Terry Pratchett was one, if not my all time, favorite author. Luckily for me, he was also one of the most prolific ones, creating an incredible rich, hilarious yet endearing universe, populated with the most unlikely yet humane characters. What drew me in, when I started reading his books twenty years ago, was his uncanny sense for the absurdities of modern physics. Therefor it shouldn’t really come as a surprise that he also wrote the best popular science book there is. To honor the man, and mark his passing, I republish this post from 2013.
Until recently, there was no competition if I were to be asked what popular science book I’d recommend to a non-physicist. It was always Terry Pratchett’s The Science of Discworld. It comes with a healthy dose of humor and makes no qualms about the fact that any popularized version of modern physics essentially boils down to “lies to children”.
ROTFL! Have you looked recently at beyond-Standard-Model theoretical physics? It’s a teetering tower of conjectures (which is not to say, of course, that that’s inherently bad, or that I can do better). However, one obvious difference is that the physicists don’t call them conjectures, as mathematicians or computer scientists would. Instead they call them amazing discoveries, striking dualities, remarkable coincidences, tantalizing hints … once again, lots of good PR lessons for us! 🙂
This was in a comment to his recent blog post where he has some fun with Nima Arkani-Hamed’s Amplituhedron. The latter is actually some of the more interesting results I have seen come out of mainstream theoretical physics, because it actually allows us to calculate something in a much more straightforward manner than before. That this is currently unfortunately restricted to the scope of an unphysical toy theory is all you need to know to understand how far current theoretical physics has ventured from actual verifiability by experiment.
For those who want to dig deeper and understand where to draw the line between current established physics and fairytale science, Jim Baggot’s book is a one stop shop. It is written in a very accessible manner and does a surprisingly good job in explaining what has been driving theoretical physics, without recourse to any math.
At the beginning, the author describes what prompted him to write the book: one too many of those fanciful produced science shows, with lots of CGI and dramatic music, that presents String theory as established fact. Catching himself yelling at the TV (I’ve been there), he decided to do something about it, and his book is the pleasant result. I am confident it will inoculate any alert reader to the pitfalls of fairytale science and equip him (or her) with a critical framework to ascertain what truthiness to assign to various theoretical physics conjectures (in popular science fare they are, of course, never referenced as such, as Scott correctly observed).
This isn’t the first book that addresses this issue. Peter Woit’s Not Even Wrong took it on, at a time when calling out String theory was a rather unpopular stance, but the timing for another book in this vein that addresses a broad lay public is excellent. As Baggott wrote his book, it was already apparent that CERN’s LHR did not pick up any signs in support of SUSY and string theory. Theorists have been long in denial about these elaborately constructed castles in the sky, but the reality seems to be slowly seeping in.
The point is that the scientific mechanism for self-correction needs to reassert itself. It’s not that SUSY and String theory didn’t produce some remarkable mathematical results. They just didn’t produce actual physics (although in unanticipated ways the Amplituhedron may get there). Trying to spin away this failure is doing science a massive disfavor. Let’s hope theoretical physicists take a cue from the the quantum computing theorists and clearly mark their conjectures. It’ll be a start.
Alternatively, they could always present the theory as it is done in this viral video. At least then it will be abundantly clear that this is more art than science (h/t Rolf D.):
Sonoluminescence is the name for a peculiar effect where cavitation in a liquid can be stimulated by sound waves to the point where the small gaseous bubbles implode so rapidly that plasma forms that produces a telltale light signal. The following video is a nice demonstration of the effect (full screen mode recommended):
Since there is plasma involved, the idea that this could be used as yet another means to accomplish fusion was first patented as early as 1982.
In itself, the phenomenon is remarkable enough, and not well understood, giving ample justification for basic research of the effect. After all, it is quite extraordinary that sound waves suffice to create such extreme conditions in a liquid.
But it is still quite a stretch to get from there to the necessary conditions for a fusion reaction. The nuclear energy barrier is orders of magnitudes larger than the energies that are involved in the chemical domain, let alone the typical energy density of sound waves. The following cartoon puts this nicely into perspective:
That is why to me this approach to fusion always seemed rather far fetched, and not very practical. So when a Science article about ten years ago claimed fusion evidence, I was skeptical, and wasn’t surprised that it was later contradicted by reports that portrayed the earlier results as ambiguous at best. I had no reason to question the Science reporting. I took the news at face value and paid little attention to this area of research until a recent report by Steven Krivit. He brings investigative journalism to the domain of science reporting and the results are not pretty:
The rebuttal to the original peer reviewed article first appeared on the Science blog without going through the usual review process.
Contrary to what was reported, the scientists undermining the original research did not work independently on reproducing the results but only performed auxiliary measurements on the same experimental set-up.
The detector they used was known to not be ideally suited to the neutron spectrum that was to be measured, and was too large to be ideally placed.
The criticism relied on an ad-hoc coincidence criteria for the photon and neutron genesis that ignored the multi-bubble cavitation design of the original experiment.
To add insult to injury, the Science journalist instrumental in causing this mess, the one who promoted the rebuttal without peer review, later went on to teach journalism.
A casual and cynical observer may wonder why Steven makes such a fuss about this. After all, American mainstream journalism outside the realm of science is also a rather poor and sordid affair. He-said-she-said reporting is equated with objectivity, and journalists are mostly reduced to being stenographers and water carriers of the political actors that they are supposed to cover (the few journalists who buck this trend I hold in the highest regard).
But there is one rather big and important difference: Journals such as Science are not just media that report to the public at large. Rather, they are the gatekeepers for what is accepted as scientific research, and must therefore be held to a higher standard. Research that doesn’t get published in peer reviewed journals may as well not exist (unless it is privately financed applied R&D, that can be immediately commercialized, and is therefore deliberately kept proprietary).
The more reputable a peer reviewed journal, the higher the impact (calculating the impact factor is a science in itself). But arguably, it is worse to get work published in a reputable journal just to have the results then demolished by the same outfit, especially if the deck is stacked against you.
