Gaussian BosonSampling, higher-order correlations, and spoofing: An update

October 10th, 2021

In my last post, I wrote (among other things) about an ongoing scientific debate between the group of Chaoyang Lu at USTC in China, which over the past year has been doing experiments that seek to demonstrate quantum supremacy via Gaussian BosonSampling; and the group of Sergio Boixo at Google, which had a recent paper on a polynomial-time classical algorithm to sample approximately from the same distributions.  I reported the facts as I understood them at the time.  Since then, though, a long call with the Google team gave me a new and different understanding, and I feel duty-bound to share that here.

A week ago, I considered it obvious that if, using a classical spoofer, you could beat the USTC experiment on a metric like total variation distance from the ideal distribution, then you would’ve completely destroyed USTC’s claim of quantum supremacy.  The reason I believed that, in turn, is a proposition that I hadn’t given a name but needs one, so let me call it Hypothesis H:

The only way a classical algorithm to spoof BosonSampling can possibly do well in total variation distance, is by correctly reproducing the high-order correlations (correlations among the occupation numbers of large numbers of modes) — because that’s where the complexity of BosonSampling lies (if it lies anywhere).

Hypothesis H had important downstream consequences.  Google’s algorithm, by the Google team’s own admission, does not reproduce the high-order correlations.  Furthermore, because of limitations on both samples and classical computation time, Google’s paper calculates the total variation distance from the ideal distribution only on the marginal distribution on roughly 14 out of 144 modes.  On that marginal distribution, Google’s algorithm does do better than the experiment in total variation distance.  Google presents a claimed extrapolation to the full 144 modes, but eyeballing the graphs, it was far from clear to me what would happen: like, maybe the spoofing algorithm would continue to win, but maybe the experiment would turn around and win; who knows?

Chaoyang, meanwhile, made a clear prediction that the experiment would turn around and win, because of

1. the experiment’s success in reproducing the high-order correlations,
2. the admitted failure of Google’s algorithm in reproducing the high-order correlations, and
3. the seeming impossibility of doing well on BosonSampling without reproducing the high-order correlations (Hypothesis H).

Given everything my experience told me about the central importance of high-order correlations for BosonSampling, I was inclined to agree with Chaoyang.

Now for the kicker: it seems that Hypothesis H is false.  A classical spoofer could beat a BosonSampling experiment on total variation distance from the ideal distribution, without even bothering to reproduce the high-order correlations correctly.

This is true because of a combination of two facts about the existing noisy BosonSampling experiments.  The first fact is that the contribution from the order-k correlations falls off like 1/exp(k).  The second fact is that, due to calibration errors and the like, the experiments already show significant deviations from the ideal distribution on the order-1 and order-2 correlations.

Put these facts together and what do you find?  Well, suppose your classical spoofing algorithm takes care to get the low-order contributions to the distribution exactly right.  Just for that reason alone, it could already win over a noisy BosonSampling experiment, as judged by benchmarks like total variation distance from the ideal distribution, or for that matter linear cross-entropy.  Yes, the experiment will beat the classical simulation on the higher-order correlations.  But because those higher-order correlations are exponentially attenuated anyway, they won’t be enough to make up the difference.  The experiment’s lack of perfection on the low-order correlations will swamp everything else.

Granted, I still don’t know for sure that this is what happens — that depends on whether I believe Sergio or Chaoyang about the extrapolation of the variation distance to the full 144 modes (my own eyeballs having failed to render a verdict!).  But I now see that it’s logically possible, maybe even plausible.

So, let’s imagine for the sake of argument that Google’s simulation wins on variation distance, even though the experiment wins on the high-order correlations.  In that case, what would be our verdict: would USTC have achieved quantum supremacy via BosonSampling, or not?

It’s clear what each side could say.

Google could say: by a metric that Scott Aaronson, the coinventor of BosonSampling, thought was perfectly adequate as late as last week — namely, total variation distance from the ideal distribution — we won.  We achieved lower variation distance than USTC’s experiment, and we did it using a fast classical algorithm.  End of discussion.  No moving the goalposts after the fact.

Google could even add: BosonSampling is a sampling task; it’s right there in the name!  The only purpose of any benchmark — whether Linear XEB or high-order correlation — is to give evidence about whether you are or aren’t sampling from a distribution close to the ideal one.  But that means that, if you accept that we are doing the latter better than the experiment, then there’s nothing more to argue about.

USTC could respond: even if Scott Aaronson is the coinventor of BosonSampling, he’s extremely far from an infallible oracle.  In the case at hand, his lack of appreciation for the sources of error in realistic experiments caused him to fixate inappropriately on variation distance as the success criterion.  If you want to see the quantum advantage in our system, you have to deliberately subtract off the low-order correlations and look at the high-order correlations.

USTC could add: from the very beginning, the whole point of quantum supremacy experiments was to demonstrate a clear speedup on some benchmark — we never particularly cared which one!  That horse is out of the barn as soon as we’re talking about quantum supremacy at all — something the Google group, which itself reported the first quantum supremacy experiment in Fall 2019, again for a completely artificial benchmark — knows as well as anyone else.  (The Google team even has experience with adjusting benchmarks: when, for example, Pan and Zhang pointed out that Linear XEB as originally specified is pretty easy to spoof for random 2D circuits, the most cogent rejoinder was: OK, fine then, add an extra check that the returned samples are sufficiently different from one another, which kills Pan and Zhang’s spoofing strategy.) In that case, then, why isn’t a benchmark tailored to the high-order correlations as good as variation distance or linear cross-entropy or any other benchmark?

Both positions are reasonable and have merit — though I confess to somewhat greater sympathy for the one that appeals to my doofosity rather than my supposed infallibility!

OK, but suppose, again for the sake of argument, that we accepted the second position, and we said that USTC gets to declare quantum supremacy as long as its experiment does better than any known classical simulation at reproducing the high-order correlations.  We’d still face the question: does the USTC experiment, in fact, do better on that metric?  It would be awkward if, having won the right to change the rules in its favor, USTC still lost even under the new rules.

Sergio tells me that USTC directly reported experimental data only for up to order-7 correlations, and at least individually, the order-7 correlations are easy to reproduce on a laptop (although sampling in a way that reproduces the order-7 correlations might still be hard—a point that Chaoyang confirms, and where further research would be great). OK, but USTC also reported that their experiment seems to reproduce up to order-19 correlations. And order-19 correlations, the Google team agrees, are hard to sample consistently with on a classical computer by any currently known algorithm.

So then, why don’t we have direct data for the order-19 correlations?  The trouble is simply that it would’ve taken USTC an astronomical amount of computation time.  So instead, they relied on a statistical extrapolation from the observed strength of the lower-order correlations — there we go again with the extrapolations!  Of course, if we’re going to let Google rest its case on an extrapolation, then maybe it’s only sporting to let USTC do the same.

