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History of Classical Gravitational Theory and General Relativity
Transcript of History of Classical Gravitational Theory and General Relativity
Theory & General Relativity Overview of gravity and motion of the
planets before Newton Life and Times of Isaac Newton Henry Cavendish and the
Universal Law of Gravitation Gravity and the bending of the
Space-Time Fabric Inertial and Gravitational Properties of Mass Schwarzschild Radius Black Holes Before Newton, some thought that the planets orbited around the Sun, and others believed that the planets and the Sun orbited Earth. Aristotle believed that the Earth had to be stationary, and the planets, the Sun, and the fixed dome of stars rotated around Earth. Galileo also observed the phases of Venus; he saw for the first time in human history that moons orbited Jupiter, which proved that the planet orbits the Sun and not the Earth. Kepler published a series of laws that described the orbits of the planets around the Sun. Still in use today, the mathematical equations provided accurate predictions of the planets’ movement under Copernican theory. He gave the force that kept them in check a name: gravity. Building on Kepler’s laws, Newton explained why the planets moved as they did around the Sun and he gave the force that kept them in check a name: gravity. Sir Isaac Newton was born in 1642 at Woolsthorpe. He developed the laws of motion and gravity. He also worked on optics and created calculus. Henry Cavendish was able to measure the gravitational constant (G) with an object called the Torsion Balance. The value of gravitational constant (G), found using the Torsion Balance, is 6.67x10-11 N (m3/kg-s2). Using the gravitational constant, Henry Cavendish was able to complete the equation g = GM/R2. The basis of general relativity is the equivalence of inertial and gravitational properties. This means that gravitational and inertial affects are not distinguishable. You can use the coordinate systems that accelerate with respect to each other. The fabric of space time twists like a vortex. All gravitational forces correspond to a bending of space time, as told by Einstein. Gravitomagnetism is the “twist.” The Schwarzschild radius is the radius
of a sphere past where no particles,
light, or information can get
past in a black hole. A black hole is a place in space where gravity pulls so that light cannot get out. The gravity is strong because matter has been squeezed into a tiny space. This happens when a star is dying. Black holes are real, but are normally invisible because no light can get out. Gravitational Lensing 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. In general relativity, the presence of matter (energy density) can curve spacetime, and the path of a light ray will be deflected as a result. This process is called gravitational lensing and in many cases can be described in analogy to the deflection of light by (e.g. glass) lenses in optics. Worm Holes In 1935, Albert Einstein and Nathan Rosen realized that general relativity allows the existence of “bridges,” originally called Einstein-Rosen bridges but now known as wormholes. These space-time tubes act as shortcuts connecting distant regions of space-time. Until recently, theorists believed that wormholes could exist for only an instant of time, and anyone trying to pass through would run into a singularity. But more recent calculations show that a truly advanced civilization might be able to make wormholes work. General THEORY of Relativity
or General HYPOTHESIS of Relativity? A hypothesis is not required to have a mathematical foundation, to arrive at a testable prediction, which is then tested. A theory does. The postulates of Relativity could be called its "hypothesis", and the theory would be the resulting complex partial differential equation and it background of different metrics and tests it has been put through. A scientific theory or law represents a hypothesis (or group of related hypotheses) which has been confirmed through repeated testing, almost always conducted over a span of many years. Generally, a law uses a handful of fundamental concepts and equations to define the rules governing a set of phenomena. A useful hypothesis enables predictions by applying deductive reasoning, often in the form of mathematical analysis. Sometimes a hypothesis is developed that must wait for new knowledge or technology to be testable.
One was the gravitational bending of starlight around the sun. The second prediction is the precession of planetary orbits about the sun. The third experimentally verified prediction is the slowing down of time due to gravity.