To me, this story raises a lot of questions and drives home that investigative science journalism is sorely lacking and badly needed. Who else is there to guard the gatekeepers?
A logarithmic scale doesn’t have the appropriate visual impact to convey how extraordinarily cold 20mK is.
Any quantum computer using superconducting Josephson junctions will have to be operated at extremely low temperatures. The D-Wave machine, for instance, runs at about 20 mK, which is much colder than anything in nature (including deep space). A logarithmic scale like the chart to the right, while technically correct, doesn’t really do this justice. This animated onefrom D-Wave’s blog shows this much more drastically when scaled linearly (the first link goes to an SVG file that should play in all modern browsers, but it takes ten seconds to get started).
Given that D-Wave’s most prominent use case is the field of machine learning, a casual observer may be misled to think that the term “AI winter” refers to the propensity of artificial neural networks to blossom in this frigid environment. But what the term actually stands for is the brutal hype cycle that ravaged this field of computer science.
One of the original first casualties of the collapse of artificial intelligence research in 1969 was the ancestor of the kind of learning algorithms that are now often implemented on D-Wave’s machines. This incident is referred to as the XOR affair, and the story that circulates goes like this: “Marvin Minsky, being a proponent of structured AI, killed off the connectionism approach when he co-authored the now classic tome, Perceptrons. This was accomplished by mathematically proving that a single layer perceptron is so limited it cannot even be used (or trained for that matter) to emulate an XOR gate. Although this does not hold for multi-layer perceptrons, his word was taken as gospel, and smothered this promising field in its infancy.”
Marvin Minsky begs to differ, and argues that he of course knew about the capabilities of artificial neural networks with more than one layer, and that if anything, only the proof that working with local neurons comes at the cost of some universality should have had any bearing. It seems impossible to untangle the exact dynamics that led to this most unfortunate AI winter, yet in hindsight it seems completely misguided and avoidable, given that a learning algorithm (Backpropagation) that allowed for the efficient training of multi-layer perceptrons had already been published a year prior, but at the time it received very little attention.
The fact is, after Perceptrons was published, symbolic AI flourished and connectionism was almost dead for a decade. Given what the authors wrote in the forward to the revised 1989 edition, there is little doubt how Minsky felt about this:
“Some readers may be shocked to hear it said that little of significance has happened in this field [since the first edition twenty year earlier]. Have not perceptron-like networks under the new name connectionism – become a major subject of discussion at gatherings of psychologists and computer scientists? Has not there been a “connectionist revolution?” Certainly yes, in that there is a great deal of interest and discussion. Possibly yes, in the sense that discoveries have been made that may, in time, turn out to be of fundamental importance. But certainly no, in that there has been little clear-cut change in the conceptual basis of the field. The issues that give rise to excitement today seem much the same as those that were responsible for previous rounds of excitement. The issues that were then obscure remain obscure today because no one yet knows how to tell which of the present discoveries are fundamental and which are superficial. Our position remains what it was when we wrote the book: We believe this realm of work to be immensely important and rich, but we expect its growth to require a degree of critical analysis that its more romantic advocates have always been reluctant to pursue – perhaps because the spirit of connectionism seems itself to go somewhat against the grain of analytic rigor.” [Emphasis added by the blog author]
When fast-forwarding to 2013 and the reception that D-Wave receives from some academic quarters, this feels like deja-vu all over again. Geordie Rose, founder and current CTO of D-Wave, unabashedly muses about spiritual machines, although he doesn’t strike me as a particularly romantic fellow. But he is very interested in using his amazing hardware to make for better machine learning, very much in “the spirit of connectionism”. He published an excellent mini-series on this at D-Wave’s blog (part 1, 2, 3, 4, 5, 6, 7). It would be interesting to learn if Minsky was to find fault with the analytic rigor on display here (He is now 86 but I hope he is still going as strong as ten years ago when this TED talk was recorded).
So, if we cast Geordie in the role of the 21st century version of Frank Rosenblatt (the inventor of the original perceptron) then we surely must pick Scott Aaronson as the modern day version of Marvin Minsky. Only that the argument this time is not about AI, but how ‘quantum’ D-Wave’s device truly is. The argument feels very similar: On one side, the theoretical computer scientist, equipped with boat-loads of mathematical rigor, strongly prefers the gate model of quantum computing. On the other one, the pragmatist, whose focus is to build something usable within the constraints of what chip foundries can produce at this time.
But the ultimate irony, it seems, at least in Scott Aaronson’s mind, is that the AI winter is the ultimate parable of warning to make his case (as was pointed out by an anonymous poster to his blog). I.e. he thinks the D-Wave marketing hype can be equated to the over-promises of AI research in the past. Scott fears that if the company cannot deliver, the babe (I.e. Quantum Computing) will be thrown out with the bathwater, and so he blogged:
“I predict that the very same people now hyping D-Wave will turn around and—without the slightest acknowledgment of error on their part—declare that the entire field of quantum computing has now been unmasked as a mirage, a scam, and a chimera.”
A statement that of course didn’t go unchallenged in the comment section (Scott’s exemplary in allowing this kind of frankness on his blog).
I don’t pretend to have any deeper conclusion to draw from these observations, and will leave it at this sobering thought: While we expect science to be conducted in an eminently rational fashion, history gives ample examples of how the progress of science happens in fits and starts and is anything but rational.
Nature clearly favours hot fusion no matter how cold the light. The cold glow in this image stems from a Blue Giant that is believed to orbit a black hole in the Cygnus X-1 system.
If you lived through the eighties there are certain things you could not miss, and since this is a science blog I am of course not referring to fashion aberrations, like mullets and shoulder pads, but rather to what is widely regarded as one of the most notorious science scandals to date: Fleischmann and Pons Cold Fusion, the claim of tapping the ultimate energy source within a simple electrochemical cell.
This blog’s author’s photo proves that he lived through the eighties. Since this driver’s licence picture was taken the same year as the Fleischmann and Pons disaster, the half smile was all that I could muster.
