PHYSICS 002C Lecture 19

PHYSICS 002C Lecture 19 - PHYSICS 002C Lecture 19 Serway...

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1 PHYSICS 002C Lecture 19 May 13, 2009 Serway and Jewett Chapter 9 – Relativity Chap 9 Prelude – What is time? What is space? Michelson and Morley measured a shift of less than 0.04 fringes. After arguing about the ether being drag dragged about by the earth like the atmosphere is, the conclusion is that the there aint no ether. Must the conclusion be that we are nowhere and going nowhere too? Actually the entire universe gives us a preferred frame (coordinate system) for Rotation Absolute velocity. Relative to the rest of the universe as measured by the Doppler shift of the 2.7 K black body radiation left over from the Big Bang the local group of galaxies is moving (627±220) km/s. [Ap. J. 419, 1-6 (1993)] Chap 9.3 Einstein’s principle of relativity All the laws of physics are the same in any inertial frame (coordinate system). In the absence of an ether, this means that the speed of light is the same in any inertial reference frame. This principle is reasonable but totally incomprehensible. It means that space and time are not separate as they would be in a Newtonian or Galilean world. Newton said: “Absolute time flows without relation to anything external” WMAP image of the 2.7 K cosmic microwave background blackbody anisotropy showing the dipole due to the earth’s velocity relative to the rest of the universe. The small structure is indicating something about the sound waves in the early universe, thus constraining models of how it formed. This is not correct when we have things moving very fast. We still don’t know what time is, but certain events occur regularly in an inertial frame and are regular to other regularly occurring events. Time is defined by ever better clocks . -480 The sun dial and water clock 1761 The John Harrison chronometer wins British Longitude Prize. 1850 The day = 86 400 sec Harrison's Chronometer H5 ±0.1 s per d 1960 1 sec =1/31 556 925.9747of the tropical year of 1900. 1967 1 sec = the duration of 9 192 631 770 periods of Cs 133 at 0 K. 2010 Optical clocks will define the second to 1 part in 10 20 . Speed of light measurements : Römer 1676; Fizeau 1849: 313,300 km/s; Michelson 1926: 299,796±4 km/s; Now 299,792,458 m/s exactly. Q. What is the number of seconds light takes to travel from sun to Earth? Radius of Earth’s orbit is 1.5 10 11 m. a) 500; b) 10,000; c) 0.500; d) 10 6 ; e) 3.15 10 7 .
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Römer’s and Fizeau’s measurements of the speed of Light.
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PHYSICS 002C Lecture 19 - PHYSICS 002C Lecture 19 Serway...

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