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The Gentleman Laureate (Sir Anthony Leggett)

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The Nobel Prize has always vaguely irritated me. The idea that one’s entire research career might somehow be neatly defined by what a bunch of Swedes happen to find noteworthy has long struck me as arbitrary at best and, in my darker moments, a sad commentary on our need for self-affirmation.

Richard Feynman typically summed it up best when asked if his work on quantum electrodynamics fully merited being awarded the Prize: “I don’t know anything about the Nobel Prize and what’s worth what … I’ve already got the prize. The prize is the pleasure of finding the thing out, the kick of the discovery, the observation that other people use it. Those are the real things. The honors are unreal.” 

On the other hand, it’s clear that these sorts of major prizes and awards have their uses. Life without the annual Nobel announcements, for example, would mean that the mainstream media would pay even less attention than usual to scientific discoveries, literary accomplishments, or the enlightened few who are advancing the cause of global peace.

The Nobel Prize does one other very useful thing too: it provides a sort of academic bulletproofing for those who might wish to indulge in more general musings on the future of their field, speculations which are invariably great fun for the rest of us who might be unwilling or unable to follow technical arguments in detail.

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Along with two others (Alexei Abrikosov and Vitaly Ginsburg), Tony Leggett won the Nobel Prize for physics in 2003 for “pioneering contributions to the theory of superconductors and superfluids” and is universally appreciated as that very rare bird indeed: an unequivocally brilliant and unreservedly decent person. In a world filled to the brim with tedious academic posturing and self-proclaimed geniuses, Leggett has earned the reputation of, as a friend of mine once neatly put it, the one Nobel Laureate that people would most enthusiastically invite over to dinner.

He is also, in his own quiet and unpretentious way, one of physics’ most penetrating and thoughtful popularizers. In 1987, one year earlier than Steven Hawking’s A Brief History of Time and more than a decade before Brian Greene’s The Elegant Universe, Tony penned The Problems of Physics, an insightful and punchy itemization of the physics landscape according to four basic categories: the very small (particle physics), the very large (cosmology), the very complex (condensed matter physics), and the very unclear (foundations of quantum theory).

The book is a delightfully written summary that is surprisingly relevant today, notwithstanding all of our modern advances. Likely for these reasons, Oxford University Press elected to re-issue it in 2006.

The last category of The Problems of Physics is a particularly intriguing one. Back in 1987, discussions of foundational aspects of quantum mechanics were regarded by the vast majority of working physicists as roughly on par with astrology or alchemy in terms of respectability. Tony, however, 16 years before his bulletproofing Nobel was awarded, clearly felt no hesitation to boldly stroll into the quantum labyrinth.

Indeed he has spent a significant percentage of his professional scientific life quietly probing the foundations of quantum mechanics, determined to find where the theory will break down. On the surface, this might not sound terribly surprising. After all, quantum mechanics has long been recognized as a framework fraught with a bevy of conceptual and logical difficulties that has tormented some of the best scientific minds the world has ever known, including luminaries such as Albert Einstein and Erwin Schrödinger who did so much to develop the theory in the first place.

But precisely for this reason, modern physics has distanced itself from efforts to penetrate the mystery that is quantum theory, summarily branding all of that business as “intractable philosophy”, while anxiously moving on to attacking problems it might actually solve (such as superfluidity). After all, however it might trouble us conceptually, it can’t be denied that quantum mechanics works like a charm.

Once again Richard Feynman, set the tone: “Do not keep saying to yourself, if you can possibly avoid it, ‘But how can it be like that?’ because you will get ‘down the drain’ into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.”

Tony Leggett, however, in his ever so polite, understated way stubbornly refused to give in:

“What really worries me is Schrödinger’s cat. The formulas of quantum mechanics haven’t changed a whit as we go from the description it gives of the photon to the description it gives of the cat. If we refuse to make a particular interpretation at the microscopic level, then we have no business reintroducing that interpretation at the macroscopic level.

“The evidence for this statement is there at the microscopic level in the form of interference patterns, but everyone agrees that, at the level of the cat, it has gone away. But does the fact that the evidence against a particular interpretation of the formalism has gone away by the time we get to the cat mean that we can freely reintroduce that interpretation? I say, ‘no’. If you decide that a particular interpretation of a general formalism is not valid at the micro level then it can’t be at the macro level.”

What separates Leggett from many of the others concerned about the foundations of quantum theory, and incidentally unites him with Feynman, is his insistence on the importance of experiment to probe our theoretical constructs:

“Perhaps I’m just ultraconservative, but my attitude has always been that physics is an experimental subject; you don’t want to push your theoretical speculations too far beyond what we can currently access experimentally. I suppose that’s why I’ve always stayed within the confines of condensed matter physics, or things somewhat related to condensed matter physics, because I like the fact that, if I have an idea, there is some hope that my experimental colleagues will be able to test it during my lifetime.”

Three decades later, the physics world has caught up to Professor Leggett. The rise of quantum information theory, quantum computing and quantum cryptography has breathed new life into the business of probing the limits of quantum theory.

“When I first started thinking seriously about this, way back around 1980, I quite seriously hoped that when you got to the level of the so-called ‘flux qubit’ – where the two states you’re talking about are different in the behavior of something like, say, ten billion electrons – by that time something else might have happened. Right now, it looks as if quantum mechanics is working fine at that level.”

When I pushed him to speculate on what physicists will believe 50 years from now, he responded: “In 50 years, I think there will have been a major revolution in cosmology, and I think there’s a small but non-zero chance that we will have pushed quantum mechanics in the direction of the macroscopic world to the point where it will fail and break down.”

Not much cause for enthusiasm, then, for quantum philosophers anxious to see some revolutionary developments. But what if we take a still longer view? Will quantum mechanics definitely break down at some point? I pressed him.

“Yes”, he responded, firmly and unhesitatingly.

He may seem like a kindly English grandfather, but the scientific will that drives Sir Anthony Leggett is as hard as steel.

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For a complete list of Ideas Roadshow videos with Tony, click here. The IR eBook The Problems of Physics containing the unabridged Ideas Roadshow conversation with Tony and a range of additional resources is available on Amazon.

University staff and students may already have full access to all Ideas Roadshow resources on our Academic Portal through an institutional subscription (subscribers include Harvard, Princeton, Imperial College, University of Michigan, and many more), while select high school teachers and members of the general public have access to our School and Public Library Portals.  For more information please contact irena@ideasroadshow.com.

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1 Comment

  1. […] Nima Arkani-Hamed’s two-part Ideas Roadshow conversation called The Power of Principles is available as part of the series called Rethinking Physics which is available on Vimeo On Demand, see here. This series also features in-depth conversations with Paul Steinhardt, Freeman Dyson, Artur Ekert, and Tony Leggett. […]

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