Archive for December, 2013

BosonSampling Lecture Notes from Rio

Saturday, December 28th, 2013

Update (January 3): There’s now a long interview with me about quantum computing in the Washington Post (or at least, on their website).  The interview accompanies their lead article about quantum computing and the NSA, which also quotes me (among many others), and which reports—unsurprisingly—that the NSA is indeed interested in building scalable quantum computers but, based on the Snowden documents, appears to be quite far from that goal.

(Warning: The interview contains a large number of typos and other errors, which might have arisen from my infelicities in speaking or the poor quality of the phone connection.  Some were corrected but others remain.)


The week before last, I was in Rio de Janeiro to give a mini-course on “Complexity Theory and Quantum Optics” at the Instituto de Física of the Universidade Federal Fluminense.  Next week I’ll be giving a similar course at the Jerusalem Winter School on Quantum Information.

In the meantime, my host in Rio, Ernesto Galvão, and others were kind enough to make detailed, excellent notes for my five lectures in Rio.  You can click the link in the last sentence to get them, or here are links for the five lectures individually:

If you have questions or comments about the lectures, leave them here (since I might not check the quantumrio blog).

One other thing: I can heartily recommend a trip to Rio to anyone interested in quantum information—or, for that matter, to anyone interested in sunshine, giant Jesus statues, or (especially) fruit juices you’ve never tasted before.  My favorite from among the latter was acerola.  Also worth a try are caja, mangaba, guarana, umbu, seriguela, amora, and fruta do conde juices—as well as caju and cacao, even though they taste almost nothing like the more commercially exportable products from the same plants (cashews and chocolate respectively).  I didn’t like cupuaçu or graviola juices.  Thanks so much to Ernesto and everyone else for inviting me (not just because of the juice).

Update (January 2): You can now watch videos of my mini-course at the Jerusalem Winter School here.

Videos of the other talks at the Jerusalem Winter School are available from the same site (just scroll through them on the right).

Merry Christmas! My quantum computing research explained, using only the 1000 most common English words

Tuesday, December 24th, 2013

[With special thanks to the Up-Goer Five Text Editor, which was inspired by this xkcd]

I study computers that would work in a different way than any computer that we have today.  These computers would be very small, and they would use facts about the world that are not well known to us from day to day life.  No one has built one of these computers yet—at least, we don’t think they have!—but we can still reason about what they could do for us if we did build them.

How would these new computers work? Well, when you go small enough, you find that, in order to figure out what the chance is that something will happen, you need to both add and take away a whole lot of numbers—one number for each possible way that the thing could happen, in fact. What’s interesting is, this means that the different ways a thing could happen can “kill each other out,” so that the thing never happens at all! I know it sounds weird, but the world of very small things has been known to work that way for almost a hundred years.

So, with the new kind of computer, the idea is to make the different ways each wrong answer could be reached kill each other out (with some of them “pointing” in one direction, some “pointing” in another direction), while the different ways that the right answer could be reached all point in more or less the same direction. If you can get that to happen, then when you finally look at the computer, you’ll find that there’s a very good chance that you’ll see the right answer. And if you don’t see the right answer, then you can just run the computer again until you do.

For some problems—like breaking a big number into its smallest parts (say, 43259 = 181 × 239)—we’ve learned that the new computers would be much, much faster than we think any of today’s computers could ever be. For other problems, however, the new computers don’t look like they’d be faster at all. So a big part of my work is trying to figure out for which problems the new computers would be faster, and for which problems they wouldn’t be.

You might wonder, why is it so hard to build these new computers? Why don’t we have them already? This part is a little hard to explain using the words I’m allowed, but let me try. It turns out that the new computers would very easily break. In fact, if the bits in such a computer were to “get out” in any way—that is, to work themselves into the air in the surrounding room, or whatever—then you could quickly lose everything about the new computer that makes it faster than today’s computers. For this reason, if you’re building the new kind of computer, you have to keep it very, very carefully away from anything that could cause it to lose its state—but then at the same time, you do have to touch the computer, to make it do the steps that will eventually give you the right answer. And no one knows how to do all of this yet. So far, people have only been able to use the new computers for very small checks, like breaking 15 into 3 × 5. But people are working very hard today on figuring out how to do bigger things with the new kind of computer.

