A Note to The Reader

Excerpt. © Reprinted by permission. All rights reserved.

Werner Heisenberg, the pioneer who, at age twenty-five, first laid down the laws of the fundamental behavior of matter and light, was an old man when he sat down to write about his life. The book he wrote is not an autobiography of the man but an autobiography of his intellect, entirely a series of reconstructed conversations. His two most famous papers are solo affairs–one introducing quantum mechanics (the laws of the fundamental behavior of matter and light) and the other on the uncertainty principle (where, at any given time, the more specific a particle’s position, the more vague its speed and direction, and vice versa). But the roots of each solitary paper reach deep into months of heated and careful conversation with most of the great names of quantum physics.

“Science rests on experiments,” wrote Heisenberg, but “science is rooted in conversations.”

Nothing could be farther from the impression physics textbooks give to students. There, physics seems to be a perfect sculpture sitting in a vacuum-sealed case, as if brains, only tenuously connected to bodies, had given birth to insights fully-formed. These Athena-like theories and Zeus-like theorists seem shiny, glassy, smooth–sometimes, if the light is right, you can see through them into the mysteries and beauties of the physical universe; but there is hardly a trace of humanity, or any sense of questions still to be answered.

Physics, in actuality, is a never-ending search made by human beings. Gods and angels do not come bearing perfectly formed theories to disembodied prophets who instantly write textbooks. The schoolbook simplifications obscure the crooked, strange, and fascinating paths that stretch out from each idea, not only back into the past but also onward into the future. While we aspire to universality and perfection, we only lie if we write as if we have achieved it.

Conversations are essential to science. But the off-the-cuff nature of conversation poses a difficulty. It is rare, even in these digital times, to have a complete transcript of every word spoken between two people on a given day, even if that conversation someday leads to a new understanding of the world. The result is that history books rarely have much of the to and fro of human interaction. Heisenberg’s statement suggests that something is therefore lost.

Poring through the memoirs and biographies of the quantum physicists of the twentieth century, I felt as if I were watching a movie–the cast of characters was so vivid and the plot twists so unexpected. While the strength of science is its ability to slough off the contingencies of history and reach toward pure knowledge, this knowledge is built, one puzzle-piece at a time, by people living their lives in specific times and places with specific passions. Science unfolds in some directions rather than in others because of circumstances. Characters (not faceless brains) and plot twists (not the relentless forward march of truth) almost guarantee that this is true.

As Tom Wolfe wrote at the beginning of The Electric Kool-Aid Acid Test: “I have tried not only to tell what the Pranksters did but to re-create the mental atmosphere or subjective reality of it. I don’t think their adventure can be understood without that.” Wolfe was recounting a very different kind of mental history, but his point, I found, is even more true about the portentous history of science and intellect that unfolded as the age of entanglement.

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This is a book of conversations, a book about how the give-and-take between physicists repeatedly changed the direction in which quantum physics developed, just as conversations, subtly or dramatically, change the world we live in and experience every day. All the conversations in this book occurred in some form, on the date specified in the text, and I have fully documented the substance of every one. (The endnotes detailing the source of each quote–one word of notes for every five words of text–speak for themselves.) Most are composed of direct quotes (or close paraphrases) from the trove of letters, papers, and memoirs that these physicists left behind. When these quotes are stitched together with occasional connective tissue (e.g. “Nice to see you,” or, “I agree”), I have shaped these insertions as closely as I can to the character, beliefs, and history of the people involved. (A glance at the notes will separate quote from filler.)

Here is a sample from the text, from a conversation that took place in the summer of 1923 on a streetcar in Copenhagen between two of the founders of the quantum theory, Albert Einstein and Niels Bohr, and its first great teacher, Arnold Sommerfeld.

“It’s good to see you doing so well,” says Einstein, sitting down beside Bohr on the streetcar.
Bohr shakes his head, smiling: “My life from the scientific point of view passes off in periods of over-happiness and despair…as I know that both of you understand…of feeling vigorous and overworked, of starting papers and not getting them published, because all the time I am gradually changing my views about this terrible riddle which the quantum theory is.”

“I know,” says Sommerfeld, “I know.”

Einstein’s eyes almost close; he is nodding. “That is a wall before which I am stopped. The difficulties are terrible.” He looks up and smiles: “The theory of relativity was only a sort of respite which I gave myself during my struggles with the quanta.”

We know that the conversation (of which this interchange represents a tiny piece) happened because Bohr mentioned it in an interview late in his life with his son and one of his closest colleagues. The content of the conversation is easy to gather from a look at what the three men were working on and writing friends about around the same time. Here Bohr, in the interview, describes that day in 1923:

Sommerfeld was not impractical, not quite impractical; but Einstein was not more practical than I and, when he came to Copenhagen, I naturally fetched him from the railway station….
We took the streetcar from the station and talked so animatedly about things that we went much too far past our destination. So we got off and went back. Thereafter we again went too far, I can’t remember how many stops, but we rode back and forth in the streetcar because Einstein was really interested at that time; we don’t know whether his interest was more or less skeptical–but in any case we went back and forth many times in the streetcar and what people thought of us, that is something else.

