Grasping Reality with Both Hands: Economist Brad DeLong's Semi-Daily Journal

My First Dead-Tree Literary Theory Publication Is...

...a contribution to Framing Theory’s Empire. John Holbo writes:

The Valve - A Literary Organ | Framing Theory’s Empire - Event and Text: It’s finally a book! Framing Theory’s Empire [amazon]; or get it from the publisher, Parlor Press, directly. You can download the entire book as a free PDF from the Parlor site.  I’m still waiting for my paper copy to show up. (Any of you contributors out there gotten yours yet?) I think the cover is rather handsome. But, then: a father should love his child. The lovely Belle Waring and I designed it together.

A book, eh? See here! What’s all this about? ‘Theory’? Yes, exactly! In the English/humanities department sense: the idiomatically ofless sort, you might say; as in, ‘I do theory’. The stuff that started in the 60’s, got really big in the 80’s. Then either went away or is still hanging around, depending who you ask. (If you ask me: it’s still hanging around.)

If you spent late 2005 in a coma and missed all the glory, we staged a ‘book event’, round-table reviewing the Patai and Corral edited Theory’s Empire (Columbia UP, 2005). See the sidebar for link. Framing Theory’s Empire contains contributions to that event, cleaned up, polished up, edited. (I’ve written an introduction, talking about these issues. If you care to read it.)

The contributors are: Scott McLemee (he generously contributed a preface), John Holbo, Mark Bauerlein, Michael Bérubé, John McGowan, Scott Kaufman, Sean McCann, Daniel Green, Adam Kotsko, Tim Burke, Amardeep Singh, Jonathan Mayhew, Jonathan Goodwin, Chris Cagle, Christopher Conway, Kathleen Lowrey, Brad DeLong, Matthew Greenfield, Morris Dickstein, Jeffrey Wallen, John Emerson, Mark Kaplan, Jodi Dean, Kenneth Rufo, Daphne Patai, Will H. Corral. (Patai and Corral were kind enough to contribute an “Afterword”. At the moment Amazon is giving them erroneous prominence, in the author line. I’ll have to see whether I can get Amazon to correct that. Not that I mind so very much. They themselves will probably be even more annoyed, because it might create some product confusion with Theory’s Empire itself.)

It’s the perfect stocking stuffer for the humanities graduate student on YOUR list!

I think it turned out to be a really great book. In addition to several posts that turned out to be just plain really solid essays, there is some lively, sharp conversation between several participants. There’s intelligent back and forth, actual addressing of critical points and hashing of differences, which is not something one always gets in themed anthologies. I think the informal quality of many of the pieces turns out to be a real virtue as well. It suits the topic. But you tell me. What do you think of the book? What do you think about our event, two years on?

I’m glad to get this done as well because, frankly, my Glassbead Books efforts for Parlor haven’t been quite rolling off the assembly-line, as I had originally hoped. It turns out making books is incredibly hard and time consuming, and folks don’t do stuff when you tell them to, and it’s hard to get folks to commit to helping out. Academics are always busy. I’m hoping that, with a grand total of TWO titles out now we’ve actually got a series. That is, a line, not just a single point. Anyway, next comes our Moretti book - I think. I want to get these things rolling out a lot faster.

Scott Aaronson: PHYS771: Quantum Computing Since Democritus

A course I would like to take:

PHYS771: Quantum Computing Since Democritus:

PHYS771 Lecture 1: Atoms and the Void; PHYS771 Lecture 10: Quantum Computing; PHYS771 Lecture 10.5: Penrose; PHYS771 Lecture 11: Decoherence and Hidden Variables.

---

http://www.cs.princeton.edu/theory/complexity/; http://www.amazon.com/Emperor-New-Mind-Concerning-Computers/dp/0192861980/sr=8-1/qid=1158134107/ref=pd_bbs_1/103-6440007-3621459?ie=UTF8&s=books; http://www.springerlink.com/content/w236774414114626/.

Scott Aaronson: PHYS771: Lecture 10.5: Penrose

Aha!: Scott Aaronson on Roger Penrose: "if we can only approach mathematical truth with the same unreliable, savannah-optimized tools that we use for doing the laundry, ordering Chinese takeout, etc. -- then it seems we ought to grant computers the same liberty of being fallible. But in that case, the claimed distinction between humans and machines would seem to evaporate...":

PHYS771 Lecture 10.5: Penrose: So, you guys finally finished reading Roger Penrose's The Emperor's New Mind? What did you think of it? (Since I forgot to record this lecture, the class responses are tragically lost to history. But if I recall correctly, the entire class turned out to consist of -- YAWN -- straitlaced, clear-thinking materialistic reductionists who correctly pointed out the glaring holes in Penrose's arguments. No one took Penrose's side, even just for sport.)

