Wednesday, December 12, 2018

How to write a science best-seller

Everyone knows how science writing works. Academic scientists labour with great diligence to tease nuanced truths from theory and experiment, only for journalists and popularizers to reduce them to simplistic sound bites for the sake of a good story.

I’ve been moved to ponder that narrative by the widespread appearance on Christmas science/non-fiction books lists of two books by leading science academics: Steven Pinker’s Enlightenment Now and Robert Plomin’s Blueprint. I reviewed both books at length in Prospect, and my feelings about both of them were surprisingly similar: they have some important and valuable things to say, but are both infuriating too in terms of what they fudge, leave out or misrepresent.

I won’t recapitulate those views here. Plomin has taken some flak for the genetic determinism that his book seems to encourage – most recently from Angela Saini in the latest Prospect, whose conclusion I fully endorse: “Scientists… should concentrate on engaging with historians and social scientists to better understand humans not as simple biological machines but as complex, social beings.” Pinker has been excoriated in one or two places (most vigorously, and some would say predictable, by John Gray) for using the “Enlightenment” ahistorically as a concept to be moulded at will to fit his agenda (not to mention his simplistic and obsolete characterization of Nietzsche).

What both books do is precisely what the caricature of science journalism above is said to do, albeit with more style and more graphs: to eschew nuance and caveats in order to tell a story that is only partly true.

And here’s the moral: it works! By delivering a controversial message in this manner, both books have received massive media attention. If they had been more careful, less confrontational, more ready to tell a complex story, I very much doubt that they would have been awarded anything like as much coverage.

Now, my impression here – having spoken to both Pinker and Plomin – is that they both genuinely believe what they wrote. Yes, Pinker did acknowledge that he was using a simplified picture of the Enlightenment for rhetorical ends, and in conversation Plomin and I were broadly in agreement most of the time about what genetic analyses do and don’t show about human behaviour. But I don’t think either of them was setting out cynically to present a distorted message in order to boost book sales. What seems to be happening here is more in the line of a tacit collusion between academics keen to push a particular point of view (nothing wrong with that in itself) and publishers keen to see an eye-catching and controversial message. And we have, of course, been here before (The God Delusion, anyone?).

Stephen Hawking’s book Brief Answers to the Big Questions was also a popular book choice for 2018 that, in a different way, often veered towards the reductively simplistic, though it seemed to fall only to me (so far as I was able) and my esteemed colleague Michael Brooks to point that out in our reviews.

It seems, then, increasingly to be the job of science writers and critics, like Angela and Michael, to hold the “specialists” to account – and not vice versa.

I could nobly declare that I decline to adopt such a tactic to sell my own books. But the truth is that I couldn’t do it even if I wanted to. My instincts are too set against it. For one thing, it would cause me too much discomfort, even pain, to knowingly ignore or cherry-pick historical or scientific facts (which isn’t to say that I will sometimes get them wrong), or to decline to enter areas of enquiry that might dilute a catchy thesis. But perhaps even more importantly, I would find simplistic narratives and theses to be just a bit too boring to sustain me through a book project. What interests me is not winning some constructed argument but exploring ideas – including the fascinating ideas in Enlightenment Now and Blueprint.

Wednesday, October 31, 2018

Musical illusions

Here's the English version of my column on music cognition for the current issue of the Italian science magazine Sapere.

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“In studying [optical] illusions”, writes Kathryn Schulz in her book Being Wrong, “scientists aren’t learning how our visual system fails. They are learning how it works.” What Schulz means is that normal visual processing is typically a matter of integrating confusing information into a plausible story that lets us navigate the world. Colour constancy is a good example: the brain “corrects” for variations in brightness so that objects don’t appear to change hue as the lighting conditions alter. The famous “checkerboard shadow” illusion devised by vision scientist Edward Adelson fools this automatic recalibration of perception.


Adelson’s checkerboard illusion. The squares A and B are the same shade of grey.

In this regard as in many others, auditory perception mirrors the visual. The brain often rearranges what we hear to create something that “makes more sense” – with the same potential for creating illusions. Psychologist of music Diana Deutsch has delved deeply into the subject of musical illusions, some of which are presented on a CD released by Philomel in 1995. Several of these have to be heard through stereo headphones: they deliver different pitches to the left and right ears, which the brain reassigns to create coherence. For example, in the “scale illusion” the notes of two simultaneous scales – one ascending, one descending – are sent alternately to each ear. But what one hears is a much simpler pattern: an ascending scale in one ear, descending in the other. Here the brain is choosing to perceive the more likely pattern, even though it’s wrong.

