Reply to Hanson

I was privileged to receive a reply from Robin Hanson on my critique of his largely excellent book The Elephant in the Brain with co-author Kevin Simler. I think in several cases he rebutted something other than what I argued, but I encourage you to read it and judge for yourself.

Given the high-profile book reviews that are probably forthcoming from places like the Wall Street Journal, I thank Robin for taking the time to engage with the little guys!


I’ll follow Robin’s lead and switch to first names.

Some say we should have been more academic and detailed, while other say we should have been more accessible and less detailed….Count Jess as someone who wanted a longer book.

It’s true that I’d have preferred a longer book with more details, but I think I gestured at ways Kevin and Robin could hold length constant while increasing convincingness. And there are ways of keeping the book accessible while augmenting the rigor (e.g., endnotes), although of course they are more work.

Yes for each motive one can distinguish both a degree of consciousness and also a degree of current vs past adaptation. But these topics were not essential for our main thesis, making credible claims on them takes a lot more evidence and argument, and we already had trouble with trying to cover too much material for one book.

I was mostly happy with how the authors handled the degree of consciousness. However, I think the current- vs past-adaptation distinction is very important for designing institutions, which Kevin and Robin correctly list as one of the main applications of the book’s material. For instance, should the arXiv host comments on papers, and how should they be implemented to avoid pissing contests?… [continue reading]

Comments on Simler and Hanson

Drawing on a large academic literature in topics like sociology, behavioral economics, anthropology, and psychology, and especially the (generalized) theory of signalling, Robin Hanson has assembled a large toolbox for systemically understanding hypocrisy, i.e., the ways in which people’s actions systematically and selfishly deviate from their verbalized explanations. Although he would be the first to admit that many of these ideas have been discovered and rediscovered repeatedly over centuries (or millennia) with varying degrees of clarity, and although there is much I am not convinced by, I find the general framework deeply insightful, and his presentation to be more clear, analytical, and descriptive (rather than disruptively normative) than other accounts. Most of this I have gathered from his renowned blogging at Overcoming Bias, but I have always wished for a more concise (and high status!) form factor that I could point others to. At long last, Hanson and his co-author Kevin Simler have written a nice book that largely satisfies me: The Elephant in the Brain (Amazon). I highly recommend it.

The reason I title these sorts of blog posts “Comments on…” is so I can present some disorganized responses to a work without feeling like I need to build a coherent thesis or pass overall judgment. I do not summarize the book below, so this post will mostly be useful for people who have read it. (You might think of this as a one-sided book club discussion rather than a book review.) But since I will naturally tend to focus on the places where I disagree with the authors, let me emphasize: the basic ideas of this book strike me as profound and probably mostly true.… [continue reading]

Links for December 2017

  • GiveWell has released their yearly top-charities list. CEA has announced they are running donor lotteries in addition to EA Funds. And OpenPhil gives up on finding the most neglected biological research, moves to opportunistic model of just funding good stuff when they see it (which probably has important lessons about the difficulty of transferring human knowledge).
  • Uber driver’s get paid to take footage from a dash camera as raw data for self-driving cars.
  • Blue Origin demos it’s sub-orbital space tourism ride, complete with a full-length video from inside the passenger viewing area:

    You can identify the several minutes of weightlessness by the floating particles.

  • Geoffrey Hinton on visualizing higher dimensions: ‘To deal with hyper-planes in a 14-dimensional space, visualize a 3-D space and say “fourteen” to yourself very loudly. Everyone does it.’
  • The explanation for why Europe is warm for it’s lattitude is more complicated than just the gulf stream: If you turn the jet stream off in climate models, there is a still a large temperature difference.
  • The primary use for my iPad is reading and annotating papers. It’s new secondary use is as a whiteboard during Skype. WebWhiteboard and AWW App both facilitate public whiteboards without needing a login/signup, and work pretty well with your browser on iPad. WebWhiteboard has a limited and dated interface, but is fairly reliable. AWW App has a more modern interface, but seems to have slow/unreliable servers. Then there are a ton of options that require signup, but I don’t know whether any are worth using.
  • By way of Eric Rogstad and Tyler Cowen is this new-to-me idea: In the same way that, theoretically, the value of fiat currency is set by a given demand for a medium of exchange, the “fundamental” value of a bitcoin might be determined by a given demand for stores of value.
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PDF Guru is like Chrome for PDF readers

This is a quick post to highlight an excellent new PDF reader on macOS call PDF Guru (iTunes store). It is a recently revamped version of PDF Reader X.

