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RICHARD FEYNMAN DISHONEST OR JUST SILLY?
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Pentcho Valev
Jul 15, 2015, 4:13:13 PM7/15/15
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http://www.feynmanlectures.caltech.edu/I_15.html
Richard Feynman (The Feynman Lectures on Physics, Volume 1, Chapter 15-1): "Another consequence of the [Maxwell's] equations is that if the source of the disturbance is moving, the light emitted goes through space at the same speed c. This is analogous to the case of sound, the speed of sound waves being likewise independent of the motion of the source. This independence of the motion of the source, in the case of light, brings up an interesting problem: Suppose we are riding in a car that is going at a speed u, and light from the rear is going past the car with speed c. Differentiating the first equation in (15.2) gives dx'/dt=dx/dt-u, which means that according to the Galilean transformation the apparent speed of the passing light, as we measure it in the car, should not be c but should be c-u. For instance, if the car is going 100,000 mi/sec, and the light is going 186,000 mi/sec, then apparently the light going past the car should go 86,000 mi/sec. In any case, by measuring the speed of the light going past the car (if the Galilean transformation is correct for light), one could determine the speed of the car. A number of experiments based on this general idea were performed to determine the velocity of the earth, but they all failed - they gave no velocity at all. We shall discuss one of these experiments [the Michelson-Morley experiment] in detail..."
This seems to be a deliberately confused teaching (or the teacher does not know what he is talking about):
1. The independence of the motion of the source by no means brings up the "interesting problem" where the dependence/independence of the motion of the observer is discussed. Maxwell's 19th century electromagnetic theory did indeed predict independence of the motion of the source for the speed of light but at the same time predicted dependence on the motion of the observer.
2. There is no analogy between light-going-past-the-car thought experiment and the Michelson-Morley experiment.
3. Originally (prior to FitzGerald and Lorentz advancing the ad hoc length contraction hypothesis), the Michelson-Morley experiment confirmed the Galilean transformation (that is, it showed that the speed of the light passing by is measured in the car to be c'=c-u).
Pentcho Valev
Richard Feynman (The Feynman Lectures on Physics, Volume 1, Chapter 15-1): "Another consequence of the [Maxwell's] equations is that if the source of the disturbance is moving, the light emitted goes through space at the same speed c. This is analogous to the case of sound, the speed of sound waves being likewise independent of the motion of the source. This independence of the motion of the source, in the case of light, brings up an interesting problem: Suppose we are riding in a car that is going at a speed u, and light from the rear is going past the car with speed c. Differentiating the first equation in (15.2) gives dx'/dt=dx/dt-u, which means that according to the Galilean transformation the apparent speed of the passing light, as we measure it in the car, should not be c but should be c-u. For instance, if the car is going 100,000 mi/sec, and the light is going 186,000 mi/sec, then apparently the light going past the car should go 86,000 mi/sec. In any case, by measuring the speed of the light going past the car (if the Galilean transformation is correct for light), one could determine the speed of the car. A number of experiments based on this general idea were performed to determine the velocity of the earth, but they all failed - they gave no velocity at all. We shall discuss one of these experiments [the Michelson-Morley experiment] in detail..."
This seems to be a deliberately confused teaching (or the teacher does not know what he is talking about):
1. The independence of the motion of the source by no means brings up the "interesting problem" where the dependence/independence of the motion of the observer is discussed. Maxwell's 19th century electromagnetic theory did indeed predict independence of the motion of the source for the speed of light but at the same time predicted dependence on the motion of the observer.
2. There is no analogy between light-going-past-the-car thought experiment and the Michelson-Morley experiment.
3. Originally (prior to FitzGerald and Lorentz advancing the ad hoc length contraction hypothesis), the Michelson-Morley experiment confirmed the Galilean transformation (that is, it showed that the speed of the light passing by is measured in the car to be c'=c-u).
Pentcho Valev
Pentcho Valev
Jul 15, 2015, 4:35:12 PM7/15/15
to
http://www.feynmanlectures.caltech.edu/II_42.html
The Feynman Lectures on Physics, Volume 2, Chapter 42-6: "Suppose we put a clock at the "head" of the rocket ship - that is, at the front end - and we put another identical clock at the "tail," as in fig. 42-16. Let's call the two clocks A and B. If we compare these two clocks when the ship is accelerating, the clock at the head seems to run fast relative to the one at the tail. To see that, imagine that the front clock emits a flash of light each second, and that you are sitting at the tail comparing the arival of the light flashes with the ticks of clock B. (...) You can see, then, that if the two flashes were emitted from clock A one second apart, they would arrive at clock B with a separation somewhat less than one second... (...) But now let's think of the rocket ship at rest in the earth's gravity. The same thing happens."