Alright, so let me try a new tack: who can summarize Penrose's argument (or more correctly, a half-century-old argument adapted by Penrose) in a few sentences? How about this: Gödel's First Incompleteness Theorem tells us that no computer, working within a fixed formal system F such as Zermelo-Fraenkel set theory, can prove the sentence: G(F) = "This sentence cannot be proved in F." But we humans can just "see" the truth of G(F) -- since if G(F) were false, then it would be provable, which is absurd! Therefore the human mind can do something that no present-day computer can do. Therefore consciousness can't be reducible to computation.

Alright, class: problems with this argument?

Yeah, there are two rather immediate ones:

Why does the computer have to work within a fixed formal system F?

Can humans "see" the truth of G(F)?

Actually, the response I prefer encapsulates both of the above responses as "limiting cases." Recall from Lecture 3 that, by the Second Incompleteness Theorem, G(F) is equivalent to Con(F): the statement that F is consistent. Furthermore, this equivalence can be proved in F itself for any reasonable F. This has two important implications.

First, it means that when Penrose claims that humans can "see" the truth of G(F), really he's just claiming that humans can see the consistency of F! When you put it that way, the problems become more apparent: how can humans see the consistency of F? Exactly which F's are we talking about: Peano Arithmetic? ZF? ZFC? ZFC with large cardinal axioms? Can all humans see the consistency of all these systems, or do you have to be a Penrose-caliber mathematician to see the consistency of the stronger ones? What about the systems that people thought were consistent, but that turned out not to be? And even if you did see the consistency of (say) ZF, how would you convince someone else that you'd seen it? How would the other person know you weren't just pretending? (Models of Zermelo-Fraenkel set theory are like those 3D dot pictures: sometimes you really have to squint...)

The second implication is that, if we grant a computer the same freedom that Penrose effectively grants to humans -- namely, the freedom to assume the consistency of the underlying formal system -- then the computer can prove G(F). So the question boils down to this: can the human mind somehow peer into the Platonic heavens, in order to directly perceive (let's say) the consistency of ZF set theory? If the answer is no -- if we can only approach mathematical truth with the same unreliable, savannah-optimized tools that we use for doing the laundry, ordering Chinese takeout, etc. -- then it seems we ought to grant computers the same liberty of being fallible. But in that case, the claimed distinction between humans and machines would seem to evaporate. (Perhaps Turing himself said it best: "If we want a machine to be intelligent, it can't also be infallible. There are theorems that say almost exactly that.")

In my opinion, then, Penrose doesn't need to be talking about Gödel's theorem at all. The Gödel argument turns out to be just a mathematical restatement of the oldest argument against reductionism in the book: "sure a computer could say it perceives G(F), but it'd just be shuffling symbols around! When I say I perceive G(F), I really mean it! There's something it feels like to be me!" The obvious response is equally old: "what makes you so sure that it doesn't feel like anything to be a computer?"...

Opening the Black Box:

Alright, look: Roger Penrose is one of the greatest mathematical physicists on Earth. Is it possible that we've misconstrued his thinking? To my mind, the most plausible-ish versions of Penrose's argument are the ones based on an "asymmetry of understanding": namely that, while we know the internal workings of a computer, we don't yet know the internal workings of the brain. How can one exploit this asymmetry? Well, given any known Turing machine M, it's certainly possible to construct a sentence that stumps M: S(M) = "Machine M will never output this sentence." There are two cases: either M outputs S(M), in which case it utters a falsehood, or else M doesn't output S(M), in which case there's a mathematical truth to which it can never assent.

The obvious response is, why can't we play the same game with humans? "Roger Penrose will never output this sentence." Well, conceivably there's an answer: because we can formalize what it means for M to output something, by examining its inner workings. (Indeed, "M" is really just shorthand for the appropriate Turing machine state diagram.) But can we formalize what it means for Penrose to output something? The answer depends on what we believe about the internal workings of the brain (or more precisely, Penrose's brain)! And this leads to Penrose's view of the brain as "non-computational." A common misconception is that Penrose thinks the brain is a quantum computer. In reality, a quantum computer would be much weaker than he wants! As we saw before, quantum computers don't even seem able to solve NP-complete problems in polynomial time. Penrose, by contrast, wants the brain to solve uncomputable problems, by exploiting hypothetical collapse effects from a yet-to-be-discovered quantum theory of gravity....

In Shadows, Penrose offers the following classification of views on consciousness:

Consciousness is reducible to computation (the view of strong-AI proponents)

Sure, consciousness can be simulated by a computer, but the simulation couldn't produce "real understanding" (John Searle's view)

Consciousness can't even be simulated by computer, but nevertheless has a scientific explanation (Penrose's own view, according to Shadows)

Consciousness doesn't have a scientific explanation at all (the view of 99% of everyone who ever lived)

Now it seems to me that... Penrose is retreating from view C to view B. For as soon as we say that passing the Turing Test isn't good enough -- that one needs to "pry open the box" and examine a machine's internal workings to know whether it thinks or not -- what could possibly be the content of view C that would distinguish it from view B?... I want to bend over backwards to see if I can figure out what Penrose might be saying. In science, you can always cook up a theory to "explain" the data you've seen so far: just list all the data you've got, and call that your "theory"! The obvious problem here is overfitting. Since your theory doesn't achieve any compression of the original data -- i.e., since it takes as many bits to write down your theory as to write down the data itself -- there's no reason to expect your theory to predict future data. In other words, your theory is a useless piece of shit....