For a short time it felt like humanity’s prayers to deliver us from fossil fuel had been answered (at least to those who believe in that sort of thing). Of course, paying the ever increasing price at the gas pump is a constant (painful) reminder that this euphoric moment at the end of eighties was but a short lived aberration. But back then it felt so real. After all, there already existed a well-known process that allowed for nuclear fusion at room temperature, catalyzed by the enigmatic muons. One of the first scientific articles that I read in English was on that phenomenon, and it was published just a couple of years earlier. So initial speculations abounded, that maybe muons in the cosmic background radiation could somehow help trigger the reported reaction (although there was no explanation given as to how this low muon flux density could possibly accomplish this). While my fringe blog focuses on the intrepid researchers who, despite the enormous blow back, still work on Fleischman Pons-style research, this post is about the former, the oft forgotten muon-catalyzed fusion.
It is a beautiful nuclear reaction, highlighting one of the most basic peculiarities of quantum mechanics: Quantum Tunnelling and Heisenberg uncertainty principle. Both of these are direct consequences of the manifest wave properties of matter at this scale. The former allows matter to seep into what should be impenetrable barriers, and the latter describes how a bound point particle is always “smeared out” over a volume – as if points are an abstraction that nature abhors. Last but not least, it showcases the mysterious muon, a particle that seems to be identical to electrons in every way but the mass and stability (about 200 times more mass and a pretty long half life of about 2 μs). Because it behaves just like a heavier twin of the electron, it can substitute the latter in atoms and molecules.
The Heisenberg uncertainty principle states that the product of momentum (mass times velocity) and position ‘certainty’ has a lower bound. Usually the term uncertainty is simply interpreted probabilistically in terms of the deviation of the expectation value. But this view, while formally entirely correct, obstructs the very real physical implication of trying to squeeze a particle into a small space, because the momentum uncertainty then becomes a very real physical effect of quantum matter. The particle’s velocity distribution will become ever broader, forcing the matter outwards and creating an orbital ‘cloud’ (e.g. specifically the spherical hydrogen s-orbital). There is really no good analogy in our everyday experience, they all sound silly: My version is that of a slippery soap in a spherical sink, the harder you try to grasp it the more powerful you send it flying. If you were to map all trajectories of the soap over time, you will find that on average it was anywhere in the sink with the probability decreasing towards the rim (that is unless you squeeze it so hard that it acquires enough speed to jump out of the sink – I guess that would be an analog to ionization). In the atomic and chemical realm, on the other hand, the very concept of a trajectory doesn’t hold up (unless you are dealing with Rydberg atoms). You may as well think of electron orbitals as charge distributions (as this is exactly how they behave in the chemical domain).
Because the momentum rather then the velocity enters into the equation, the orbitals for a heavier version of the electron will be considerably smaller, i.e. about 2oo times smaller for the muon, as this is the factor by which the particle’s velocity can be reduced in order to still get the same momentum. So muonic hydrogen is much smaller than the electron version. That’s already all that is needed to get fusion going, because if two heavy hydrogen nucleons are bound in a muonic μH2 molecule they are far too close for comfort. Usually the repellent force of the electrostatic Coulomb potential should be enough to keep them apart, but the quantum tunnel effect allows them to penetrate the ‘forbidden’ region. And at this distance, the probability that both nucleons occupy the same space becomes large enough to get measurable incidents of nuclear fusion i.e. μH2 → μHe.
The hydrogen used in the experimental realization is not the usual kind, but as with other fusion realizations, the heavier hydrogen isotopes deuterium and tritium are required, and since there is only one muon in the mix the d-t hydrogen is ionized. so that the equation looks more like this: (d-μ-t)+ → n + α (with the n indicating a fast neutron and the α a Helium-4 nucleus.)
The latter causes a lot of trouble as the muon ‘sticks’ to this alpha particle with a 1% chance (making it a muonic helium ion). If this happens, this muon is no longer available to catalyze more fusion events. This, in combination with the limited life time of the muons, and the ‘set-up’ required by the muons to bind to the hydrogen isotopes, is the limiting factor of this reaction.
Without a constant massive resupply of muons the reaction tempers off quickly. Despite decades of research this problem could never be surmounted. It takes pions to make muons, and the former are only produced in high energy particle collisions. This costs significantly more energy than the cold muon catalyzed fusion can recoup.
But there is one Australian company that claims that it has found a new, less costly way to make pions. They are certainly a very interesting ‘cold fusion’ start-up and at first glance seem far more credible than the outfits that my fringe blog covers. But on the other hand, this company treats their proprietary pion production process with a level of secrecy that is reminiscent of the worst players in the LENR world. I could not find any hint of how this process is supposed to work and why it supposedly can produce sufficient amounts of muons to make this commercially exploitable. (Pions could also be generated in two photon processes, but this would require even more input energy). So on second read the claims of Australian’s Star Scientific don’t really sound any less fantastic than the boasting of any other cold fusion outfit.
The current top political news of the day (Snowden leak) brings into sharp relief why encryption and the capabilities to break it receive so much attention.
It puts into context why a single algorithm (Shor’s) accounts for most of quantum computing’s notoriety and why quantum encryption receives so much funding.
Recently, Bennett and Riedel (BR) argued that thermodynamics is not essential in the Kirchhoff-law–Johnson-noise (KLJN) classical physical cryptographic exchange method in an effort to disprove the security of the KLJN scheme. They attempted to prove this by introducing a dissipation-free deterministic key exchange method with two batteries and two switches. In the present paper, we first show that BR’s scheme is unphysical and that some elements of its assumptions violate basic protocols of secure communication. Furthermore we crack the BR system with 100% success via passive attacks, in ten different ways, and demonstrate that the same cracking methods do not function for the KLJN scheme that employs Johnson noise to provide security underpinned by the Second Law of Thermodynamics. We also present a critical analysis of some other claims by BR; for example, we prove that their equations for describing zero security do not apply to the KLJN scheme. Finally we give mathematical security proofs for each of the attacks on the BR scheme and conclude that the information theoretic (unconditional) security of the KLJN method has not been successfully challenged.
