History Interesting anecdotes in the history of physics?

[pines-demon]

Goudsmit Summer

Spin is definitely of the most mysterious properties about quantum mechanics. Otto Stern and Walther Gerlach discovered hints of it experimentally but did not know what it was. Wolfgang Pauli postulated an extra quantum number to explain electron occupations in atoms. Alfred Landé had come up with the concept of a g-factor, but did not think it was a property of the electron itself. However the physicists that are credited with theoretical tying all together are George Uhlenbeck and Samuel Goudsmit who were working for Paul Ehrenfest. The way Uhlenbeck describes their discovery is very atypical. Uhlenbeck refers to that period as the "Goudsmit Summer" (who was working past time there) and involves Hendrik Lorentz. It shows how serendipitous the discovery was.

It starts with Goudsmit realization:

When the day came I had to tell Uhlenbeck about the Pauli principle - of course using my own quantum numbers - then he said to me:

But don't you see what this implies? It means that there is a fourth degree of freedom for the electron. It means that the electron has a spin, that it rotates.

Now, I can also exactly tell you the difference between Uhlenbeck and me as physicists. In those days, all through the summer when I told Uhlenbeck about Landé and Heisenberg, for instance, or about [Friedrich] Paschen, then he asked:

Who is that?

He had never heard of them, strange. And when he said:

That means a fourth degree of freedom,

then I asked him:

What is a degree of freedom?

In any case, when he made his remark, it was luck that I knew all these things about the spectra, and I then said:

That fits precisely in our hydrogen scheme which we wrote about four weeks ago. And if one now allows the electron to be magnetic with the appropriate magnetic moment, then one can understand all those complicated Zeeman-effects. They come out naturally, as well as the Landé formulae and everything, it works beautifully.

Ehrenfest followed this to Lorentz (Abraham Pais account):

The discovery note is dated 17 October 1925. One day earlier Ehrenfest had written to Lorentz asking him for an opportunity to have

his judgment and advice on a very witty idea of Uhlenbeck about spectra.

Lorentz listened attentively when George went out to see him soon thereafter, and then raised an objection. The spinning electron should have a magnetic energy on the order of $\mu^2/r^3$, where $\mu$ is its magnetic moment and $r$ its radius. Equate this energy to $mc^2$. Then $r$ would be on the order of $10^{-12}$ cm, too big to make sense. (The weak point in this argument was to be revealed years later by the positron theory.) George, upset, went to Ehrenfest to suggest that the paper be withdrawn.

Ehrenfest replied that he had already sent off their note, and he added that its authors were young enough to be able to afford a stupidity. Some time later Lorentz handed Uhlenbeck a sheaf of papers with calculations of spinning electrons orbiting a nucleus. This work was to become the last paper by the grand master of the classical electron theory. It was presented to the Como conference in September 1927.

Goudsmit says also that they were contacted by Werner Heisenberg:

Directly, the next day, I received a letter from Heisenberg and he refers to our "mutige Note" (courageous note). I did not even know we needed courage to publish that. I wasn't courageous at all. I think I still have Heisenberg's letter. In it he writes a formula ... I did not understand a bit of it. And then he says somewhere:

What have you done with the factor 2?

Which factor? Not the slightest notion, and the formula given without derivation.

Heisenberg was referring to the fine structure, the problem of 2 would be later be solved by Llewellyn Thomas (Thomas precession).

Goudsmit also adds this dark joke (it is worse if you know Ehrenfest story):

In passing I have to mention a typical Ehrenfest anecdote, not such a nice one, perhaps. Lorentz lived in Haarlem and all these celebrities, [Ernst] Rutherford, Madame Curie, [Niels] Bohr, [Albert] Einstein and very many others travelled by train, a special train, from Leiden to Haarlem. And the week before one of those rare fatal train accidents had occurred and I said to Ehrenfest:

Wouldn't it be dreadful if that train had an accident?

And Ehrenfest replied:

Yes, that would be dreadful, but think of all the young physicists who then could get jobs...

I end with this nice words from Goudsmit about the history of physics and his word for young scientists:

What the historians forget - and also the physicists - is that in the discoveries in physics chance, luck plays a very, very great role. Of course, we do not always recognize this. If someone is rich then he says "Yes, I have been clever, that is why I am rich"! And the same is being said of some one who does something in physics "yes, a really clever guy...". Admittedly, there are cases like Heisenberg, Dirac and Einstein, there are some exceptions. But for most of us luck plays a very important role and that should not be forgotten.

[...]


That is the way the history looks and it is a somewhat curious history. Who, precisely, should get credit for it? Such things are not possible without also giving credit to all other people who have contributed. But one aspect stands out which is of particular importance for young people. First: you need not be a genius to make an important contribution to physics because, I do admit, the electron spin is an important contribution. That I know now, then we did not know, but now I do. They all told me so.