Another example reveals the limitations of pitch perception. A familiar tune (Yankee Doodle) is played with each note assigned a random octave. It sounds incomprehensible. The test shows that, in deciphering melody, we attend not so much to absolute pitch class (a C or D, say) as to relative pitch: how big pitch jumps are between successive notes. Arnold Schoenberg’s twelve-tone serialism ignored this, which is why the persistence of his “tone rows” is often inaudible.

Perhaps the strangest thing about optical illusions is that we enjoy them, even if – indeed, because – we find them perplexing. Instead of being upset by the brain’s inability to “get it right”, we are apt to laugh – not a common response to wrongness, although it’s actually how a lot of comedy works. You might, then, expect to find musical illusions put to pleasurable use in music, especially by jokers like Mozart. But they are rather rare, maybe because we simply won’t notice them unless we see the score. Something like the scale illusion is used, however, in the second movement of Rachmaninov’s Second Suite for Two Pianos, where two sets of seesawing notes on each piano are heard as two sets of single repeated notes. It seems likely that Rachmaninov (not noted for jocularity) wasn’t just having fun – it’s merely easier to play these rapid quavers using pitch jumps rather than on the same note.

Monday, October 29, 2018

Why brief answers are sometimes not enough

I reviewed Stephen Hawking's last book Brief Answers to the Big Questions for New Scientist, but it needed shortening and, in the print version, didn't come out as I'd intended. Here's the original.

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Most people as famous as Stephen Hawking have their character interrogated with forensic intimacy. But Hawking’s personality was in its way as insulated as the Queen’s, impermeably fortified by the role allotted to him. There’s a hint in Brief Answers that he knew this: “I fit the stereotype of a disabled genius”, he writes. Unworldly intelligence, a wry sense of humour, and tremendous resilience against adversity: that seemed to suffice for the celebrity in the wheelchair with the computerized voice (itself another part of the armour, of course).

It made me uneasy though. The public Hawking was that stereotype, and while it was delightful to see how he demolished the does-he-take-sugar laziness that links physical with mental disability, he did so only by taking matters to the other extreme ("such a mind in such a body!"). It perhaps suited Hawking that the media were content with the cliché – he didn’t give much impression of caring for the touchy-feely. (Eddie Redmayne, who played Hawking in the 2014 biopic The Theory of Everything, reminds us in his foreword that the physicist would have preferred the film to have “more physics and fewer feelings”.) But his story suggests we still have some way to go in integrating people with disabilities into able-bodied society.

I approached this book, a collection of Hawking’s later essays on “big questions”, with some trepidation. You know you won’t go wrong with the cosmology, relativity and quantum mechanics, but in other areas, even within science, it’s touch and go. The scientific essays supply a series of now-familiar Greatest Hits: his work with Roger Penrose on gravitational singularities and their relation to the Big Bang; his realization that black holes will emit energy (Hawking radiation) from their event horizons; his speculations about the origin of the universe in a chance quantum fluctuation; the debate – still unresolved – about whether black holes destroy information. Hawking, as Kip Thorne reminds us in his introduction, helped to integrate several of the central concepts of physics: general relativity, quantum mechanics, thermodynamics and information theory. It’s a phenomenal body of work.

Sometimes there’s a plainness to his prose that can be touching even while it sounds like an anodyne self-help manual: “Be brave, be curious, be determined, overcome the odds. It can be done.” Who would argue with Hawking’s right to that sentiment? His plea for the importance of inspirational teaching, his concerns about climate change and environmental degradation, his contempt for Trump and the regressive aspects of Brexit, and (albeit not here) his championing of the NHS, sometimes made you glad to have Hawking on your side. People listened.

A common danger with collections of this kind is repetition, which the editors have been curiously unconcerned to avoid. But the recurring and familiar passages are in themselves quite telling, for they show Hawking curating his image: the boy who was always taking things apart but not always managing to put them back together again, the man who told us to “look up at the stars and no down at your feet.”

