Shtetl-Optimized

Many of you will have seen the happy news today that Avi Wigderson and László Lovász share this year’s Abel Prize (which now contends with the Fields Medal for the highest award in pure math). This is only the second time that the Abel Prize has been given wholly or partly for work in theoretical computer science, after Szemerédi in 2012. See also the articles in Quanta or the NYT, which actually say most of what I would’ve said for a lay audience about Wigderson’s and Lovász’s most famous research results and their importance (except, no, Avi hasn’t yet proved P=BPP, just taken some major steps toward it…).

On a personal note, Avi was both my and my wife Dana’s postdoctoral advisor at the Institute for Advanced Study in Princeton. He’s been an unbelievably important mentor to both of us, as he’s been for dozens of others in the CS theory community. Back in 2007, I also had the privilege of working closely with Avi for months on our Algebrization paper. Now would be a fine time to revisit Avi’s Permanent Impact on Me (or watch the YouTube video), which is the talk I gave at IAS in 2016 on the occasion of Avi’s 60th birthday.

Huge congratulations to both Avi and László!

Back at MIT, whenever I taught my graduate course on Quantum Complexity Theory (see here for lecture notes), I had a tradition of showcasing the student projects on this blog: see here (Fall 2010), here (Fall 2012), here (Fall 2014). I was incredibly proud that, each time I taught, at least some of the projects led to publishable original research—sometimes highly significant research, like Paul Christiano’s work on quantum money (which led to my later paper with him), Shelby Kimmel’s work on quantum query complexity, Jenny Barry’s work on quantum partially observable Markov decision processes (“QOMDPs”), or Matt Coudron and Henry Yuen’s work on randomness expansion (which led to their later breakthrough in the subject).

Alas, after I moved to UT Austin, for some reason I discontinued the tradition of these blog-showcases—and inexcusably, I did this even though the wonderful new research results continued! Now that I’m teaching Quantum Complexity Theory at UT for the third time (via Zoom, of course), I decided that it was finally time to remedy this. To keep things manageable, this time I’m going to limit myself to research projects that began their lives in my course and that are already public on the arXiv (or in one case, that will soon be).

So please enjoy the following smorgasbord, from 2016 and 2019 iterations of my course! And if you have any questions about any of the projects—well, I’ll try to get the students to answer in the comments section! Thanks so much and congratulations to the students for their work.

From the Fall 2016 iteration of the course

William Hoza (project turned into a joint paper with Cole Graham), Universal Bell Correlations Do Not Exist.

We prove that there is no finite-alphabet nonlocal box that generates exactly those correlations that can be generated using a maximally entangled pair of qubits. More generally, we prove that if some finite-alphabet nonlocal box is strong enough to simulate arbitrary local projective measurements of a maximally entangled pair of qubits, then that nonlocal box cannot itself be simulated using any finite amount of entanglement. We also give a quantitative version of this theorem for approximate simulations, along with a corresponding upper bound.

Patrick Rall, Signed quantum weight enumerators characterize qubit magic state distillation.

Many proposals for fault-tolerant quantum computation require injection of ‘magic states’ to achieve a universal set of operations. Some qubit states are above a threshold fidelity, allowing them to be converted into magic states via ‘magic state distillation’, a process based on stabilizer codes from quantum error correction.
We define quantum weight enumerators that take into account the sign of the stabilizer operators. These enumerators completely describe the magic state distillation behavior when distilling T-type magic states. While it is straightforward to calculate them directly by counting exponentially many operator weights, it is also an NP-hard problem to compute them in general. This suggests that finding a family of distillation schemes with desired threshold properties is at least as hard as finding the weight distributions of a family of classical codes.
Additionally, we develop search algorithms fast enough to analyze all useful 5 qubit codes and some 7 qubit codes, finding no codes that surpass the best known threshold.

From the Spring 2019 iteration of the course

Ying-Hao Chen, 2-Local Hamiltonian with Low Complexity is QCMA-complete.

We prove that 2-Local Hamiltonian (2-LH) with Low Complexity problem is QCMA-complete by combining the results from the QMA-completeness of 2-LH and QCMA-completeness of 3-LH with Low Complexity. The idea is straightforward. It has been known that 2-LH is QMA-complete. By putting a low complexity constraint on the input state, we make the problem QCMA. Finally, we use similar arguments as in [Kempe, Kitaev, Regev] to show that all QCMA problems can be reduced to our proposed problem.

Jeremy Cook, On the relationships between Z-, C-, and H-local unitaries.

Quantum walk algorithms can speed up search of physical regions of space in both the discrete-time [arXiv:quant-ph/0402107] and continuous-time setting [arXiv:quant-ph/0306054], where the physical region of space being searched is modeled as a connected graph. In such a model, Aaronson and Ambainis [arXiv:quant-ph/0303041] provide three different criteria for a unitary matrix to act locally with respect to a graph, called Z-local, C-local, and H-local unitaries, and left the open question of relating these three locality criteria. Using a correspondence between continuous- and discrete-time quantum walks by Childs [arXiv:0810.0312], we provide a way to approximate N×N H-local unitaries with error δ using O(1/√δ,√N) C-local unitaries, where the comma denotes the maximum of the two terms.

Joshua A. Cook, Approximating Unitary Preparations of Orthogonal Black Box States.

In this paper, I take a step toward answering the following question: for m different small circuits that compute m orthogonal n qubit states, is there a small circuit that will map m computational basis states to these m states without any input leaving any auxiliary bits changed. While this may seem simple, the constraint that auxiliary bits always be returned to 0 on any input (even ones besides the m we care about) led me to use sophisticated techniques. I give an approximation of such a unitary in the m = 2 case that has size polynomial in the approximation error, and the number of qubits n.

Sabee Grewal (project turned into a joint paper with me), Efficient Learning of Non-Interacting Fermion Distributions.

We give an efficient classical algorithm that recovers the distribution of a non-interacting fermion state over the computational basis. For a system of n non-interacting fermions and m modes, we show that O(m²n⁴log(m/δ)/ε⁴) samples and O(m⁴n⁴log(m/δ)/ε⁴) time are sufficient to learn the original distribution to total variation distance ε with probability 1−δ. Our algorithm empirically estimates the one- and two-mode correlations and uses them to reconstruct a succinct description of the entire distribution efficiently.

Sam Gunn and Niels Kornerup, Review of a Quantum Algorithm for Betti Numbers.