Then I want to say one more thing: even if you make a minor contribution, if it is not important, then this gives an enormous satisfaction. Therefore I do believe that one should not always aspire to tackle what is most important, but try to have fun working in physics and obtain results.

References:

The credit here goes Angela Collier, who brought my attention to this story in recent video about Bose-Einstein statistics:


Also:

• S. A. Goudsmit, "The discovery of the electron spin" (1971) (lecture translated to English)
• Abraham Pais, "George Uhlenbeck and the discovery of electron spin" (1989), Physics Today

 

[pines-demon]

A humble reward for a bonus problem

In quantum optics, there is was a historic problem of constructing a phase operator. Technically, the conjugate variable of the number of photons operator $\hat{n}$ has a conjugate operator that would be related to the phase of the wave $\hat{\phi}$ (it can be constructed by thinking the anhilation operator as $\hat{a}=e^{i\hat{\phi}}\sqrt{\hat{n}}$). Dirac noticed however that if this is true, the uncertainty principle reads $$\Delta n \Delta \phi\geq \frac12,$$ which is not possible, as the uncertainty of $\hat{n}$ decreases, $\hat{\phi}$ increases but is limited to go from 0 to $2\pi$ (there are other problems as $\hat{\phi}$ is not defined for certain states).

Dirac discussed this in his famous textbook The Principles of Quantum Mechanics, but dropped it from the book in later editions.

During the fall of 1962, Peter A. Carruthers was lecturing on quantum mechanics in Cornell University, he decided to include the problem of the definition of the phase operator as a homework wihout telling the students that it was an open problem. He added at the bottom of the problem that

A bonus will be given for an answer to this question.

Three students took the problem seriously: Jonathan Glogower, Jack Sarfatt and Leonard Susskind. Sarfartt published in 1963. He writes in a note at the end of the paper:

Reference has been made to the difficulty in the definition of the phase operator in quantum mechanics. Recent work by L. Susskind, J. Glogower and J. Sarfatt shows that it is impossible to define a phase operator because of the existence of a lowest state for the number operator of the oscillator. Thus, the uncertainty relation $\Delta n \Delta \phi \geq 1$ is meaningless...

One year later, Susskind and Glogower published their solution which is considered the final solution. The solution consist on writing operators $\hat{C}$ and $\hat{S}$ that represent the operators related to the cosine and sine of the phase which are well behaved.

It is not clear on how much contribution there was between Sarfatt and Susskind & Glogower. Carruthers and Michael Martin Nieto wrote a review about the problem and solution, but got a correction from Sarfatt:

In turn I ran across the fact that a Hermitian phase operator could not be defined in informal discussions with the late Dr. David Falcoff and some of his students at Brandeis during 1961-1962. Glogower was responsible for the ingenious mathematical solution of certain recursion relations, and Susskind did the bulk of the work on the proper form of the commutation relations for the $\hat{C}$ and $\hat{S}$ operators as well as the appropriate eigenfunctions. There is no question that Susskind completed the greater part of the final work on his own, but there is equally no question that the paper never would have been written were it not for my participation inthe crucial initial stages when we were not even clear about the qualitative nature of the problem.

Susskind kind of repented of not includding Sarfatt:

...Any way I feel bad about forgetting to acknowledge you. Glo and myself debated whether to put you as an author or Acknowledgement and in the scuffle I forgot...
–Lenny

Carruthers was kind of bothered that he was not included either, writing to Sarfatt:

They (SG) did not acknowledge my aid either, although I spent alot of time encouraging them and in reading the final MS!... I’d like tore mind you that in the fall of 1962 I gave a homework problem in which I asked for a discussion of the existence of $\phi$. My curiosity on this point arose independently of your own, as I recall.

Carruthers was not very wealthy at that time, so the prize ended up being a single Budweiser beer!

References

• M.M. Nieto "Quantum Phase and Quantum Phase Operators: Some Physics and Some History", arXiv:hep-th/9304036 (1993)

Interestingly enough, Sarfatt changed his name to Sarfatti, left physics, and went to work on the problem of consciousness.

 

[Hornbein]

Sarfatti was one of the creatures of the swamp that was (is?) Usenet's sci.physics. Once he responded to a critic by letterbombing him, saturating his email with junk.

 

[pines-demon]

Sarfatti was one of the creatures of the swamp that was (is?) Usenet's sci.physics. Once he responded to a critic by letterbombing him, saturating his email with junk.

Fundamental Fysiks Group, Stargate project, flying saucers... quite a wacky character

 

[pines-demon]

Mysticism in 20th century physics

It seems that in the early 20th century, the writings of philosopher Arthur Schopenhauer and others introduced various intellectuals (including physicists) to concepts of Bhuddishm and Hinduism.