In fact, building the new kind of computer is so hard, that some people even believe it won’t be possible! But my answer to them is simple. If it’s not possible, then that’s even more interesting to me than if it is possible! And either way, the only way I know to find out the truth is to try it and see what happens.

Sometimes, people pretend that they already built one of these computers even though they didn’t. Or they say things about what the computers could do that aren’t true. I have to admit that, even though I don’t really enjoy it, I do spend a lot of my time these days writing about why those people are wrong.

Oh, one other thing. Not long from now, it might be possible to build computers that don’t do everything that the new computers could eventually do, but that at least do some of it. Like, maybe we could use nothing but light and mirrors to answer questions that, while not important in and of themselves, are still hard to answer using today’s computers. That would at least show that we can do something that’s hard for today’s computers, and it could be a step along the way to the new computers. Anyway, that’s what a lot of my own work has been about for the past four years or so.

Besides the new kind of computers, I’m also interested in understanding what today’s computers can and can’t do. The biggest open problem about today’s computers could be put this way: if a computer can check an answer to a problem in a short time, then can a computer also find an answer in a short time? Almost all of us think that the answer is no, but no one knows how to show it. Six years ago, another guy and I figured out one of the reasons why this question is so hard to answer: that is, why the ideas that we already know don’t work.

Anyway, I have to go to dinner now. I hope you enjoyed this little piece about the kind of stuff that I work on.

Luke Muehlhauser interviews me about philosophical progress

Saturday, December 14th, 2013

I’m shipping out today to sunny Rio de Janeiro, where I’ll be giving a weeklong course about BosonSampling, at the invitation of Ernesto Galvão.  Then it’s on to Pennsylvania (where I’ll celebrate Christmas Eve with old family friends), Israel (where I’ll drop off Dana and Lily with Dana’s family in Tel Aviv, then lecture at the Jerusalem Winter School in Theoretical Physics), Puerto Rico (where I’ll speak at the FQXi conference on Physics of Information), back to Israel, and then New York before returning to Boston at the beginning of February.  Given this travel schedule, it’s possible that blogging will be even lighter than usual for the next month and a half (or not—we’ll see).

In the meantime, however, I’ve got the equivalent of at least five new blog posts to tide over Shtetl-Optimized fans.  Luke Muehlhauser, the Executive Director of the Machine Intelligence Research Institute (formerly the Singularity Institute for Artificial Intelligence), did an in-depth interview with me about “philosophical progress,” in which he prodded me to expand on certain comments in Why Philosophers Should Care About Computational Complexity and The Ghost in the Quantum Turing Machine.  Here are (abridged versions of) Luke’s five questions:

1. Why are you so interested in philosophy? And what is the social value of philosophy, from your perspective?

2. What are some of your favorite examples of illuminating Q-primes [i.e., scientifically-addressable pieces of big philosophical questions] that were solved within your own field, theoretical computer science?

3. Do you wish philosophy-the-field would be reformed in certain ways? Would you like to see more crosstalk between disciplines about philosophical issues? Do you think that, as Clark Glymour suggested, philosophy departments should be defunded unless they produce work that is directly useful to other fields … ?

4. Suppose a mathematically and analytically skilled student wanted to make progress, in roughly the way you describe, on the Big Questions of philosophy. What would you recommend they study? What should they read to be inspired? What skills should they develop? Where should they go to study?

5. Which object-level thinking tactics … do you use in your own theoretical (especially philosophical) research?  Are there tactics you suspect might be helpful, which you haven’t yet used much yourself?

For the answers—or at least my answers—click here!

PS. In case you missed it before, Quantum Computing Since Democritus was chosen by Scientific American blogger Jennifer Ouellette (via the “Time Lord,” Sean Carroll) as the top physics book of 2013.  Woohoo!!

