Quantum Entanglement; nature’s great tease

I’ve just read the best book on the history of quantum mechanics that I’ve come across, called The Age of Entanglement, subtitled When Quantum Physics was Reborn, by Louisa Gilder. It’s an even more extraordinary achievement when one discovers that it’s Gilder’s first book, yet one is not surprised to learn it had an 8 year gestation. It’s hard to imagine a better researched book in this field.

Gilder takes an unusual approach, where she creates conversations between key players, as she portrays them, using letters and anecdotal references by the protagonists. She explains how she does this, by way of example, in a preface titled A Note To The Reader, so as not to mislead us that these little scenarios were actually recorded. Sometimes she quotes straight from letters.

When I taught a fiction-writing course early last year, someone asked me is biography fiction or non-fiction? My answer was that as soon as you add dialogue, unless it’s been recorded, it becomes fiction. An example is Schindler’s Ark by Thomas Keneally, who explained that he wrote it as a novel because ‘that is his craft’. In the case of Gilder’s book, I would call these scenarios quasi-fictional. The point is that they work very well, whether they be fictional or not, in giving flesh to the characters as well as the ideas they were exploring.

She provides an insight into these people and their interactions, at a level of perspicuity, that one rarely sees. In particular, she provides an insight into their personal philosophies and prejudices that drove their explorations and their arguments. The heart of the book is Bell’s Theorem or Bell’s Inequality, which I’ve written about before (refer Quantum Mechanical Philosophy, Jul.09). She starts the book off like a Hollywood movie, by providing an excellent exposition of Bell’s Theorem for laypeople (first revealed in 1964) then jumping back in time to the very birth of quantum mechanics (1900) when Planck coined the term, h, (now known as Planck’s constant) to satisfactorily explain black body radiation. Proceeding from this point, Gilder follows the whole story and its amazing cast of characters right up to 2005.

In between there were 2 world wars, a number of Nobel Prizes, the construction of some very expensive particle accelerators and a cold war, which all played their parts in the narrative.

David Mermin, a solid state physicist at Cornell gave the best exposition of Bell’s Theorem to non-physicists, for which the great communicator, Richard Feynman, gave him the ultimate accolade by telling him that he had achieved what Feynman himself had been attempting to achieve yet failed to realise.

Bell’s Theorem, in essence, makes predictions about entangled particles. Entangled particles counter-intuitively suggest action-at-a-distance occurring simultaneously, contradicting everything else we know about reality, otherwise known as ‘classical physics’. Classical physics includes relativity theory which states that nothing, including communication between distinct objects, can occur faster than the speed of light. This is called ‘locality’. Entanglement, which is what Bell’s Theorem entails, suggests the opposite, which we call ‘non-locality’.

Gilder’s abridged version of Mermin’s exposition is lengthy and difficult to summarise, but, by the use of tables, she manages to convey how Bell’s Theorem defies common sense, and that’s the really important bit to understand. Quantum mechanics defies what our expectations are, and Bell’s great contribution to quantum physics was that his famous Inequality puts the conundrum into a succinct and testable formula.

Most people know that Bohr and Einstein were key players and philosophical antagonists over quantum theory. The general view is that Bohr ultimately won the argument, and was further justified by the successful verification of Bell’s Theorem, while Einstein was consigned to history as having discovered two of the most important theories in physics (the special and general theories of relativity) but stubbornly rejected the most empirically successful theory of all time, quantum mechanics. Gilder’s book provides a subtle but significantly different perspective. Whilst she portrays Einstein as unapologetically stubborn, he played a far greater role in the development of quantum theory than popular history tends to grant him. In particular, it could be argued that he understood the significance of Bell’s Theorem many decades before Bell actually conceived it.

Correspondence, referenced by Gilder, suggests that Schrodinger’s famous Cat thought experiment originally arose from a suggestion by Einstein, only Einstein envisaged a box containing explosives that were both exploded and un-exploded at the same time. Einstein also supported De Broglie at a time when everyone else ignored him, and he acknowledged that de Broglie had ‘lifted a corner of the great veil’.

Curiously, the cover of her book contains 3 medallion-like photographic portraits, in decreasing size: Albert Einstein, Erwin Schrodinger and Louis de Broglie; all quantum mechanic heretics. Gilder could have easily included David Bohm and John Bell as well, if that was her theme.

Why heretics? Because they all challenged the Copenhagen interpretation of quantum mechanics, led by Bohr and Heisenberg, and which remains the ‘conventional’ interpretation to this day, even though the inherent conundrum of entanglement remains its greatest enigma.

