A “BOOK OF CONVERSATIONS” BETWEEN PHYSICISTS ABOUT QUANTUM THEORY
In her ‘Note to the Reader,’ author Louisa Gilder explains, “This is a book of conversations, a book about how the give-and-take between physicists repeated change the direction in which quantum physics developed… 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 each one… Most are composed of direct quotes (or close paraphrases) from the trove of letters, papers, and memoirs that these physicists left behind. When occasional connective tissue (e.g., ‘Nice to see you,’ or ‘I agree’) was necessary, I tried to keep it both innocuous and also sensitive to the character, beliefs, and history of the people involved. (Pg. xiv)
She observes in the Introduction, “The mysteries embedded in quantum mechanics provoked four major reactions from its founder: orthodoxy, heresy, agnosticism, and simple misunderstanding. Three of the theory’s founders ([Niels] Bohr, [Werner] Heisenberg, and Wolfgang Pauli) gave it its orthodox exegesis, which came to be known as the Copenhagen interpretation. Three more founders (including Einstein) were heretics, believing that something was rotten in the quantum theory they had played such a role in developing, Finally, pragmatic people said, 'The time is not yet ripe for understanding these things, and confused people dismissed the mysteries with simplistic explanations.'” (Pg. 4)
She records, “in 1909, only nine years after quantum theory’s tentative debut, Albert Einstein began to worry that it implied a world composed of non-separable pieces that were ‘not… mutually independent.’… they seemed to exert ‘a mutual influence… of a quite mysterious nature’ on each other, or even seemed to affect each other in what he ridiculed as ‘spooky action-at-a-distance,’ or ‘a sort of telepathic coupling.’ To him it was clear that this meant a fatal flaw in the theory.” (Pg. 6)
She notes, “Bell’s theorem showed that the world of quantum mechanics… is composed of entities that are either… not locally causal, not fully separable, and even not real unless observed. If the entities of the quantum world are not locally causal, then an action measuring a particle can have instantaneous ‘spooky’ effects across the universe… The most extreme version of nonseparability is the idea that the quantum entities do no become solid until they are observed, like the proverbial tree that makes no sound when it falls unless a listener is around. Einstein found the implications ludicrous: ‘Do you really believe the moon is not there is nobody looks?’” (Pg. 9-10)
She recounts, “Einstein and Bohr would draw different morals from this difficultly of forming a picture of atomic behavior. Bohr would soon say it couldn’t be done. The behavior of atoms, and their insides, were irreducibly unvisualizable. Einstein would say there was something wrong with a physics that would come to this conclusion.” (Pg. 45)
She reports a conversation: “‘I admit that I am strongly attracted,’ said Heisenberg slowly, ‘by the simplicity, and beauty, of the mathematical schemes with which nature suddenly spreads out before us---the almost frightening simplicity and wholeness of the relationships, for which none of us was in the least prepared. I know you have felt this, too.’ Einstein sat smoking and nodding. Then he said, ‘Still, I should never claim that I really understood what is meant by the simplicity of natural laws.’” (Pg. 88)
She says, “One day, after Einstein had asked for the umpteenth time if Bohr really believed God played dice to determine the future, a smile dawned on Bohr’s face. ‘Einstein,’ he said, ‘stop telling God how to run the world.’” (Pg. 113)
She says of the famous EPR paper, “the paper famously (and significantly) defined an ‘element of reality’: ‘If, without in any way disturbing a system, we can predict with certainty the value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity… While we have shown that the wave function does not provide a complete description of the physical reality, we have left open the question of whether or not such a description exists. We believe, however, that such a theory is possible.” (Pg. 160)
She records, “‘One can even construct quite burlesque cases,’ wrote Schrödinger. He described ‘a cat shut up in a steel chamber with a diabolical apparatus…’ This apparatus involves a vial of poison which will be smashed by a hammer… [after] the decay of a single radioactive atom. If the atom decays, the cat breathes the poison; if not, the cat remains safe… There is so little radioactive substance ‘that in the course of ah hour PERHAPS one atom of it disintegrates, but also with equal probability not even one… If one has left this entire system to itself for an hour, then one will say to himself that the cat is still living, if in that time no atom has disintegrated. The first atomic decay would have poisoned it. The [wave-]function of the entire system would express this situation by having the living and the dead cat mixed or smeared out.’ With this…. A cat in a superposition of simultaneous death and live---Schrödinger demonstrated the desperate state of a theory that required measurement to make it work.” (Pg. 173)
She summarizes, “Every step---from the entanglement abstractly inherent in Schrödinger’s wave equation to EPR, when Einstein imagined just what this implied, to Bell’s closer scrutiny, finding it a testable conflict, to … bringing that conflict into the lab---was a step closer to incarnation. But this story had to far rested in the hands of the theorists. Nineteen sixty-nine was the year in which the experimentalists took command of the age of entanglement.” (Pg. 260)
She imagines a conversation: “‘Does the chair exist when you’re not there to look at it?’… This is what I found infuriating… It’s the whole Bishop Berkeley question of ‘If a tree falls in the forest and no one hears it, does it make a sound?’ Quantum mechanics answers the bishop, ‘No.’ If you close the box, is the chair still there? How about a shoe? You’d be pretty surprised if your shoes changed color in the box coming home from the shoe store. How about ions?... So if you put an ion in your box, is it in the box when you close the lid? What if you have two photons in an entangled state … and you put one in the box you’re holding and one in the box I’m holding? Are they there?... Is IT in the box when you close the lid?” (Pg. 279)
She concludes, “What is more likely is that that new way of seeing things will involve an imaginative leap that will astonish us. In any case, it seems that the quantum mechanical description will be superceded. In this it is like all theories made by man. But to an unusual extent its ultimate fate is apparent in its internal structure. It carries in itself the seeds of its own destruction.” (Pg. 330)
Gilder’s reconstruction of these “conversations” makes for smoother reading (and she is an excellent writer); but some readers may find this makes the book more like a “novelization” than a genuine historical work.