The original post on this subject resulted in a high quality follow-up discussion on LinkedIn that I hope may get triggered again. After all, science is more fun as a spectator sport with well-informed running commentary.
Usually, I don’t write about personal matters on this blog. This is a biographical blog post I’d rather not have written this soon.
My father, before he met my mother, climbing the Cheops pyramid in Giza.
My father was born into what nowadays would be considered a very poor family. They lived in rural Franken (Franconia), a part of the state of Bavaria, an area set apart by the distinct dialect of its people that, while vaguely German, certainly doesn’t sound anything like Bavarian.
He was the ninth of eleven children. Being born during the short and darkest period of nationalistic megalomania, his mother was thus a nominee for the Cross of Honor of the German Mother. His father, by all accounts, bought hook, line, and sinker into the Nazi ideology, and thus little Adolf was named after the genocidal leader of Germany at that time. He would later often joke that his parents were prescient enough to chose ‘Konrad’ as his middle name, since Konrad Adenauer turned out to be the first chancellor of (West) Germany after the war. Yet he stubbornly refused to go by his middle name, since this wasn’t the name his mother used.
She must have been at the core of this large family, a simple, uneducated woman with, I imagine, a very big heart. Unlike my father’s father, who died before I was born, I got to meet her as a little boy, but back then I didn’t know what to make of her. She wore a big apron and smelled strange, of all sorts of food stuffs, and due to her dialect I couldn’t understand a word she was saying. All I remember is that she thought I was funny, and I made her laugh. I guess that counts for something. Later, her funeral would be the first I ever attended, but I was too young to really understand the significance then. My father insisted that she didn’t buy into the Nazi ideology like his father had, and told me that she remained a loyal customer of the Jewish peddler who came through the village (until he no longer did), her rationale simply being that he was even poorer than they.
It may be that this story resulted from a misremembered idealization of his mother, but there is one very good reason why I tend to believe this story, and that is the gentleness of his personality. I presume that this innate good naturedness must have been nurtured in his formative years in no small part by his mother’s example. It is as if he was incapable of thinking badly of people. This attitude, combined with his ability to listen very well, proved to be a great asset for his chosen profession, but it was also very much exploited by ‘businessmen’. As a distant cousin and fellow M.D. (of the Jewish and American branch of my family) once put it: Doctors are the equivalent of plankton in the food chain of the financial industry.
This is not to imply that he was naive, quite the contrary. He learned early not to blindly trust in authority, nor to expect that the world would always make sense. During the war, there weren’t enough priests to go around, but one of the French prisoners of war who was assigned to the area to work the fields happened to be a catholic chaplain. This prisoner was asked to read the mass on Sundays. All the villagers then bent their knees to this Frenchman, and he’d also take their confessions. Nonetheless, when back in the fields, some men treated him as badly (if not more so) than all the other PoWs. This absurdity made a deep impression on my father.
His older brothers survived the war, but one came back severely crippled, and after Germany was finally defeated, all bread winners of the family were out of a job. Most Germans in the immediate aftermath of the war struggled to put food on the table. Being in a rural area at least allowed them to live off the land to some extent, but there was no money for anything else. The kids would go barefoot most of the time, and every child had to work as much as possible to make due. My father’s job was to tend the geese. I guess one has to imagine it similarly bucolic as in this image.
To him it was an idyllic childhood, as he was too young to fully comprehend the fears and worries of the adults. But he recalled that without shoes the soles of his feet would grow so hard that when once he stepped on a bee he didn’t even notice the sting.
Nothing at the time would have indicated that he was to become a doctor, nor was this the intent of his parents.
He was sent to a Catholic school. The idea was that he should become a priest. Religion was important to his mother, and it probably was a grave disappointment when, despite donning the robes of the monastic school, he declared after graduation that he’d rather study science.
He never regretted it, telling me that he decided quite early, and had to pretend that the priesthood was for him in order to not jeopardize his education. He counted himself lucky to have figured this out quickly, especially when contemplating the emotional
upheaval that some of his peers went through who became priests, but then later had to resign after they fell in love.
He first enrolled in physics, but struggled with the math. It was when he changed to medical school that he finally found his true calling. By then the German economy was booming and the young republic could already afford to give scholarships and interest free loans to disenfranchised students. This didn’t cover all the costs of living, but well-paying jobs in manufacturing were aplenty those days, and working at the ball bearing plant in Schweinfurt between the terms allowed him to make ends meet.
After he passed the medical state exam, and before moving on to his medical internship, he and a fellow student decided that it was a good time to finally see some more of the world. They drove a VW beetle from Germany down to Spain, set off to North Africa at Gibraltar, and from there drove through Morocco, Algeria, Libya, Tunisia, and Egypt, where the above photo was taken. They completed the loop around the
Mediterranean sea through Israel, Lebanon, Syria, Turkey and then Greece. Being medical students, they didn’t really particularly plan for the trip, they just took their car and set out to drive the distance. They had no break-downs. I don’t know if they just got lucky or if the legendary reliability of the original beetle was as good as promised in the vintage ad to the right (German text is: “The VW runs, and runs and runs ….”).
There was no hostility to Westerners then, and also very little tourism. When they visited the ruins of Carthage in Libya they were the only visitors. At one point, they put up their tent on some private land. When they woke up in the morning they found the owner waiting, not to scold them, but rather to invite them to a hearty breakfast and tea, and this was well enough communicated despite the lack of a common language.
Given that my entire life the ongoing violence in the Middle East has been headline news, it is hard to fathom that such a tour was possible less than fifty years ago.