We looked into the algorithm for calculating Betti numbers presented by Lloyd, Garnerone, and Zanardi (LGZ). We present a new algorithm in the same spirit as LGZ with the intent of clarifying quantum algorithms for computing Betti numbers. Our algorithm is simpler and slightly more efficient than that presented by LGZ. We present a thorough analysis of our algorithm, pointing out reasons that both our algorithm and that presented by LGZ do not run in polynomial time for most inputs. However, the algorithms do run in polynomial time for calculating an approximation of the Betti number to polynomial multiplicative error, when applied to some class of graphs for which the Betti number is exponentially large.

William Kretschmer, Lower Bounding the AND-OR Tree via Symmetrization.

We prove a simple, nearly tight lower bound on the approximate degree of the two-level AND-OR tree using symmetrization arguments. Specifically, we show that ~deg(ANDm∘ORn)=Ω(~√(mn)). To our knowledge, this is the first proof of this fact that relies on symmetrization exclusively; most other proofs involve the more complicated formulation of approximate degree as a linear program [BT13, She13, BDBGK18]. Our proof also demonstrates the power of a symmetrization technique involving Laurent polynomials (polynomials with negative exponents) that was previously introduced by Aaronson, Kothari, Kretschmer, and Thaler [AKKT19].

Jiahui Liu and Ruizhe Zhang (project turned into a joint paper with me, Mark Zhandry, and Qipeng Liu),
New Approaches for Quantum Copy-Protection.

Quantum copy protection uses the unclonability of quantum states to construct quantum software that provably cannot be pirated. Copy protection would be immensely useful, but unfortunately little is known about how to achieve it in general. In this work, we make progress on this goal, by giving the following results:
– We show how to copy protect any program that cannot be learned from its input/output behavior, relative to a classical oracle. This improves on Aaronson [CCC’09], which achieves the same relative to a quantum oracle. By instantiating the oracle with post-quantum candidate obfuscation schemes, we obtain a heuristic construction of copy protection.
– We show, roughly, that any program which can be watermarked can be copy detected, a weaker version of copy protection that does not prevent copying, but guarantees that any copying can be detected. Our scheme relies on the security of the assumed watermarking, plus the assumed existence of public key quantum money. Our construction is general, applicable to many recent watermarking schemes.

John Kallaugher, Triangle Counting in the Quantum Streaming Model. Not yet available but coming soon to an arXiv near you!

We give a quantum algorithm for counting triangles in graph streams that uses less space than the best possible classical algorithm.

Many of you have surely already seen the news that the Kouwenhoven group in Delft—which in 2018 published a paper in Nature claiming to have detected Majorana particles, a type of nonabelian anyon—have retracted the paper and apologized for “insufficient scientific rigour.” This work was considered one of the linchpins of Microsoft’s experimental effort toward building topological quantum computers.

Like most quantum computing theorists, I guess, I’m thrilled if Majorana particles can be created using existing technology, I’m sad if they can’t be, but I don’t have any special investment in or knowledge of the topic, beyond what I read in the news or hear from colleagues. Certainly Majorana particles seem neither necessary nor sufficient for building a scalable quantum computer, although they’d be a step forward for the topological approach to QC.

The purpose of this post is to invite informed scientific discussion of the relevant issues—first and foremost so that I can learn something, and second so that my readers can! I’d be especially interested to understand:

1. Weren’t there, like, several other claims to have produced Majoranas? What of those then?
2. If, today, no one has convincingly demonstrated the existence of Majoranas, then do people think it more likely that they were produced but not detected, or that they weren’t even produced?
3. How credible are the explanations as to what went wrong?
4. Are there any broader implications for the prospects of topological QC, or Microsoft’s path to topological QC, or was this just an isolated mistake?

So there’s an interesting new paper on the arXiv by Feng Pan and Pan Zhang, entitled “Simulating the Sycamore supremacy circuits.” It’s about a new tensor contraction strategy for classically simulating Google’s 53-qubit quantum supremacy experiment from Fall 2019. Using their approach, and using just 60 GPUs running for a few days, the authors say they managed to generate a million correlated 53-bit strings—meaning, strings that all agree on a specific subset of 20 or so bits—that achieve a high linear cross-entropy score.

Alas, I haven’t had time this weekend to write a “proper” blog post about this, but several people have by now emailed to ask my opinion, so I thought I’d share the brief response I sent to a journalist.

This does look like a significant advance on simulating Sycamore-like random quantum circuits! Since it’s based on tensor networks, you don’t need the literally largest supercomputer on the planet filling up tens of petabytes of hard disk space with amplitudes, as in the brute-force strategy proposed by IBM. Pan and Zhang’s strategy seems most similar to the strategy previously proposed by Alibaba, with the key difference being that the new approach generates millions of correlated samples rather than just one.

I guess my main thoughts for now are:

1. Once you knew about this particular attack, you could evade it and get back to where we were before by switching to a more sophisticated verification test — namely, one where you not only computed a Linear XEB score for the observed samples, you also made sure that the samples didn’t share too many bits in common.  (Strangely, though, the paper never mentions this point.)
2. The other response, of course, would just be to redo random circuit sampling with a slightly bigger quantum computer, like the ~70-qubit devices that Google, IBM, and others are now building!

Anyway, very happy for thoughts from anyone who knows more.

As I lay bedridden this week, knocked out by my second dose of the Moderna vaccine, I decided I should blog some more half-baked ideas because what the hell? It feels therapeutic, I have tenure, and anyone who doesn’t like it can close their broswer tab.

So: although I’ve written tens of thousands of words, on this blog and elsewhere, about interpretations of quantum mechanics, again and again I’ve dodged the question of which interpretation (if any) I really believe myself. Today, at last, I’ll emerge from the shadows and tell you precisely where I stand.

I hold that all interpretations of QM are just crutches that are better or worse at helping you along to the Zen realization that QM is what it is and doesn’t need an interpretation.  As Sidney Coleman famously argued, what needs reinterpretation is not QM itself, but all our pre-quantum philosophical baggage—the baggage that leads us to demand, for example, that a wavefunction |ψ⟩ either be “real” like a stubbed toe or else “unreal” like a dream. Crucially, because this philosophical baggage differs somewhat from person to person, the “best” interpretation—meaning, the one that leads most quickly to the desired Zen state—can also differ from person to person. Meanwhile, though, thousands of physicists (and chemists, mathematicians, quantum computer scientists, etc.) have approached the Zen state merely by spending decades working with QM, never worrying much about interpretations at all. This is probably the truest path; it’s just that most people lack the inclination, ability, or time.

Greg Kuperberg, one of the smartest people I know, once told me that the problem with the Many-Worlds Interpretation is not that it says anything wrong, but only that it’s “melodramatic” and “overwritten.” Greg is far along the Zen path, probably further than me.