There’s no doubt that Hawking cared passionately about the future of humankind and the potential of science to improve it. His advocacy resembles the old-fashioned boosterism into which H. G. Wells often strayed in later life, tempered like Wells by an awareness of the destructive potential of technologies in malicious or plain foolish hands. But what are Hawking’s resources for developing that agenda? One of the most striking features of this book is the lack of extra-curricular references – to art, music, philosophy, literature, say. This would not matter so much (though it’s a bit odd) if it were not that the scope of some of pieces exposes these gaps painfully.

Beginning an essay called “Is there a God” by saying that “people will always cling to religion, because it gives comfort, and they do not trust or understand science” tells you pretty much what to expect from it, and you’d not be wrong. God, as no theologian said ever, is all about explaining the origin of the universe. And most people, Hawking tells us, define God as “a human-like being, with whom one can have a personal relationship.” I suspect “most people’s” views of what a molecule or light is would bear similarly scant resemblance to what well-informed folks say on the matter, but I doubt Hawking would give those views precedence.

As for history, try this: “People might well have argued that it was a waste of money to send Columbus on a wild goose chase. Yet the discovery of the New World made a profound difference to the Old. Just think, we wouldn’t have had the Big Mac or KFC.” The lame joke might have been just about tolerable if one didn’t sense it is there because Hawking could think of nothing to put in its place. This remark, as you might guess, is part of a defense of human space exploration, during which Hawking demonstrates no more inclination to probe the real reasons for the space race in the 1960s than he does to examine what Columbus was all about. He feels that the human race has no future if we don’t colonize space, although it isn’t clear why his generally dim view of our self-destructive idiocies becomes so rosy once we are on other worlds. Maybe the answer lies with the fact that here, as elsewhere, his main point of reference is Star Trek. But I suspect he knew he was preaching to the converted, so that mere assertion (“We have no other option”) was all he needed in lieu of argument.

There’s a glib insouciance to some of the other scientific speculations too. “If there is intelligent life elsewhere”, he writes, “it must be a very long way away otherwise it would have visited earth by now. And I think we would’ve known if we had been visited; it would be like the film Independence Day.” Assertion again replaces explanation in Hawking’s assumption apropos artificial intelligence that the human brain is just like a computer, as if this were not hotly disputed among neuroscientists. Here too, his vision seems mainly informed by the science fiction within easiest reach: his fears for the dangers of AI conjure up the Terminator series’ Skynet and tropes of supercomputers declaring themselves God and fusing the plug. Science fiction has plenty to tell us about our fears of the present, but probably rather less about the realities of the future.

It is best, too, not to rely on Hawking’s history of science, which for example parrots the myth of Max Planck postulating the quantum to avoid the ‘ultraviolet catastrophe’ of blackbody radiation. (Planck did not mention it.) Don’t expect more than the usual clichés: here comes Feynman, playing the bongos in a strip joint (what a guy!), there goes Einstein riding on a light wave.

This is all, in a sense, so very unfair. Hawking was a great scientist who had a remarkable life, but in another universe without motor neurone disease (well, he did like the Many Worlds interpretation of quantum mechanics) we’d have no reason to confer such authority on his thoughts about all and sundry, or to notice or care that he entered the peculiar time-warp that is Stringfellows “gentlemen’s club”. We would not deny him the right to his ordinariness, and we would see his occasional brash arrogance and egotism for no more or less than it is.

There’s every reason to believe that Hawking enjoyed his fame, and that’s a cheering thought. The Hawking phenomenon is our problem, not his. He likes to remind us that he was born on the same date that Galileo died, but it’s Brecht’s Galileo that comes to mind here: to paraphrase, unhappy is the land that needs a guru.

Thursday, September 13, 2018

The "dark woman of DNA" goes missing again

There’s a curious incident that took place at the excellent "Schrödinger at 75: The Future of Life" meeting in Dublin last week that I’ve been pondering ever since.

One of the eminent attendees was James Watson, who was, naturally, present at the conference dinner. And one of the movers behind the meeting gave an impromptu (so it seemed) speech that acknowledged Watson’s work with Crick and its connection to Schrödinger’s “aperiodic crystal.” Fair enough.

Then he added that he wanted to recognize also the contribution of the “third man” of DNA, Maurice Wilkins – and who could cavil at that, given Wilkins’ Dublin roots? Wilkins, after all, was another physicist-turned-biologist who credited Schrödinger’s book What Is Life? as an important influence.

