An Example of a "Learning Process" Journal (using the 2 colored box format)

"Simply Einstein" by Richard Wolfson (Chap. 5, Ether Dreams. pp. 55 - 67)

• "Sound moves at 700 miles per hour relative to air, the medium in which sound waves are a disturbance. So what's the corresponding answer for light? ... Without an answer, Maxwell's equations are on shaky ground because their prediction of electromagnetic waves moving with speed c is meaningless." [p. 55]
• "Ether is supposed to be to electromagnetic waves what air is to sound waves - the medium in which the waves are a disturbance." [p. 56]
• "The speed of each type of wave - sound waves, wate waves, stadium waves, earthquake waves, etc, - is its speed relative to its particular medium. Why not the same for light?" [p. 59]
• By 1880 "Together, Newton's mechanics and Maxwell's electromagnetism seem to explain all known physical phenomena. ... Light is understood as an electromagnetic wave, propogating with speed c through a Universe-permeating medium called ether. Astronomical observations show that the speed of light does not depend on the motion of its source and that Earth must be in motion relative to the ether. The only thing remaining to solidify the picture of electromagnetic waves in the ether is to measure the Earth's motion. But as of 1880 no experiment has succeeded in doing so." [p. 67]

This is the clearest description I have seen so far on the historical situation in science before Einstein's 1905 paper.

"Simply Einstein" by Richard Wolfson (Chap. 6, Crisis in Physics. pp. 68 - 77)

• "Michelson ... 1887 ... among the most famous experiments in all of science." [p. 70]
• "Earth must be moving through the ether, yet the Michelson-Morley experiment shows that it isn't." [p. 76]

The actual description of the experiment, particularly the final displays which consisted of interference patterns of light waves, is excellent.

"Simply Einstein" by Richard Wolfson (Chap. 7, Einstein to the Rescue. pp. 71 - 85)

• "Albert Einstein was 8 years old when Michelson and Morley performed their 1887 experiment." [p. 78]
• "In 1905 Einstein was a young father of 26 years, devoted to his family, to his work at the patent office, and to his physics." [p. 80]
• "In 1905 Einstein completed a total of six scientific papers. The fourth paper was titled 'On the Electrodynamics of Moving Bodies'. " [p. 81]
• "The Principle of Relativity: ... The laws of physics are the same in all uniformly moving reference frames." [p. 81 - 82]
• "... there's no preferred state of motion for describing physical reality. ... All states of ... uniform motion ... are equally valid. There's no such thing as being absolutely at rest or in motion. Only statements about relative motion make sense." [p. 82]
• "So there is no ether. ... As Einstein put it ... 'the introduction of ... ether will prove to be superfluous.' " [p. 84]
• "There's a disturbing implication of relativity's assertion regarding the speed of light. Observers in different reference frames must still get the same value for the speed of light, even though they're moving relative to each other. ... It's that consequence - the invariance of the speed of light, even for observers who are moving relative to one another - that's so troubling and that's going to lead to a radical revision of your commonsense notions of space and time." [p. 84]
• "... concentrate on where the invariance of c comes from. It results from nothing more than the Principle of Relativity, as applied to the laws of electromagnetism with their prediction of electromagnetic waves (including light) going at speed c." [p. 84]
• "(1) The laws of electromagnetism predict electromagnetic waves going at the speed c and (2) The laws of physics are valid in all reference frames; thus, the conclusion that electromagnetic waves go at c must be valid in all reference frames. From the invariance of c follow the many seemingly counterintuitive results of special relativity." [p. 85]

Here is the URL for the paper: http://www.fourmilab.ch/etexts/einstein/specrel/specrel.pdf

This was obtained by googling the title. It was not translated into English until 1923!

"Simply Einstein" by Richard Wolfson (Chap. 8, Stretching Time. pp. 86 - 108)

• "Relativity is ultimately about the absence of any favored reference frame in the physical Universe." [p. 86]
• "When talking aobut relativity, pledge to use only relativistically correct language! Watch out for phrases like 'the moving clock', 'the observer at rest', or 'high-speed spaceship'. Unless it's clear what these things are moving or at rest with respect to, then the phrases are meaningless." [p. 91]
• "Only relative motion matters. That's why it's called relativity." [p. 92]
• "Time and space are not absolute, but relative to one's frame of reference. Measures of time intervlas and of spatial distances are simply different in different reference frames." [p. 94]
• "... the idea of an event. Events play a major role in relativity, because they involve both time and space. ... An event is completely specified by giving a time and a place." [p. 96]
• Consider the example of box with a mirror on the ceiling. From inside the box one measures the time for a light beam to travel from the floor to the ceiling and back again. Now consider a situation where the box is moving horizontally and is viewed from a point outside the box. The same situation now watches the light travel further (obliquely) and hence for a longer period of time. Thus the two observers both watch the same event, but disagree on the time it took. The longer time for the second observer is called time dilation.
• "The time between two events is shortest when measured in a reference frame where the two events occur at the same place." [p. 102]

I had a bit of difficulty with the section on time dilation. The difficulty is with language. When two different values of elapsed time for the same event are given, does the smaller value mean that time is going faster or slower? The amount of time is less, which means that the clock is going faster.

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