I’ve only used it for a week, but it’s the best PDF reader I’ve experienced for reading academic articles. It’s snappy and reminds me of Chrome when it first came out. Draggable tabs. Split view. Plays well with Zotero. Can easily add native PDF annotation and search through the existing ones. (And it saves annotations fast when you close the file.Competitors either do this slowly or, like Skim, use a non-native annotation format that can’t be read by other PDF readers.) The UI for “find” displays a lot of info intuitively.Edit 2018-1-12: And you can search for any unicode character! Really useful for searching a document for math. Everything is just nicely designed. I haven’t yet run into a limitation on the free version, but it’s worth upgrading to Pro to support the developer (only $20).

Beware that this is the first version following a big re-write of PDF Reader X, and it’s not completely stable. I’ve gotten it to crash a few times, but the developer has been very responsive to feedback and I’d wager on the stability improving soon. (Edit 2018-1-7: After upgrading to the new version, 3.0.20A, a couple weeks ago, I haven’t experienced any crashes. Looks stable.)

I’m advertising Guru because I think the current selection of PDF readers for academic reading is pretty bad.I have no connection to the developer. I strongly prefer Guru (instability and all) over these other PDF readers on maxOS that I have tried: FoxIt, Preview, Adobe Acrobat Reader, and Skim.… [continue reading]

Links for November 2017

  • For several months, Fermat’s Library has offered a Chrome extension called Librarian for browsing PDFs on the arXiv that automatically parses references to clickable journal links and bibtex entries. Very recently they added the ability to publicly comment, visible to anyone else running Librarian. Should be lower friction than commenting on (also excellent) SciRate.
  • Just heard about this story showing that the AZ governor means business:

    Three weeks into his new job as Arizona’s governor, Doug Ducey made a move that won over Silicon Valley and paved the way for his state to become a driverless car utopia.

    It was January 2015 and the Phoenix area was about to host the Super Bowl. Mr. Ducey learned that a local regulator was planning a sting on Lyft and Uber drivers to shut down the ride-hailing services for operating illegally. Mr. Ducey, a Republican who was the former chief executive of the ice cream chain Cold Stone Creamery, was furious.

    “It was the exact opposite message we should have been sending,” Mr. Ducey said in an interview. “We needed our message to Uber, Lyft and other entrepreneurs in Silicon Valley to be that Arizona was open to new ideas.” If the state had a slogan, he added, it would include the words “open for business.”

    Mr. Ducey fired the regulator who hatched the idea of going after ride-hailing drivers and shut down the entire agency, the Department of Weights and Measures. By April 2015, Arizona had legalized ride-sharing.

  • The last time a US Air Force bomber downed an enemy plane using its tail gun was 1972, but B-52s — which have been in service for a baffling 65 years — still carried (highly modernized) tail guns up until 1991 when a US air-to-surface missile mistakenly locked on to the tail gun’s radar and nearly destroyed the plane.
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Branches as hidden nodes in a neural net

I had been vaguely aware that there was an important connection between tensor network representations of quantum many-body states (e.g., matrix product states) and artificial neural nets, but it didn’t really click together until I saw Roger Melko’s nice talk on Friday about his recent paper with Torlai et al.:There is a title card about “resurgence” from Francesco Di Renzo’s talk at the beginning of the talk you can ignore. This is just a mistake in KITP’s video system.

[Download MP4]   [Other options]

In particular, he sketched the essential equivalence between matrix product states (MPS) and restricted Boltzmann machinesThis is discussed in detail by Chen et al. See also good intuition and a helpful physicist-statistician dictionary from Lin and Tegmark. (RBM) before showing how he and collaborators could train an efficient RBM representations of the states of the transverse-field Ising and XXZ models with a small number of local measurements from the true state.