I imagined at this stage we might get a nod to the “fourth person” of DNA Rosalind Franklin, whose role was also central but was of course for some years under-recognized. But no. Instead the speaker spoke of how it was when Wilkins showed Watson his X-ray photo of DNA that Watson became convinced crystallography could crack the structure.

You could hear a ripple go around the dining hall. Wilkins’ photo?! Wasn’t it Franklin’s photo – Photo 51 – that provided Watson and Crick with the crucial part of the puzzle?

Well, yes and no. It doesn’t seem too clear who actually took Photo 51, and it seems more likely to have been Franklin’s student Ray Gosling. Neither is it completely clear that this photo was quite so pivotal to Watson and Crick’s success. Neither, indeed, is it really the case that Wilkins did something terribly unethical in showing Watson the photo (which was in any event from the Franklin-Gosling effort), given that it had already been publicly displayed previously. Matthew Cobb examines this part of the story carefully and thoroughly in his book Life’s Greatest Secret (see also here and here).

But nevertheless. Watson’s appalling treatment of Franklin, the controversy about Photo 51, and the sad fact that Franklin died before a Nobel became a possibility, are all so well known that it seemed bizarre, to the point of confrontational, to make no mention of Franklin at all in this context, and right in front of Watson himself to boot.

I figured that the attribution of “the photo” to Wilkins was so peculiar that it could only have another explanation than error or denial. I don’t know the details of the story well enough, but I told myself that the speaker must be referring to some other, earlier occasion when Wilkins had shown Watson more preliminary crystallographic work of his own that persuaded Watson this was an avenue worth pursuing.

And perhaps that is true – I simply don’t know. But if so, to refer to it in this way, when everyone is going to think of the notorious Photo 51 incident, is at best perverse and at worst a deliberate provocation. Even Adam Rutherford, sitting next to me, who knows much more about the story of DNA than I or most other people do, was confused by what he could possibly have meant.

Well, with Franklin’s name still conspicuous by its absence, Watson stood up to take a bow, which prompts me to make a request of scientific meeting and dinner organizers. Please do your attendees the favour of not forcing them to have to decide whether to reluctantly applaud Watson or join the embarrassed cohort of those who feel they can no longer do so in good conscience.

Friday, September 07, 2018

What Is Life? Schrödinger at 75

The conference “Schrödinger at 75: The Future of Life” in Dublin, from which I’m now returning, was a fabulous event, packed with good talks equally from eminent folks (including several Nobel laureates) and young rising stars. Ostensibly an exploration of the legacy of Erwin Schrödinger’s influential 1944 book What Is Life?, based on the lectures he gave 75 years ago as director of physical sciences at the Dublin Institute for Advanced Study (on which, more here), it was in fact largely a wonderful excuse to get a bunch of very smart people in the same hall to talk about many areas of the life (and chemical) sciences today and to speculate about what the future holds for them. I think I took away something interesting from every talk.

There was of course much dutiful nodding towards Schrödinger’s book, and also to some of his writing elsewhere, especially his essays in Mind and Matter (1958), where he offered some speculations about mind and consciousness (about half of the speakers worked on aspects of brain, mind and cognition). This didn’t seem merely tokenistic to me – I felt that all the speakers who mentioned Schrödinger had a genuine respect for his ideas. This is all the more interesting given that, as I say in my Nature piece, there wasn’t in some ways a great deal that was truly new and productive of further research in the book. Of course, what gets mentioned most is Schrödinger’s reference to a “code-script” that governs life and which is inherited, and his suggestion that this is encoded in the chromosomes as an “aperiodic crystal”. That image certainly resonated with Francis Crick, who wrote to Schrödinger in 1953 to tell him so.



But the idea of a “code”, as well as the notion that it could be replicated in a manner reminiscent of the ‘templating’ of structure in a crystal, were not really new. It seems rather to be something about the way Schrödinger expressed this idea that mattered, and indeed I can see why: his book is beautifully written, achieving persuasive force without seeming like the imposition of an arrogant physicist.

All of this I enjoyed. But what I missed was a historical presentation that could have put these tributes to What Is Life? in context. There was, for instance, a sense of unease about Schrödinger’s references to “order” and “organization”. What exactly was he getting at here? One suggestion was that “order” here was standing in for that crucial missing word: “information”. But this isn’t really true. Schrödinger’s “code-script” was presented as the means by which an organism’s “organization” is maintained, although quite how it does so he found wholly mysterious, even if the inter-generational transmission of the script by the “aperiodic crystal” was far less so.