23, Me, and the Right to Misinterpret Probabilities

Wednesday, December 11th, 2013

If you’re the sort of person who reads this blog, you may have heard that 23andMe—the company that (until recently) let anyone spit into a capsule, send it away to a DNA lab, and then learn basic information about their ancestry, disease risks, etc.—has suspended much of its service, on orders from the US Food and Drug Administration.  As I understand it, on Nov. 25, the FDA ordered 23andMe to stop marketing to new customers (though it can still serve existing customers), and on Dec. 5, the company stopped offering new health-related information to any customers (though you can still access the health information you had before, and ancestry and other non-health information is unaffected).

Of course, the impact of these developments is broader: within a couple weeks, “do-it-yourself genomics” has gone from an industry whose explosive growth lots of commentators took as a given, to one whose future looks severely in doubt (at least in the US).

The FDA gave the reasons for its order in a letter to Ann Wojcicki, 23andMe’s CEO.  Excerpts:

For instance, if the BRCA-related risk assessment for breast or ovarian cancer reports a false positive, it could lead a patient to undergo prophylactic surgery, chemoprevention, intensive screening, or other morbidity-inducing actions, while a false negative could result in a failure to recognize an actual risk that may exist.  Assessments for drug responses carry the risks that patients relying on such tests may begin to self-manage their treatments through dose changes or even abandon certain therapies depending on the outcome of the assessment.  For example, false genotype results for your warfarin drug response test could have significant unreasonable risk of illness, injury, or death to the patient due to thrombosis or bleeding events that occur from treatment with a drug at a dose that does not provide the appropriately calibrated anticoagulant effect …  The risk of serious injury or death is known to be high when patients are either non-compliant or not properly dosed; combined with the risk that a direct-to-consumer test result may be used by a patient to self-manage, serious concerns are raised if test results are not adequately understood by patients or if incorrect test results are reported.

To clarify, the DNA labs that 23andMe uses are already government-regulated.  Thus, the question at issue here is not whether, if 23andMe claims (say) that you have CG instead of CC at some particular locus, the information is reliable.  Rather, the question is whether 23andMe should be allowed to tell you that fact, while also telling you that a recent research paper found that people with CG have a 10.4% probability of developing Alzheimer’s disease, as compared to a 7.2% base rate.  More bluntly, the question is whether ordinary schmoes ought to be trusted to learn such facts about themselves, without a doctor as an intermediary to interpret the results for them, or perhaps to decide that there’s no good reason for the patient to know at all.

Among medical experts, a common attitude seems to be something like this: sure, getting access to your own genetic data is harmless fun, as long as you’re an overeducated nerd who just wants to satisfy his or her intellectual curiosity (or perhaps narcissism).  But 23andMe crossed a crucial line when it started marketing its service to the hoi polloi, as something that could genuinely tell them about health risks.  Most people don’t understand probability, and are incapable of parsing “based on certain gene variants we found, your chances of developing diabetes are about 6 times higher than the baseline” as anything other than “you will develop diabetes.”  Nor, just as worryingly, are they able to parse “your chances are lower than the baseline” as anything other than “you won’t develop diabetes.”

I understand this argument.  Nevertheless, I find it completely inconsistent with a free society.  Moreover, I predict that in the future, the FDA’s current stance will be looked back upon as an outrage, with the subtleties in the FDA’s position mattering about as much as the subtleties in the Church’s position toward Galileo (“look, Mr. G., it’s fine to discuss heliocentrism among your fellow astronomers, as a hypothesis or a calculational tool—just don’t write books telling the general public that heliocentrism is literally true, and that they should change their worldviews as a result!”).  That’s why I signed this petition asking the FDA to reconsider its decision, and I encourage you to sign it too.

