Monday, March 25, 2019

Quantum Computers Are Analog Computers

Today's topic may be a little afield of conventional engineering ethics, but it involves billions of dollars at risk and the future of an entire engineering-intensive industry, so that's enough to make it an ethical concern already. 

Most engineers have heard of Moore's Law, the observation that eventually became the backbone of the semiconductor industry's road map or marching orders:  the doubling of computing power every two years.  In recent years, Moore's Law has run into difficulties because you simply can't make conventional transistor logic gates too small, or else the electrons don't stay where you want them to because of their quantum nature. 

But not to worry:  for close to four decades now, we've been told that when conventional computer logic circuits can no longer be improved, the industry will switch to "quantum computers," which are based on an entirely different principle that takes advantage of quantum effects, and Moore's Law or its quantum equivalent will keep advancing computer power indefinitely into the future.  This transition to quantum computing has been held out as the best hope for continued progress, and currently it's taken quite seriously by major players in hardware, software, and finance.  IBM and Microsoft, among others, are spending tons of money on quantum computing, and each year  thousands of research papers (mostly theoretical ones) are published about it.

In the face of all this optimism comes one Mikhail Dyakunov, a Russian-born physicist currently at the Universit√©-Montpelier-CNRS in France.  Dyakunov is well-known for his discoveries in plasma and quantum physics over a long career (he is 78).  And last November, the website of the professional engineering magazine IEEE Spectrum published his article "The Case Against Quantum Computing," in which he expresses serious doubts that a practical quantum computer capable of anything more than what conventional computers can do now will ever be built.

Along the way, he gives the most straightforward non-technical explanation of what a quantum computer is that I have seen, and I've seen many over the years.  The gist of the difficulty, he says, is that conventional computers store information as transistor states which are either on or off.  With a clear definition of on and off in terms of a current, say, it's not that challenging to set up and process data in the form of on-or-off bits, which are the essence of what we mean by "digital."  Discrete unambiguous states are the key to the entire conventional-computer intellectual construct, and while errors do occur, there are well-known and not terribly demanding ways to correct them.  That is how we got to where we are today.

But the fundamental logical unit in a quantum computer is not a conventional on-or-off current or voltage.  It is the quantum state of a "qubit" which can be exemplified by, for instance, the direction that the magnetic axis of an electron points in.  And as long as you are not taking a measurement (roughly equivalent to reading out data), the information that makes quantum computing work is the exact angle of that spin with respect to some reference direction.  And that angle is not just up or down, 1 or 0, but can take on any value between plus and minus 90 degrees. 

Back where I come from, a computer which stores information in the form of continuous physical states is called an analog computer.  Most people younger than 40 have little or no memory of analog computers, but surprisingly sophisticated problems were solved on these things from the early 20th century up to the 1960s.  However, they were comparatively slow and had very limited accuracy, typically a percent or so.  And when digital computers came along, virtually all analog computers became museum pieces (think of how many people you see using slide rules these days).  One of the last ones to go was a curious system that took synthetic-aperture radar (SAR) data from a flying airplane and transformed the data into light and dark patches on photographic film.  Then the film was placed into an optical system that performed a Fourier transform on the data and presto!  you obtained the real-space version of the SAR radar image:  the actual mountains and valleys that the plane flew over.  Since this gizmo used light waves, and light waves are fundamentally quantum in nature, I suppose you could have called that a quantum computer, though nobody did.

And you can bet nobody who is promoting quantum computing is going to refer to their goal as an analog computer, because for decades, "analog" has been an embarrassing term in the world of computation.  But guess what—Dyakunov has explained to us mortals that quantum computers have to manipulate and store data in analog form.  And the same kinds of problems of accuracy and errors that caused the analog-computer dinosaurs to die off are currently keeping quantum computers from getting any farther than they have so far, which is not very (no practical quantum computers are in commercial production).  You think reading out a analog computer's shaft position accurately is hard?  Try measuring the spin of a single electron without disturbing it.  I may be oversimplifying things, ut that seems to be the essence of what has to be done.  And Dyakunov points out that the experts themselves say they'll need thousands of logical qubits to do anything useful, and perhaps up to a thousand physical qubits per logical qubit to have enough information to correct the inevitable errors. 