What we need to know here is that “organization” had become a biological power-word, a symbol of what it was about living systems that distinguishes them from non-living. In the early nineteenth century this unique property of life was conferred by élan vital in the formulation of vitalism. As vitalism waned, it had to become something more tangible and physical. Some believed, like Thomas Henry Huxley, that the key was a special chemical composition, which made up the stuff of “protoplasm”, the primal living substance from which all life was descended. But as the chemical complexity and heterogeneity of living matter became apparent from the work of late nineteenth-century physiologists, and as the cell came to be seen as the fundamental unit of life, the idea arose that life was distinguished by some peculiar state of “organization” below the level that microscopes could resolve. There were a few tantalizing glimpses of this subcellular organization, for example in the stained chromosome fibres and organelles like the nucleus and mitochondria. These were, however, nothing but blurry blobs, offering no real clue about how their (presumably) molecular nature gave them the apparent agency that distinguished life.

And so, as Andrew Reynolds has shown, “order” and “organization” served a role that was barely more than metaphorical, patching over an ignorance about “what is life”. There’s nothing deplorable about that; it’s the kind of thing science must do all the time, giving a name to an absence of understanding so that it can be contained and built into contingent theories. But for Schrödinger to still be using it in the 1940s shows how his biological reading was rather archaic, for by that stage it had already become apparent that cell physiology relies on enzyme action, and crystallographers like J. Desmond Bernal and Bill Astbury were beginning to apply X-ray crystallography to these proteins to understand their structure. Sure, the origins and nature of the “organization” that cells seemed to exhibit were still pretty obscure, but it was getting less necessary to invoke that nebulous concept.

There were also suggestions at the Dublin meeting that Schrödinger’s “order” was what he meant with his talk of “negative entropy”. There’s some justification to think that, but Schrödinger wasn’t just thinking about how cells prevent their “organization” from falling into entropic disarray. He was puzzled by how this organization could exist in the first place. I don’t think one can really understand his discussion of order and entropy in What Is Life? unless one recognizes that many physical scientists in the early twentieth century considered the molecular world to be fundamentally random. It seems remarkable to me that no accounts of What Is Life? that I have seen refer to Schrodinger’s 1944 essay in Nature on “The Statistical Law in Nature”, where it is almost as if Schrödinger is telling us: ‘this is what I’m thinking about in my book’. The article is a paean to Ludwig Boltzmann, whose influence Schrödinger felt strongly in his early years at Vienna. Schrödinger seems to assert here that there are no laws in nature that do not rely on the statistical averaging over the behaviours of countless microscopic particles. It would have seemed all but meaningless then to suppose that one could speak about law-like, deterministic behaviour at the level of individual molecules, and quantum mechanics had seemed only to confirm this. That is what puzzled Schrödinger so much about the apparent persistence of phenotypic traits that seemed necessarily to arise from the specific details of genes at the molecular scale.

As a consequence, What Is Life? reads a little weirdly to chemists today, or indeed even by the 1950s, to whom the notion that a complex molecule can adopt and sustain a particular structure even in the face of thermal fluctuations seemed unproblematic. Schrödinger’s invocation of quantum mechanics to explain this phenomenon looks rather laboured now, and is quite possibly a part of what irritated Linus Pauling and Max Perutz about the book. It’s also why Schrödinger seems so keen to cement the structure of the gene in place as a “solid”, rather than simply regarding it as a large molecule carrying a linear code.

And what about that code itself? This wasn’t interrogated at the meeting, which was a shame. Indeed, it was sometimes still attributed by speakers the all-mighty agency that Schrödinger himself gave it. It rather astonishes me to see how the claim that the genome contains “all the information you need to make the organism” raises no eyebrows. What surprises me is that scientists are typically a rather sceptical crowd, and demand evidence to support the claims they make. But there is, to my knowledge, no evidence whatsoever that one can make even the simplest organism, let alone a human, from the information contained in the genome. Oh, but surely you can? You can (in principle, and now in some cases in practice) just make the genome from scratch, put it in a cell, and off it goes… Wait. Put it in a cell? So you need a cell to actually enact the “code-script”? Well sure, but the cell goes without saying, right?