Here is the first quote on which this particular short section of the conversation is based. It comes from a letter Bohr wrote to a British colleague in August of 1918:

I know that you understand…how my life from the scientific point of view passes off in periods of over-happiness and despair, of feeling vigorous and overworked, of starting papers and not getting them published, because all the time I am gradually changing my views about this terrible riddle which the quantum theory is.

How can a passage written five years earlier be relevant? Some things had changed for Bohr in the intervening years, but what he touches on in the letter had remained the same–the excitement, dejection, and overwork (during this whole period he was building his institute of physics in Copenhagen); the long, arduous papers only partially published; and, most of all, his struggle to understand the quantum theory, which until Heisenberg’s breakthrough in 1925 stood on shifting sand.

Here is the second quote, from a journey by train a year before. The astronomer of the Paris Observatory rode with Einstein from Belgium to Paris and asked him about the quantum problem. “That is a wall before which one is stopped,” Einstein replied. “The difficulties are terrible; for me, the theory of relativity was only a sort of respite which I gave myself during their examination.” His opinions on the subject were the same at the time of our scene in the summer of 1923; by next summer an unexpected letter from India would help him chip a crack in this quantum wall.

As for the filler: Bohr was the kind of person whose happiness was infectious–he would indeed have been looking well when he picked up Einstein to show him his newly-completed institute, no matter how overworked and secretly despairing he might actually be. And Sommerfeld, always intellectually engaged with Bohr during those early years of the quantum theory, would have known intimately what Bohr meant by “this terrible riddle.”

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I believe the risks of telling the story in this way are outweighed by the reward: a sense of how, through minds meeting minds, the quantum theory unfolded. Please check the notes (found on page 351) if ever it seems that someone “couldn’t have said that!”, and the glossary on page 337 for any unfamiliar physical terms. I am hopeful of earning your trust, and of honoring Heisenberg’s sense of how science is really done.

–LLG, October 17, 2007.

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Postscript

The risks of telling the story in this way have recently been highlighted. In the “Note to the Reader” above I had picked an example that would bring to the fore the speculative, collage-like nature of the conversations in the book. So it is not such a surprise that this example I used was the one which proved to conflict partially with further research.

Sommerfeld, it turns out, was not in the streetcar with Bohr that day in 1923, and in fact, neither was Einstein.

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Bohr told the story of his streetcar ride with Einstein in the course of a rambling conversation during a long Scandinavian summer day at his Zealand beach house, half a century ago. It was the 12th of July, 1961, and Bohr was almost 76 (he would die in the next year). His son Aage and his most devoted assistant, Leon Rosenfeld, were interviewing him. Bohr guessed that Einstein had come after giving a speech in the Swedish town of Göteburg (which was 1923, when the town celebrated its 300th aniversary).

But the Bohr archive, comparing notes with the Einstein archive, now believes that Einstein visited Copenhagen only once–in 1920, after a speaking trip to Kristiania (as Oslo was called until 1924, in honor of a long-ago Norwegian and Danish king). Immediately afterwards Einstein wrote to his father-figure, the great Dutch physicist Hendrik Lorentz:

The trip to Kristiania was really beautiful; the most beautiful were the hours I spent with Bohr in Copenhagen. He is a highly gifted and excellent man.

It is a good omen for physics that prominent physicists are mostly also splendid people.

Einstein and Bohr’s biographer, Abraham Pais, wrote in Niels Bohr’s Times (p. 228) “I have not found any comment by Bohr on this visit.” It is rather nice to realize now that Bohr’s streetcar story is in fact describing those “beautiful hours.”

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Sommerfeld’s name came into Bohr’s telling of this tale, not because he was there (as I had believed) but because talking of those events brought him to Bohr’s mind. Bohr, Sommerfeld, and Einstein in those days were in close communication–Bohr and Sommerfeld as they elaborated their atomic model, and Einstein and Sommerfeld as they discussed general relativity during its genesis. The twenty years between 1908 and 1928 were Sommerfeld’s heyday as a mathematical physicist (during which he supervised the Ph.D. theses of an incredible total of four future Nobel Laureates).

What, then, in 1920, would have engrossed Einstein and Bohr so much that they repeatedly missed their stop? Well, the focus of their discussions and disagreements in 1920 was the same as in 1923: the light-quantum. Again, let me emphasize that looking at the notes will show exactly when (and to whom) each man made the statement which I have woven into the conversation.

All of which is to say that the mission of this book is to complement the existing histories and textbooks with a reminder of the wonderful unsettledness of conversation, interchange, and experiment, and the moments in which these occasionally flash into inspired clarity. This book is a celebration of the glorious, human mess that incubates discovery, as well as of its flawed and heroic searchers.

–LLG, March 25, 2009.