In sum, Dyakunov thinks the quantum-computing fad may be going the way of the superconducting-computer fad, which flared in the 1980s and died in the early 2000s when conventional silicon-based computers overtook them performance-wise.  For a time, it was easier to build smaller logic gates out of something called Josephson junctions than it was to make silicon gates.  The problem with Josephson junctions is that they have to be cooled to a few millikelvin with liquid helium, which leads to all kinds of interface problems.  Ironically, Josephson junctions are one of the leading contenders for the best path to qubits, but handling millikelvin circuits hasn't gotten much easier in the meantime. 

The late science-fiction writer Arthur C. Clarke made a famous comment about elderly scientists: "When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong."  By this criterion, we should ignore Dyakunov and keep working on quantum computers.  But it would be interesting if he turns out to be right. 

Sources:  I read Dyakunov's article in the March 2019 hard-copy issue of IEEE Spectrum, pp. 24-29, but a version is also available online at  I also referred to for Dyakunov's date of birth and the Wikipedia article on him, and the Arthur C. Clarke entry in Wikiquote for what is known as Clarke's First Law. 

Monday, March 18, 2019

Are the 737 Max 8 Crashes Single-Point Failures?

A friend of mine who formerly worked at NASA was talking about his volunteer work at his church, which is to operate the video camera that records the pastor's sermon.  He's going to ask them to buy a second camera, and when I asked him why, he said, "Single-point failure.  That camera goes out, we're up a creek without a paddle." 

The same concept that can be applied to as humble and non-life-threatening a situation as recording sermons also applies to highly complex systems such as Boeing's 737 Max 8, a new version of the popular 737 aircraft that is in service around the world.  But new evidence from the Mar. 10, 2019 crash of a 737 Max 8 outside Addis Ababa, Ethiopia in which 157 people died indicates that a single-point failure may be responsible for both that disaster and a similar crash of another 737 Max 8 on Oct. 28, 2018 in Indonesia that killed 189.

The single-point failure possibility involves a new anti-stall system called MCAS, which Boeing installed on the Max 8 version of their 737s when the two engines were moved forward compared to earlier versions.  Because this move made the aircraft more prone to stall, the MCAS system was intended to make the plane handle more like older 737s, reducing the need for extensive pilot retraining.  But evidently, pilots were not thoroughly informed that the new MCAS system was in place and activated until the Ethiopian crash brought attention to the system.

The system works by monitoring information from two sensors called angle-of-attack (AOA) sensors.  These are small fins that stick out from the side of the aircraft rather like wind vanes, and rotate to sense the direction of local airflow with respect to the fuselage.  In a stall, the plane is tilted nose-up excessively with respect to the direction of airflow.  This makes the sensor turn at an angle that the onboard computers use to figure out that it's time to take over the controls from the pilot and push the nose down.

Normally, according to a post on, the onboard computer takes the output of both AOA sensors into account, and if one indicates a stall and the other doesn't, perhaps just a warning is issued to the pilot.  But according to a New York Times report, the MCAS anti-stall system activates even if only one of the two sensors says the nose is too high.  If anything happens to make one of the sensors give a false reading—a stray updraft from the backwash of a flight that just took off, for example—the MCAS goes into action and pushes the nose down, even if the takeoff is proceeding normally.

The altitude records of both 737s involved in the crashes in Ethiopia and Indonesia show that the pilots went on a desperate roller-coaster ride, executing climbs and descents every half-minute or so three or four times before the final descent and crash.  This is consistent with a struggle between the MCAS and the pilots, although other causes could be responsible as well.  Following the Ethiopian crash, China and many other countries grounded all 737 Max 8 and Max 9 planes, and later last week, the U. S. followed suit.

Boeing says it is working on a software upgrade for the planes involved, but it may not be available until April, and so until then, millions of dollars' worth of aviation assets will be out of service.  But that's better than having another 737 crash on takeoff. 

It is too soon to draw definite conclusions about the causes of these crashes.  That has to wait for the analyses of black-box records and other pertinent data.  But investigators have already found that the horizontal stabilizer in the Ethiopian plane was set to push the nose down, which is not something you normally do on takeoff.  And the fact that the MCAS can be triggered by only one AOA sensor is enough reason to take measures such as grounding planes until a remedy can be developed and installed.

Planes are designed by people who work in organizations, and successful designs of safe planes emerge from an exceedingly complex process involving thousands of designers, technicians, supervisors, inspectors, regulators, and other interested parties.  Successful companies manage to evolve with new young staff replacing retired engineers and managers while maintaining the core principles and knowledge that is essential to making planes safe.  And one of those core principles, so easy to understand that even I get it, is to avoid single-point-failure situations whenever possible by installing backup systems and procedures. 

