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Unformatted text preview: 1 Announcements • Test #3 Next Thursday, Nov 10 • Bring your UNM ID! • Bring two number 2 pencils • Review for test on Wednesday, Nov 9 at 3:25pm Black Holes A stellar mass black hole accreting material from a companion star 2 Black Holes and General Relativity The Equivalence Principle Let's go through the following series of thought experiments and arguments: 1) Imagine you are far from any source of gravity, in free space, weightless . If you shine a light or throw a ball, it will move in a straight line . General Relativity : Einstein's description of gravity (extension of Newton's). Published in 1915. It begins with: 3 2. If you are in freefall , you are also weightless. Einstein says these are equivalent. So in freefall, the light and the ball also travel in straight lines. 3. Now imagine two people in freefall on Earth, passing a ball back and forth. From their perspective, they pass the ball in a straight line . From a stationary perspective, the ball follows a curved path. So will a flashlight beam , but curvature of light path is small because light is fast (but not infinitely so). The different perspectives are called frames of reference . 4 4. Gravity and acceleration are equivalent . An apple falling in Earth's gravity is the same as one falling in an elevator accelerating upwards, in free space. 5. All effects you would observe by being in an accelerated frame of reference you would also observe when under the influence of gravity. 5 Examples : 1) Bending of light . If light travels in straight lines in free space, then gravity causes light to follow curved paths....
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 Fall '09
 Black Holes, General Relativity, Black hole, Clicker question, event horizon

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