Metaphors in biology are always imperfect and often treacherous, but I think this one (a simile, really) has some mileage: saying that the genome is the complete blueprint for an organism is a bit like saying that the Oxford English Dictionary is a blueprint for King Lear. It’s all in there, right? Ok, there’s a lot in there that you don’t need for Lear, but then there’s a lot of junk in the genome too (perhaps!). Sure, to get Lear out of the OED you need to feed the words into William Shakespeare, but Shakespeare goes without saying, right?

For a human, it’s still more complicated. Human cells can of course replicate in a culture medium, but none has ever replicated into an embryo, let alone a person. What they can do – what some induced stem cells can do – is proliferate into an embryoid, an organoid with embryo-like structures. But that won’t make a human. For that, you need not only a cell but a uterus. It’s rather like saying, so the text of King Lear has “all the information” – and then giving it to, say, a Chinese factory worker in Lanzhou. Well OK, so to actually enact Lear in a meaningful way it has to be read by someone who reads English – or translated… But come on, the English goes without saying…

Once we start talking in terms of the information needed to make an organism, though, quite what’s in the genome becomes far less clear. Indeed, we know for sure that maternal factors supply some vital information for the early development of a fertilized egg. And the self-organizing abilities of cells can only create an organism in the right context: every cell needs the right signals from its environment for the whole to assemble properly. Genes somehow encode neurons, but neurons don’t develop properly if they don’t get stimuli from their environment during a critical period.

Are these environmental signals and context then a part of the information needed to make an organism “as nature [meaning evolution, I guess] intends”? Is an understanding of English a part of the information needed for King Lear to be anything more than marks on paper?

Evidently this is an issue of how “information” acquires meaning, which of course was notoriously what Shannon left out of his information theory. And that is why information in Shannon’s sense is greatest when the Shannon entropy is greatest. Periodic solids have rather low entropy. What is needed in biology, then, is a theory for where meaningful information comes from and how it gives rise to causal flows. There’s no doubt that lots of meaningful information is encoded in the genome that contributes to how organisms are built and how they function. But when we say that “the genome contains all the information needed to build an organism”, we are dealing with ill-defined terms. What I solely missed at this meeting was a presentation about how a theory of biological information can be developed, and how to define and measure “meaning” within that theory. Daniel Dennett acknowledged this lacuna in his keynote address, saying that understanding “semantic information” as opposed to Shannon information is still “work in progress”.

A close reading of Schrödinger starts us in that direction too, and is a part of his legacy.

Monday, August 27, 2018

Don't just count qubits

The rapid advances in quantum computing as a technology with real applications are reflected in the increases in the number of qubits these devices have available for computation. In 1998, laboratory prototypes could boast just two: enough for a proof of principle but little more. Today that figure has risen to 72 in the latest device reported by Google. Given that the number of states available in principle to systems of N qubits is 2^N, this is an enormous difference. The ability to hold this number of qubits in entangled states involves a herculean feat of quantum engineering.

It’s not surprising, then, that media reports tend to focus on the number of qubits a quantum computer has at its disposal as the figure of merit. The qubit count is also commonly regarded as the determinant of the machine’s capabilities, most famously with the widely repeated claim that 50 qubits marks the threshold of “quantum supremacy”, when a quantum computer becomes capable of things to all intents and purposes impossible for classical devices.

The problem is that this is all misleading. What a quantum computer can and can’t accomplish depends on many things, of which the qubit count is just one. For one thing, the quality of the qubits is critical: how noisy they are, and how likely to incur errors. There is also the question of their heterogeneity. Qubits manufactured from superconducting circuits will generally differ in their precise characteristics and performance, whereas quantum computers that use trapped-ion qubits benefit from having them all identical. And because qubits can only be kept coherent for short times before quantum decoherence scrambles them, how fast they can be switched can determine how many logic operations you can perform in the time available. The power of the device then depends also on the number of gate operations your algorithm needs: its so-called depth.

There is also the question of connectivity: does every qubit couple with every other, or are they for instance coupled only to two neighbours in a linear array?

The performance of a quantum computer therefore needs a better figure of merit than a crude counting of qubits. Researchers at IBM have suggested one, which they call the “quantum volume” – an attempt to fold all of these features into a single number. And this isn’t, then, a way of evaluating which of two devices “performs better”, but quantifies the power of a particular computation. Device performance will depend on what you’re asking it to do. Particular architectures and hardware will work well for some tasks than for others (see here).