You shouldn’t confuse the Zen Anti-Interpretation with “Shut Up And Calculate.” The latter phrase, mistakenly attributed to Feynman but really due to David Mermin, is something one might say at the beginning of the path, when one is as a baby. I’m talking here only about the endpoint of the path, which one can approach but never reach—the endpoint where you intuitively understand exactly what a Many-Worlder, Copenhagenist, or Bohmian would say about any given issue, and also how they’d respond to each other, and how they’d respond to the responses, etc. but after years of study and effort you’ve returned to the situation of the baby, who just sees the thing for what it is.

I don’t mean to say that the interpretations are all interchangeable, or equally good or bad. If you had to, you could call even me a “Many-Worlder,” but only in the following limited sense: that in fifteen years of teaching quantum information, my experience has consistently been that for most students, Everett’s crutch is the best one currently on the market. At any rate, it’s the one that’s the most like a straightforward picture of the equations, and the least like a wobbly tower of words that might collapse if you utter any wrong ones.  Unlike Bohr, Everett will never make you feel stupid for asking the questions an inquisitive child would ask; he’ll simply give you answers that are as clear, logical, and internally consistent as they are metaphysically extravagant. That’s a start.

The Copenhagen Interpretation retains a place of honor as the first crutch, for decades the only crutch, and the one closest to the spirit of positivism. Unfortunately, wielding the Copenhagen crutch requires mad philosophical skillz—which parts of the universe should you temporarily regard as “classical”? which questions should be answered, and which deflected?—to the point where, if you’re capable of all that verbal footwork, then why do you even need a crutch in the first place? In the hands of amateurs—meaning, alas, nearly everyone—Copenhagen often leads away from rather than toward the Zen state, as one sees with the generations of New-Age bastardizations about “observations creating reality.”

As for deBroglie-Bohm—well, that’s a weird, interesting, baroque crutch, one whose actual details (the preferred basis and the guiding equation) are historically contingent and tied to specific physical systems. It’s probably the right crutch for someone—it gets eternal credit for having led Bell to discover the Bell inequality—but its quirks definitely need to be discarded along the way.

Note that, among those who approach the Zen state, many might still call themselves Many-Worlders or Copenhagenists or Bohmians or whatever—just as those far along in spiritual enlightenment might still call themselves Buddhists or Catholics or Muslims or Jews (or atheists or agnostics)—even though, by that point, they might have more in common with each other than they do with their supposed coreligionists or co-irreligionists.

Alright, but isn’t all this Zen stuff just a way to dodge the actual, substantive questions about QM, by cheaply claiming to have transcended them? If that’s your charge, then please help yourself to the following FAQ about the details of the Zen Anti-Interpretation.

1. What is a quantum state? It’s a unit vector of complex numbers (or if we’re talking about mixed states, then a trace-1, Hermitian, positive semidefinite matrix), which encodes everything there is to know about a physical system.
   
2. OK, but are the quantum states “ontic” (really out in the world), or “epistemic” (only in our heads)? Dude. Do “basketball games” really exist, or is that just a phrase we use to summarize our knowledge about certain large agglomerations of interacting quarks and leptons? Do even the “quarks” and “leptons” exist, or are those just words for excitations of the more fundamental fields? Does “jealousy” exist? Pretty much all our concepts are complicated grab bags of “ontic” and “epistemic,” so it shouldn’t surprise us if quantum states are too. Bad dichotomy.
   
3. Why are there probabilities in QM? Because QM is a (the?) generalization of probability theory to involve complex numbers, whose squared absolute values are probabilities. It includes probability as a special case.
   
4. But why do the probabilities obey the Born rule? Because, once the unitary part of QM has picked out the 2-norm as being special, for the probabilities also to be governed by the 2-norm is pretty much the only possibility that makes mathematical sense; there are many nice theorems formalizing that intuition under reasonable assumptions.
   
5. What is an “observer”? It’s exactly what modern decoherence theory says it is: a particular kind of quantum system that interacts with other quantum systems, becomes entangled with them, and thereby records information about them—reversibly in principle but irreversibly in practice.
   
6. Can observers be manipulated in coherent superposition, as in the Wigner’s Friend scenario? If so, they’d be radically unlike any physical system we’ve ever had direct experience with. So, are you asking whether such “observers” would be conscious, or if so what they’d be conscious of? Who the hell knows?
   
7. Do “other” branches of the wavefunction—ones, for example, where my life took a different course—exist in the same sense this one does? If you start with a quantum state for the early universe and then time-evolve it forward, then yes, you’ll get not only “our” branch but also a proliferation of other branches, in the overwhelming majority of which Donald Trump was never president and civilization didn’t grind to a halt because of a bat near Wuhan.  But how could we possibly know whether anything “breathes fire” into the other branches and makes them real, when we have no idea what breathes fire into this branch and makes it real? This is not a dodge—it’s just that a simple “yes” or “no” would fail to do justice to the enormity of such a question, which is above the pay grade of physics as it currently exists. 
   
8. Is this it? Have you brought me to the end of the path of understanding QM? No, I’ve just pointed the way toward the beginning of the path. The most fundamental tenet of the Zen Anti-Interpretation is that there’s no shortcut to actually working through the Bell inequality, quantum teleportation, Shor’s algorithm, the Kochen-Specker and PBR theorems, possibly even a … photon or a hydrogen atom, so you can see quantum probability in action and be enlightened. I’m further along the path than I was twenty years ago, but not as far along as some of my colleagues. Even the greatest quantum Zen masters will be able to get further when new quantum phenomena and protocols are discovered in the future. All the same, though—and this is another major teaching of the Zen Anti-Interpretation—there’s more to life than achieving greater and greater clarity about the foundations of QM. And on that note…

To those who asked me about Claus Peter Schnorr’s claim to have discovered a fast classical factoring algorithm, thereby “destroying” (in his words) the RSA cryptosystem, see (e.g.) this Twitter thread by Keegan Ryan, which explains what certainly looks like a fatal error in Schnorr’s paper.

A month ago, UT Austin changed its email policies—banning auto-forwarding from university accounts to Gmail accounts, apparently as a way to force the faculty and other employees to separate their work email from their personal email, and thereby comply with various government regulations. Ever since that change, the email part of my life has been a total, unmitigated disaster. I’ve missed (or been late to see) dozens of important work emails, with the only silver lining being that that’s arguably UT’s problem more than it is mine!

And yes, I’ve already gone to technical support; the only answer I’ve gotten is that (in so many words) there is no answer. Other UT faculty are somehow able to deal with this because they are them; I am unable to deal with it because I am me. As a mere PhD in computer science, I’m utterly unqualified to set up a technical fix for this sort of problem.