If what the Times reported is true, someone dropped the ball with regard to the MCAS system's behavior in response to only one erroneous sensor.  It could take months or years to figure out how this design error happened.  But the lesson is one that has to be learned if Boeing is to recover from this sequence of disasters, which it probably will. 

It's also possible that the accidents involved pilot error in combination with a misbehaving MCAS.  If the pilots didn't know that the MCAS was even installed, or were unfamiliar with what flying the plane with an activated MCAS is like, their actions with regard to it may have contributed to the crashes.  Part of the problem here is that the MCAS rarely activates under typical flight conditions.  Perhaps there is something about the meteorological conditions at the two airports involved which gave rise to a single AOA sensor error that persisted long enough to cause the accidents. 

These and other speculations will have to await the full accident reports, which may not be available for months.  But in the absence of more knowledge, grounding the 737 Max 8 and 9 planes until the single-point-failure problem with MCAS can be addressed and demonstrated to be fixed is the wisest course.   

Postscript:  After I posted this blog, I received an informative email from a reader who wishes to remain anonymous.  He has given me permission to post it here, as it sheds more light on the concept of single-point failure:

Dear Mr. Stephan,

     I am writing to you in order to add some of my thoughts on your recent post  'Are the 737 Max 8 Crashes Single-Point Failures?' 

     In determining a single point of failure it would seem necessary to choose a boundary for the system or sub-system and also define what the goal of the system is.  In your example the goal is to record the pastor's sermon, and the entire system consists of a video camera and an operator.  So, in this case the video camera is a single point of failure, and adding a second camera provides redundancy.

     In the case of the MCAS the overall goal is to maintain a safe flight path.  The failure of a single AOA sensor may cause the MCAS to make inappropriate changes to the horizontal stabilizer trim.  But there are other subsystems that provide redundancy, most notably the stabilizer trim cut out switches.  The proper use of these switches is a memory item for both pilot and co-pilot.  So, in this broader context, the AOA sensor may not be a single point of failure with regards to the goal of maintaining a safe flight path.

     This design was probably used as the failure to pitch down at the onset of a stall at low level may result in a condition from which recovery is impossible, while an erroneous change in horizontal stabilizer trim can be corrected by timely intervention by the pilots.

And finally, I would like to thank you for your blog.  It provides detailed and nuanced analyses of engineering problems that I have not found elsewhere.

(Name withheld)


Boeing 737 technical site:

Juan Browne's (a 777 pilot and an air frame and power plant mechanic) YouTube channel:

FAA Advisory Circulars:

Mentor Pilot (a 737 pilot and line training captain) YouTube Channel:

Monday, March 11, 2019

Ignoring the Experts: Autism and Vaccinations

By necessity, engineers are experts in their professional field compared to the public at large.  And as we've discussed many times before, expertise confers both privileges and responsibilities.  Most of the time, engineers and other experts who inform the general public about questions of interest find that the public at least listens to them, and usually takes what they say seriously.  But not always.  And when expert advice and information is ignored, we have to go beyond strict logic and rational thought and deal with a wider range of human behavior.

All that is to preface an issue that on the surface, seems to fly in the face of logic and even common sense:  the question of whether autism is caused by the routine measles-mumps-rubella (MMR) vaccine that, until recently, was a non-controversial part of every baby's medical care in industrialized countries. 

Then in 1998, one Dr. Andrew Wakefield published an article claiming that he'd found a link between the unexplained rise in incidence of autism and something about the MMR vaccine, possibly the tiny amount of mercury present in it used as a preservative. 

To parents of autistic children searching for a reason why their son or daughter has such a debilitating disease, Dr. Wakefield seemed like a godsend.  Here at last was something to blame.  At the time, his report made huge headlines and spawned parents' groups who took up the cause of delaying or abstaining altogether from MMR vaccines. 

Trouble was, according to the vast majority of medical experts, Dr. Wakefield's paper was deeply flawed.  Of course, other labs and researchers got onto the bandwagon and started investigating the alleged link.  From what I have read and from a recent report in the Annals of Internal Medicine on a Danish study of over 600,000 children for eleven years, there is no statistical link between MMR vaccine and autism.  None.  It just doesn't happen, according to the best and most judicious scientific knowledge we have today.  And this is not new news.  In 2010, Wakefield was found by the British General Medical Council to be guilty of dishonesty in connection with his paper, which was retracted by Lancet, the journal that published it.  Wakefield is as discredited as a professional can get. 