As you’ve heard me belabor ad nauseum, I think identifying and defining branches is the key outstanding task inhibiting progress in resolving the measurement problem. I had already been thinking of branches as a sort of “global” tensor in an MPS, i.e., there would be a single index (bond) that would label the branches and serve to efficiently encode a pure state with long-range entanglement due to the amplification that defines a physical measurement process. (More generally, you can imagine branching events with effects that haven’t propagated outside of some region, such as the light-cone or Lieb-Robinson bound, and you might even make a hand-wavy connection to entanglement renormalization.) But I had little experience with constructing MPSs, and finding efficient representations always seemed like an ad-hoc process yielding non-unique results.… [continue reading]

Links for October 2017

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Models of decoherence and branching

[This is akin to a living review, which will hopefully improve from time to time. Last edited 2017-11-26.]

This post will collect some models of decoherence and branching. We don’t have a rigorous definition of branches yet but I crudely define models of branching to be models of decoherenceI take decoherence to mean a model with dynamics taking the form U \approx \sum_i \vert S_i\rangle\langle S_i |\otimes U^{\mathcal{E}}_i for some tensor decomposition \mathcal{H} = \mathcal{S} \otimes \mathcal{E}, where \{\vert S_i\rangle\} is an (approximately) stable orthonormal basis independent of initial state, and where \mathrm{Tr}[ U^{\mathcal{E}}_i \rho^{\mathcal{E} \dagger}_0 U^{\mathcal{E}}_j ] \approx 0 for times t \gtrsim t_D and i \neq j, where \rho^{\mathcal{E}}_0 is the initial state of \mathcal{E} and t_D is some characteristic time scale. which additionally feature some combination of amplification, irreversibility, redundant records, and/or outcomes with an intuitive macroscopic interpretation. I have the following desiderata for models, which tend to be in tension with computational tractability:

  • physically realistic
  • symmetric (e.g., translationally)
  • no ad-hoc system-environment distinction
  • Ehrenfest evolution along classical phase-space trajectories (at least on Lyapunov timescales)

Regarding that last one: we would like to recover “classical behavior” in the sense of classical Hamiltonian flow, which (presumably) means continuous degrees of freedom.In principle you could have discrete degrees of freedom that limit, as \hbar\to 0, to some sort of discrete classical systems, but most people find this unsatisfying. Branching only becomes unambiguous in some large-N limit, so it seems satisfying models are necessarily messy and difficult to numerically simulate.… [continue reading]

Comments on Weingarten’s preferred branch

A senior colleague asked me for thoughts on this paper describing a single-preferred-branch flavor of quantum mechanics, and I thought I’d copy them here. Tl;dr: I did not find an important new idea in it, but this paper nicely illustrates the appeal of Finkelstein’s partial-trace decoherence and the ambiguity inherent in connecting a many-worlds wavefunction to our direct observations.

We propose a method for finding an initial state vector which by ordinary Hamiltonian time evolution follows a single branch of many-worlds quantum mechanics. The resulting deterministic system appears to exhibit random behavior as a result of the successive emergence over time of information present in the initial state but not previously observed.

We start by assuming that a precise wavefunction branch structure has been specified. The idea, basically, is to randomly draw a branch at late times according to the Born probability, then to evolve it backwards in time to the beginning of the universe and take that as your initial condition. The main motivating observation is that, if we assume that all branch splittings are defined by a projective decomposition of some subsystem (‘the system’) which is recorded faithfully elsewhere (‘the environment’), then the lone preferred branch — time-evolving by itself — is an eigenstate of each of the projectors defining the splits. In a sense, Weingarten lays claim to ordered consistency [arxiv:gr-qc/9607073] by assuming partial-trace decoherenceNote on terminology: What Finkelstein called “partial-trace decoherence” is really a specialized form of consistency (i.e., a mathematical criterion for sets of consistent histories) that captures some, but not all, of the properties of the physical and dynamical process of decoherence.[continue reading]