So the bottom line is: from now on, if you want me to see an email, send it to scott@scottaaronson.com. Really. If you try sending it to aaronson@cs.utexas.edu, it will land in a separate inbox that I can access only with great inconvenience. And if, God forbid, you try sending it to aaronson@utexas.edu, the email will bounce and I’ll never see it at all. Indeed, a central purpose of this post is just to have a place to point the people who contact me every day, shocked that their emails to me bounced.

This whole episode has given me immense sympathy for Hillary Clinton, and for the factors that led her to set up clintonemail.com from her house. It’s not merely that her private email server was a laughably trivial reason to end the United States’ 240-year run of democratic government. Rather it’s that, even on the narrow question of emails, I now feel certain that Hillary was 100% right. Bureaucracy that impedes communication is a cancer on human civilization.

Update: Thanks so much to commenter Avraham and to my colleague Etienne Vouga, who quickly gave me the crucial information that tech support would not, and thereby let me solve this problem. I can once again easily read emails sent to aaronson@cs.utexas.edu … well, at least for now! I’m now checking about aaronson@utexas.edu. Again, though, scott@scottaaronson.com to be safe.

This past week, I spent so much mental energy worrying about the fate of Scott Alexander that I almost forgot that right here in Texas, I’m surrounded by historic scenes of Third-World-style devastation: snowstorms and sub-freezing temperatures for which our infrastructure was completely unprepared; impassable roads; burst gas and water pipes; millions without electricity or heat or clean water; the UT campus a short walk from me converted into a giant refugee camp.

For all those who asked: my family and I are fine. While many we know were without power for days (or are still without power), we lucked out by living close to a hospital, which means that they can’t shut off the electricity to our block. We are now on a boil-water notice, like all of Austin, and we can’t take deliveries or easily go anywhere, and the university and schools and daycares are all closed (even for remote learning). Which means: we’re simply holed up in our house, eating through our stockpiled food, the kids running around being crazy, Dana and I watching them with one eye and our laptops with the other. Could be worse.

In some sense, it’s not surprising that the Texas infrastructure would buckle under weather stresses outside the envelope of anything it was designed for or saw for decades. The central problem is that our elected leaders have shown zero indication of understanding the urgent need, for Texas’ economic viability, to do whatever it takes to make sure nothing like this ever happens again. Ted Cruz, as everyone now knows, left for Cancun; the mayor of Colorado City angrily told everyone to fend for themselves (and then resigned); and Governor Abbott has been blaming frozen wind turbines, a tiny percentage of the problem (frozen gas pipes are a much bigger issue) but one that plays with the base. The bare minimum of a sane response might be, I dunno,

• acknowledging the reality that climate change means that “once-per-century” weather events will be every couple years from now on,
• building spare capacity (nuclear would be ideal … well, I can dream),
• winterizing what we have now, and
• connecting the Texas grid to the rest of the US.

If I were a Texas Democrat, I’d consider making Republican incompetence on infrastructure, utilities, and public health my only campaign issues.

Alright, now back to watching the Mars lander, which is apparently easier to build and deploy than a reliable electric grid.

Note: To get myself into the spirit of writing this post, tonight I watched the 2019 movie Mr. Jones, about the true story of the coverup of Stalin’s 1932-3 mass famine by New York Times journalist Walter Duranty. Recommended!

In my last post, I wrote that despite all my problems with Cade Metz’s New York Times hit piece on Scott Alexander, I’d continue talking to journalists—even Metz himself, I added, assuming he’d still talk to me after my public disparagement of his work. Over the past few days, though, the many counterarguments in my comments section and elsewhere gradually caused me to change my mind. I now feel like to work with Metz again, even just on some quantum computing piece, would be to reward—and to be seen as rewarding—journalistic practices that are making the world worse, and that this consideration overrides even my extreme commitment to openness.

At the least, before I could talk to Metz again, I’d need a better understanding of how the hit piece happened. What was the role of the editors? How did the original hook—namely, the rationalist community’s early rightness about covid-19—disappear entirely from the article? How did the piece manage to evince so little curiosity about such an unusual subculture and such a widely-admired writer? How did it fail so completely to engage with the rationalists’ ideas, instead jumping immediately to “six degrees of Peter Thiel” and other reductive games? How did an angry SneerClubber, David Gerard, end up (according to his own boast) basically dictating the NYT piece’s content?

It’s always ripping-off-a-bandage painful to admit when trust in another person was wildly misplaced—for then who else can we not trust? But sometimes that’s the truth of it.

I continue to believe passionately in the centrality of good journalism to a free society. I’ll continue to talk to journalists often, about quantum computing or whatever else. I also recognize that the NYT is a large, heterogeneous institution (I myself published in it twice); it’s not hard to imagine that many of its own staff take issue with the SSC piece.

But let’s be clear about the stakes here. In the discussion of my last post, I described the NYT as “still the main vessel of consensus reality in human civilization” [alright, alright, American civilization!]. What’s really at issue, beyond the treatment of a single blogger, is whether the NYT can continue serving that central role in a world reshaped by social media, resurgent fascism, and entitled wokery.

Sure, we all know that the NYT has been disastrously wrong before: it ridiculed Goddard’s dream of spaceflight, denied the Holodomor, relegated the Holocaust to the back pages while it was happening, published the fabricated justifications for the Iraq War. But the NYT and a few other publications were still the blockchain of reality, the engine of the consensus of all that is, the last bulwark against the conspiracists and the anti-vaxxers and the empowered fabulists and the horned insurrectionists storming the Capitol, because there was no ability to coordinate around any serious alternative. I’m still skeptical that there’s a serious alternative, but I now look more positively than I did just a few days ago on attempts to create one.

To all those who called me naïve or a coward for having cooperated with the NYT: believe me, I’m well aware that I wasn’t born with much backbone. (I am, after all, that guy on the Internet who famously once planned on a life of celibate asceticism, or more likely suicide, rather than asking women out and thereby risking eternal condemnation as a misogynistic sexual harasser by the normal, the popular, the socially adept, the … humanities grads and the journalists.) But whenever I need a pick-me-up, I tell myself that rather than being ashamed about my lack of a backbone, I can take pride in having occasionally managed to stand even without one.

Updates (Feb. 14, 2021): Scott Alexander Siskind responds here.

Last night, it occurred to me that despite how disjointed it feels, the New York Times piece does have a central thesis: namely, that rationalism is a “gateway drug” to dangerous beliefs. And that thesis is 100% correct—insofar as once you teach people that they can think for themselves about issues of consequence, some of them might think bad things. It’s just that many of us judge the benefit worth the risk!

Happy Valentine’s Day everyone!