Here are some comments that might help clarify my views:

(1) I signed up for 23andMe a few years ago, as did the rest of my family.  The information I gained from it wasn’t exactly earth-shattering: I learned, for example, that my eyes are probably blue, that my ancestry is mostly Ashkenazi, that there’s a risk my eyesight will further deteriorate as I age (the same thing a succession of ophthalmologists told me), that I can’t taste the bitter flavor in brussels sprouts, and that I’m an “unlikely sprinter.”  On the other hand, seeing exactly which gene variants correlate with these things, and how they compare to the variants my parents and brother have, was … cool.  It felt like I imagine it must have felt to buy a personal computer in 1975.  In addition, I found nothing the slightest bit dishonest about the way the results were reported.  Each result was stated explicitly in terms of probabilities—giving both the baseline rate for each condition, and the rate conditioned on having such-and-such gene variant—and there were even links to the original research papers if I wanted to read them myself.  I only wish that I got half as much context and detail from conventional doctor visits—or for that matter, from most materials I’ve read from the FDA itself.  (When Dana was pregnant, I was pleasantly surprised when some of the tests she underwent came back with explicit probabilities and base rates.  I remember wishing doctors would give me that kind of information more often.)

(2) From my limited reading and experience, I think it’s entirely possible that do-it-yourself genetic testing is overhyped; that it won’t live up to its most fervent advocates’ promises; that for most interesting traits there are just too many genes involved, via too many labyrinthine pathways, to make terribly useful predictions about individuals, etc.  So it’s important to me that, in deciding whether what 23andMe does should be legal, we’re not being asked to decide any of these complicated questions!  We’re only being asked whether the FDA should get to decide the answers in advance.

(3) As regular readers will know, I’m far from a doctrinaire libertarian.  Thus, my opposition to shutting down 23andMe is not at all a corollary of reflexive opposition to any government regulation of anything.  In fact, I’d be fine if the FDA wanted to insert a warning message on 23andMe (in addition to the warnings 23andMe already provides), emphasizing that genetic tests only provide crude statistical information, that they need to be interpreted with care, consult your doctor before doing anything based on these results, etc.  But when it comes to banning access to the results, I have trouble with some of the obvious slippery slopes.  E.g., what happens when some Chinese or Russian company launches a competing service?  Do we ban Americans from mailing their saliva overseas?  What happens when individuals become able just to sequence their entire genomes, and store and analyze them on their laptops?  Do we ban the sequencing technology?  Or do we just ban software that makes it easy enough to analyze the results?  If the software is hard enough to use, so only professional biologists use it, does that make it OK again?  Also, if the FDA will be in the business of banning genomic data analysis tools, then what about medical books?  For that matter, what about any books or websites, of any kind, that might cause someone to make a poor medical decision?  What would such a policy, if applied consistently, do to the multibillion-dollar alternative medicine industry?

(4) I don’t understand the history of 23andMe’s interactions with the FDA.  From what I’ve read, though, they have been communicating for five years, with everything 23andMe has said in public sounding conciliatory rather than defiant (though the FDA has accused 23andMe of being tardy with its responses).  Apparently, the key problem is simply that the FDA hasn’t yet developed a regulatory policy specifically for direct-to-consumer genetic tests.  It’s been considering such a policy for years—but in the meantime, it believes no one should be marketing such tests for health purposes before a policy exists.  Alas, there are very few cases where I’d feel inclined to support a government in saying: “X is a new technology that lots of people are excited about.  However, our regulatory policies haven’t yet caught up to X.  Therefore, our decision is that X is banned, until and unless we figure out how to regulate it.”  Maybe I could support such a policy, if X had the potential to level cities and kill millions.  But when it comes to consumer DNA tests, this sort of preemptive banning seems purposefully designed to give wet dreams to Ayn Rand fans.

(5) I confess that, despite everything I’ve said, my moral intuitions might be different if dead bodies were piling up because of terrible 23andMe-inspired medical decisions.  But as far as I know, there’s no evidence so far that even a single person was harmed.  Which isn’t so surprising: after all, people might run to their doctor terrified about something they learned on 23onMe, but no sane doctor would ever make a decision solely on that basis, without ordering further tests.

