were incorrect, they would be at a loss; an important underpinning of their models would be weakened. "Of course, there is more at stake in the question "Was Einstein right?" than keeping astrophysicists happy (and employed). General relativity is a fundamental theory of the nature of space, time, and gravitation, and has profoundly influenced how we view the universe. But like any theory of nature, it cannot stand on its own. It must face the test of experiment and observation. No matter how profound it may be, no matter how beautiful or elegant it may appear, it must be discarded if it does not agree with observation. Unfortunately, observations of quasars, pulsars, and the like don't in themselves tell us much about general relativity. The reason is that these objects involve such complex physics that we can't easily distinguish the effects of general relativity from the other forces at work. So to find out if Einstein was right, we look at different kinds of tests. "This book is about those tests. It is about an intensive twenty-year effort, beginning around 1960, to check the predictions of General Relativity accurately, and to find new predictions to check." Chapter 1. The Renaissance of General Relativity Chapter 2. The Straight Road to Curved Space-Time Chapter 3. The Gravitational Red Shift of Light and Clocks Chapter 4. The Departure of Light from the Straight and Narrow Chapter 5. The Perihelion Shift of Mercury: Triumph or Trouble? Chapter 6. The Time Delay of Light: Better Late Than Never Chapter 7. Do the Earth and the Moon Fall the Same? Chapter 8. The Rise and Fall of the Brans-Dicke Theory Chapter 9. Is the Gravitational Constant Constant? Chapter 10. The Binary Pulser: Gravity Waves Exist! Chapter 11. The Frontiers of Experimental Relativity Chapter 12. Astronomy after the Renaissance: Is General Relativity Useful? Crank information http://www.crank.net/einstein.html http://groups.google.com/groups?q=gr...author%3Aretic http://groups.google.com/groups?q=gr...thor%3Aretiche http://groups.google.com/groups?q=gr...hor%3Areticher http://groups.google.com/groups?q=gr...or%3Areticher1 |
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#3
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[snip]
Mathematics should never be used without the an intelligent understanding of the mechanisms involved, as was the practice prior to Dr. Einstein's work. (In the case of GTR, one of the errors was the fact that the definition of a straight line currently in use is inadequate even for Euclidean geometry. A straight line is more properly defined as the shortest distance between two points WHICH REMAINS WITHIN THE GEOMETRY IN QUESTION. This additional requirement is automatically met in Euclidean Geometry, but, in the case of non-Euclidean geometry, the shortest distance between two points does not meet that definition. In the two dimensional non-Euclidean geometry represented by the Earth's surface, the shortest distance between New York and Los Angeles is not a great circle as we have been taught, it is through a tunnel which passes about 200 miles below the Mississippi river.) What do you mean, a straight line is defined as the shortest distance between to points? Distance is a function d: M x M --- [0,\infty). This is scalar valued, where as a line is a geometric object. You probably want to say that a line is a geodesic in your model geometry. If your geometry is geodesically complete, then you know that you can find a geodesic segment whose length realizes the distance between the two points in question with the path metric. Your model geometry should be thought as abstractly defined. Your geometric object is your universe. You cannot leave your universe (maybe you can but not here). If you are not on your manifold, then where are you? Your not in your universe. I can map 2-dimensional Euclidean into 3-space so that when I draw a Euclidean straight line between two points in the image of the 2-plane, the line does not stay within the image of the 2-plane. The point is that this is not an isometric embedding, where the 2-plane has the standard Euclidean structure. Does this mean that you've been lied to about Euclidean lines? No, it means you need to be careful about viewing your manifold in an ambient manifold. Your geometry should not depend on an embedding. You took the point of view of viewing Euclidean space abstractly and not living inside some ambient space, so there was no need for your "additional requirement". Try that with elliptic geometry or hyperbolic geometry. Your example in elliptic geometry is ill conceived. You're thinking of the 2-sphere in 3-space but this is not an isometric embedding. The standard Euclidean metric does not restrict to the path metric on the 2-sphere with the standard elliptic structure. The elliptic structure on the 2-sphere is geodesically complete, where the sphere with the induced metric from your embedding is not. Just because your Riemannian manifold lives inside some ambient manifold, does not mean that its structure is induced from the ambient manifold. Think about the 2-torus living inside 3-space. The induced structure is very different from the flat 2-torus. Read Thurston's Geometry and Topology of 3-manifolds. Try Peter Scott's article on the Geometry of 3-manifolds. You could also flip through Ratcliffe's Foundations of Hyperbolic Manifolds. Ben |
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