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Back in June, New York Times technology reporter Cade Metz, who I’d previously known from his reporting on quantum computing, told me that he was writing a story about Scott Alexander, Slate Star Codex, and the rationalist community. Given my position as someone who knew the rationalist community without ever really being part of it, Cade wondered whether I’d talk with him. I said I’d be delighted to.

I spent many hours with Cade, taking his calls and emails morning or night, at the playground with my kids or wherever else I was, answering his questions, giving context for his other interviews, suggesting people in the rationalist community for him to talk to, in exactly the same way I might suggest colleagues for a quantum computing story. And then I spent just as much time urging those people to talk to Cade. (“How could you possibly not want to talk? It’s the New York Times!”) Some of the people I suggested agreed to talk; others refused; a few were livid at me for giving a New York Times reporter their email addresses without asking them. (I apologized; lesson learned.)

What happened next is already the stuff of Internet history: the NYT’s threat to publish Scott’s real surname; Scott deleting his blog as a way to preempt that ‘doxing’; 8,000 people, including me, signing a petition urging the NYT to respect Scott’s wish to keep his professional and blog identities separate; Scott resigning from his psychiatry clinic and starting his own low-cost practice, Lorien Psychiatry; his moving his blog, like so many other writers this year, to Substack; then, a few weeks ago, his triumphant return to blogging under his real name of Scott Siskind. All this against the backdrop of an 8-month period that was world-changingly historic in so many other ways: the failed violent insurrection against the United States and the ouster, by democratic means, of the president who incited it; the tragedy of covid and the long-delayed start of the vaccination campaign; the BLM protests; the well-publicized upheavals at the NYT itself, including firings for ideological lapses that would’ve made little sense to our remote ancestors of ~2010.

And now, as an awkward coda, the New York Times article itself is finally out (non-paywalled version here).

It could’ve been worse. I doubt it will do lasting harm. Of the many choices I disagreed with, I don’t know which were Cade’s and which his editors’. But no, I was not happy with it. If you want a feature-length, pop condensation of the rationalist community and its ideas, I preferred this summer’s New Yorker article (but much better still is the book by Tom Chivers).

The trouble with the NYT piece is not that it makes any false statements, but just that it constantly insinuates nefarious beliefs and motives, via strategic word choices and omission of relevant facts that change the emotional coloration of the facts that it does present. I repeatedly muttered to myself, as I read: “dude, you could make anything sound shady with this exact same rhetorical toolkit!”

Without further ado, here’s a partial list of my issues:

1. The piece includes the following ominous sentence: “But in late June of last year, when I approached Siskind to discuss the blog, it vanished.”  This framing, it seems to me, would be appropriate for some conman trying to evade accountability without ever explaining himself. It doesn’t make much sense for a practicing psychiatrist who took the dramatic step of deleting his blog in order to preserve his relationship with his patients—thereby complying with an ethical code that’s universal among psychiatrists, even if slightly strange to the rest of us—and who immediately explained his reasoning to the entire world. In the latter framing, of course, Scott comes across less like a fugitive on the run and more like an innocent victim of a newspaper’s editorial obstinacy.
   
2. As expected, the piece devotes enormous space to the idea of rationalism as an on-ramp to alt-right extremism.  The trouble is, it never presents the idea that rationalism also can be an off-ramp from extremism—i.e., that it can provide a model for how even after you realize that mainstream sources are confidently wrong on some issue, you don’t respond by embracing conspiracy theories and hatreds, you respond by simply thinking carefully about each individual question rather than buying a worldview wholesale from anyone.  Nor does the NYT piece mention how Scott, precisely because he gives right-wing views more charity than some of us might feel they deserve, actually succeeded in dissuading some of his readers from voting for Trump—which is more success than I can probably claim in that department! I had many conversations with Cade about these angles that are nowhere reflected in the piece.
   
3. The piece gets off on a weird foot, by describing the rationalists as “a group that aimed to re-examine the world through cold and careful thought.”  Why “cold”?  Like, let’s back up a few steps: what is even the connection in the popular imagination between rationality and “coldness”? To me, as to many others, the humor, humanity, and warmth of Scott’s writing were always among its most notable features.
   
4. The piece makes liberal use of scare quotes. Most amusingly, it puts scare quotes around the phrase “Bayesian reasoning”!
   
5. The piece never mentions that many rationalists (Zvi Mowshowitz, Jacob Falkovich, Kelsey Piper…) were right about the risk of covid-19 in early 2020, and then again right about masks, aerosol transmission, faster-spreading variants, the need to get vaccines into arms faster, and many other subsidiary issues, even while public health authorities and the mainstream press struggled for months to reach the same obvious (at least in retrospect) conclusions.  This omission is significant because Cade told me, in June, that the rationalist community’s early rightness about covid was part of what led him to want to write the piece in the first place (!).  If readers knew about that clear success, would it put a different spin on the rationalists’ weird, cultlike obsession with “Bayesian reasoning” and “consequentialist ethics” (whatever those are), or their nerdy, idiosyncratic worries about the more remote future?
   
6. The piece contains the following striking sentence: “On the internet, many in Silicon Valley believe, everyone has the right not only to say what they want but to say it anonymously.” Well, yes, except this framing makes it sound like this is a fringe belief of some radical Silicon Valley tribe, rather than just the standard expectation of most of the billions of people who’ve used the Internet for most of its half-century of existence.
   
7. Despite thousands of words about the content of SSC, the piece never gives Scott a few uninterrupted sentences in his own voice, to convey his style. This is something the New Yorker piece did do, and which would help readers better understand the wit, humor, charity, and self-doubt that made SSC so popular.  To see what I mean, read the NYT’s radically-abridged quotations from Scott’s now-classic riff on the Red, Blue, and Gray Tribes and decide for yourself whether they capture the spirit of the original (alright, I’ll quote the relevant passage myself at the bottom of this post). Scott has the property, shared by many of my favorite writers, that if you just properly quote him, the words leap off the page, wriggling free from the grasp of any bracketing explanations and making a direct run for the reader’s brain. All the more reason to quote him!
   
8. The piece describes SSC as “astoundingly verbose.”  A more neutral way to put it would be that Scott has produced a vast quantity of intellectual output.  When I finish a Scott Alexander piece, only in a minority of cases do I feel like he spent more words examining a problem than its complexities really warranted.  Just as often, I’m left wanting more.
   
9. The piece says that Scott once “aligned himself” with Charles Murray, then goes on to note Murray’s explosive views about race and IQ. That might be fair enough, were it also mentioned that the positions ascribed to Murray that Scott endorses in the relevant post—namely, “hereditarian leftism” and universal basic income—are not only unrelated to race but are actually progressive positions.
   