Twenty Reasons to Believe Oswald Acted Alone

Monday, December 2nd, 2013

As the world marked the 50th anniversary of the JFK assassination, I have to confess … no, no, not that I was in on the plot.  I wasn’t even born then, silly.  I have to confess that, in between struggling to make a paper deadline, attending a workshop in Princeton, celebrating Thanksgivukkah, teaching Lily how to pat her head and clap her hands, and not blogging, I also started dipping, for the first time in my life, into a tiny fraction of the vast literature about the JFK assassination.  The trigger (so to speak) for me was this article by David Talbot, the founder of Salon.com.  I figured, if the founder of Salon is a JFK conspiracy buff—if, for crying out loud, my skeptical heroes Bertrand Russell and Carl Sagan were both JFK conspiracy buffs—then maybe it’s at least worth familiarizing myself with the basic facts and arguments.

So, what happened when I did?  Were the scales peeled from my eyes?

In a sense, yes, they were.  Given how much has been written about this subject, and how many intelligent people take seriously the possibility of a conspiracy, I was shocked by how compelling I found the evidence to be that there were exactly three shots, all fired by Lee Harvey Oswald with a Carcano rifle from the sixth floor of the Texas School Book Depository, just as the Warren Commission said in 1964.  And as for Oswald’s motives, I think I understand them as well and as poorly as I understand the motives of the people who send me ramblings every week about P vs. NP and the secrets of the universe.

Before I started reading, if someone forced me to guess, maybe I would’ve assigned a ~10% probability to some sort of conspiracy.  Now, though, I’d place the JFK conspiracy hypothesis firmly in Moon-landings-were-faked, Twin-Towers-collapsed-from-the-inside territory.  Or to put it differently, “Oswald as lone, crazed assassin” has been added to my large class of “sanity-complete” propositions: propositions defined by the property that if I doubt any one of them, then there’s scarcely any part of the historical record that I shouldn’t doubt.  (And while one can’t exclude the possibility that Oswald confided in someone else before the act—his wife or a friend, for example—and that other person kept it a secret for 50 years, what’s known about Oswald strongly suggests that he didn’t.)

So, what convinced me?  In this post, I’ll give twenty reasons for believing that Oswald acted alone.  Notably, my reasons will have less to do with the minutiae of bullet angles and autopsy reports, than with general principles for deciding what’s true and what isn’t.  Of course, part of the reason for this focus is that the minutiae are debated in unbelievable detail elsewhere, and I have nothing further to contribute to those debates.  But another reason is that I’m skeptical that anyone actually comes to believe the JFK conspiracy hypothesis because they don’t see how the second bullet came in at the appropriate angle to pass through JFK’s neck and shoulder and then hit Governor Connally.  Clear up some technical point (or ten or fifty of them)—as has been done over and over—and the believers will simply claim that the data you used was altered by the CIA, or they’ll switch to other “anomalies” without batting an eye.  Instead, people start with certain general beliefs about how the world works, “who’s really in charge,” what sorts of explanations to look for, etc., and then use their general beliefs to decide which claims to accept about JFK’s head wounds or the foliage in Dealey Plaza—not vice versa.  That being so, one might as well just discuss the general beliefs from the outset.  So without further ado, here are my twenty reasons:

1. Conspiracy theorizing represents a known bug in the human nervous system.  Given that, I think our prior should be overwhelmingly against anything that even looks like a conspiracy theory.  (This is not to say conspiracies never happen.  Of course they do: Watergate, the Tobacco Institute, and the Nazi Final Solution were three well-known examples.  But the difference between conspiracy theorists’ fantasies and actual known conspiracies is this: in a conspiracy theory, some powerful organization’s public face hides a dark and terrible secret; its true mission is the opposite of its stated one.  By contrast, in every real conspiracy I can think of, the facade was already 90% as terrible as the reality!  And the “dark secret” was that the organization was doing precisely what you’d expect it to do, if its members genuinely held the beliefs that they claimed to hold.)

2. The shooting of Oswald by Jack Ruby created the perfect conditions for conspiracy theorizing to fester.  Conditioned on that happening, it would be astonishing if a conspiracy industry hadn’t arisen, with its hundreds of books and labyrinthine arguments, even under the assumption that Oswald and Ruby both really acted alone.

3. Other high-profile assassinations to which we might compare this one—for example, those of Lincoln, Garfield, McKinley, RFK, Martin Luther King Jr., Gandhi, Yitzchak Rabin…—appear to have been the work of “lone nuts,” or at most “conspiracies” of small numbers of lowlifes.  So why not this one?