Is that true? If, instead of flashes, bullets were shot from A each second, would they "arrive at clock B with a separation somewhat less than one second"? Einsteinians? Is Feynman right?
Einsteinians:
http://4.bp.blogspot.com/-s3BsmtvBIik/UezWM5z2WAI/AAAAAAAAPU0/FgcLmjhydR4/s1600/heads%2Bsand.jpg
Pentcho Valev
The Feynman Lectures on Physics, Volume 2, Chapter 42-6: "Suppose we put a clock at the "head" of the rocket ship - that is, at the front end - and we put another identical clock at the "tail," as in fig. 42-16. Let's call the two clocks A and B. If we compare these two clocks when the ship is accelerating, the clock at the head seems to run fast relative to the one at the tail. To see that, imagine that the front clock emits a flash of light each second, and that you are sitting at the tail comparing the arival of the light flashes with the ticks of clock B. (...) You can see, then, that if the two flashes were emitted from clock A one second apart, they would arrive at clock B with a separation somewhat less than one second... (...) But now let's think of the rocket ship at rest in the earth's gravity. The same thing happens."
Is that true? If, instead of flashes, bullets were shot from A each second, would they "arrive at clock B with a separation somewhat less than one second"? Einsteinians? Is Feynman right?
Einsteinians:
http://4.bp.blogspot.com/-s3BsmtvBIik/UezWM5z2WAI/AAAAAAAAPU0/FgcLmjhydR4/s1600/heads%2Bsand.jpg
Pentcho Valev
Pentcho Valev
Aug 4, 2015, 5:25:18 AM8/4/15
to
http://www.pbs.org/wgbh/nova/blogs/physics/2015/04/physics-needs-philosophy/
Tim Maudlin: "...so many physicists strongly discourage questions about the nature of reality. The reigning attitude in physics has been "shut up and calculate": solve the equations, and do not ask questions about what they mean. But putting computation ahead of conceptual clarity can lead to confusion. Take, for example, relativity's iconic "twin paradox." Identical twins separate from each other and later reunite. When they meet again, one twin is biologically older than the other. (Astronaut twins Scott and Mark Kelly are about to realize this experiment: when Scott returns from a year in orbit in 2016 he will be about 28 microseconds younger than Mark, who is staying on Earth.) No competent physicist would make an error in computing the magnitude of this effect. But even the great Richard Feynman did not always get the explanation right. In "The Feynman Lectures on Physics," he attributes the difference in ages to the acceleration one twin experiences: the twin who accelerates ends up younger. But it is easy to describe cases where the opposite is true, and even cases where neither twin accelerates but they end up different ages. The calculation can be right and the accompanying explanation wrong."
Einstein also taught that the youthfulness of the travelling twin was due to the turn-around acceleration:
http://en.wikisource.org/wiki/Dialog_about_objections_against_the_theory_of_relativity
Dialog about Objections against the Theory of Relativity, 1918, Albert Einstein: "During the partial processes 2 and 4 the clock U1, going at a velocity v, runs indeed at a slower pace than the resting clock U2. However, this is more than compensated by a faster pace of U1 during partial process 3. According to the general theory of relativity, a clock will go faster the higher the gravitational potential of the location where it is located, and during partial process 3 U2 happens to be located at a higher gravitational potential than U1. The calculation shows that this speeding ahead constitutes exactly twice as much as the lagging behind during the partial processes 2 and 4."
John Norton teaches the same story:
http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/spacetime_tachyon/index.html
John Norton: "Then, at the end of the outward leg, the traveler abruptly changes motion, accelerating sharply to adopt a new inertial motion directed back to earth. What comes now is the key part of the analysis. The effect of the change of motion is to alter completely the traveler's judgment of simultaneity. The traveler's hypersurfaces of simultaneity now flip up dramatically. Moments after the turn-around, when the travelers clock reads just after 2 days, the traveler will judge the stay-at-home twin's clock to read just after 7 days. That is, the traveler will judge the stay-at-home twin's clock to have jumped suddenly from reading 1 day to reading 7 days. This huge jump puts the stay-at-home twin's clock so far ahead of the traveler's that it is now possible for the stay-at-home twin's clock to be ahead of the travelers when they reunite."