You might wonder: why didn’t we have to worry about any of this stuff with the other path to quantum supremacy, the one via random circuit sampling with superconducting qubits?  The reason is that, with random circuit sampling, all the correlations except the highest-order ones are completely trivial — or, to say it another way, the reduced state of any small number of output qubits is exponentially close to the maximally mixed state.  This is a real difference between BosonSampling and random circuit sampling—and even 5-6 years ago, we knew that this represented an advantage for random circuit sampling, although I now have a deeper appreciation for just how great of an advantage it is.  For it means that, with random circuit sampling, it’s easier to place a “sword in the stone”: to say, for example, here is the Linear XEB score achieved by the trivial classical algorithm that outputs random bits, and lo, our experiment achieves a higher score, and lo, we challenge anyone to invent a fast classical spoofing method that achieves a similarly high score.

With BosonSampling, by contrast, we have various metrics with which to judge performance, but so far, for none of those metrics do we have a plausible hypothesis that says “here’s the best that any polynomial-time classical algorithm can possibly hope to do, and it’s completely plausible that even a noisy current or planned BosonSampling experiment can do better than that.”

In the end, then, I come back to the exact same three goals I would’ve recommended a week ago for the future of quantum supremacy experiments, but with all of them now even more acutely important than before:

1. Experimentally, to increase the fidelity of the devices (with BosonSampling, for example, to observe a larger contribution from the high-order correlations) — a much more urgent goal, from the standpoint of evading classical spoofing algorithms, than further increasing the dimensionality of the Hilbert space.
2. Theoretically, to design better ways to verify the results of sampling-based quantum supremacy experiments classically — ideally, even ways that could be applied via polynomial-time tests.
3. For Gaussian BosonSampling in particular, to get a better understanding of the plausible limits of classical spoofing algorithms, and exactly how good a noisy device needs to be before it exceeds those limits.

Thanks so much to Sergio Boixo and Ben Villalonga for the conversation, and to Chaoyang Lu and Jelmer Renema for comments on this post. Needless to say, any remaining errors are my own.

The Physics Nobel, Gaussian BosonSampling, and Dorian Abbot

October 5th, 2021

1. Huge congratulations to the winners of this year’s Nobel Prize in Physics: Syukuro Manabe and Klaus Hasselmann for climate modelling, and separately, Giorgio Parisi for statistical physics. While I don’t know the others, I had the great honor to get to know Parisi three years ago, when he was chair of the committee that awarded me the Tomassoni-Chisesi Prize in Physics, and when I visited Parisi’s department at Sapienza University of Rome to give the prize lecture and collect the award. I remember Parisi’s kindness, a lot of good food, and a lot of discussion of the interplay between theoretical computer science and physics. Note that, while much of Parisi’s work is beyond my competence to comment on, in computer science he’s very well-known for applying statistical physics methods to the analysis of survey propagation—an algorithm that revolutionized the study of random 3SAT when it was introduced two decades ago.

2. Two weeks ago, a group at Google put out a paper with a new efficient classical algorithm to simulate the recent Gaussian BosonSampling experiments from USTC in China. They argued that this algorithm called into question USTC’s claim of BosonSampling-based quantum supremacy. Since then, I’ve been in contact with Sergio Boixo from Google, Chaoyang Lu from USTC, and Jelmer Renema, a Dutch BosonSampling expert and friend of the blog, to try to get to the bottom of this. Very briefly, the situation seems to be that Google’s new algorithm outperforms the USTC experiment on one particular metric: namely, total variation distance from the ideal marginal distribution, if (crucially) you look at only a subset of the optical modes, say 14 modes out of 144 total. Meanwhile, though, if you look at the kth-order correlations for large values of k, then the USTC experiment continues to win. With the experiment, the correlations fall off exponentially with k but still have a meaningful, detectable signal even for (say) k=19, whereas with Google’s spoofing algorithm, you choose the k that you want to spoof (say, 2 or 3), and then the correlations become nonsense for larger k.

Now, given that you were only ever supposed to see a quantum advantage from BosonSampling if you looked at the kth-order correlations for large values of k, and given that we already knew, from the work of Leonid Gurvits, that very small marginals in BosonSampling experiments would be easy to reproduce on a classical computer, my inclination is to say that USTC’s claim of BosonSampling-based quantum supremacy still stands. On the other hand, it’s true that, with BosonSampling especially, more so than with qubit-based random circuit sampling, we currently lack an adequate theoretical understanding of what the target should be. That is, which numerical metric should an experiment aim to maximize, and how well does it have to score on that metric before it’s plausibly outperforming any fast classical algorithm? One thing I feel confident about is that, whichever metric is chosen—Linear Cross-Entropy or whatever else—it needs to capture the kth-order correlations for large values of k. No metric that’s insensitive to those correlations is good enough.

3. Like many others, I was outraged and depressed that MIT uninvited Dorian Abbot (see also here), a geophysicist at the University of Chicago, who was slated to give the Carlson Lecture in the Department of Earth, Atmospheric, and Planetary Sciences about the atmospheres of extrasolar planets. The reason for the cancellation was that, totally unrelatedly to his scheduled lecture, Abbot had argued in Newsweek and elsewhere that Diversity, Equity, and Inclusion initiatives should aim for equality for opportunity rather than equality of outcomes, a Twitter-mob decided to go after him in retaliation, and they succeeded. It should go without saying that it’s perfectly reasonable to disagree with Abbot’s stance, to counterargue—if those very concepts haven’t gone the way of floppy disks. It should also go without saying that the MIT EAPS department chair is free to bow to social-media pressure, as he did, rather than standing on principle … just like I’m free to criticize him for it. To my mind, though, cancelling a scientific talk because of the speaker’s centrist (!) political views completely, 100% validates the right’s narrative about academia, that it’s become a fanatically intolerant echo chamber. To my fellow progressive academics, I beseech thee in the bowels of Bertrand Russell: why would you commit such an unforced error?

Yes, one can imagine views (e.g., open Nazism) so hateful that they might justify the cancellation of unrelated scientific lectures by people who hold those views, as many physicists after WWII refused to speak to Werner Heisenberg. But it seems obvious to me—as it would’ve been obvious to everyone else not long ago—that no matter where a reasonable person draws the line, Abbot’s views as he expressed them in Newsweek don’t come within a hundred miles of it. To be more explicit still: if Abbot’s views justify deplatforming him as a planetary scientist, then all my quantum computing and theoretical computer science lectures deserve to be cancelled too, for the many attempts I’ve made on this blog over the past 16 years to share my honest thoughts and life experiences, to write like a vulnerable human being rather than like a university press office. While I’m sure some sneerers gleefully embrace that implication, I ask everyone else to consider how deeply they believe in the idea of academic freedom at all—keeping in mind that such a commitment only ever gets tested when there’s a chance someone might denounce you for it.