4. Oswald seems to have perfectly fit the profile of a psychopathic killer (see, for example, Case Closed by Gerald Posner).  From very early in his life, Oswald exhibited grandiosity, resentment, lack of remorse, doctrinaire ideological fixations, and obsession with how he’d be remembered by history.

5. A half-century of investigation has failed to link any individual besides Oswald to the crime.  Conspiracy theorists love to throw around large, complicated entities like the CIA or the Mafia as potential “conspirators”—but in the rare cases when they’ve tried to go further, and implicate an actual human being other than Oswald or Ruby (or distant power figures like LBJ), the results have been pathetic and tragic.

6. Oswald had previously tried to assassinate General Walker—a fact that was confirmed by his widow Marina Oswald, but that, incredibly, is barely even discussed in the reams of conspiracy literature.

7. There’s clear evidence that Oswald murdered Officer Tippit an hour after shooting JFK—a fact that seems perfectly consistent with the state of mind of someone who’d just murdered the President, but that, again, seems to get remarkably little discussion in the conspiracy literature.

8. Besides being a violent nut, Oswald was also a known pathological liar.  He lied on his employment applications, he lied about having established a thriving New Orleans branch of Fair Play for Cuba, he lied and lied and lied.  Because of this tendency—as well as his persecution complex—Oswald’s loud protestations after his arrest that he was just a “patsy” count for almost nothing.

9. According to police accounts, Oswald acted snide and proud of himself after being taken into custody: for example, when asked whether he had killed the President, he replied “you find out for yourself.”  He certainly didn’t act like an innocent “patsy” arrested on such a grave charge would plausibly act.

10. Almost all JFK conspiracy theories must be false, simply because they’re mutually inconsistent.  Once you realize that, and start judging the competing conspiracy theories by the standards you’d have to judge them by if at most one could be true, enlightenment may dawn as you find there’s nothing in the way of just rejecting all of them.  (Of course, some people have gone through an analogous process with religions.)

11. The case for Oswald as lone assassin seems to become stronger, the more you focus on the physical evidence and stuff that happened right around the time and place of the event.  To an astonishing degree, the case for a conspiracy seems to rely on verbal testimony years or decades afterward—often by people who are known confabulators, who were nowhere near Dealey Plaza at the time, who have financial or revenge reasons to invent stories, and who “remembered” seeing Oswald and Ruby with CIA agents, etc. only under drugs or hypnosis.  This is precisely the pattern we would expect if conspiracy theorizing reflected the reality of the human nervous system rather than the reality of the assassination.

12. If the conspiracy is so powerful, why didn’t it do something more impressive than just assassinate JFK? Why didn’t it rig the election to prevent JFK from becoming President in the first place?  (In math, very often the way you discover a bug in your argument is by realizing that the argument gives you more than you originally intended—vastly, implausibly more.  Yet every pro-conspiracy argument I’ve read seems to suffer from the same problem.  For example, after successfully killing JFK, did the conspiracy simply disband?  Or did it go on to mastermind other assassinations?  If it didn’t, why not?  Isn’t pulling the puppet-strings of the world sort of an ongoing proposition?  What, if any, are the limits to this conspiracy’s power?)

13. Pretty much all the conspiracy writers I encountered exude total, 100% confidence, not only in the existence of additional shooters, but in the guilt of their favored villains (they might profess ignorance, but then in the very next sentence they’d talk about how JFK’s murder was “a triumph for the national security establishment”).  For me, their confidence had the effect of weakening my own confidence in their intellectual honesty, and in any aspects of their arguments that I had to take on faith.  The conspiracy camp would of course reply that the “Oswald acted alone” camp also exudes too much confidence in its position.  But the two cases are not symmetric: for one thing, because there are so many different conspiracy theories, but only one Oswald.  If I were a conspiracy believer I’d be racked with doubts, if nothing else then about whether my conspiracy was the right one.