Feynman, Einstein and Norton are wrong of course but the problem is more serious than that. We all live in Einstein's schizophrenic world where the youthfulness of the travelling twin is due to the turn-around acceleration, on the one hand, and is not due to the turn-around acceleration, on the other:
http://www.fnal.gov/pub/today/archive/archive_2014/today14-05-02_NutshellReadMore.html
Don Lincoln: "Some readers, probably including some of my doctoral-holding colleagues at Fermilab, will claim that the difference between the two twins is that one of the two has experienced an acceleration. (After all, that's how he slowed down and reversed direction.) However, the relativistic equations don't include that acceleration phase; they include just the coasting time at high velocity."
http://www.damtp.cam.ac.uk/research/gr/members/gibbons/gwgPartI_SpecialRelativity2010.pdf
Gary W. Gibbons FRS: "In other words, by simply staying at home Jack has aged relative to Jill. There is no paradox because the lives of the twins are not strictly symmetrical. This might lead one to suspect that the accelerations suffered by Jill might be responsible for the effect. However this is simply not plausible because using identical accelerating phases of her trip, she could have travelled twice as far. This would give twice the amount of time gained."
http://www.ferovanemocnice.cz/images/articles/f_pic31.jpg
Pentcho Valev
Tim Maudlin: "...so many physicists strongly discourage questions about the nature of reality. The reigning attitude in physics has been "shut up and calculate": solve the equations, and do not ask questions about what they mean. But putting computation ahead of conceptual clarity can lead to confusion. Take, for example, relativity's iconic "twin paradox." Identical twins separate from each other and later reunite. When they meet again, one twin is biologically older than the other. (Astronaut twins Scott and Mark Kelly are about to realize this experiment: when Scott returns from a year in orbit in 2016 he will be about 28 microseconds younger than Mark, who is staying on Earth.) No competent physicist would make an error in computing the magnitude of this effect. But even the great Richard Feynman did not always get the explanation right. In "The Feynman Lectures on Physics," he attributes the difference in ages to the acceleration one twin experiences: the twin who accelerates ends up younger. But it is easy to describe cases where the opposite is true, and even cases where neither twin accelerates but they end up different ages. The calculation can be right and the accompanying explanation wrong."
Einstein also taught that the youthfulness of the travelling twin was due to the turn-around acceleration:
http://en.wikisource.org/wiki/Dialog_about_objections_against_the_theory_of_relativity
Dialog about Objections against the Theory of Relativity, 1918, Albert Einstein: "During the partial processes 2 and 4 the clock U1, going at a velocity v, runs indeed at a slower pace than the resting clock U2. However, this is more than compensated by a faster pace of U1 during partial process 3. According to the general theory of relativity, a clock will go faster the higher the gravitational potential of the location where it is located, and during partial process 3 U2 happens to be located at a higher gravitational potential than U1. The calculation shows that this speeding ahead constitutes exactly twice as much as the lagging behind during the partial processes 2 and 4."
John Norton teaches the same story:
http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/spacetime_tachyon/index.html
John Norton: "Then, at the end of the outward leg, the traveler abruptly changes motion, accelerating sharply to adopt a new inertial motion directed back to earth. What comes now is the key part of the analysis. The effect of the change of motion is to alter completely the traveler's judgment of simultaneity. The traveler's hypersurfaces of simultaneity now flip up dramatically. Moments after the turn-around, when the travelers clock reads just after 2 days, the traveler will judge the stay-at-home twin's clock to read just after 7 days. That is, the traveler will judge the stay-at-home twin's clock to have jumped suddenly from reading 1 day to reading 7 days. This huge jump puts the stay-at-home twin's clock so far ahead of the traveler's that it is now possible for the stay-at-home twin's clock to be ahead of the travelers when they reunite."
Feynman, Einstein and Norton are wrong of course but the problem is more serious than that. We all live in Einstein's schizophrenic world where the youthfulness of the travelling twin is due to the turn-around acceleration, on the one hand, and is not due to the turn-around acceleration, on the other:
http://www.fnal.gov/pub/today/archive/archive_2014/today14-05-02_NutshellReadMore.html
Don Lincoln: "Some readers, probably including some of my doctoral-holding colleagues at Fermilab, will claim that the difference between the two twins is that one of the two has experienced an acceleration. (After all, that's how he slowed down and reversed direction.) However, the relativistic equations don't include that acceleration phase; they include just the coasting time at high velocity."
http://www.damtp.cam.ac.uk/research/gr/members/gibbons/gwgPartI_SpecialRelativity2010.pdf
Gary W. Gibbons FRS: "In other words, by simply staying at home Jack has aged relative to Jill. There is no paradox because the lives of the twins are not strictly symmetrical. This might lead one to suspect that the accelerations suffered by Jill might be responsible for the effect. However this is simply not plausible because using identical accelerating phases of her trip, she could have travelled twice as far. This would give twice the amount of time gained."
http://www.ferovanemocnice.cz/images/articles/f_pic31.jpg
Pentcho Valev
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