As a result, a media tendency to present quantum computation as a competition between rivals – IBM vs Google, superconducting-qubits vs trapped ions – does the field no favours. Of course one can’t deny that competitiveness exists, as well as a degree of commercial secrecy – this is a business with huge stakes, after all. But no one expects any overall “winner” to be anointed. It’s unfortunate, then, that this is how things looks if we judge from the “qubit counter” created by MIT Tech Review. As a rough-and-ready timeline of how the applied tech of the field is evolving, this might be just about defensible. But some fear that this sort of presentation does more harm than good, and we should certainly not see it as a guide to who is currently “in the lead”.

Friday, June 08, 2018

Myths of Copenhagen

Discussing the Copenhagen interpretation of quantum mechanics with Adam Becker and Jim Baggott makes me think it would be worthwhile setting down how I see it. I don’t claim that this is necessarily the “right” way to look at Copenhagen (there probably isn’t a right way), and I’m conscious that what Bohr wrote and said is often hard to fathom – not, I think, because his thinking was vague, but because he struggled to express it through the limited medium of language. Many people have pored over Bohr’s words more closely than I have, and they might find different interpretations. So if anyone takes issue with what I say here, please do tell me.

Part of the problem too, as Adam said (and reiterates in his excellent new book What is Real?, is that there isn’t really a “Copenhagen interpretation”. I think James Cushing makes a good case that it was largely a retrospective invention of Heisenberg’s, quite possibly as an attempt to rehabilitate himself into the physics community after the war. As I say in Beyond Weird, my feeling is that when we talk about “Copenhagen”, we ought really to stick as close as we can to Bohr – not just for consistency but also because he was the most careful of the Copenhagenist thinkers.

It’s perhaps for this reason too that I think there are misconceptions about the Copenhagen interpretation. The first is that it denies any reality beyond what we can measure: that it is anti-realist. I see no reason to think this. People might read that into Bohr’s famous words: “There is no quantum world. There is only an abstract quantum physical description.” But it seems to me that the meaning here is quite clear: quantum mechanics does not describe a physical reality. We cannot mine it to discover “bits of the world”, nor “histories of the world”. Quantum mechanics is the formal apparatus that allows us to make predictions about the world. There is nothing in that formulation, however, that denies the existence of some underlying stratum in which phenomena take place that produce the outcomes quantum mechanics enables us to predict.

Indeed, what Bohr goes on to say makes this perfectly clear: “It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.” (Here you can see the influence of Kant on Bohr, who read him.) Here Bohr explicitly acknowledges the existence of “nature” – an underlying reality – but doesn’t think we can get at it, beyond what we can observe.

This is what I like about Copenhagen. I don’t think that Bohr is necessarily right to abandon a quest to probe beneath the theory’s capacity to predict, but I think he is right to caution that nothing in quantum mechanics obviously permits us to make assumptions about that. Once we accept the Born rule, which makes the wavefunction a probability density distribution, we are forced to recognize that.

Here’s the next fallacy about the Copenhagen interpretation: that it insists classical physics, such as governs measuring apparatus, works according to fundamentally different rules from quantum physics, and we just have to accept that sharp division.

Again, I understand why it looks as though Bohr might be saying that. But what he’s really saying is that measurements exist only in the classical realm. Only there can we claim definitive knowledge of some quantum state of affairs – what the position of an electron “is”, say. This split, then, is epistemic: knowledge is classical (because we are).

Bohr didn’t see any prospect of that ever being otherwise. What’s often forgotten is how absolute the distinction seemed in Bohr’s day between the atomic/microscopic and the macroscopic. Schrödinger, who was of course no Copenhagenist, made that clear in What Is Life?, which expresses not the slightest notion that we could ever see individual molecules and follow their behaviour. To him, as to Bohr, we must describe the microscopic world in necessarily statistical terms, and it would have seemed absurd to imagine we would ever point to this or that molecule.

Bohr’s comments about the quantum/classical divide reflect this mindset. It’s a great shame he hasn’t been around to see it dissolve – to see us probe the mesoscale and even manipulate single atoms and photons. It would have been great to know what he would have made of it.