It wouldn’t be his last world travel, he also signed up to be ship’s surgeon for an ocean cargo vessel which took a three month tour to South America. This travel was complicated by the fact that he fell head-over-heels in love with the woman who would become my mother after having already signed up for the trip. On the crossing back to Europe he learned that my mother, a fellow M.D., had contracted hepatitis after accidentally pricking herself with a used needle. It is astounding how well he already knew her back then; He realized that no matter how sick she was, she’d insist on coming to the harbour to be there when he made landfall. So he gave a wrong date for his arrival to make sure she’d stay in the hospital. This white lie endeared him greatly to my mother’s parents, who quickly became convinced that he was the best husband she could ever hope for, especially as in this unemancipated time, they considered my mother ‘damaged goods’. She was divorced, with a little girl from her first marriage. Such circumstances required extraordinary measures to make this woman palatable to my father’s conservative, Catholic family. He managed to get the first marriage of my mother declared null and void by the Vatican, and so she became the rare Lutheran who got to enjoy two Catholic weddings.
Unlike most men of his era, he was happy to have found a woman who was his professional equal in all respects. Taking measure of her ambition, he only had one request: that she not specialize in his field, orthopaedics. Doing so would have inevitably lead to conflicts in second guessing each others diagnoses. So my mother turned to internal medicine.
They shared a common practice for their entire working life, and for their breed of doctor, that means until death parts them from their profession. Even after his death my mother intends to keep their practice open.
My hope is that the dedication to her work and patients will help her to cope with the enormity of her loss.
Practicing medicine often means fighting a losing battle. In the end my father benefited from the depth of his faith, which he kept despite his critical distance to the Catholic establishment (Hans Küng was his kind of theologian). He told me that he imagined his last days to be worse than what he experienced – although this was when the worst was yet to come, at that later point he couldn’t speak any more. But it was clear in his demeanor that he did not fear death, and he endured with inspiring grace, still enjoying every good moment that was to be.
In life and death he was a humble, yet extraordinarily great man. There are no bounds to my gratitude for having been so privileged to call this man my father.
Ever so often a piece of pop science writing pops up that stands out. It’s like a good bottle of wine, you want to savour it slowly, and the next day when you wake up with a slight hangover and realize that maybe it was a bit disagreeable, you are still content that you have some more of it in your cellar.
Penrose’s “The Emperor’s New Mind” falls into this category for me. Despite all of the author’s immense scientific sophistication, it felt like he fell into the trap that my very first physics prof put like this: “The difference between theologians and philosophers is that the former have to argue towards a certain end.” In the final analysis, I find, it was a religious text.
After an exhausting rekindling of the D-Wave melee on his blog, Scott Aaronson’s latest paper, “The Ghost in the Quantum Turing Machine”, is a welcome change of pace. Yet, given the subject matter I was mentally preparing for a similar experience as with Penrose, especially in light of the instant rejection that this paper received from some experts on Bayesian inference, such as Robert Tucci.
Scott’s analysis may be dismissed as Copenhagen Interpretation on steroids, but while the innate problems with this old QM workhorse are quite apparent, in the end I think it actually manages to yet again deliver a plausible result (despite some apparent absurdities along the way). The structure of the essay is quite clever, as Scott anticipates many objections that could be raised, and at times it almosts reads like a 21st century version of a Platonic dialog. I think he missed some issues, and I will revisit this in a later post, but overall I think the big picture holds, and it is well painted.
Scott has always been a good writer. His book “Quantum Computing since Democritus“
I find thoroughly enjoyable. Although unlike the Hitchhiker’s Guide to the Galaxy (the real thing, not the book) it still had to fit the dead tree format, and so there are gaps in the millennia of QC history covered. Scott had to pick and chose what’s most important to him in this story, and that means that the 495 complexity classes known to humanity these days get a fair share of attention. After all, he is a complexity theorist. Even to the best writer, making that part flow like honey will be difficult, but it gives an excellent window into how Scott approaches the subject. It also lays bare that the field is in similar dire straights as physics was, when the number of elementary particles exploded without much understanding of exactly what was going on. So for now, we are stuck with a complexity class zoo rather than an elementary particle one, waiting for some kind of standard. model that’ll impose order.
This latest, more contemplative paper is unburdened by this particular heavy load, yet takes on another one: The age old philosophical question of free will, which is very close to the question of consciousness and AI that Penrose pondered. It starts out with a beautifully written homage to Turing. The last piece of writing that resonated this strongly with me had an unapologetically religious sub-text (this blog entry penned by Kingsley Jones). So I was certain I was in for another Penrose moment.
The bait and switch that followed, to the much more decidable question of what minimal necessary resource nature needs to provide to make free will a valid concept, came as a pleasant surprise. All the more, as this question seems so obvious in hindsight, but apparently hasn’t been refined in this manner before.
It is a very good question, an important one, but for now your inclination toward or away from belief in this resource (which goes by the name Knightian uncertainty) is up to your religious leanings, and I don’t know if you actually have the freedom to make this choice.
Yet, just as D-Wave was mostly off the radar with regards to quantum computing, there is another Vancouver based high tech venture that could similarly upset fusion research.
The hot fusion plasma ball up in the sky, when compared to the general fusion challenge down here on earth, is really, really big; It generates an enormous amount of pressure at its core, creating the kind of critical density that assists in sustaining the fusion reaction. So just heating a plasma to the Sun’s core temperature (about 16 million K) will not suffice, we have to do about ten times more than that in order to compensate for the lack of gravitational pressure. It shouldn’t be surprising that designing a reactor chamber that can hold the hottest thing in our solar system poses a significant engineering challenge.
On the other hand, the idea of tackling the second parameter, the plasma’s pressure, in a controllable manner, was generally regarded as technically impossible (not counting NIF like implosion scenarios that more mimic the runaway implosion of a H-bomb, which is why they are interesting to the military).
This common wisdom held until General Fusion entered the fray and made the case that advances in electronics and process control opened up the possibility to tackle the density side of the fusion equation. And then they built this:
A device that would fit nicely into the engine room of a spaceship and not look out of place on a SciFi set.
This device is following the age-old engineering adage that if you want compression you use a piston, and if you want large compression you use a large piston which focuses all the energy into a tiny space. The trick is to be able to do this in such a precise fashion that you can coordinate it with the injection of fuel gas along a central axis, so that you can get a succession of pulsed fusion ignitions with each coordinated firing of the pneumatic pistons.
As with most fusion reactor schemes, the envisioned reactor will be fairly compact.