Update: Princeton’s James Madison Program has volunteered to host Abbot’s Zoom talk in place of MIT. The talk is entitled “Climate and the Potential for Life on Other Planets.” Like probably hundreds of others who heard about this only because of the attempted cancellation, I plan to attend!

Unrelated Bonus Update: Here’s a neat YouTube video put together by the ACM about me as well as David Silver of AlphaGo and AlphaZero, on the occasion of our ACM Prizes in Computing.

“Is China Ahead in the Quantum Computing Race?”

September 26th, 2021

Please enjoy an hourlong panel discussion of that question on YouTube, featuring yours truly, my former MIT colleague Will Oliver, and political scientist and China scholar Elsa Kania. If you’re worried that the title sounds too sensationalistic, I hope my fellow panelists and I will pleasantly surprise you with our relative sobriety! Thanks so much to QC Ware for arranging the panel (full disclosure: I’m QC Ware’s scientific adviser).

Was Scientific American Sokal’d?

September 24th, 2021

Here’s yesterday’s clickbait offering from Scientific American, the once-legendary home of Martin Gardner’s Mathematical Games column:

Why the Term ‘JEDI’ Is Problematic for Describing Programs That Promote Justice, Equity, Diversity and Inclusion

The sad thing is, I see few signs that this essay was meant as a Sokal-style parody, although in many ways it’s written as one. The essay actually develops a 100% cogent, reasoned argument: namely, that the ideology of the Star Wars films doesn’t easily fit with the new ideology of militant egalitarianism at the expense of all other human values, including irony, humor, joy, and the nurturing of unusual talents. The authors are merely oblivious to the conclusion that most people would draw from their argument: namely, so much the worse for the militant egalitarianism then!

I predict that this proposal—to send the acronym “JEDI” the way of “mankind,” “blacklist,” and, err, “quantum supremacy”—will meet with opposition even from the wokeists themselves, a huge fraction of whom (in my experience) have soft spots for the Star Wars franchise. Recall for example that in 2014, Laurie Penny used Star Wars metaphors in her interesting response to my comment-171, telling male nerds like me that we need to learn to accept that “[we’re] not the Rebel Alliance, [we’re] actually part of the Empire and have been all along.” Admittedly, I’ve never felt like part of an Empire, although I’ll confess to some labored breathing lately when ascending flights of stairs.

As for me, I spent much of my life opposed in principle to Star Wars—I hated how the most successful “science fiction” franchise of all time became that way precisely by ditching any pretense of science and fully embracing mystical woo—but sure, when the chips are down, I’m crazy and radical enough to take the side of Luke Skywalker, even if a team of woke theorists is earnestly, unironically explaining to me that lightsabers are phallocentric and that Vader ranks higher on the intersectional oppression axis because of his breathing problem.

Meantime, of course, the US continues to careen toward its worst Constitutional crisis since the Civil War, as Trump prepares to run again in 2024, and as this time around, the Republicans are systematically purging state governments of their last Brad Raffenspergers, of anyone who might stand in the way of them simply setting aside the vote totals and declaring Trump the winner regardless of the actual outcome. It’s good to know that my fellow progressives have their eyes on the ball—so that when that happens, at least universities will no longer be using offensive acronyms like “JEDI”!

My ACM TechTalk on quantum supremadvantage

September 15th, 2021

This Erev Yom Kippur, I wish to repent for not putting enough quantum computing content on this blog. Of course, repentance is meaningless unless accompanied by genuine reform. That being the case, please enjoy the YouTube video of my ACM TechTalk from last week about quantum supremacy—although, as you’ll see if you watch the thing, I oscillate between quantum supremacy and other terms like “quantum advantage” and even “quantum supremadvantage.” This represents the first time ever that I got pushback about a talk before I’d delivered it for political reasons—the social-justice people, it turns out, are actually serious about wanting to ban the term “quantum supremacy”—but my desire to point out all the difficulties with their proposal competed with my desire not to let that issue overshadow my talk.

And there’s plenty to talk about! While regular Shtetl-Optimized readers will have already heard (or read) most of what I say, I make some new comments, including about the new paper from last week, the night before my talk (!), by the USTC group in China, where they report a quantum supremacy experiment based on random circuit sampling with a superconducting chip, this time with a record-setting 60 qubits and 24 layers of gates. On the other hand, I also stress how increasing the circuit fidelity has become a much more urgent issue than further increasing the number of qubits (or in the case of BosonSampling, the number of photons), if our goal is for these experiments to remain a couple steps ahead of classical spoofing algorithms.

Anyway, I hope you enjoy my lovingly handcrafted visuals. Over the course of this pandemic, I’ve become a full convert to writing out my talks with a stylus pen rather than PowerPointing them—not only is it faster for me, not only does it allow for continuous scrolling rather than arbitrary divisions into slides, but it enforces simplicity and concision in ways they should be enforced.

While there was only time for me to field a few questions at the end of the talk, I later supplied written answers to 52 questions (!!) that I hadn’t gotten to. If you have a question, please check to see if it’s already there, and otherwise ask away in the comments!

Thanks so much to Yan Timanovsky for inviting and organizing this talk, and to whurley for hosting it.

Open Problems Related to Quantum Query Complexity

September 14th, 2021

Way back in 2005, I posed Ten Semi-Grand Challenges for Quantum Computing Theory, on at least half of which I’d say there’s been dramatic progress in the 16 years since (most of the challenges were open-ended, so that it’s unclear when to count them as “solved”). I posed more open quantum complexity problems in 2010, and some classical complexity problems in 2011. In the latter cases, I’d say there’s been dramatic progress on about a third of the problems. I won’t go through the problems one by one, but feel free to ask in the comments about any that interest you.

Shall I push my luck as a problem-poser? Shall or shall not, I have.

My impetus, this time around, was a kind invitation by Travis Humble, the editor-in-chief of the new ACM Transactions on Quantum Computing, to contribute a perspective piece to that journal on the occasion of my ACM Prize. I agreed—but only on the condition that, rather than ponderously pontificate about the direction of the field, I could simply discuss a bunch of open problems that I wanted to see solved. The result is below. It’s coming soon to an arXiv near you, but Shtetl-Optimized readers get it first.

Open Problems Related to Quantum Query Complexity (11 pages, PDF)

by Scott Aaronson

Abstract: I offer a case that quantum query complexity still has loads of enticing and fundamental open problems—from relativized QMA versus QCMA and BQP versus IP, to time/space tradeoffs for collision and element distinctness, to polynomial degree versus quantum query complexity for partial functions, to the Unitary Synthesis Problem and more.

Some of the problems on my new hit-list are ones that I and others have flogged for years or even decades, but others, as far as I know, appear here for the first time. If your favorite quantum query complexity open problem, or a problem I’ve discussed in the past, is missing, that doesn’t mean that it’s been solved or is no longer interesting—it might mean I simply ran out of time or energy before I got to it.

