Ring of Letters

The Men of Ideas, in the early part of the twentieth century, formulated and exchanged many of their ideas through written correspondence. These took the form of a series of long, articulate letters sometimes spanning years or even decades.

While reading some of the most dedicated correspondences (much of it online, much of it in books) I noticed two things: First, the fertile exchange between the physicists who founded both Quantum Mechanics and Relativity and the twin giants of psycho-analysis, Freud and Jung. Second, was that the most voluminous and dedicated correspondences formed a chain, actually a nicely closed ring. The Ring of Letters.

The Einstein-Freud Correspondence
Einstein, a champion for peace, famously worked to assemble a group of intellectual leaders to bring pressure on politicians. Here, he works on bringing Freud into the fold. The exchanges between them are wonderful to read.
As Einstein writes, "I am convinced that almost all great men who, because of their accomplishments, are recognized as leaders even of small groups share the same ideals. But they have little influence on the course of political events. It would almost appear that the very domain of human activity most crucial to the fate of nations is inescapably in the hands of wholly irresponsible political rulers."
And Freud shares his ideas, "You are amazed that it is so easy to infect men with the war fever, and you surmise that man has in him an active instinct for hatred and destruction, amenable to such stimulations. I entirely agree with you. I believe in the existence of this instinct and have been recently at pains to study its manifestations. In this connection may I set out a fragment of that knowledge of the instincts, which we psychoanalysts, after so many tentative essays and gropings in the dark, have compassed? "

The Freud-Jung Correspondence
It appears that Jung struggled to get out from Freud's shadow. Their relationship, as seen through their letters, comes across as both fertile and diseased. They exchanged nearly 400 letters in the course of seven years.
As Trilling writes, about one episode, in the New York Times "A few days later Jung wrote Freud, coolly but with amenity, even with the avowal of his wish to continue in personal if no longer in intellectual closeness. Freud replied in kind; he commented on the fainting episode, about which Jung had enquired, and contended by saying, "A bit of neurosis that I ought really look into." The minimizing phrase seems to have put Jung into a state of hysterical rage. He insolently replies that "this 'bit' should, in my opinion, be taken very seriously indeed because it leads 'usque ad instar voluntariae mortist ('to the semblance of voluntary death']. I have suffered from this bit in my dealings with you. . ." and more to the same effect and in the same tone."

The Jung-Pauli Correspondence
Pauli was one of the founders of Quantum Mechanics and author of the Exclusion principle which dictates how like particles behave. Without it, for example, we wouldnt understand the behavior of Neutron stars. Jung was the proponent of Synchronicity, a mystical view of the world with creative notions of cause and effect.
And yet these two were close collaborators - exchanging numerous letters, collaborating on exotic ideas.
In the preface to a collected volume of letters, we are told:
"In their joint volume, Jung and Pauli presented the synchronicity principle. It presumes that indestructible energy has a dual relationship to the space-time continuum: on the one hand, there is the constant connection through effect--that is, causality; and on the other, there is an inconstant connection through contigence, equivalence, or meaning that is itself synchronicity. For a physicist, equations are not objectively accurate reflections of material reality but structurally accurate relationship-connections. For Jung, synchronicities are meaningful only when an individual experiences them. This creates another "relationship of complementarity between the occurrence or cessation of synchronistic phenomena and the relative state of unconsciousness or consciousness of the individual who experiences it."

The Pauli-Heisenberg Correspondence
Pauli was Werner Heisenberg's closest scientific collaborator. Between them, they exchanged hundreds of letters in which they worked to resolve the conundrums of Quantum Physics. Heisenberg is best known to the scientific layman as the author of the Uncertainty Principle, which dictates limitations on complementary properties in subatomic particles.
In fact, Heisenberg first outlined the Uncertainty Relation in a letter to Pauli. The Pauli-Heisenberg letters have not yet been made available to the public. But there is much speculation that they will reveal that Pauli had an even greater role to play in the development of the fundamental principles of quantum physics than is currently believed.

The Heisenberg-Bohr Correspondence
The correspondence between Heisenberg and Bohr has become famous for one key reason: the questions around whether Heisenberg was helping Nazi Germany to build an atomic bomb.
From the Bohr letters:
"At that time I had no knowledge at all of the preparations that were under way in England and America, and when I did not reply and perhaps looked doubtful, you told me that I had to understand that in recent years you had occupied yourself almost exclusively with this question and were certain that it could be done. ...There was no hint on your part that efforts were being made by German physicists to prevent such an application of atomic science. ...my alarm was not lessened by hearing from the others at the Institute that Weizsäcker had stated how fortunate it would be for the position of science in Germany after the victory that you could help so significantly towards this end."

The Bohr-Einstein Correspondence
The conversations between Bohr and Einstein were about the fundamental nature of reality. Einstein, a disbeliever in quantum mechanics, kept pushing Bohr and Bohr, one of the founders of quantum mechanics and the man responsible for our modern view of the atom, kept pushing back.
These two giants, in their long debates, sketched out many of the puzzles of modern physics and consequently much of the legacy that modern scientists have to confront. I have linked to a picture of the two men, deep in talks, architecting the Universe.