Schrödinger's dog
Erwin Schrödinger was influenced by Schopenhauer writings, so much that he named his dog Atman, the Hindu concept of personal reality/soul, and yes Schrödinger had a dog not a cat, he hated cats apparently. In his famous book What is Life?, he writes things like

The earliest records to my knowledge date back some 2500 years or more. From the early great Upanishads the recognition

ATHMAN = BRAHMAN

(the personal self equals the omnipresent, all-comprehending eternal self) was in Indian thought considered, far from being blasphemous, to represent the quintessence of deepest insight into the happenings of the world. The striving of all the scholars of Vedanta was, after having learnt to pronounce with their lips, really to assimilate in their minds this grandest of all thoughts.

How does the idea of plurality (so emphatically opposed by the Upanishad writers) arise at all? Consciousness finds itself intimately connected with, and dependent on, the physical state of a limited region of matter, the body. (Consider the changes of mind during the development of the body, as puberty, ageing, dotage, etc., or consider the effects of fever, intoxication, narcosis, lesion of the brain and so on.) Now, there is a great plurality of similar bodies. Hence the pluralization of consciousnesses or minds seems a very suggestive hypothesis. Probably all simple ingenuous people, as well as the great majority of western philosophers, have accepted it.

Ying-yang duality

Similar to Schrödinger, Niels Bohr once said:

I go into the Upanishads to ask questions

Bohr was involved in some mysticism. So much in fact that many of his contributions (complementarity principle, correspondence principle) read like esoteric passages now-a-days. At some point, Albert Einstein called out Bohr for this and Bohr tried to dismiss the idea

Utterances of this kind would naturally in many minds evoke the impression of an underlying mysticism foreign to the spirit of science; at the above mentioned [Copenhagen] Congress [for the Unity of Science] in 1936 I therefore tried to clear up such misunderstandings... I am afraid that I had in this respect little success in convincing my listeners, for whom the dissent among the physicists themselves was naturally a cause of skepticism.

However, it did not stop Bohr to embrace some mysticism in his identity. When he was knighted in Denmark, he did not have a family coat of arms, so he made one and added a ying-yang simbol.

The avatar of Vishnu
J. Robert Oppenheimer was so invested in Hinduism that he learned Sanskrit. Philosopher David Hawkins that discussed with him said:

Oppenheimer had been a student of Sanskrit and Hindu scripture. This interest may have begun from his earlier association with Bohr, the philosopher-physicist. Once, before the war, Oppenheimer and I discussed those ancient writings. I mentioned something in my reading of Plato, and he said,

I have read the Greeks; I find the Hindus deeper.

But it wasn't a put-down of a younger friend, just something strongly felt.

During the death of Roosevelt, Oppenheimer said:

Faith is the substance of things hoped for; what a man's faith is, he is.

a passage from the Bhagavad Ghita.

Perhaps the most iconic line of Oppenheimer is the one that he recorded after Trinity, the first test of a nuclear bomb.

We knew the world would not be the same. A few people laughed, a few people cried. Most people were silent. I remembered the line from the Hindu scripture, the Bhagavad Gita; Vishnu is trying to persuade the Prince that he should do his duty and, to impress him, takes on his multi-armed form and says,

Now I am become Death, the destroyer of worlds.

I suppose we all thought that, one way or another.

Sources:

• E. Schrödinger, What is Life?, 1944
• Letters (1994), Bulletin of the Atomic Scientists, 50:5, 3-60, doi:10.1080/00963402.1994.11456544
• J.M. Marin, 'Mysticism' in quantum mechanics: the forgotten controversy, European Journal of Physics, Volume 30, Number 4 (2009), doi:10.1088/0143-0807/30/4/014
• V. Kulkarni, What Erwin Schrödinger Said About the Upanishads, The Wire Science (2000)

 

[pines-demon]

When Bardeen was wrong

John Bardeen was one of the giants of solid state physics, up to this day the only person with two Nobel Prizes in Physics (1956 for the transistor and 1972 for BCS theory of superconductivity). However, when a 23 young man predicted of a superconducting tunneling current across a gap between two superconductors, Bardeen was very skeptical.

The young man was Brian Josephson, 23 years old at the time working under supervision of Brian Pippard. Phillip W. Anderson had suggested the problem to Josephson. He submitted his prediction to Physical Letters in 1962. Bardeen wrote that Cooper pair tunneling was "impossible" as these quasiparticles only existed in the superconductors. Ten days later Bardeen wrote a commentary to Physical Review Letters:

In a recent note, Josephson uses a somewhat similar formulation to discuss the possibility of superfluid flow across the tunneling region, in which no quasi-particles are created. However, as pointed out by the author (reference 3), pairing does not extend into the barrier, so that there can be no such superfluid flow.