10. The piece says that Scott once had neoreactionary thinker Nick Land on his blogroll. Again, important context is missing: this was back when Land was mainly known for his strange writings on AI and philosophy, before his neoreactionary turn.
    
11. The piece says that Scott compared “some feminists” to Voldemort.  It didn’t explain what it took for certain specific feminists (like Amanda Marcotte) to prompt that comparison, which might have changed the coloration. (Another thing that would’ve complicated the picture: the rationalist community’s legendary openness to alternative gender identities and sexualities, before such openness became mainstream.)
    
12. Speaking of feminists—yeah, I’m a minor part of the article.  One of the few things mentioned about me is that I’ve stayed in a rationalist group house.  (If you must know: for like two nights, when I was in Bay Area, with my wife and kids. We appreciated the hospitality!) The piece also says that I was “turned off by the more rigid and contrarian beliefs of the Rationalists.” It’s true that I’ve disagreed with many beliefs espoused by rationalists, but not because they were contrarian, or because I found them noticeably more “rigid” than most beliefs—only because I thought they were mistaken!
    
13. The piece describes Eliezer Yudkowsky as a “polemicist and self-described AI researcher.”  It’s true that Eliezer opines about AI despite a lack of conventional credentials in that field, and it’s also true that the typical NYT reader might find him to be comically self-aggrandizing.  But had the piece mentioned the universally recognized AI experts, like Stuart Russell, who credit Yudkowsky for a central role in the AI safety movement, wouldn’t that have changed what readers perceived as the take-home message?
    
14. The piece says the following about Shane Legg and Demis Hassabis, the founders of DeepMind: “Like the Rationalists, they believed that AI could end up turning against humanity, and because they held this belief, they felt they were among the only ones who were prepared to build it in a safe way.”  This strikes me as a brilliant way to reframe a concern around AI safety as something vaguely sinister.  Imagine if the following framing had been chosen instead: “Amid Silicon Valley’s mad rush to invest in AI, here are the voices urging that it be done safely and in accord with human welfare…”

Reading this article, some will say that they told me so, or even that I was played for a fool.  And yet I confess that, even with hindsight, I have no idea what I should have done differently, how it would’ve improved the outcome, or what I will do differently the next time. Was there some better, savvier way for me to help out? For each of the 14 points listed above, were I ever tempted to bang my head and say, “dammit, I wish I’d told Cade X, so his story could’ve reflected that perspective”—well, the truth of the matter is that I did tell him X! It’s just that I don’t get to decide which X’s make the final cut, or which ideological filter they’re passed through first.

On reflection, then, I’ll continue to talk to journalists, whenever I have time, whenever I think I might know something that might improve their story. I’ll continue to rank bend-over-backwards openness and honesty among my most fundamental values. Hell, I’d even talk to Cade for a future story, assuming he’ll talk to me after all the disagreements I’ve aired here! [Update: commenters’ counterarguments caused me to change my stance on this; see here.]

For one thing that became apparent from this saga is that I do have a deep difference with the rationalists, one that will likely prevent me from ever truly joining them. Yes, there might be true and important things that one can’t say without risking one’s livelihood. At least, there were in every other time and culture, so it would be shocking if Western culture circa 2021 were the lone exception. But unlike the rationalists, I don’t feel the urge to form walled gardens in which to say those things anyway. I simply accept that, in the age of instantaneous communication, there are no walled gardens: anything you say to a dozen or more people, you might as well broadcast to the planet. Sure, we all have things we say only in the privacy of our homes or to a few friends—a privilege that I expect even the most orthodox would like to preserve, at any rate for themselves. Beyond that, though, my impulse has always been to look for non-obvious truths that can be shared openly, and that might light little candles of understanding in one or two minds—and then to shout those truths from the rooftops under my own name, and learn what I can from whatever sounds come in reply.

So I’m thrilled that Scott Alexander Siskind has now rearranged his life to have the same privilege. Whatever its intentions, I hope today’s New York Times article draws tens of thousands of curious new readers to Scott’s new-yet-old blog, Astral Codex Ten, so they can see for themselves what I and so many others saw in it. I hope Scott continues blogging for decades. And whatever obscene amount of money Substack is now paying Scott, I hope they’ll soon be paying him even more.

---

Alright, now for the promised quote, from I Can Tolerate Anything Except the Outgroup.

The Red Tribe is most classically typified by conservative political beliefs, strong evangelical religious beliefs, creationism, opposing gay marriage, owning guns, eating steak, drinking Coca-Cola, driving SUVs, watching lots of TV, enjoying American football, getting conspicuously upset about terrorists and commies, marrying early, divorcing early, shouting “USA IS NUMBER ONE!!!”, and listening to country music.

The Blue Tribe is most classically typified by liberal political beliefs, vague agnosticism, supporting gay rights, thinking guns are barbaric, eating arugula, drinking fancy bottled water, driving Priuses, reading lots of books, being highly educated, mocking American football, feeling vaguely like they should like soccer but never really being able to get into it, getting conspicuously upset about sexists and bigots, marrying later, constantly pointing out how much more civilized European countries are than America, and listening to “everything except country”.

(There is a partly-formed attempt to spin off a Grey Tribe typified by libertarian political beliefs, Dawkins-style atheism, vague annoyance that the question of gay rights even comes up, eating paleo, drinking Soylent, calling in rides on Uber, reading lots of blogs, calling American football “sportsball”, getting conspicuously upset about the War on Drugs and the NSA, and listening to filk – but for our current purposes this is a distraction and they can safely be considered part of the Blue Tribe most of the time)

… Even in something as seemingly politically uncharged as going to California Pizza Kitchen or Sushi House for dinner, I’m restricting myself to the set of people who like cute artisanal pizzas or sophsticated foreign foods, which are classically Blue Tribe characteristics.

[updates: here’s the paper, and here’s Robin’s brief response to some of the comments here]

This month Robin Hanson, the famous and controversy-prone George Mason University economics professor who I’ve known since 2004, was visiting economists here in Austin for a few weeks. So, while my fear of covid considerably exceeds Robin’s, I met with him a few times in the mild Texas winter in an outdoor, socially-distanced way. It took only a few minutes for me to remember why I enjoy talking to Robin so much.

See, while I’d been moping around depressed about covid, the vaccine rollout, the insurrection, my inability to focus on work, and a dozen other things, Robin was bubbling with excitement about a brand-new mathematical model he was working on to understand the growth of civilizations across the universe—a model that, Robin said, explained lots of cosmic mysteries in one fell swoop and also made striking predictions. My cloth facemask was, I confess, unable to protect me from Robin’s infectious enthusiasm.