Enjoy! And tell me what I missed or got wrong or has a trivial solution that I overlooked.

Exciting opportunities at Kabul University!

September 5th, 2021

Update (Sept. 6): Alright, as promised in this post, I’ve now matched a reader’s generosity by donating $2,000 to NARAL’s Avow fund, which is fighting for abortion rights for women in Texas. Woke people on Twitter, I invite you/youse/y’all to figure out some creative ways to condemn me for that. Normally, early fall is the time when I’d use this blog to advertise positions in quantum information and theoretical computer science at the University of Texas at Austin, for prospective PhD students, postdocs, and faculty. This year, you might say, anyone trying to recruit academics to Texas has a … teensy bit of a PR problem. We already had PR problems, first over the “failure by design” of our electrical grid in the winter, second over Governor Abbott’s battle against local mask mandates, which has made Texas the second-most notoriously covid-friendly state after Florida. Now, of course, Texas has effectively outlawed abortion—well, after the 6th week, which is before many women even realize they’re pregnant, and when the fetus is still the size of a grain of rice and looks like this. There are no exceptions for rape or incest, and—this is the “novel” part—there’s a bounty system, with$10,000+ fines for anyone who helps in any way with an abortion, payable to anyone who snitches on them. Texas has openly defied Roe v. Wade and, for the first time in half a century, has gotten five Supreme Court justices (three appointed by Donald Trump) to go along with it. Roe v. Wade is de facto no longer the law of the United States.

And as for our recruiting at UT Austin … I fear we might as well now be trying to recruit colleagues to Kabul University. It’s like, imagine some department chair at Kabul U., this week, trying to woo a star female physicist from abroad: “Oh, don’t worry … you’ll get used to wearing a burqa in no time! And the ban on being alone with unrelated males is actually a plus for you; it just means you’ll be freed from onerous teaching and committee assignments. Best yet, I’ve received personal assurances from our local Taliban commander that you almost certainly won’t be stoned for your licentiousness and whoredom. Err … no offense, those were his words, not mine.”

For five years, my recruiting pitches for UT Austin have often involved stressing how Austin is a famously hip, tolerant, high-tech, educated city—a “blueberry in the tomato soup,” as Rick Perry put it—and how Texas itself might indeed turn blue any election cycle, given the explosive growth of its metropolitan population, and how the crazy state politics is unlikely to affect an Austinite’s personal life—at least, by noticeably more than the crazy national politics would affect their personal life. I can no longer make this pitch with a straight face, or certainly not to women.

Like, I’m lucky that none of the women in my close family have ever needed an abortion, and that if they did, it would be easy for them to travel out of Texas to get one. But having carried to term two healthy but difficult pregnancies, my wife Dana has often stressed to me how insane she finds the very idea of being forced by the government to go through with such an ordeal. If women considering moving to Texas feel likewise, I can’t argue with them. More than that: if Texas continues on what half the country sees as a journey back to the Middle Ages, with no opt-outs allowed for the residents of its left-leaning urban centers, Dana and I will not be able to remain here, and many of our friends won’t either.

So why aren’t we packing our bags already? Partly because the current situation is inherently, obviously unstable. SB8 can’t long remain the law of Texas while Roe v. Wade remains the law of the United States: one of them has to give. I confess to being confused about why some abortion provider in Texas, with funding from national pro-choice groups, hasn’t already broken the law, welcomed a lawsuit, and forced the courts to rule explicitly on whether Roe v. Wade still stands and why or why not, rather than gutting a core part of American jurisprudence literally under cover of night. I’m also confused about why some solid blue state, like Massachusetts or Hawaii, isn’t right now passing a law that would let any citizen sue any other for carrying a firearm—thereby forcing the five Supreme Hypocrites, in striking down that law, to admit that they don’t believe after all that state laws get to trample what the Supreme Court has held to be constitutional rights, merely by outsourcing the enforcement to random vigilantes.

My best guess is that Thomas, Alito, Gorsuch, Kavanaugh, and Barrett are already plotting to replace Roe by something much more restrictive, albeit probably not quite as shockingly draconian as Texas’s current ban on all abortions after six weeks, nor quite as breathtakingly insane as its bounty system for anyone who snitches about abortions. My best guess is that they saw last week’s ruling as a way to test the waters and soften the country up: if you’re going to rescind what multiple generations of Americans have grown up seeing as a fundamental right, best not to do it too suddenly. My best guess is that Democrats will respond by making abortion a central campaign issue in 2022 and 2024, and that given the public’s 58%-32% support for Roe, the Democrats will do pretty well with that—to the point where, like the proverbial dog that finally catches the car, Republicans might come to regret actually sinking their jaws into Roe, rather than just conspicuously chasing it down the street for half a century.

I have friends who are sincere, thoughtful pro-lifers. I admire, if nothing else, their principled dedication to a moral stance that regularly gets condemned in academia. But I’d also say to them: even if you think of abortion as murder, a solid majority of Americans don’t, and it’s hard to see a stable way of getting what you want that skips the step where you change those Americans’ minds. Indeed, there’s long been a pro-choice critique of Roe, which says that, by short-circuiting the political loosening of abortion restrictions that was already underway in the 70s, Roe fueled the growth of the radical right that’s now all but destroyed America. For Roe falsely convinced pro-lifers that all they needed to do was seize control of the Supreme Court, by any means fair or foul, when what they really needed to do was convince the public.

And, let’s be honest, convincing the public means convincing them to adopt a religious as opposed to secular framework for morality. (And not just any religious framework: Orthodox Jews, for example, while not exactly fans of abortion, are fine with it under many circumstances. In the Jewish view, so the old classic goes, the fetus attains full personhood only after graduating medical school.) Of the Americans who want abortion to be illegal in all or most cases, 94% are at least “fairly certain” that God exists, and 79% are “absolutely certain”—consistent with my experience of having met highly intelligent and articulate pro-lifers, but never secular ones. Modulo Lizardman’s Constant, virtually all pro-lifers have metaphysical commitments about God and the soul that presumably do some of the heavy lifting for them. If the case for a blanket abortion ban can be made in terms that are compelling to a secular, rationalist, tradeoffs-based morality, no one seems to have done it yet.

From the standpoint of secular moral philosophy, my own opinion is that no one has ever improved on the searching analysis of the abortion question that Carl Sagan and Ann Druyan published in 1990. After painstakingly laying out scientific facts, moral hypotheticals, and commonsense principles, Sagan and Druyan ultimately conclude that the right question to ask is when the fetus develops something that’s recognizably a human brain, processing thoughts and emotions. In practice, that probably means drawing a hard line at the end of the second trimester. Coincidentally, that’s almost exactly where Roe v. Wade drew the line, but Sagan and Druyan’s reasoning is completely different: they reject Roe‘s criterion of viability outside the womb, as both morally irrelevant and contingent on medical technology.