But none of this seems to matter to a persistent group of people who keep sharing and encouraging the idea that vaccines cause autism.  In the latest attempt to stifle this misinformation, the president of the American Academy of Pediatrics, Dr. Kyle Yasuda, wrote letters to Google, Facebook, and Pinterest, asking them to do more about the vaccine misinformation that is spread through YouTube, Instagram, and Google's search engine. 

Dr. Yasuda cites the danger of increased measles outbreaks, such as the one that occurred in connection with Disneyland in the winter of 2014-2015.  Over a hundred cases were identified in this outbreak, and four out of five of the victims were either unvaccinated or could not show proof that they had been vaccinated for measles.  One out of five of the victims had to be hospitalized.

While in my long-ago youth, measles was just part of growing up, it wasn't a necessary rite of passage.  It can lead to complications involving many bodily systems and can even kill you.  A world without measles is unquestionably a better world than one with the disease.  And until Dr. Wakefield started meddling with his fraudulent paper, we were well on the way to eradicating measles much as smallpox has been eradicated—through systematic vaccinations and the hunting down of outbreaks with treatment, isolation, and more vaccinations.

But something has changed in the way U. S. society (and societies in many other Western countries) view experts and their opinions.  Maybe it started in the general 1960s rebellion against authority.  Granted, the 1950s were a little too conformist for many peoples' taste.  But most of what everybody knows is known by authority.  If we all had to learn our physics, chemistry, and mathematics from experience, most of us would never finish and we would be continually reinventing the wheel.  In case you hadn't noticed, one of the big differences between what G. K. Chesterton called "civilization versus savagery" is that civilization accumulates knowledge (and sometimes even wisdom), thus saving succeeding generations from the trouble and expense of figuring the world out all over again. 

With the advent of the Internet, this process became much easier.  Instead of shipping piles of paper around, we ship bits, which are much lighter.  So light, in fact, that any yahoo with a computer and Internet connection can set himself up as an authority and, once he finds the key phrases that trigger fears or anxieties enough to get his message to go viral, he can get more attention than those who have dedicated their lives to the pursuit of expertise and truly know what they are talking about. 

I am sure that some of the parents of autistic children are entirely sincere in their belief that autism is caused by vaccinations.  But sincerity of belief on the part of individuals makes absolutely no difference to objective truth, which is true for everybody all the time.  That's what objective truth means.  Part of the problem is that for many people in advanced countries, the worst thing that's happened to them is not that bad compared to routine life occurrences that were common fifty or a hundred years ago.  I am old enough to recall the fear that every summer brought when a few kids in town would come down with polio.  That was banished with the polio vaccine, at least in the U. S.  But people who grow up protected by things that ward off terrible diseases, sometimes do not appreciate what the protection is doing for them, and are liable to throw it away if persuaded that along with the great but invisible good it does, the protection (e. g. MMR vaccines) is even suspected of doing some harm—especially if it is mysterious harm such as having a baby born with autism.

Engineers tend to think that logic reigns supreme, and if you just explain a thing to someone and make them see the logic in it, they'll automatically agree with you.  The ongoing controversy about autism and vaccines shows that this assumption is a bad one.  And wise engineers should be prepared to deal with the emotionality and, yes, even irrationality, of the public whenever their activities get into controversial areas.

Sources:  An online version of the article "New study finds no autism, vaccine link" by Nicole Villalpando of the Austin American-Statesman appeared on Mar. 5, 2019 at  I also referred to the CDC summary of the California measles outbreak at and the Wikipedia article on Dr. Andrew Wakefield.

Monday, March 04, 2019

Bipartisanship Isn't Dead, At Least About PFAS

Anyone who pays attention to U. S. news these days cannot be blamed for assuming that bipartisanship—specifically, the joint sponsorship of bills by both Democrats and Republicans—is ancient history, maybe even to the extent that they've installed separate Democratic and Republican bathrooms at the Capitol.  But a small glimmer of bipartisanship came last Friday when seven Democratic senators and an equal number of Republicans introduced a bill to classify a group of chemicals known as PFAS as toxic and worthy of Superfund cleanup efforts.  And the newly named chief of the U. S. Environmental Protection Agency, Andrew Wheeler, says he's going to do something about PFAS, and has received both grudging approval on the part of opponents of the current administration and criticism that what he's proposing doesn't go nearly far enough. 

Maybe you already know all about PFAS, but I didn't, so here's a brief summary of what they are and why they're in the news.