As I listened, I went through the classic stages of reaction to a new Hansonian proposal: first, bemusement over the sheer weirdness of what I was being asked to entertain, as well as Robin’s failure to acknowledge that weirdness in any way whatsoever; then, confusion about the unstated steps in his radically-condensed logic; next, the raising by me of numerous objections (each of which, it turned out, Robin had already thought through at length); finally, the feeling that I must have seen it this way all along, because isn’t it kind of obvious?

Robin has been explaining his model in a sequence of Overcoming Bias posts, and will apparently have a paper out about the model soon the paper is here! In this post, I’d like to offer my own take on what Robin taught me. Blame for anything I mangle lies with me alone.

To cut to the chase, Robin is trying to explain the famous Fermi Paradox: why, after 60+ years of looking, and despite the periodic excitement around Tabby’s star and ‘Oumuamua and the like, have we not seen a single undisputed sign of an extraterrestrial civilization? Why all this nothing, even though the observable universe is vast, even though (as we now know) organic molecules and planets in Goldilocks zones are everywhere, and even though there have been billions of years for aliens someplace to get a technological head start on us, expanding across a galaxy to the point where they’re easily seen?

Traditional answers to this mystery include: maybe the extraterrestrials quickly annihilate themselves in nuclear wars or environmental cataclysms, just like we soon will; maybe the extraterrestrials don’t want to be found (whether out of self-defense or a cosmic Prime Directive); maybe they spend all their time playing video games. Crucially, though, all answers of that sort founder against the realization that, given a million alien civilizations, each perhaps more different from the others than kangaroos are from squid, it would only take one, spreading across a billion light-years and transforming everything to its liking, for us to have noticed it.

Robin’s answer to the puzzle is as simple as it is terrifying. Such civilizations might well exist, he says, but if so, by the time we noticed one, it would already be nearly too late. Robin proposes, plausibly I think, that if you give a technological civilization 10 million or so years—i.e., an eyeblink on cosmological timescales—then either

1. the civilization wipes itself out, or else
2. it reaches some relatively quiet steady state, or else
3. if it’s serious about spreading widely, then it “maxes out” the technology with which to do so, approaching the limits set by physical law.

In cases 1 or 2, the civilization will of course be hard for us to detect, unless it happens to be close by. But what about case 3? There, Robin says, the “civilization” should look from the outside like a sphere expanding at nearly the speed of light, transforming everything in its path.

Now think about it: when could we, on earth, detect such a sphere with our telescopes? Only when the sphere’s thin outer shell had reached the earth—perhaps carrying radio signals from the extraterrestrials’ early history, before their rapid expansion started. By that point, though, the expanding sphere itself would be nearly upon us!

What would happen to us once we were inside the sphere? Who knows? The expanding civilization might obliterate us, it might preserve us as zoo animals, it might merge us into its hive-mind, it might do something else that we can’t imagine, but in any case, detecting the civilization would presumably no longer be the relevant concern!

(Of course, one could also wonder what happens when two of these spheres collide: do they fight it out? do they reach some agreement? do they merge? Whatever the answer, though, it doesn’t matter for Robin’s argument.)

On the view described, there’s only a tiny cosmic window in which a SETI program could be expected to succeed: namely, when the thin surface of the first of these expanding bubbles has just hit us, and when that surface hasn’t yet passed us by. So, given our “selection bias”—meaning, the fact that we apparently haven’t yet been swallowed up by one of the bubbles—it’s no surprise if we don’t right now happen to find ourselves in the tiny detection window!

This basic proposal, it turns out, is not original to Robin. Indeed, an Overcoming Bias reader named Daniel X. Varga pointed out to Robin that he (Daniel) shared the same idea right here—in a Shtetl-Optimized comment thread—back in 2008! I must have read Daniel Varga’s comment then, but (embarrassingly) it didn’t make enough of an impression for me to have remembered it. I probably thought the same as you probably thought while reading this post:

“Sure, whatever. This is an amusing speculation that could make for a fun science-fiction story. Alas, like with virtually every story about extraterrestrials, there’s no good reason to favor this over a hundred other stories that a fertile imagination could just as easily spin. Who the hell knows?”

This is where Robin claims to take things further. Robin would say that he takes them further by developing a mathematical model, and fitting the parameters of the model to the known facts of cosmic history. Read Overcoming Bias, or Robin’s forthcoming paper, if you want to know the details of his model. Personally, I confess I’m less interested in those details than I am in the qualitative points, which (unless I’m mistaken) are easy enough to explain in words.

The key realization is this: when we contemplate the Fermi Paradox, we know more than the mere fact that we look and look and we don’t see any aliens. There are other relevant data points to fit, having to do with the one sample of a technological civilization that we do have.

For starters, there’s the fact that life on earth has been evolving for at least ~3.5 billion years—for most of the time the earth has existed—but life has a mere billion more years to go, until the expanding sun boils away the oceans and makes the earth barely habitable. In other words, at least on this planet, we’re already relatively close to the end. Why should that be?

It’s an excellent fit, Robin says, to a model wherein there are a few incredibly difficult, improbable steps along the way to a technological civilization like ours—steps that might include the origin of life, of multicellular life, of consciousness, of language, of something else—and wherein, having achieved some step, evolution basically just does a random search until it either stumbles onto the next step or else runs out of time.

Of course, given that we’re here to talk about it, we necessarily find ourselves on a planet where all the steps necessary for blog-capable life happen to have succeeded. There might be vastly more planets where evolution got stuck on some earlier step.

But here’s the interesting part: conditioned on all the steps having succeeded, we should find ourselves near the end of the useful lifetime of our planet’s star—simply because the more time is available on a given planet, the better the odds there. I.e., look around the universe and you should find that, on most of the planets where evolution achieves all the steps, it nearly runs out the planet’s clock in doing so. Also, as we look back, we should find the hard steps roughly evenly spaced out, with each one having taken a good fraction of the whole available time. All this is an excellent match for what we see.

OK, but it leads to a second puzzle. Life on earth is at least ~3.5 billion years old, while the observable universe is ~13.7 billion years old. Forget for a moment about the oft-stressed enormity of these two timescales and concentrate on their ratio, which is merely ~4. Life on earth stretches a full quarter of the way back in time to the Big Bang. Even as an adolescent, I remember finding that striking, and not at all what I would’ve guessed a priori. It seemed like obviously a clue to something, if I could only figure out what.

The puzzle is compounded once you realize that, even though the sun will boil the oceans in a billion years (and then die in a few billion more), other stars, primarily dwarf stars, will continue shining brightly for trillions more years. Granted, the dwarf stars don’t seem quite as hospitable to life as sun-like stars, but they do seem somewhat hospitable, and there will be lots of them—indeed, more than of sun-like stars. And they’ll last orders of magnitude longer.