Reasonable people could disagree with the details of Sagan and Druyan’s analysis. But if we agree that

(1) a sperm and unfertizilied egg have a “personhood” of 0,

(2) a newborn baby has a “personhood” of 1, and

(3) whatever “personhood” is, it’s somehow tied to the gradual growth of neurons and dendrites in the physical universe, rather than to a mystical and discontinuous moment of ensoulment,

… then by the intermediate value theorem, for all p∈(0,1), there’s going to be some stage of fetal development where the fetus has a personhood of p. Which means that we’re going to be drawing a debatable line, making a compromise, just like the majority did in Roe. To me, one of the strangest aspects of the abortion debate is how both sides came to view Roe v. Wade as the “pro-choice maximalist position,” forgetting how it itself was an attempted compromise between conflicting moral intuitions.

Another strange aspect of the debate is how the most visible representatives of both sides seem to have given up, decades ago, on actually arguing for their positions. Maybe it’s because people simply threw up their hands in futility; or because all the ground had been covered with nothing left to say; or because the debate was so obviously entangled with religion, and we have a polite norm of not arguing about religion; or because both positions hardened into tribal identity markers, to be displayed rather than defended. Whatever the reason, though, by the mid-90s everything became about border skirmishes one or two steps removed from the actual question: e.g., if the woman is under 18, should her parents be notified? should she be shown pictures of her fetus and given a 24-hour waiting period in hopes she’ll reconsider? is this judicial nominee hiding his or her anti-abortion views?

Now that Texas and five Supreme Court justices have launched a frontal assault on Roe—it’s impossible to see it any other way—it seems to me that the long armistice is over. The pro-life side will have to make the case for its moral framework to a populace that will suddenly be paying more attention—and that includes tens of millions of Americans who hadn’t even been born the last time mainstream figures debated abortion head-on. The pro-choice side can then counterargue for its moral framework. If any pro-lifers are raring for this fight, I’ll point out that one of the most dramatic demographic changes, since the last time abortion was a “hot war,” has been a doubling in the percentage of Americans who are atheist, agnostic, or religiously unaffiliated.

Let me close this post with two things.

Firstly, if anyone is still unclear where I stand: over the next week, I will match Shtetl-Optimized readers’ donations to NARAL up to \$2,000. If you’d like to participate, just leave a comment with the amount you donated. If I’ve argued with certain strains of feminism on this blog, that gives me all the more obligation to support the strains that I regard as fundamentally correct.

Secondly, come join us at the University of Kab … I mean Texas at Austin! For grad students, see here; for faculty, see here; for postdocs, email me a CV and recent publications and have two reference letters sent to me by December 31st. In the US, the east coast is now being ravaged beyond recognition by hurricanes and the west coast by wildfires. Here in Texas, all we have to deal with is extreme heat, a failing electrical grid, runaway covid, and now the ban on abortion. Hook ’em Hadamards!

“The Chair”: A Straussian interpretation

August 31st, 2021

[Warning: spoilers follow!]

Last week Dana and I watched the full first season of The Chair, the Netflix drama that stars Sandra Oh as Ji-Yoon Kim, incoming chairwoman of the English department at the fictional Pembroke University. As the rave reviews promised, I found the show to be brilliantly written and acted. At times, The Chair made me think about that other academia-centered sitcom, The Big Bang Theory, which I freely confess I also enjoyed. But The Chair is much more highbrow (and more political), it’s about the humanities rather than STEM, and it’s mostly about academics who are older than the ones in Big Bang, both biologically and professionally.

I wouldn’t call The Chair “realistic”: the sets, stuffed with imposing bookshelves, paintings of great scholars, etc., look like how a TV producer might imagine university buildings, rather than the relatively humdrum reality. But in less than three hours, the show tackles a staggering number of issues that will be recognizable and relevant to anyone in academia: cratering enrollments, a narrow-minded cost-cutting dean, a lack of free time and a desperate search for childcare, a tenure case that turns into a retention case, a woke scandal (about which more later), a faculty revolt against Ji-Yoon culminating in a vote of no confidence, and much more. There’s also an elaborate side plot involving the actor (and real-life former literary scholar) David Duchovny, who portrays himself, being invited to lecture at Pembroke, which is not the sort of thing most academics have experience with, but which I suppose many viewers will enjoy.

The show is written at a high enough level that its stumbles are those of a daring acrobat. In the main narrative arc of the first season, the writers set themselves an absurdly ambitious (and, I think, laudable) goal: namely, to dramatize a conflict between a free-spirited professor, and woke students trying to cancel that professor for a classroom “microaggression,” in a way that fully empathizes with both sides. I don’t know if the show actually succeeds at this, but that’s partly because I don’t know if it’s possible to succeed.

To start with some background: in Pembroke’s English department, there are old, traditionalist white males, who give lectures extolling the Great Men of Literature, and who apparently still wield considerable power. Meanwhile, critical theorists are presented as young, exciting upstarts bravely challenging the status quo. People with recent experience of English departments should correct me if I’m wrong, but my sense is that this is pretty anachronistic—i.e., that the last powerful traditionalists in humanities departments were routed by the 80s or 90s at the latest, so that students in the Twitter-and-smartphone era (when The Chair is set) would be about as likely to encounter them as they would professors sitting around in charcoal suits smoking pipes.

There were also some of what felt to me like … intersectional oversights? Ji-Yoon, being Korean-American, is repeatedly approached by Black female students and faculty as a “fellow woman of color,” with whom they can commiserate about the entrenched power of the department’s white males. The show never examines how woke discourse has increasingly reclassified Asian-Americans as “white-adjacent”—as, for example, in the battles over gifted and magnet programs or admissions to Harvard. Likewise, woke students are shown standing arm-in-arm with Pembroke’s Jewish community, to denounce (what we in the audience know to be) a phantom antisemitic incident. Left unexplored is how, in the modern woke hierarchy, Jews have become just another kind of privileged white person (worse, of course, if they have ties to Israel).

This brings me to the first season’s central conflict, which revolves around Bill Dobson, a handsome middle-aged white male professor who’s revered as the department’s greatest genius on the basis of his earlier work, but who, after the death of his wife, is now washed-up, flippant, and frequently drunk or high. In one class session, while lecturing about intellectuals who found the strength to resist fascism despite their own nihilistic impulses, Bill makes a Nazi salute and shouts “Heil Hitler!,” as a theatrical reminder to the students about the enormity of what those intellectuals were fighting. Alas, a woke student captures that moment on their smartphone camera and shares it on social media. The clip of Bill making the Heil salute goes viral, shorn of all exculpatory context. Soon, crowds of students are waving placards and screaming “No Nazis at Pembroke!” outside the English building. In a desperate effort to make his PR crisis go away, the dean initiates termination proceedings against Bill—the principles of academic freedom and even Bill’s tenure be damned. Ji-Yoon, of course, as Bill’s chair, is caught smack in the middle of this. It’s complicated even further by Ji-Yoon’s and Bill’s romantic feelings for each other, and further still by Bill’s role as the babysitter of Ji-Yoon’s adopted daughter.