Fluorine is the most chemically reactive of the halogens, a group of elements in the periodic table that includes chlorine, iodine, and bromine.  Fluorine is the faithful-forever element:  whatever fluorine bonds to tends to stay bonded to it.  So chemicals made with fluorine substituted for chlorine, for instance, tend to be very stable and last forever unless you put them in high-temperature incinerators, for example. 

One of the most familiar chemicals that use fluorine is polytetrafluoroethylene, known more widely under the trade name Teflon.  Shortly after the discovery of Teflon and related fluorinated compounds after World War II, they were hailed for their stability and apparent lack of toxicity.  Besides Teflon, chemists found that they could make effective and long-lasting surfactants with a group of fluorinated chemicals that are known by the general name of PFAS (perfluorinated alkylated substances). 

Surfactants are used in detergents to dissolve grease in water solutions and also to change the way surfaces react to water.  Typically, a surfactant will be a longish molecule with a hydrophobic end that likes to be in oil, and a hydrophilic end that likes to be in water.  You may have seen an experiment in which you put a few drops of oil on the surface of water in a clean pan.  The oil forms round bubble-like globules with sharp boundaries.  Then putting just a tiny amount of dish soap in the middle of the pan will cause the oil droplets to run away toward the edge of the pan like pigeons when a cat shows up.  PFAS compounds form long-lasting foams and have been used in firefighting foam for years.

Trouble is, owing to their persistent chemical nature, these compounds don't biodegrade.  And because they are easily dissolved and travel in water, they are found in drinking water in many states and have been detected in the blood of newborn babies.  And that isn't good, because the U. S. Centers for Disease Control says that PFAS chemicals are implicated in a number of adverse human health effects, such as increased levels of cholesterol and cancer, lowered fertility in women, and interference with physiological development in children. 

The U. S. military was one of the biggest users of PFAS, as the military specification for fire-fighting foam used for petroleum fires virtually required the use of PFAS in it.  Over the years, manufacturers have discovered that the stuff accumulates in humans and have begun phasing it out voluntarily, but that does nothing about the tons of it that is still lying around wherever firefighting teams have practiced using foam, which means hundreds of both civilian and military locations all across the U. S. 

So what's to be done?  Well, recognizing the problem is the first step, and that seems to be happening now.  The hazards of PFAS to humans are not as clearly defined as we'd like them to be, but they're sufficiently serious that major steps to remediate PFAS contamination are justified.  And that's just what the PFAS Action Act of 2019 would do.  Designation of a place as a Superfund site means federal dollars are available to clean it up, even if it means digging up tons of soil and running it through an incinerator or equally extreme and costly measures.  The fact that an equal number of Republican and Democratic senators have joined forces on this measure is a rare sign that there are still a few things that the parties can still agree on. 

Practically speaking, the chemicals have lost whatever commercial sponsorship they may have had, as their U. S. manufacturers have abandoned them, hopefully for chemicals that are of comparable effectiveness while being less toxic.  I don't know what happens when you try to fight a fire with Dawn dish soap instead of PFAS foam, but things probably don't go as well.  Nevertheless, it's the nature of technologists to learn from their mistakes and make improvements, not only in the direct performance of the product, but in what happens to it after it's used and what it does in its so-called afterlife. 

A particularly sad aspect of this story is that while firefighters know they are going into a risky business, running into burning buildings while everyone else is fleeing, they may not have been fully apprised of a more subtle hazard associated with their calling:  the hazards of being exposed to all kinds of nasty chemicals that are present in both fires and in firefighting chemicals.  Many burning plastics give off very carcinogenic chemicals, and that is one reason why cancer has been the leading cause of death among U. S. firefighters since 2005, according to a 2017 report.  Not only do they deal with carcinogens in fires, they've been unwittingly spreading toxic chemicals around every time they use foam to put one out, too. 

This is probably more about PFAS chemicals than you perhaps wanted to find out.  But every now and then it's good to see that the system—science, technology, government—does still work.  Maybe not as well as it could or as fast as it could, but we've identified a problem in PFAS chemicals.  U. S. companies have quit making them, lawmakers are agreeing to do something about them, and the rest of us can go on about our business knowing that at least one matter of concern is getting some kind of coordinated attention. 

Sources:  I consulted the following sources:  the website of the Environmental Working Group, which carried a press release on the Superfund-naming bill at; the CDC, which lists PFAS health effects at; the website The Hill, which criticizes Wheeler for not being fast or active enough at; and information about PFAS and aviation at  I thank my sister for her hospitality during my recent stay in Ft. Worth, where I followed her past a nearby fire station as she walked her dog and told me about the connection between firefighters and cancer, which is documented at