This device may be testing the limits of mechanical engineering, but if it can create the condition it aims for, then our current understanding of plasma and nuclear physics clearly indicates that it will result in fusion.
The interior of the reactor chamber will have to be cooled with liquid lead. Despite this high energy density, the overall footprint of just the reactor itself is fairly compact, no bigger than the typical dimensions of a commercial nuclear fission reactor. If this design pans out, these reactors could be used to retrofit existing nuclear power stations with a fusion core, converting them to a much cleaner energy source that does not come with the risk of accidentally triggering an uncontrollable nuclear chain-reaction.
The timeline for bringing this to the market is aggressive. If General Fusion delivers on it, there will be a commercial fusion offering available before ITER even opens its doors.
Given that the latter is not even attempting to deliver a commercial ready design yet, the company will be without competition (unless some of the other commercial fusion ventures such as LPP should beat them).
Fortunately, with this company it won’t be hard to decide when and if they manage to deliver on their promises (there won’t be any grounds for the kind of academic backlash that D-Wave has to endure). Unlike in the world of fringe science, where even the simple act of measuring (supposedly) substantial energy gain is obfuscated to the point of utter hilarity, once General Fusion achieves energy net gain, there will be little doubt that we entered the dawn of a new energy age.
Mongols knew that a horse was either dead or alive, but never in a state of superposition between the twain.
Kingsley Jones, an Australian theoretical physicist turned entrepreneur, recently introduced what he dubs Mongol physics, a bold undertaking to “fix” QM and QED.
The name is aptly chosen, because if he succeeds in this, most of academic physics will be as taken by surprise as Europe was when the Golden Horde arrived. After all, physics doesn’t perceive these theories as defective, despite the enduring confusion as to what QM interpretation makes the most sense.
Kingsley dubs Erwin Schrödinger “Mongul #1” and there is a good reason for this. Having just received my copy of his collected papers, the first thing I came across was this little gem that I include below. The fact that it reads just as relevant 60 years later speaks volumes. The only thing that has changed since then is that clever ways were found to deal with the runaway infinities in QED, so that accurate numbers could be forced out of it. Schrödinger knew better than to hinge any of his arguments on these major technical challenges at the time. Rather, the article details his discomfort with the Copenhagen interpretation based on very fundamental considerations. Makes me wonder how he’d feel about the fact that his cat in a box, that he made up to mock the status quo, entered popular culture as a supposedly valid illustration of quantum weirdness.
(Austrian copyright protection expires after 70 years, yet due to the fact that scans of the article are freely accessible at this University of Vienna site, I assume this text to be already placed in the public domain and hence free for online reproduction. Please note this is not a translation. Schrödinger was fluent in several languages and originally penned this in English)
THE MEANING OF WAVE MECHANICS
by Erwin Schrödinger (For the July Colloquium, Dublin 1952)
Louis de Broglie’s great theoretical discovery of the wave phenomenon associated with the electron was followed within a few years, on the one hand by incontrovertible experimental evidence (based on interference patterns) of the reality of the de Broglie waves (Davisson and Germer, G. P. Thomson), and on the other hand by a vast generalization of his original ideas, which embraces the entire domain of physics and chemistry, and may be said to hold the field today along the whole line, albeit not precisely in the way de Broglie and his early followers had intended.
For it must have given to de Broglie the same shock and disappointment as it gave to me, when we learnt that a sort of transcendental, almost psychical interpretation of the wave phenomenon had been put forward, which was very soon hailed by the majority of leading theorists as the only one reconcilable with experiments, and which has now become the orthodox creed, accepted by almost everybody, with a few notable exceptions. Our disappointment consisted in the following. We had believed. that the eigenfrequencies of the wave phenomenon, which were in exact numerical agreement with the, until then so called, energy levels, gave a rational understanding of the latter. We had confidence that the mysterious “fit and jerk theory” about the jump-like transition from one energy level to another was now ousted. Our wave equations could be expected to describe any changes of this kind as slow and actually describable processes. This hope was not informed by personal predilection for continuous description, but if anything, by the wish for any kind of description at all of these changes. It was a dire necessity. To produce a coherent train of light, waves- of 100 cm length and more, as is observed in fine spectral lines, takes a time comparable with the average interval between transitions. The transition must be coupled with the production of the wave train. Hence if one does not understand the transition, but only understands the “stationary states”, one understands nothing. For the emitting system is busy all the time in producing the trains of light waves, it has no time left to tarry in the cherished “stationary states”, except perhaps in the ground state.
Another disconcerting feature of the probability interpretation was and is that the wave function is deemed to change in two entirely distinct fashions; it is thought to be governed by the wave equation as long as no observer interferes with the system, but whenever an observer makes a measurement, it is deemed to change into an eigenfunction of that eigenvalue of the associated operator that he has measured. I know only of one timid attempt (J. von Neumann in his well known book) to put this “change by measurement” to the door of a perturbing operator introduced by the measurement, and thus to have it also controlled solely by the wave equation. But the idea was not pursued, partly because it seemed unnecessary to those who were prepared to swallow the orthodox tenet, partly because it could hardly be reconciled with it. For in many cases the alleged change involves an actio in distans, which would contradict a firmly established principle, if the change referred to a physical entity. The non-physical character of the wave function (which is sometimes said to embody merely our knowledge) is even more strongly emphasized by the fact that according to the orthodox view its change by measurement is dependent on the observer’s taking cognizance of the result. Moreover the change holds only for the observer who does. If you are present, but are not informed of the result, then for you even if you have the minutest knowledge both of the wave function before the measurement and of the appliances that were used, the changed wave function is irrelevant, not existing, as it were; for you there is, at best, a wave function referring to the measuring appliances plus the system under consideration, a wave function in which the one adopted by the knowing observer plays no distinguished role.