As all of this unfolds, the show seems immensely interested in pinning the blame on Bill’s “tragic flaws,” minor though they seemed to me—mostly just pride and unseriousness. (E.g., trying to lampoon the absurd charge of Nazism, Bill offhandedly mentions that he’s always wanted to visit Hitler’s mountain retreat, and on another occasion belts out “Springtime for Hitler” from The Producers.) The woke students, by contrast, are portrayed as earnest, understandably upset, and legitimately terrified about hate crimes on campus. If they, too, have opportunistic motives to attack Bill, the show never examines them.

In one sentence, then, here’s my beef with The Chair: its script portrays a mob, step by step, destroying an innocent man’s life over nothing, and yet it wants me to feel the mob’s pain, and be disappointed in its victim for mulishly insisting on his innocence (even though he is, in fact, innocent).

With real-life woke controversies, there often lingers the question of whether the accused might really be a racist, fascist, sexual predator, or whatever else, adequate proof or no. What’s different here is that we know that Bill Dobson is none of those things, we know he’s decent to his core, because the writers have painstakingly shown us that. And yet, in a weird narrative pretzel, we’re nevertheless supposed to be mad at him, and to sympathize with the campaign to cancel him.

A casual perusal of other reviews of The Chair told me that these reactions were far from universal. Here, for example, is what one viewer wrote:

I can appreciate that this is probably close to the reality that most women/of color experience in higher education. I enjoyed watching the scenes with Joan and Yaz [two female professors] the most but the rest was a drag. I couldn’t understand why Ji-Yoon was into Bill, or why anyone was into Bill. I found him to be an insufferable man-baby. That is such a turn off. So she’d put him straight but then still be pining for him. He wreaked [sic] of entitled, white male, tenured privilege and never showed any contrition for his actions or even awareness of their impact. i’m so tired of the “brilliant _” being used to justify coddling someone. And for the rest of the stuffy old patriarchal farts– boot them out! They weren’t good teachers and weren’t able to meet the needs of today’s students.

I asked myself: did this person watch the same show? It’s like, the script couldn’t possibly have been clearer about Bill’s character, the fact that he’s the polar opposite of the woke students’ mental construct. And yet, if the show had drawn an unambiguous corollary from Bill’s goodness—namely, that the effort to cancel him is a moral travesty—then The Chair itself might have been denounced as conservative (or at least classical liberal) propaganda, and those who’d otherwise form its core viewership wouldn’t have watched.

So, if I were a literary critic like the ones on the show, I might argue that The Chair begs for a Straussian interpretation. Sure, there’s an “overt” reading, wherein Bill Dobson is done in by his own hubris, or wherein it’s a comedy of errors with no one to blame. But then there’s also an “esoteric” reading, wherein Bill is the victim of an extremely specific modern-day collective insanity, one that future generations might look back on with little more ambivalence than we look back on McCarthyism. The writers of The Chair might hint at this latter reading, through their sympathetic portrayal of Bill and the obviousness of the injustice done to him, but they can never make it too explicit, because of the political and cultural constraints under which they themselves operate.

Under this theory, it presumably falls to those slightly outside the world portrayed in The Chair—like, let’s imagine, a theoretical computer science blogger who himself was denounced for woke heresies to the point where he has little more to lose in that direction—to make the esoteric reading explicit. Unless and until, of course, a second season comes along to undermine that reading entirely.

Please cheer me up

August 27th, 2021

Update: Come to think of it, let’s circle back to the thing about kids under 13 getting banned from taking the SAT, as a ridiculous unintended consequence of some federal regulation. I wonder whether this is a campaign this blog could spearhead that would have an actual chance of making a positive difference in the world (!!), rather than just giving me space to express myself, to vent my impotent rage at the tragic failures of our civilization and the blankfaces who sleep soundly despite knowing that they caused those failures.  What if, like, a whole bunch of us wrote to the College Board, or whatever federal agency enforces the regulation that the College Board is worried about, and we asked them whether a solution might be found in which parents gave permission on the web form for their under-13s to take the SAT, given how memorable this opportunity was for many of us, how it was a nerd rite of passage, and how surely none of us have any wish to deny that opportunity to the next generation, so let’s work together to solve this?

I’m depressed that, all over the world, the values of the Enlightenment are humiliated and in retreat, while the values of the Taliban are triumphant. The literal Taliban of course, but also a thousand mini-Talibans of every flavor, united in their ideological certainty.

I’m depressed that now and for the future, the image of the United States before the world—deservedly so—is one of desperate Afghans plunging to their deaths from the last airplanes out of Kabul. I’m depressed that, while this historic calamity was set in motion by Donald Trump, the president who bears direct, immediate moral responsibility for it is the one I voted for. And knowing what I know now, I’d still have voted for him—but with an ashen face.

I’m depressed that, on social media, the same people who seven years ago floridly denounced me, because, while explaining how as a young person I overcame the urge to suicide and finally achieved some semblance of a normal life, I made a passing reference to a vanished culture of arranged marriages, to which I seemed better-adapted than to the world of today—these very same people are the ones sagely resigned to millions of Afghan women and girls actually forced into unwanted marriages, tortured, and raped, who explain that there’s nothing the US can or should do about this, even that it was folly to imagine we could impose parochial Western values, like women’s rights, on a culture that doesn’t want them. These are the people who saw fit to lecture me on my feminist failings.

I’m depressed that there’s an exceedingly good chance that both of my kids will get covid, as they’ve returned to school and preschool in Austin, TX, where the Delta variant is raging out of control, new reports of cases among the kids’ schoolmates come almost every day, Daniel has been quarantined at home for the past week because of one such case, there’s no vaccination mandate (and a looming battle over mask mandates), and—crucially, tragically, incredibly—the FDA has not only slow-walked approval of covid vaccines for children under 12, but has pushed back the approval even further than it previously planned, ignoring unprecedented public objections from the American Academy of Pediatrics. The FDA blankfaces have done this in spite of the reality, obvious to anyone with eyes and a brain, that they’re thereby consigning thousands of children to their deaths, that whatever ultra-rare risks the vaccine poses to children are infinitesimal compared to the overwhelming benefit.