Symmetries and solutions

Here is an underemphasized way to frame the relationship between trajectories and symmetries (in the sense of Noether’s theorem)You can find this presentation in “A short review on Noether’s theorems, gauge symmetries and boundary terms” by Máximo Bañados and Ignacio A. Reyes (H/t Godfrey Miller).. Consider the space of all possible trajectories q(t) for a system, a real-valued Lagrangian functional L[q(t)] on that space, the “directions” \delta q(t) at each point, and the corresponding functional gradient \delta L[q(t)]/\delta q(t) in each direction. Classical solutions are exactly those trajectories q(t) such that the Lagrangian L[q(t)] is stationary for perturbations in any direction \delta q(t), and continuous symmetries are exactly those directions \delta q(t) such that the Lagrangian L[q(t)] is stationary for any trajectory q(t). That is,

(1)   \begin{align*} q(t) \mathrm{\,is\, a\,}\mathbf{solution}\quad \qquad &\Leftrightarrow \qquad \frac{\delta L[q(t)]}{\delta q(t)} = 0 \,\,\,\, \forall \delta q(t)\\ \delta q(t) \mathrm{\,is\, a\,}\mathbf{symmetry} \qquad &\Leftrightarrow \qquad \frac{\delta L[q(t)]}{\delta q(t)} = 0 \,\,\,\, \forall q(t). \end{align*}

There are many subtleties obscured in this cartoon presentation, like the fact that a symmetry \delta q(t), being a tangent direction on the manifold of trajectories, can vary with the tangent point q(t) it is attached to (as for rotational symmetries). If you’ve never spent a long afternoon with a good book on the calculus of variations, I recommend it.


(↵ returns to text)

  1. You can find this presentation in “A short review on Noether’s theorems, gauge symmetries and boundary terms” by Máximo Bañados and Ignacio A. Reyes (H/t Godfrey Miller).
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Links for August-September 2017

  • Popular-level introduction to the five methods used to identify exoplanets.
  • Another good profile of the SEP.
  • ArXiv gets some money to improve stuff.
  • Flying fish are hard to believe. It’s something of a tragedy that fish capable of long-distance flight never evolved (that we know of?). They are so bird like it’s startling, and this ability has evolved independently multiple times.
  • In addition to Russia and China, the US also at one time had ICBMs deployed by rail.
  • On nuclear decommissioning:

    For nuclear power plants governed by the United States Nuclear Regulatory Commission, SAFSTOR (SAFe STORage) is one of the options for nuclear decommissioning of a shut down plant. During SAFSTOR the de-fuelled plant is monitored for up to sixty years before complete decontamination and dismantling of the site, to a condition where nuclear licensing is no longer required. During the storage interval, some of the radioactive contaminants of the reactor and power plant will decay, which will reduce the quantity of radioactive material to be removed during the final decontamination phase.

    The other options set by the NRC are nuclear decommissioning which is immediate dismantling of the plant and remediation of the site, and nuclear entombment which is the enclosure of contaminated parts of the plant in a permanent layer of concrete.Mixtures of options may be used, for example, immediate removal of steam turbine components and condensors, and SAFSTOR for the more heavily radioactive containment vessel. Since NRC requires decommissioning to be completed within 60 years, ENTOMB is not usually chosen since not all activity will have decayed to an unregulated background level in that time.

  • The fraction of the federal budget devoted to NASA peaked in 1966, three years before the Moon landing.
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How to think about Quantum Mechanics—Part 7: Quantum chaos and linear evolution

[Other parts in this series: 1,2,3,4,5,6,7.]

You’re taking a vacation to Granada to enjoy a Spanish ski resort in the Sierra Nevada mountains. But as your plane is coming in for a landing, you look out the window and realize the airport is on a small tropical island. Confused, you ask the flight attendant what’s wrong. “Oh”, she says, looking at your ticket, “you’re trying to get to Granada, but you’re on the plane to Grenada in the Caribbean Sea.” A wave of distress comes over your face, but she reassures you: “Don’t worry, Granada isn’t that far from here. The Hamming distance is only 1!”.

After you’ve recovered from that side-splitting humor, let’s dissect the frog. What’s the basis of the joke? The flight attendant is conflating two different metrics: the geographic distance and the Hamming distance. The distances are completely distinct, as two named locations can be very nearby in one and very far apart in the other.