It was Bohr who apparently said that anyone who claims they understand quantum mechanics doesn’t comprehend it at all, or words to that effect. When we come across something that is new to us, that we don’t readily understand, the brain looks for an already known context in which to place it. In an essay I wrote on Epistemology (July 2008) I made the point that we only understand new knowledge when we incorporate it into existing knowledge. The best example is when we look up a word in a dictionary – it’s always explained by using words that we already know. I also pointed out that this plays a role in storytelling where we are continuously incorporating new knowledge into existing knowledge as the story progresses. Without this innate human cognitive ability we’d give up on a story after the first page.

Well the trap with quantum mechanics is that we attempt to understand it in the context of what we already know, when, really, we can’t. It’s only when you understand the mystery of quantum mechanics that you can truly say: I understand it. In other words, when you finally understand what can’t be known, or can’t be predicted, as we generally do with so-called ‘classical physics’. Quantum mechanics obeys different rules, and when you appreciate that they don’t meet our normal ‘cause and effect’ expectations, then you are on the track of appreciating the conundrum. It’s a great credit to Gilder that she conveys this aspect of quantum physics, both in theory and in experiment, better than any other writer I’ve read.

Some thumbnail sketches based on Gilder’s research are worth relaying. She consistently portrays Neils Bohr as a charismatic leader who dominated as much by personality as by intellect. People loved him, but, consequently, found it difficult to oppose him, is the impression that she gives. The great and famous exception was Einstein, who truly did have a mind of his own, but also Wolfgang Pauli, who was famously known to be the most critical critic of any physicist.

John Wheeler, who in the latter part of the 20th Century, became Bohr’s greatest champion said of his early days with Bohr: “Nothing has done more to convince me that there once existed friends of mankind with the human wisdom of Confucius and Buddha, Jesus and Pericles, Erasmus and Lincoln, than walks and talks under the beech trees of Klampenborg Forest with Neils Bohr.” Could there be any greater praise?

Einstein wrote of Max Planck: “an utterly honest man who thinks of others rather than himself. He has, however, one fault: he is clumsy in finding his way about foreign trains of thought.” As for Lorentz, with whom he was corresponding with at the same time as Planck, he found him “astonishingly profound… I admire this man as no other, I would say I love him.”

Much later in the story, Gilder relates an account of how a 75 year-old Planck made a personal presentation to Hitler, attempting to explain how his dismissal of Jewish scientists from academic positions would have disastrous consequences for Germany. Apparently, he barely opened his mouth before he was given a severe dressing-down by the dictator and told where to go. Nevertheless, the story supports Einstein’s appraisal of the man from a generation earlier.

Gilder doesn’t provide a detailed portrait of Paul Dirac or P.A.M. Dirac, as he’s often better-known, but we know he was a very reserved and eccentric individual, whose mathematical prowess effectively forecast the existence of anti-matter. The Dirac equation is no less significantly prophetic than Einstein’s famous equation, E=mc².

Wolfgang Pauli’s great contribution to physics was the famous Pauli exclusion principle, which I learnt in high school, and provides the explanation as to why atoms don’t all collapse in on each other, and, why, when you touch something you don’t sink into it. He also predicted the existence of the neutrino. Pauli’s personal life went into a steep decline in the 1930s when he suffered from chronic depression and alcoholism. His life turned around after he met Carl Jung and became a lifelong friend. ‘In two years of Jung’s personal analysis and friendship, Pauli shed his depression. In 1934 he met and married Franca Bertram, who would be his companion for the rest of his life.’

This friendship with Jung led to a contradiction in the light of our 21st Century sensibilities, according to Gilder:

’Pauli could tell Bohr to “shut up” and Einstein that his ideas were “actually not stupid”… But in the words of Franca Pauli, “the extremely rational thinker subjected himself to total dependence on Jung’s magical personality.”’

Schrodinger is as well known for his libertine attitude towards sexual relationships as he is for his famous equation. His own wife became the mistress of Schrodinger’s close friend and mathematician, Hermann Weil, whilst Schrodinger had a string of mistresses. But the identity of his lover-companion, when he was famously convalescing from tuberculosis in an Alpine resort in Arosa and conjured up the wave equations that bear his name, is still unknown to this day.

When Schrodinger died in 1961, Max Born (another Nobel Prize winner in the history of quantum mechanics) wrote the following eulogy:

“His private life seemed strange to bourgeois people like ourselves. But all this does not matter. He was a most loveable person, independent, amusing, temperamental, kind, and generous, and he had a most perfect and efficient brain.”

It was Born who turned Schrodinger’s equations into a probability function that every quantum theorist uses to this day. Born was a regular correspondent with Einstein, but is now almost as famously known in pop culture as being grandfather to Australian songstress, Olivia Newton John (not mentioned in Gilder’s book).