Since I worry that I wasn’t clear enough, how about this: in a just world, the FDA in its current form would be dismantled, and all those who needlessly delayed the delivery of covid vaccines to children would be tried for manslaughter [while I still think the case for authorizing covid vaccines for kids right now is overwhelmingly clear, I hereby retract this particular remark, which was based on a factor 5-10 overestimate of the covid mortality risk for kids—for more, see this comment]. The blankfaces have already killed more people through pointlessly delaying the approval of covid vaccines than their agency could plausibly have saved through its entire history: do they need to take the children as well? As far as I’m concerned, those who defend the status quo—those who meet the on-the-ground reality of overflowing pediatric hospitals with obfuscatory words about procedures and best practices and the need for yet more data—are no better either morally or intellectually than the anti-vaxx conspiracy theorists, their rightly-reviled cousins.

As icing on the cake, I’m depressed that the College Board is no longer administering the SAT to children under 13, apparently because of federal regulations—-which means that Johns Hopkins CTY’s famed Study of Exceptional Talent, a program that made a big difference in my life three decades ago, has been suspended indefinitely. Imagine being a nerdy 11-year-old in 2021: no more tracking, no more gifted programs, no more magnet schools, no more acceleration, no getting vaccinated against deadly disease (!!), … oh, and if perchance you felt the urge to take the SAT, just to prove that you could outscore the grownups who decided to impose all this on you, then no, you’re no longer allowed to do that either.

The one bright spot in the endlessly bleak picture is that Daniel, my 4-year-old son, now plays a pretty mean chess game, if not quite at the level of Beth Harmon. Having just learned the rules a few months ago, Daniel now gives me and Dana (admittedly, no one would mistake either of us for Magnus Carlsen) extremely competitive matches; just yesterday he beat several adults in a park. Daniel has come to spend much of his free time (and now that he’s quarantined, he has a lot) playing chess against his iPad and watching chess videos. To be clear, he has very little emotional maturity even for a 4-year-old, and unlike me at the same age, he has no overwhelming passion for numbers or counting, but with chess I’ve finally found a winner. Now I just need to hope that they don’t ban chess-playing for children under 13.

So that’s it, it’s off my chest. Commenters: what else have you got that might cheer me up?

Stephen Wiesner (1942-2021)

August 13th, 2021

These have not been an auspicious few weeks for Jewish-American-born theoretical physicists named Steve who made epochal contributions to human knowledge in the late 1960s, and who I had the privilege to get to know a bit when they were old.

This morning, my friend and colleague Or Sattath brought me the terrible news that Stephen Wiesner has passed away in Israel. [Because people have asked: I’ve now also heard directly from Wiesner’s daughter Sarah.]

Decades ago, Wiesner left academia, embraced Orthodox Judaism, moved from the US to Israel, and took up work there as a construction laborer—believing (or so he told me) that manual labor was good for the soul. In the late 1960s, however, Wiesner was still a graduate student in physics at Columbia University, when he wrote Conjugate Coding: arguably the foundational document of the entire field of quantum information science. Famously, this paper was so far ahead of its time that it was rejected over and over from journals, taking nearly 15 years to get published. (Fascinatingly, Gilles Brassard tells me that this isn’t true: it was rejected once, from IEEE Transactions on Information Theory, and then Wiesner simply shelved it.) When it finally appeared, in 1983, it was in SIGACT News—a venue that I know and love, where I’ve published too, but that’s more like the house newsletter for theoretical computer scientists than an academic journal.

But it didn’t matter. By the early 1980s, Wiesner’s ideas had been successfully communicated to Charlie Bennett and Gilles Brassard, who refashioned them into the first scheme for quantum key distribution—what we now call BB84. Even as Bennett and Brassard received scientific acclaim for the invention of quantum cryptography—including, a few years ago, the Wolf Prize (often considered second only to the Nobel Prize), at a ceremony in the Knesset in Jerusalem that I attended—the two B’s were always careful to acknowledge their massive intellectual debt to Steve Wiesner.

Let me explain what Wiesner does in the Conjugate Coding paper. As far as I know, this is the first paper ever to propose that quantum information—what Wiesner called “polarized light” or “spin-1/2 particles” but we now simply call qubits—works differently than classical bits, in ways that could actually be useful for achieving cryptographic tasks that are impossible in a classical world. What could enable these cryptographic applications, wrote Wiesner, is the fact that there’s no physical means for an attacker or eavesdropper to copy an unknown qubit, to produce a second qubit in the same quantum state. This observation—now called the No-Cloning Theorem—would only be named and published in 1982, but Wiesner treats it in his late-1960s manuscript as just obvious background.

Wiesner went further than these general ideas, though, to propose an explicit scheme for quantum money that would be physically impossible to counterfeit—a scheme that’s still of enormous interest half a century later (I teach it every year in my undergraduate course). In what we now call the Wiesner money scheme, a central bank prints “quantum bills,” each of which contains a classical serial number as well as a long string of qubits. Each qubit is prepared in one of four possible quantum states:

• |0⟩,
• |1⟩,
• |+⟩ = (|0⟩+|1⟩)/√2, or
• |-⟩ = (|0⟩-|1⟩)/√2.

The bank, in a central database, stores the serial number of every bill in circulation, as well as the preparation instructions for each of the bill’s qubits. If you want to verify a bill as genuine—this, as Wiesner knew, is the big drawback—you have to bring it back to the bank. The bank, using its secret knowledge of how each qubit was prepared, measures each qubit in the appropriate basis—the {|0⟩,|1⟩} basis for |0⟩ or |1⟩ qubits, the {|+⟩,|-⟩} basis for |+⟩ or |-⟩ qubits—and checks that it gets the expected outcomes. If even one qubit yields the wrong outcome, the bill is rejected as counterfeit.

Now consider the situation of a counterfeiter, who holds a quantum bill but lacks access to the bank’s secret database. When the counterfeiter tries to copy the bill, they won’t know the right basis in which to measure each qubit—and if they make the wrong choice, then it’s not only that they fail to make a copy; it’s that the measurement destroys even the original copy! For example, measuring a |+⟩ or |-⟩ qubit in the {|0⟩,|1⟩} basis will randomly collapse the qubit to either |0⟩ or |1⟩—so that, when the bank later measures the same qubit in the correct {|+⟩,|-⟩} basis, it will see the wrong outcome, and realize that the bill has been compromised, with 1/2 probability (with the probability increasing to nearly 1 as we repeat across hundreds or thousands of qubits).

Admittedly, the handwavy argument above, which Wiesner offered, is far from a security proof by cryptographers’ standards. In 2011, I pointed that out on StackExchange. My post, I’m happy to say, spurred Molina, Vidick, and Watrous to write a beautiful 2012 paper, where they rigorously proved for the first time that in Wiesner’s money scheme, no counterfeiter consistent with the laws of quantum mechanics can turn a single n-qubit bill into two bills that both pass the bank’s verification with success probability greater than (3/4)n (and this is tight). But the intuition was already clear enough to Wiesner in the 1960s.