To sum up, our temporal position relative to the lifetime of the sun makes it look as though life on earth was just a lucky draw from a gigantic cosmic Poisson process. By contrast, our position relative to the lifetime of all the stars makes it look as though we arrived crazily, freakishly early—not at all what you’d expect under a random model. So what gives?

Robin contends that all of these facts are explained under his bubble scenario. If we’re to have an experience remotely like the human one, he says, then we have to be relatively close to the beginning of time—since hundreds of billions of years from now, the universe will likely be dominated by near-light-speed expanding spheres of intelligence, and a little upstart civilization like ours would no longer stand a chance. I.e., even though our existence is down to some lucky accidents, and even though those same accidents probably recur throughout the cosmos, we shouldn’t yet see any of the other accidents, since if we did see them, it would already be nearly too late for us.

Robin admits that his account leaves a huge question open: namely, why should our experience have been a “merely human,” “pre-bubble” experience at all? If you buy that these expanding bubbles are coming, it seems likely that there will be trillions of times more sentient experiences inside them than outside. So experiences like ours would be rare and anomalous—like finding yourself at the dawn of human history, with Hammurabi et al., and realizing that almost every interesting thing that will ever happen is still to the future. So Robin simply takes as a brute fact that our experience is “earth-like” or “human-like”; he then tries to explain the other observations from that starting point.

Notice that, in Robin’s scenario, the present epoch of the universe is extremely special: it’s when civilizations are just forming, when perhaps a few of them will achieve technological liftoff, but before one or more of the civilizations has remade the whole of creation for its own purposes. Now is the time when the early intelligent beings like us can still look out and see quadrillions of stars shining to no apparent purpose, just wasting all that nuclear fuel in a near-empty cosmos, waiting for someone to come along and put the energy to good use. In that respect, we’re sort of like the Maoris having just landed in New Zealand, or Bill Gates surveying the microcomputer software industry in 1975. We’re ridiculously lucky. The situation is way out of equilibrium. The golden opportunity in front of us can’t possibly last forever.

If we accept the above, then a major question I had was the role of cosmology. In 1998, astronomers discovered that the present cosmological epoch is special for a completely different reason than the one Robin talks about. Namely, right now is when matter and dark energy contribute roughly similarly to the universe’s energy budget, with ~30% the former and ~70% the latter. Billions of years hence, the universe will become more and more dominated by dark energy. Our observable region will get sparser and sparser, as the dark energy pushes the galaxies further and further away from each other and from us, with more and more galaxies receding past the horizon where we could receive signals from them at the speed of light. (Which means, in particular, that if you want to visit a galaxy a few billion light-years from here, you’d better start out while you still can!)

So here’s my question: is it just a coincidence that the time—right now—when the universe is “there for the taking,” potentially poised between competing spacefaring civilizations, is also the time when it’s poised between matter and dark energy? Note that, in 2007, Bousso et al. tried to give a sophisticated anthropic argument for the value of the cosmological constant Λ, which measures the density of dark energy, and hence the eventual size of the observable universe. See here for my blog post on what they did (“The array size of the universe”). Long story short, for reasons that I explain in the post, it turns out to be essential to their anthropic explanation for Λ that civilizations flourish only (or mainly) in the present epoch, rather than trillions of years in the future. If we had to count civilizations that far into the future, then the calculations would favor values of Λ much smaller than what we actually observe. This, of course, seems to dovetail nicely with Robin’s account.

Let me end with some “practical” consequences of Robin’s scenario, supposing as usual that we take it seriously. The most immediate consequence is that the prospects for SETI are dimmer than you might’ve thought before you’d internalized all this. (Even after having interalized it, I’d still like at least an order of magnitude more resources devoted to SETI than what our civilization currently spares. Robin’s assumptions might be wrong!)

But a second consequence is that, if we want human-originated sentience to spread across the universe, then the sooner we get started the better! Just like Bill Gates in 1975, we should expect that there will soon be competitors out there. Indeed, there are likely competitors out there “already” (where “already” means, let’s say, in the rest frame of the cosmic microwave background)—it’s just that the light from them hasn’t yet reached us. So if we want to determine our own cosmic destiny, rather than having post-singularity extraterrestrials determine it for us, then it’s way past time to get our act together as a species. We might have only a few hundred million more years to do so.

Update: For more discussion of this post, see the SSC Reddit thread. I especially liked a beautiful comment by “Njordsier,” which fills in some important context for the arguments in this post:

Suppose you’re an alien anthropologist that sent a probe to Earth a million years ago, and that probe can send back one high-resolution image of the Earth every hundred years. You’d barely notice humans at first, though they’re there. Then, circa 10,000 years ago (99% of the way into the stream) you begin to see plots of land turned into farms. Houses, then cities, first in a few isolated places in river valleys, then exploding across five or six continents. Walls, roads, aqueducts, castles, fortresses. Four frames before the end of the stream, the collapse of the population on two of the continents as invaders from another continent bring disease. At T-minus three frames, a sudden appearance of farmland and cities on the coasts those continents. At T-minus two frames, half the continent. At the second to last frame, a roaring interconnected network of roads, cities, farms, including skyscrapers in the cities that were just trying villas three frames ago. And in the last frame, nearly 80 percent of all wilderness converted to some kind of artifice, and the sky is streaked with the trails of flying machines all over the world.

Civilizations rose and fell, cultures evolved and clashed, and great and terrible men and women performed awesome deeds. But what the alien anthropologist sees is a consistent, rapid, exponential explosion of a species bulldozing everything in its path.

That’s what we’re doing when we talk about the far future, or about hypothetical expansionist aliens, on long time scales. We’re zooming out past the level where you can reason about individuals or cultures, but see the strokes of much longer patterns that emerge from that messy, beautiful chaos that is civilization.

Update (Jan. 31): Reading the reactions here, on Hacker News, and elsewhere underscored for me that a lot of people get off Robin’s train well before it’s even left the station. Such people think of extraterrestrial civilizations as things that you either find or, if you haven’t found one, you just speculate or invent stories about. They’re not even in the category of things that you have any serious hope to reason about. For myself, I’d simply observe that trying to reason about matters far beyond current human experience, based on the microscopic shreds of fact available to us (e.g., about the earth’s spatial and temporal position within the universe), has led to some of our species’ embarrassing failures but also to some of its greatest triumphs. Since even the failures tend to be relatively cheap, I feel like we ought to be “venture capitalists” about such efforts to reason beyond our station, encouraging them collegially and mocking them only gently.