M. de Broglie, so I believe, disliked the probability interpretation of wave mechanics as much as I did. But very soon and for a long period one had to give up opposing it, and to accept it as an expedient interim solution. I shall point out some of the reasons why the originally contemplated alter-native seemed deceptive and, after all, too naive. The points shall be numbered for later reference; the illustrating examples are representative of wide classes.
i) As long as a particle, an electron or proton etc., was still believed to be a permanent, individually identifiable entity, it could not adequately be pictured in our mind as a wave parcel. For as a rule, apart from artificially constructed and therefore irrelevant exceptions, no wave parcel can be indicated which does not eventually disperse into an ever increasing volume of space.
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ii) The original wave-mechanical model of the hydrogen atom is not self-consistent. The electronic cloud effectively shields the nuclear charge towards outside, making up a neutral whole, but is inefficient inside; in computing its structure its own field that it will produce must not be taken into account, only the field of the nucleus.
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iii) It seemed impossible to account for e.g. Planck’s radiation formula without assuming that a radiation oscillator (proper mode of the hohlraum) can only have energies nhν, with n an integer (or perhaps a half odd integer). Since this holds in all cases of thermodynamic equilibrium that do not follow the classical law of equipartition we are thrown back to the discrete energy states with abrupt transitiona between them, and thus to the probability interpretation.
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iv) Many non-equilibrium processes suggest even more strongly the “transfer of whole quanta”; the typical, often quoted example is the photoelectric effect, one of the pillars of Einstein’s hypothesis of light quanta in 1905.
All this was known 25 years ago, and abated the hopes of “naive” wave-mechanista. The now orthodox view about the wave function as “probability amplitude” was put forward and was worked out into a scheme of admirable logical consistency. Let us first review the situation after the state of knowledge we had then. The view suggested by (iii) and (iv), that radiation oscillators, electrons and similar constituents of observable systems always find themselves at one of their respective energy levels except when they change abruptly to another one handing the balance over to, or receiving it from, some other system, this view, so I maintain, is in glaring contradiction with the above mentioned scheme in spite of the admirable logical self-consistency of the latter. For one of the golden rules of this scheme is, that any observable is always found at one of its eigenvalues, when you measure it, but that you must not say that it has any value, if you do not measure it. To attribute sharp energy values to all those constituents, whose energies we could not even dream of measuring (except in a horrible nightmare), is not only gratuitous but strictly forbidden by this rule.
Now let us review the situation as it is today. Two new aspects have since arisen which I consider very relevant for reconsidering the interpretation. They are intimately connected. They have not turned up suddenly. Their roots lie far back, but their bearing was only very gradually recognized.
I mean first the recognition that the thing which has always been called a particle and, on the strength of habit, is still called by some such name is, whatever it may be, certainly not an individually identifiable entity. I have dwelt on this point at length elsewhere [“Endeavour”, Vol.IX, Number 35, July 1950; reprinted in the Smithsonian Institution Report for 1950, pp. 183, – 196; in German “Die Pyramide”, Jan. and Feb. 1951 (Austria)]. The second point is the paramount importance of what is sometimes called “second quantization”.
To begin with, if a particle is not a permanent entity, then of the four difficulties labelled above, (i) is removed. As regards (ii), the quantization of de Broglie’s waves around a nucleus welds into one comprehensive scheme all the 3n-dimensional reprasentations that I had. proposed for the n-body problems. It is not an easy scheme, but it is logically clear and it can be so framed that only the mutual Coulomb energies enter.
As regards (iii) – keeping to the example of black body radiation – the situation is this. If the radiation is quantized each radiation oscillator (proper mode) obtains the frequencies or levels nhν. This is sufficient to produce Planck’s formula for the radiation in a cavity surrounded by a huge heat bath. I mean to say, the level scheme suffices: it is not necessary to assume that each oscillator is at one of its levels, which is absurd from any point of view. The same holds for all thermodynamical equilibria. I have actually given a general proof of this in the last of my “Collected Papers” (English version: Blackie and Son, Glasgow 1928). A better presentation is added as an appendix to the forthcoming 2nd impression of “Statistical Thermodynamics” (Cambridge University Press).
Under (iv) we alluded to a vast range of phenomena purported to be conclusive evidence for the transfer of whole quanta. But I do not think they are, provided only that one holds on to the wave aspect throughout the whole process. One must, of course, give up thinking of e.g. an electron as of a tiny speck of something moving within the wave train along a mysterious unknowable path. One must regard the “observation of an electron” as an event that occurs within a train of de Broglie waves when a contraption is interposed in it which by its very nature cannot but answer by discrete responses: a photographic emulsion, a luminescent screen, a Geiger counter. And one must, to repeat this, hold on to the wave aspect throughout. This includes, that the equations between frequencies and frequency differences, expressing the resonance condition that governs wave mechanics throughout, must not be multiplied by Planck’s constant h and then interpreted as tiny energy balances of microscopic processes between tiny specks of something that have, to say the least, no permanent existence.
This situation calls for a revision of the current interpretation, which involves computing transition probabilities from level to level, and disregards the fact that the wave equation, with few exceptions if any, indicates nothing of the sort, but leads each of the reacting systems into a state composed of a wide spread of energy eigenstates. To assume that the system actually leaps into just one of them which is selected by “playing dice”, as it were, is not only gratuitous, but as was pointed out above, contradicts in most cases even the current interpretation. These inconsistencies will be avoided by returning to a wave theory that is not continually abrogated by dice-miracles; not of course to the naive wave theory of yore, but to a more sophisticated one, based on second quantization and the non-individuality of “particles”. Originating from contraptions that by their very nature cannot but give a discrete, discontinuous response, the probability aspect has unduly entered the fundamental concepts and has domineeringly dictated the basic structure of the present theory.
In giving it up we must no longer be afraid of losing time-honoured atomism. It has its counterpart in the level-scheme (of second quantization) and nowhere else. It may be trusted to give atomism its due, without being aided by dice-playing.
To point here to the general failure of the present theory to obtain finite transition probabilities and finite values of the apparent mass and charge, might seem a cheap argument and a dangerous one at that. The obvious retort would be: Can you do better, sir? Let me frankly avow that I cannot. Still I beg to plead that I am at the moment groping for my way almost single-handed, as against a host of clever people doing their best along the recognized lines of thought.