Now let’s hear another joke from renowned physicist Chris Jarzynski:

The linear Schrödinger equation, however, does not give rise to the sort of nonlinear, chaotic dynamics responsible for ergodicity and mixing in classical many-body systems. This suggests that new concepts are needed to understand thermalization in isolated quantum systems. – C. Jarzynski, “Diverse phenomena, common themes” [PDF]

Ha! Get it? This joke is so good it’s been told by S. Wimberger“Since quantum mechanics is the more fundamental theory we can ask ourselves if there is chaotic motion in quantum systems as well.[continue reading]

Links for June-July 2017

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Selsam on formal verification of machine learning

Here is the first result out of the project Verifying Deep Mathematical Properties of AI SystemsTechnical abstract available here. Note that David Dill has taken over as PI from Alex Aiken. funded through the Future of Life Institute.

Noisy data, non-convex objectives, model misspecification, and numerical instability can all cause undesired behaviors in machine learning systems. As a result, detecting actual implementation errors can be extremely difficult. We demonstrate a methodology in which developers use an interactive proof assistant to both implement their system and to state a formal theorem defining what it means for their system to be correct. The process of proving this theorem interactively in the proof assistant exposes all implementation errors since any error in the program would cause the proof to fail. As a case study, we implement a new system, Certigrad, for optimizing over stochastic computation graphs, and we generate a formal (i.e. machine-checkable) proof that the gradients sampled by the system are unbiased estimates of the true mathematical gradients. We train a variational autoencoder using Certigrad and find the performance comparable to training the same model in TensorFlow.

You can find discussion on HackerNews. The lead author was kind enough to answers some questions about this work.

Q: Is the correctness specification usually a fairly singular statement? Or will it often be of the form “The program satisfied properties A, B, C, D, and E”? (And then maybe you add “F” later.)

Daniel Selsam: There are a few related issues: how singular is a specification, how much of the functionality of the system is certified (coverage), and how close the specification comes to proving that the system actually does what you want (validation).… [continue reading]

Reeh–Schlieder property in a separable Hilbert space

As has been discussed here before, the Reeh–Schlieder theorem is an initially confusing property of the vacuum in quantum field theory. It is difficult to find an illuminating discussion of it in the literature, whether in the context of algebraic QFT (from which it originated) or the more modern QFT grounded in RG and effective theories. I expect this to change once more field theorists get trained in quantum information.

The Reeh–Schlieder theorem states that the vacuum \vert 0 \rangle is cyclic with respect to the algebra \mathcal{A}(\mathcal{O}) of observables localized in some subset \mathcal{O} of Minkowski space. (For a single field \phi(x), the algebra \mathcal{A}(\mathcal{O}) is defined to be generated by all finite smearings \phi_f = \int\! dx\, f(x)\phi(x) for f(x) with support in \mathcal{O}.) Here, “cyclic” means that the subspace \mathcal{H}^{\mathcal{O}} \equiv \mathcal{A}(\mathcal{O})\vert 0 \rangle is dense in \mathcal{H}, i.e., any state \vert \chi \rangle \in \mathcal{H} can be arbitrarily well approximated by a state of the form A \vert 0 \rangle with A \in \mathcal{A}(\mathcal{O}). This is initially surprising because \vert \chi \rangle could be a state with particle excitations localized (essentially) to a region far from \mathcal{O} and that looks (essentially) like the vacuum everywhere else. The resolution derives from the fact the vacuum is highly entangled, such that the every region is entangled with every other region by an exponentially small amount.

One mistake that’s easy to make is to be fooled into thinking that this property can only be found in systems, like a field theory, with an infinite number of degrees of freedom. So let me exhibitMost likely a state with this property already exists in the quantum info literature, but I’ve got a habit of re-inventing the wheel. For my last paper, I spent the better part of a month rediscovering the Shor code… a quantum state with the Reeh–Schlieder property that lives in the tensor product of a finite number of separable Hilbert spaces:

    \[\mathcal{H} = \bigotimes_{n=1}^N \mathcal{H}_n, \qquad \mathcal{H}_n = \mathrm{span}\left\{ \vert s \rangle_n \right\}_{s=1}^\infty\]

As emphasized above, a separable Hilbert space is one that has a countable orthonormal basis, and is therefore isomorphic to L^2(\mathbb{R}), the space of square-normalizable functions.… [continue reading]