But I don’t believe there is any reason to suppose that, as is sometimes said, he felt that quantum mechanics just had to “stop working” at some particular scale, and classical physics take over. And of course today we have absolutely no reason to suppose that happens. On the contrary, the theory of decoherence (pioneered by the late Dieter Zeh) can go an awfully long way to deconstructing and demystifying measurement. It’s enabled us to chip away at Bohr’s overly pessimistic epistemological quantum-classical divide, both theoretically and experimentally, and understand a great deal about how classical rules emerge from quantum. Some think it has in fact pretty much solved the “measurement problem”, but I think that’s too optimistic, for the reasons below.

But I don’t see anything in those developments that conflicts with Copenhagen. After all, one of the pioneers of such developments, Anton Zeilinger, would describe himself (I’m reliably told) as basically a Copenhagenist. Some will object to this that Bohr was so vague that his ideas can be made to fit anything. But I believe that, in this much at least, apparent conflicts with work on decoherence come from not attending carefully enough to what Bohr said. (I think Henrik Zinkernagel’s discussions of “what Bohr said” are useful here and here.)

I think that in fact these recent developments have helped to refine Bohr’s picture until we can see more clearly what it really boils down to. Bohr saw measurement as an irreversible process, in the sense that once you had classical knowledge about an outcome, that outcome could not be undone. From the perspective of decoherence, this is now viewed in terms that sound a little like the Second Law: measurement entails the entanglement of quantum object and environment, which, as it proceeds and spreads, becomes for all practical purposes irreversible because you can’t hope to untangle it again. (We know that in some special cases where you can keep track, recoherence is possible, much as it is possible in principle to “undo” the Second Law if you keep track of all the interactions and collisions.)

This decoherence remains a “fully quantum” process, even while we can see how it gives rise to classical-like behaviour (via Zurek’s quantum Darwinism, for example). But what the theory can’t then do, as Roland Omnès has pointed out, is explain uniqueness of outcomes: why only one particular outcome is (classically) observed. In my view, that is the right way to put into more specific and updated language what Bohr was driving at with his insistence on the classicality of measurement. Omnès is content to posit uniqueness of outcomes as an axiom: he thinks we have a complete theory of measurement that amounts to “decoherence + uniqueness”. The Everett interpretation, of course, ditches uniqueness, on the grounds of “why add an extra, arbitrary axiom?” To my mind, and for the reasons explained in my book, I think this leads to a “cognitive instability”, to purloin Sean Carroll’s useful phrase, in our ability to explain the world. So the incoherence that Adam sees in Copenhagen, I see in the Everett view (albeit for different reasons).

But this then is the value I see in Copenhagen: if we stick with it through the theory of decoherence, it takes us to the crux of the matter: the part it just can’t explain, which is uniqueness of outcomes. And by that I mean (irreversible) uniqueness of our knowledge – better known as facts. What the Copenhagenists called collapse or reduction of the wavefunction boils down to the emergence of facts about the world. And because I think they – at least, Bohr – always saw wavefunction collapse in epistemic terms, there is a consistency to this. So Copenhagen doesn’t solve the problem, but it leads us to the right question (indeed, the question that confronts the Everettian view too).

One might say that the Bohmian interpretation solves that issue, because it is a realist model: the facts are there all along, albeit hidden from us. I can see the attraction of that. My problem with it is that the solution comes by fiat – one puts in the hidden facts from the outset, and then explains all the potential problems with that by fiat too: by devising a form of nonlocality that does everything you need it to, without any real physical basis, and insisting that this type of nonlocality just – well, just is. It is ingenious, and sometimes useful, but it doesn’t seem to me that you satisfactorily solve a problem by building the solution into the axioms. I don’t understand the Bohmian model well enough to know how it deals with issues of contextuality and the apparent “non-universality of facts” (as this paper by Caslav Brukner points out), but on the face of it those seem to pose problems for a realist viewpoint too.

It seems to me that a currently very fruitful way to approach quantum mechanics is to think about the issue of why the answers the world gives us seem to depend on the questions we ask (à la John Wheeler’s “20 Questions” analogy). And I feel that Bohr helps point us in that direction, and without any need to suppose some mystical “effect of consciousness on physical reality”. He didn’t have all the answers – but we do him no favours by misrepresenting his questions. A tyrannical imposition of the Copenhagen position is bad for quantum mechanics, but Copenhagen itself is not the problem.