Street-Fighting Physics!â€‹

**Week 14 19-23 April**

**Week 14 19-23 April**

**(2) Page 96, 97, 98**

**(3) Page 99**

**(4) Page 100**

**(5) Pages 101, 102**

**(6) Pages 103, 104, 105**

**(7) Pages 106, 107**

**The Mysterious Ether**

When we reached the point where we could demonstrate that light was a wave, then it was presumed that the wave must have a medium in which to travel. **All the other waves we knew about required a medium**. Since no medium was apparent between the earth and the sun, it was presumed that this medium was transparent and therefore not readily observable - it was called the "ether". The popular presumption was that this ether was stationary and filled all of space. This involved the presumption that there was an absolute reference frame in the universe, and that all the movement of planets and stars was through this ether.

These presumptions were part of the historical setting of the Michelson-Morley Experiment. With the interferometer which he invented, Michelson found no evidence of the ether, to his and everyone else's surprise. Michelson's terse description of the experiment: "The interpretation of these results is that there is no displacement of the interference bands. ...** The result of the hypothesis of a stationary ether is thus shown to be incorrect." (A. A. Michelson, Am. J. Sci, 122, 120 (1881))**

The proponents of an "ether" as a propagating medium for the light were not ready to give up the idea, and proposed that the Earth dragged the ether along with it in its orbit, thus accounting for the negative result of the interferometer experiment. Lord Rayleigh wrote to Michelson, urging him to repeat the experiment with greater accuracy to test these hypotheses. Repeated over the next 40 years with ever greater precision and the same negative result,** ****this 1887 experiment is pointed to as one of the experimental foundations of relativity, and earned Michelson the Nobel Prize in 1907.**

While proponents for the existence of a medium in space, an "ether", still exist, the standard position is that there is no medium in space. One of the reasons for this position is that there was no direct experimental evidence for the existence of the ether - everything can be explained without it, hence the **Occam's razor** approach. Another involves the preposterous mechanical properties required of a medium which supports a wave at 3 x 108 m/s. The velocity of any medium-dependent wave has the nature of the square root of an elastic property divided by an inertial or density property. To support a wave speed of the speed of light would require an incredibly high "stiffness" for space which has near zero density. A medium so tenuous that it produced no detectable drag on the planets which moved through it must yet have an incredibly high restoring force to bring it back to equilibrium once the planet passed.

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- ASTR Week 9 Spring Break
- ASTR Week 10 Lectures Low Mass Star Death
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- ASTR Week 13 Lectures Distance-Luminosity Modulus
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- ASTR Week 15 Lectures Relativistic Red Shift
- ASTR Week 16 Lectures, Big Bang
- ASTR Week 17 Lectures Finals Week

- ASTR - Galileo's Sketches
- Space Travel Posters
- How Large Is the Universe?
- The Elegant Universe - String Theory

- Home
- PHYS 110 Syllabus
- PHYS 110 Sapling Student Login
- PHYS 110 Workbook PDF
- PHYS Weekly Lectures
- PHYS Week 1 Lectures Scientific Notation
- PHYS Week 2 Lectures Metric System, Terms, Conversions
- PHYS Week 3 Lectures Scale of Universe, the Atom, History
- PHYS Week 4 Lectures Scientific Method, Volume, Mass Density
- PHYS Week 5 Lectures Vectors, Trig
- PHYS Week 6 Vector Analysis
- PHYS Week 7 Vector Analysis, Lab
- PHYS Week 8 Lectures Judgment Day
- PHYS Week 9 Spring Break!
- PHYS Week 10 Lectures Motion, Acceleration
- PHYS Week 11 Lectures Acceleration Demos
- PHYS Week 12 Lectures Kinematics - Motion in 2 Dimensions
- PHYS Week 13 Lectures Waves, Doppler, Hubble Law
- PHYS Week 14 Lectures, Michelson-Morley, Special Relativity
- PHYS Week 15 Lectures General Relativity, Black Holes
- PHYS Week 16 Lectures General Relativity, E=mc2
- PHYS Week 17 Lectures Finals Week

- ASTR 100 Syllabus
- ASTR Student Sapling Login
- ASTR Student Launchpad Login
- ASTR 100 Lab Manual PDF
- ASTR Weekly Lectures
- ASTR Week 1 Lectures - Dark Matter, Dark Energy
- ASTR Week 2 Lectures Scientific Notation
- ASTR Week 3 Lectures Astronomic Scales, History (1)
- ASTR Week 4 Lectures Brahe, Kepler, Newton, Gravity
- ASTR Week 5 Lectures Special Relativity
- ASTR Week 6 Lectures General Relativity
- ASTR Week 7 Lectures Star Formation
- ASTR Week 8 Lectures Cepheid Variable Stars
- ASTR Week 9 Spring Break
- ASTR Week 10 Lectures Low Mass Star Death
- ASTR Week 11 Lectures High Mass Star Death
- ASTR Week 12 Lectures Neutron Stars, Pulsars, Black Holes
- ASTR Week 13 Lectures Distance-Luminosity Modulus
- ASTR Week 14 Lectures, Waves, Hubble Law
- ASTR Week 15 Lectures Relativistic Red Shift
- ASTR Week 16 Lectures, Big Bang
- ASTR Week 17 Lectures Finals Week

- ASTR - Galileo's Sketches
- Space Travel Posters
- How Large Is the Universe?
- The Elegant Universe - String Theory