But let me still draw attention to a point that is seldom spoken of. I called the probability interpretation a scheme of admirable logical consistency. Indeed it gives us a set of minute prescriptions, not liable ever to be involved in contradiction, for computing the probability of a particular outcome of any intended measurement, given the wave function and the hermitian operator associated with that particular measuring device. But, of course, an abstract mathematical theory cannot possibly indicate the rules for this association between operators and measuring devices. To describe one of the latter is a long and circumstantial task for the experimentalist. Whether the device which he recommends really corresponds to the operator set up by the theorist, is not easy to decide. Yet this is of paramount importance. For a measuring appliance means now much more than it did before the advent of quantum mechanics and of its interpretation which I am opposing here. It has a physical influence on the object; it is deemed to press it infallibly into one of the eigenstates of the associated operator. If it fails to put it in an eigenstate belonging to the value resulting from the measurement, the latter is quantum-mechanically not repeatable. I cannot help feeling that the precariousness of the said association makes that beautiful, logically consistent theoretical scheme rather void. At any rate its contact with actual laboratory work is very different from what one would expect from its fundamental enunciations.
A further discussion of the points raised in this paper can be found in a forthcoming longer (but equally non-mathematical) essay in the British Journal for the Philosophy of Science.
D-Wave Cooper-pair states in real space. Now the company that derived its name from this wavefunction makes some waves of its own.
What a week for Quantum Information Science. D-Wave madesomemajornews when the first peer reviewed paper to conclusively demonstrate that their machine can drastically outperform conventional hardware was recently announced. It’s hardly a contest. For the class of optimization problems that the D-Wave machines are designed for, the algorithms executed on the conventional chip didn’t even come close. The D-Wave machine solved some of the tested problems about 3600 times faster than the best conventional algorithm. (I’ll leave it to gizmodo to not mince words).
Apparently, my back of the envelope calculation from last year, that was based on the D-Wave One performance of a brute force calculation of Ramsey numbers, wasn’t completely off. Back then I calculated that the 128 qubit chip performed at the level of about 300 Intel i7 Hex CPU cores (the current test ran on the next generation 512 qubit chip). So, I am now quite confident in my ongoing bet.
If conventional hardware requires thousands of conventional cores to beat the current D-Wave machine, then the company has certainly entered a stage where its offering becomes attractive to a wider market. Of course, other factors will weigh in when considering total cost of ownership. The biggest hurdle in this regard will be software, as to date any problem you want to tackle the D-Wave way requires dedicated coding for this machine. At first these skills will be rare and expansive to procure. On the other hand, there are other cost factors working in D-Wave’s favor: Although I haven’t seen power consumption numbers, the adiabatic nature of the chip’s architecture suggests that it will require far less wattage than a massive server farm or conventional super-computer. Ironically, while the latter operate at normal ambient temperature they will always require far more cooling effort to keep them at this temp than the D-Wave chips in their deep freeze vacuum.
That the current trajectory of our supercomputer power consumption is on an unsustainable path should be obvious by simply glancing at this chart.
Despite the efforts there are hard efficiency limits for conventional CMOS transistors. (for the original pingdom.com article click image)
D-Wave matures just at the right time to drive a paradigm change, and I hope they will pursue this opportunity aggressively.
Why it took two years for this news to be published is anybody’s guess. Did somebody just flip a switch and then forget about it? Probably more likely that this research has been considered classified for some time.
Certainly this also suggests a technology who’s time has come. Governmental and enterprise networks have been compromised at increasing rates, even causing inflammatory talk of ongoing cyber warfare. And while there have been commercial quantum encryption devices on the market for quite some time now, these have been limited to point to point connections. Having a protocol that allows the seamless integration of quantum cryptography into the existing network stack raises this to an entirely different level. This is of course no panacea against security breaches, and has been criticized as providing superfluous security illusions, since the social engineering attacks clearly demonstrate the human users as the weakest link. Nevertheless, I maintain that it has the potential to relegate brute force attacks to history’s dustbin.
The new quantum protocol uses a typical “hub-and-spoke” topology as illustrated in the following figure and explained in more detail in the original paper.
The NQC topology maps well onto those widely encountered in optical fiber networks, and permits a hierarchical trust architecture for a “hub” to act as the trusted authority (TA, “Trent”) to facilitate quantum authenticated key exchange.
Another key aspect is the quantum resource employed in the network:
The photonic phase-based qubits typically used in optical fiber QC require interferometric stability and inevitably necessitate bulky and expensive hardware. Instead, for NQC we use polarization qubits, allowing the QC transmitters – referred to as QKarDs – to be miniaturized and fabricated using integrated photonics methods [12]. This opens the door to a manufacturing process with its attendant economy of scale, and ultimately much lower-cost QC hardware.
Terry Pratchett was one, if not my all time, favorite author. Luckily for me, he was also one of the most prolific ones, creating an incredible rich, hilarious yet endearing universe, populated with the most unlikely yet humane characters. What drew me in, when I started reading his books twenty years ago, was his uncanny sense for the absurdities of modern physics. Therefor it shouldn’t really come as a surprise that he also wrote the best popular science book there is. To honor the man, and mark his passing, I republish this post from 2013.
Until recently, there was no competition if I were to be asked what popular science book I’d recommend to a non-physicist. It was always Terry Pratchett’s The Science of Discworld
This isn’t the first book that addresses this issue. Peter Woit’s Not Even Wrong took it on, at a time when calling out String theory was a rather unpopular stance, but the timing for another book in this vein that addresses a broad lay public is excellent. As Baggott wrote his book, it was already apparent that CERN’s LHR did not pick up any signs in support of SUSY and string theory. Theorists have been long in denial about these elaborately constructed castles in the sky, but the reality seems to be slowly seeping in.
” falls into this category for me. Despite all of the author’s immense scientific sophistication, it felt like he fell into the trap that my very first physics prof put like this: “The difference between theologians and philosophers is that the former have to argue towards a certain end.” In the final analysis, I find, it was a religious text.