Gilder provides a relatively detailed and bitter-sweet history of the relationship between David Bohm and J. Robert Oppenheimer, both affected in adverse ways by the cold war and McCarthy’s ‘House Un-American Activities Committee’.

I personally identify with Gilder’s portrait of Bohm more than I anticipated, not because of his brilliance or his courage, but because of his apparent neurotic disposition and insecurity and his almost naïve honesty.

Gilder has obviously accessed transcripts of his interrogation, where he repeatedly declined to answer questions “on the ground that it might incriminate and degrade me, and also, I think it infringes on my rights as guaranteed by the First Amendment.”

When he was eventually asked if he belonged to a political party, he finally said, “Yes, I am. I would say ‘Yes’ to that question.”

This raised everyone’s interest, naturally, but when he followed up the next question, “What party or association is that?” he said, “I would say definitely that I voted for the Democratic ticket.” ‘The representative from Missouri’, who asked the question, must have been truly pissed off when he pointed out that that wasn’t what he meant. To which Bohm said, in all honesty no doubt, “How does one become a member of the Democratic Pary?”

Bohm lost his career, his income, his status and everything else at a time when he should have been at the peak of his academic abilities. Even Einstein’s letter of recommendation couldn’t get him a position at the University of Manchester and he eventually went to Sao Paulo in Brasil, though he never felt at home there. Gilder sets one of her quasi-fictional scenarios in a bar, when Feynman was visiting Brasil and socialising with Bohm, deliberately juxtaposing the two personalities. She portrays Bohm as not being jealous of Feynman’s mind, but being jealous of his easy confidence in a foreign country and his sex-appeal to women. That’s the David Bohm I can identify with at a similar age.

Bohm eventually migrated to England where he lived for the rest of his life. I don’t believe he ever returned to America, though I can’t be sure how true that is. I do know he became a close friend to the Dalai Lama, because the Dalai Lama mentions their friendship in one of his many autobiographies.

According to Gilder, it’s unclear if Bohm ever forgave Oppenheimer for ‘selling out’ his friend, Bernard Peters, both of whom hero-worshipped Oppenheimer. Certainly, at the time that Oppenheimer ‘outed’ Peters as a ‘crazy red’, Bohm felt that he had betrayed him.

Bohm made a joke of the House Un-American Activities Committee based on the famous logic conundrum postulated by Bertrand Russell: “If the barber is the man who shaves all men who do not shave themselves, who shaves the barber?” Bohm’s version: “Congress should appoint a committee to investigate all committees that do not investigate themselves.”

But of all the characters, John Bell is the one about whom I knew the least, and yet he is the principal character in Gilder’s narrative, because he was not only able to grasp the essential character of quantum mechanics but to quantify it in a way that could be verified. I won’t go into the long story of how it evolved from the Einstein-Podolsky-Rosen (EPR) conjecture, except to say that Gilder covers it extremely well.

What I did find interesting was that after Bell presented his Inequality, the people who wanted to confirm it were not supported or encouraged on either side of the Atlantic. It was considered a career-stopper, and Bell himself, even discouraged up-and-coming physicists from pursuing it. That all changed, of course, when results finally came out.

After reading Gilder’s account, I went back to the interview that Paul Davies had with Bell (The Ghost in the Atom, 1986) after the famous Alain Aspect experiment had confirmed Bell’s Inequality.

Bell is critical of the conventional Copenhagen interpretation because he argues where do you draw the line between the quantum world and the classical world when you make your ‘observation’. Is it at the equipment, or is it in the optic nerve going to your brain, or is it at the neuron in the brain itself. He’s deliberately mocking the view that ‘consciousness’ is the cause of the ‘collapse’ of the quantum wave function.

In the interview he makes specific references to de Broglie and Bohm. Gilder, I noticed, sourced the same material.

“One of the things that I specifically wanted to do was to see whether there was any real objection to this idea put forward long ago by de Broglie and Bohm that you could give a completely realistic account of all quantum phenomena. De Broglie had done that in 1927, and was laughed out of court in a way that I now regard as disgraceful, because his arguments were trampled on. Bohm resurrected that theory in 1952, and was rather ignored. I thought that the theory of Bohm and de Broglie was in all ways equivalent to quantum mechanics for experimental purposes, but nevertheless it was realistic and unambiguous. But it did have the remarkable feature of action-at-a-distance. You could see that when something happened at one point there were consequences immediately over the whole of space unrestricted by the velocity of light.”

Perhaps that should be the last word in this dissertation, but I would like to point out, that, according to Gilder, Einstein made the exact same observation in 1927, when he tried to comprehend the double-slit experiment in terms of Schrodinger’s waves.