Two months later, during the 1962 International Conference on Low Temperature Physics, Josephson and Bardeen were invited to publicly debate the issue. When they met Josephson tried to explain his theory to Bardeen, but the latter quickly replied:

I don't think so.

Bardeen left after that, Josephson was upset.

During the debate, many people gathered. The discussion was civil but none of the two wanted to give in. Every time that Bardeen said that Josephson's idea was

Quite impossible.

Josephson replied:

Did you calculate it? No? I did

At the end of the debate physicist Wolfgang Klose felt that Josephson had won the debate. He recall that at the end:

Bardeen put his arm around Josephson, like a father to his son. In this attitude they left the lecture-room.

Josephson's effect was confirmed in 1963 by Anderson and John Rowell at Bell Labs. Bardeen apologized publicly, offered a postdoc to Josephson and even nominated Josephson to the Nobel Prize in Physics, which Josephson received in 1973.

Source:

• Daitch & Hoddeson (2002). True Genius: The Life and Science of John Bardeen

 

[fresh_42]

I'm not sure if we already had this anecdote, but I think it should be mentioned. It even has its own Wikipedia page.

The question asked the student to "show how it is possible to determine the height of a tall building with the aid of a barometer."

According to Snopes.com, more recent (1999 and 1988) versions identify the problem as a question in "a physics degree exam at the University of Copenhagen" and the student was Niels Bohr, and includes the following answers:

• Tying a piece of string to the barometer, lowering the barometer from the roof to the ground, and measuring the length of the string and barometer.
• Dropping the barometer off the roof, measuring the time it takes to hit the ground, and calculating the building's height assuming constant acceleration under gravity.
• When the sun is shining, standing the barometer up, measuring the height of the barometer and the lengths of the shadows of both barometer and building, and finding the building's height using similar triangles.
• Tying a piece of string to the barometer, and swinging it like a pendulum both on the ground and on the roof, and from the known pendulum length and swing period, calculate the gravitational field for the two cases. Use Newton's law of gravitation to calculate the radial altitude of both the ground and the roof. The difference will be the height of the building.
• Tying a piece of string to the barometer, which is as long as the height of the building, and swinging it like a pendulum, and from the swing period, calculate the pendulum length.
• Marking off the number of barometer lengths vertically along the emergency staircase, and multiplying this with the length of the barometer.
• Trading the barometer for the correct information with the building's janitor or superintendent.
• Measuring the pressure difference between ground and roof and calculating the height difference (the expected answer).

 

[pines-demon]

I'm not sure if we already had this anecdote, but I think it should be mentioned. It even has its own Wikipedia page.

I think it was already mentioned by you in post #161

 

[pines-demon]

Inspired by Solitaire

During the Manhattan Project, Stanisław Ulam was set in charge of a problem related to nuclear reactions. He needed to estimate fission criticality from neutron multiplication rates. The idea of how to solve it came to Ulam while bored in a hospital:

The first thoughts and attempts I made to practice were suggested by a question which occurred to me in 1946 as I was convalescing from an illness and playing solitaires. The question was what are the chances that a Canfield solitaire laid out with 52 cards will come out successfully? After spending a lot of time trying to estimate them by pure combinatorial calculations, I wondered whether a more practical method than "abstract thinking" might not be to lay it out say one hundred times and simply observe and count the number of successful plays. This was already possible to envisage with the beginning of the new era of fast computers, and I immediately thought of problems of neutron diffusion and other questions of mathematical physics, and more generally how to change processes described by certain differential equations into an equivalent form interpretable as a succession of random operations. Later [in 1946], I described the idea to John von Neumann, and we began to plan actual calculations

Von Neumann and Nicholas Metropolis implemented the algorithm in the ENIAC machine. As they needed a codename, Metropolis suggested the name "Monte Carlo simulation" based on Monte Carlo Casino, he writes:

I suggested an obvious name for the statistical method-a suggestion not unrelated to the fact that Stan had an uncle who would borrow money from relatives because he "just had to go to MonteCarlo." The name seems to have endured.

Sources:

• R. Eckhardt (1987). "Stan Ulam, John von Neumann, and the Monte Carlo method". Los Alamos Science 131–137.
• N. Metropolis (1987). "The beginning of the Monte Carlo method". Los Alamos Science: 125–130.

 

[sbrothy]

Yeah, it's easy to loose the big picture in these long threads. I do it myself now and then.

 

[Hornbein]

"The first thoughts and attempts I made to practice were suggested by a question which occurred to me in 1946"

According to Encyclopedia Britannica, the Manhattan Project was over in 1945.

 

[Frabjous]

According to Encyclopedia Britannica, the Manhattan Project was over in 1945.

The program was under military control until the AEC took over on Jan 1, 1947.