14. Every conspiracy theory I’ve encountered seems to require “uncontrolled growth” in size and complexity: that is, the numbers of additional shooters, alterations of medical records, murders of inconvenient witnesses, coverups, coverups of the coverups, etc. that need to be postulated all seem to multiply without bound.  To some conspiracy believers, this uncontrolled growth might actually be a feature: the more nefarious and far-reaching the conspiracy’s tentacles, the better.  It should go without saying that I regard it as a bug.

15. JFK was not a liberal Messiah.  He moved slowly on civil rights for fear of a conservative backlash, invested heavily in building nukes, signed off on the botched plans to kill Fidel Castro, and helped lay the groundwork for the US’s later involvement in Vietnam.  Yes, it’s possible that he would’ve made wiser decisions about Vietnam than LBJ ended up making; that’s part of what makes his assassination (like RFK’s later assassination) a tragedy.  But many conspiracy theorists’ view of JFK as an implacable enemy of the military-industrial complex is preposterous.

16. By the same token, LBJ was not exactly a right-wing conspirator’s dream candidate.  He was, if anything, more aggressive on poverty and civil rights than JFK was.  And even if he did end up being better for certain military contractors, that’s not something that would’ve been easy to predict in 1963, when the US’s involvement in Vietnam had barely started.

17. Lots of politically-powerful figures have gone on the record as believers in a conspiracy, including John Kerry, numerous members of Congress, and even frequently-accused conspirator LBJ himself.  Some people would say that this lends credibility to the conspiracy cause.  To me, however, it indicates just the opposite: that there’s no secret cabal running the world, and that those in power are just as prone to bugs in the human nervous system as anyone else is.

18. As far as I can tell, the conspiracy theorists are absolutely correct that JFK’s security in Dallas was unbelievably poor; that the Warren Commission was as interested in reassuring the nation and preventing a war with the USSR or Cuba as it was in reaching the truth (the fact that it did reach the truth is almost incidental); and that agencies like the CIA and FBI kept records related to the assassination classified for way longer than there was any legitimate reason to (though note that most records finally were declassified in the 1990s, and they provided zero evidence for any conspiracy).  As you might guess, I ascribe all of these things to bureaucratic incompetence rather than to conspiratorial ultra-competence.  But once again, these government screwups help us understand how so many intelligent people could come to believe in a conspiracy even in the total absence of one.

19. In the context of the time, the belief that JFK was killed by a conspiracy filled a particular need: namely, the need to believe that the confusing, turbulent events of the 1960s had an understandable guiding motive behind them, and that a great man like JFK could only be brought down by an equally-great evil, rather than by a chronically-unemployed loser who happened to see on a map that JFK’s motorcade would be passing by his workplace.  Ironically, I think that Roger Ebert got it exactly right when he praised Oliver Stone’s JFK movie for its “emotional truth.”  In much the same way, one could say that Birth of a Nation was “emotionally true” for Southern racists, or that Ben Stein’s Expelled was “emotionally true” for creationists.  Again, I’d say that the “emotional truth” of the conspiracy hypothesis is further evidence for its factual falsehood: for it explains how so many people could come to believe in a conspiracy even if the evidence for one were dirt-poor.

20. At its core, every conspiracy argument seems to be built out of “holes”: “the details that don’t add up in the official account,” “the questions that haven’t been answered,” etc.  What I’ve never found is a truly coherent alternative scenario: just one “hole” after another.  This pattern is the single most important red flag for me, because it suggests that the JFK conspiracy theorists view themselves as basically defense attorneys: people who only need to sow enough doubts, rather than establish the reality of what happened.  Crucially, creationism, 9/11 trutherism, and every other elaborate-yet-totally-wrong intellectual edifice I’ve ever encountered has operated on precisely the same “defense attorney principle”: “if we can just raise enough doubts about the other side’s case, we win!”  But that’s a terrible approach to knowledge, once you’ve seen firsthand how a skilled arguer can raise unlimited doubts even about the nonexistence of a monster under your bed.  Such arguers are hoping, of course, that you’ll find their monster hypothesis so much more fun, exciting, and ironically comforting than the “random sounds in the night hypothesis,” that it won’t even occur to you to demand they show you their monster.

Further reading: this article in Slate.