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# class04 - Announcements Reading for Friday TZD 1.10 1.11...

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Announcements • Reading for Friday: TZD 1.10 – 1.11 • Homework #1 due at beginning of next class. (Remember: no late HWs accepted!) Register your clicker • Register your clicker! • Help room hours posted on course page: http://www.colorado.edu/physics/phys2130 www.colorado.edu/physics/phys2130 Today First: Wrap-up Michelson Morley. Then: Let’s talk about time! • Synchronizing clocks • Time dilation and other weird stuff Last class: Michelson Morley Experimental results Over a period of about 50 years, the Michelson-Morley experiment was repeated with growing levels of sophistication. The overall result is a high level of confidence that the wavelength shift is consistent with zero. L (cm Calc. Meas. Ratio L (cm) Meas. Michelson, 1881 120 0.04 0.02 2 0.40 0.01 40 Morley & Miller, 1902-04 3220 1.13 0.015 80 Illingworth, 1927 200 0.07 0.0004 175 Joos,1930 2100 0.75 0.002 375 Shankland, et al., Rev. Mod. Phys. 27, 167 (1955) Michelson and Morley They thought that the experiment was a complete failure because no effect was found. Michelson was awarded the Nobel Prize in 1907!! True result: Speed of light is the same in all directions! Homework (part of your reading assignment): Work out the math for this experiment (TDZ, Chapter 1.5)

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Yes, but. .. Q: What if the ether is “dragged along” the surface of the earth, like air flowing around a tennis ball? A: If so, this would require a “viscosity” of the ether, and would require re- writing Maxwell’s equations. Remark: Lots of effort tried to save the idea of the ‘ether’, but none held up. There is no ether Electromagnetic waves are special. A time-changing electric field induces a magnetic field, and vice-versa. A medium (“ether”) is not necessary. Einstein’s Second Postulate of Relativity The speed of light is the same in all inertial frames of reference. This was still new in 1905 when Einstein proposed it. Now it has been tested experimentally many times. There is no ether! Suppose the earth moves through space with speed v. v c Q1 Suppose the earth moves through space with speed v. A light wave traveling at speed c with respect to faraway stars
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class04 - Announcements Reading for Friday TZD 1.10 1.11...

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