| The Geometry of Space-Time: A Teaching Package |
| >>The General Theory of Relativity (GR): The Key Ideas |
| >>The Bending of Light: Proof of GR? |
| >>Non-Euclidean Geometry: Space, but not as we know it |
| >>Exotic Geometry: A look at the Universe around us |
| By the late 19th Century all the diverse phenomena of the physical universe could be explained by a handful of simple Newtonian physical laws. For example, all the phenomena involving gravity could be explained by Newton�s laws of motion and gravity: � Every object moves uniformly in a straight line unless acted on by an external force. � When a force does act, the object�s velocity changes at a rate proportional to the force and inversely proportional to its mass. � Between any two objects in the Universe there acts a gravitational force that is proportional to the product of their masses and inversely proportional to the square of their separation. Link.1.1. These simple laws were translated into the language of math and were then manipulated to explain the orbits of the planets around the Sun, the orbits of the moons around the planets, and the fall of apples from trees; they were even used to weigh the Sun and the Earth. Link.1.2. Physicists and inventors worked side by side for many years to follow, creating new technology, all fundamentally based on Newton�s laws. (James Watt invented the first steam engine, Samuel Morse devised a version if the telegraph by understanding the laws of electricity and magnetism.) However, physicists soon became aware of a mounting evidence of cracks in the foundations, a foundation that was built entirely on the concept that space and time are absolute. � Absolute space: Newton�s notions on space were that you get what you see. Space consists of three dimensions: east-west, north-south, up- down (x, y, and z). There is only one space; it is shared by all humanity, by the Sun, by all the planets and the stars. We all move through this space in our own ways and at our own speeds, and regardless of our motion, we experience the space in the same ways. This space gives us our sense of length and breadth and height; and according to Newton (mention that this is also something that we assume to be true through common-sense) we will all agree on the length, breadth and height of an object regardless of our motion, so long as we make sufficiently accurate measurements. � Absolute time: Newton�s notions on time were similar to that of absolute space in the sense that you get what you see. It is the time that ages us, the time measured by clocks, the rotation of the Earth and the motion of the planets. According to Newton, we all, regardless of our motion, will measure the length of a conversation or the period of a planetary orbit as being the same so long as we make sufficiently accurate measurements. If the concept that space and time are absolute were to crumble then Newtonian physical law would follow. Fortunately, for years and even centuries, these laws have stood firm against any opposition, theoretically and experimentally, from the planets to electricity to heat. No crack was found-until 1881, when Albert Michelson started timing the propagation of light. The detail of the Michelson-Morley Interferometer is not to be discussed in this package. If you would like to learn more, the following links will take you to websites that discuss the matter further. www.what-is-the-speed-of-light.com/morley-speed-of-light.html hyperphysics.phy-astr.gsu.edu/hbase/relativ/mmhist.html online.cctt.org/physicslab/content/PhyAPB/lessonnotes/dualnature/MichelsonMorley.asp |
| The Relativity of Space and Time |
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