In 2003—when I was already a PhD student in quantum information, but incredibly, had never heard of Stephen Wiesner or his role in founding my field—I rediscovered the idea of quantum states |ψ⟩ that you could store, measure, and feed into a quantum computer, but that would be usefully uncopyable. (My main interest was in whether you could create “unpiratable quantum software programs.”) Only in 2006, at the University of Waterloo, did Michele Mosca and his students make the connection for me to quantum money, Stephen Wiesner, and his Conjugate Coding paper, which I then read with amazement—along with a comparably amazing followup work by Bennett, Brassard, Breidbart, and Wiesner.

But it was clear that there was still a great deal to do. Besides unpiratable software, Wiesner and his collaborators had lacked the tools in the early 1980s seriously to tackle the problem of secure quantum money that anybody could verify, not only the bank that had created the money. I realized that, if such a thing was possible at all, then just like unpiratable software, it would require cryptographic hardness assumptions, a restriction to polynomial-time counterfeiters, and (hence) ideas from quantum computational complexity. The No-Cloning Theorem couldn’t do the job on its own.

That realization led to my 2009 paper Quantum Copy-Protection and Quantum Money, and from there, to the “modern renaissance” of Wiesner’s old idea of quantum money, with well over a hundred papers (e.g., my 2012 paper with Paul Christiano, Farhi et al.’s quantum state restoration paper, their quantum money from knots paper, Mark Zhandry’s 2017 quantum lightning paper, Dmitry Gavinsky’s improvement of Wiesner’s scheme wherein the money is verified by classical communication with the bank, Broduch et al.’s adaptive attack on Wiesner’s original scheme, my shadow tomography paper proving the necessity for the bank to keep a giant database in information-theoretic quantum money schemes like Wiesner’s, Daniel Kane’s strange scheme based on modular forms…). The purpose of many of these papers was either to break the quantum money schemes proposed in previous papers, or to patch the schemes that were previously broken.

After all this back-and-forth, spanning more than a decade, I’d say that Wiesner’s old idea of quantum money is now in good enough theoretical shape that the main obstacle to its practical realization is merely the “engineering difficulty”—namely, how to get the qubits in a bill, sitting in your pocket or whatever, to maintain their quantum coherence for more than a few nanoseconds! (Or possibly a few hours, if you’re willing to schlep a cryogenic freezer everywhere you go.) It’s precisely because quantum key distribution doesn’t have this storage problem—because there the qubits are simply sent across a channel and then immediately measured on arrival—that QKD is actually practical today, although the market for it has proven to be extremely limited so far.

In the meantime, while the world waits for the quantum error-correction that could keep qubits alive indefinitely, there’s Bitcoin. The latter perversely illustrates just how immense the demand for quantum money might someday be: the staggering lengths to which people will go, diverting the electricity to power whole nations into mining rigs, to get around our current inability to realize Wiesner’s elegant quantum-mechanical solution to the same problem. When I first learned about Bitcoin, shortly after its invention, it was in the context of: “here’s something I’d better bring up in my lectures on quantum money, in order to explain how much better WiesnerCoin could eventually be, when it’s the year 2200 or whatever and we all have quantum computers wired up by a quantum Internet!” It never occurred to me that I should forget about the year 2200, liquidate my life savings, and immediately buy up all the Bitcoin I could. [Added: I’ve since learned that Wiesner’s daughter Sarah is a professional in the Bitcoin space.]

In his decades as a construction laborer, Wiesner had (as far as I know) no Internet presence; many of my colleagues didn’t even realize he was still alive. Even then, though, Wiesner never turned his back so far on his previous life, his academic life, that the quantum information faculty at Hebrew University in Jerusalem couldn’t entice him to participate in some seminars there. Those seminars are where I had the privilege to meet and talk to him several times over the last decade. He was thoughtful and kind, listening with interest as I told him how I and others were trying to take quantum money into the modern era by making it publicly verifiable.

I also vividly remember a conversation in 2013 where Steve shared his fears about the American physics establishment and military-industrial complex, and passionately urged me to

1. quit academia and get a “real job,” and
2. flee the US immediately and move my family to Israel, because of a wave of fascism and antisemitism that was about to sweep the US, just like with Germany in the 1930s.

I politely nodded along, pointing out that my Israeli wife and I had considered living in Israel but the job opportunities were better in US, silently wondering when Steve had gone completely off his rocker. Today, Steve’s urgent warning about an impending fascist takeover of the US seems … uh, slightly less crazy than in 2013? Maybe, just like with quantum money, Wiesner was simply too far ahead of his time to sound sane.

Wiesner also talked to me about his father, Jerome Wiesner, who was a legendary president of MIT—still spoken about in reverent tones when I taught there—as well as the chief science advisor to John F. Kennedy. One of JFK’s most famous decisions was to override the elder Wiesner’s fervent opposition to sending humans to the moon (Wiesner thought it a waste of money, as robots could do the same science for vastly cheaper).

While I don’t know all the details (I hope someone someday researches it and writes a book), Steve Wiesner made it clear to me that he did not get along with his famous father at all—in fact they became estranged. Steve told me that his embrace of Orthodox Judaism was, at least in part, a reaction against everything his father had stood for, including militant scientific atheism. I suppose that in the 1960s, millions of young Americans defied their parents via sex, drugs, and acoustic guitar; only a tiny number did so by donning tzitzit and moving to Israel to pray and toil with their hands. The two groups of rebels did, however, share a tendency to grow long beards.

Wiesner’s unique, remarkable, uncloneable life trajectory raises the question: who are the young Stephen Wiesners of our time? Will we be faster to recognize their foresight than Wiesner’s contemporaries were to recognize his?

Feel free to share any other memories of Stephen Wiesner or his influence in the comments.

Update (Aug. 14): See also Or Sattath’s memorial post, which (among other things) points out something that my narrative missed: namely, besides quantum money, Wiesner also invented superdense coding in 1970, although he and Bennett only published the idea 22 years later (!).

And I have more photos! Here’s Wiesner with an invention of his and another photo (thanks to his daughter Sarah). Here’s another photo from 1970 and Charlie Bennett’s handwritten notes (!) after first meeting Wiesner in 1970 (thanks to Charlie Bennett).

Another Update: Stephen’s daughter Sarah gave me the following fascinating information to share.

In the 70’s he lived in California where he worked in various Silicon Valley startups while also working weekends as part of a produce (fruits and vegetables) distribution co-op. During this time he became devoted to the ideas of solar energy, clean energy and space migration and exploration. He also became interested in Judaism. He truly wanted to help and make our world more peaceful and safe with his focus being on clean energy and branching out into space. He also believed that instead of fighting over the temple mount in Jerusalem, the Third Temple should be built in outer-space or in a structure above the original spot, an idea he tried to promote to prevent wars over land.