Now, here's the point I keep coming back to: if this is what Penrose means, then he's left the world of Gödel and Turing far behind, and entered my stomping grounds -- the Kingdom of Computational Complexity. How does Penrose, or anyone else, know that there's no small Boolean circuit to simulate Winston Churchill? Presumably we wouldn't be able to prove such a thing, even supposing (for the sake of argument) that we knew what a Churchill simulator meant! All ye who would claim the intractability of finite problems: that way lieth the P versus NP beast, from whose 2n jaws no mortal hath yet escaped....

Let's set aside the specifics of Penrose's ideas, and ask a more general question. Should quantum mechanics have any affect on how we think about the brain?... When people try to make the question more concrete, they often end up asking: "is the brain a quantum computer?" Well, it might be, but I can think of at least four good arguments against this possibility:

The problems for which quantum computers are believed to offer dramatic speedups -- factoring integers, solving Pell's equation, simulating quark-gluon plasmas, approximating the Jones polynomial, etc. -- just don't seem like the sorts of things that would have increased Oog the Caveman's reproductive success relative to his fellow cavemen.

Even if humans could benefit from quantum computing speedups, I don't see any evidence that they're actually doing so. (It's said that Gauss could immediately factor large integers in his head -- but if so, that only proves that Gauss's brain was a quantum computer, not that anyone else's is!)

The brain is a hot, wet environment, and it's hard to understand how long-range coherence could be maintained there. (With today's understanding of quantum error-correction, this is no longer a knock-down argument, but it's still an extremely strong one.)

As I mentioned earlier, even if we suppose the brain is a quantum computer, it doesn't seem to get us anywhere in explaining consciousness, which is the usual problem that these sorts of speculations are invoked to solve!...

The Brontothropic Cosmological Principle

Hoisted from Comments: Tjallen writes, apropos of the Anthropic Cosmological Principle:

Grasping Reality with Both Hands: Brad DeLong's Semi-Daily Journal: About [130] million years ago, there was the Brontothropic principle....

The fundamental constants of the universe must be such to allow the Brontosaurus to live and thrive

[No wait!--T]hey're gone...

Lawrence Hall

Lawrence Hall is the name of a building (the Lawrence Hall of Science) and a professor (Lawrence Hall of Physics). The second came to the Berkeley Monday Faculty Lunch Forum to argue that there is empirical content to the Anthropic Cosmological Principle.

What is this principle? Put it this way. Suppose somebody asks you why the universe is pervaded by an 80-20 nitrogen-oxygen gas mixture, or why it is 300K outside. The answer is that the universe isn't like that but that where you are is like that because if you wet surrounded by chlorine gas or in a place where it is 400K you--and all life like you--would be dead. Our confidence in these "anthropic" explanations is strong because we can point to places we know of that lack the 80-20 atmosphere--the asteroid belt--and places where it is not a shirtsleeve 300K--Cambridge, Massachusetts.

Can this anthropic principle be applied to more fundamental issues? Can we say that the mass of the d quark is what it is because if it were 20% lower than the neutron would be absolutely stable and there would be no stars? We cannot see any places in the multiverse where the mass of the down quark is lower, but our predecessors did not know about the asteroid belt and other places lacking an 80-20 atmosphere, and the anthropic explanation for why there is oxygen around for us to breathe was just as valid then for them as it is for us. Is it doing science to use this anthropic principle--or is it just meaningless and tautological? After all, pretty much everything in the universe has to be the way that it is for there to be a physicist with the same name as a building talking in the Seaborg Room of the Berkeley Faculty Club Monday at lunchtime--start with Lawrence Hall as your premise, and you have "explained" everything, in some sense.

Lawrence Hall thinks that there is empirical content, and his argument goes like this:

• The section of the multiverse that we are in has picked its version of the laws of physics through some process.

• We describe the laws of physics by picking theories and parameter values.

• The way we describe does not match one-to-one to the way this part of the multiverse picks the parameter values.

• Therefore there is a probability pressure gradient out there as we look at possible free parameter values for our theories--either low values are much more probable for this part of the multiverse, or high values.

• So, from our perspective, we would expect to find ourselves in a part of the universe that seems "close" to catastrophe--we should expect, over and over again, to do our calculations and then exclaim: "Wow! We are lucky that parameter X isn't 20% lower (or higher) than it is! If it were, then we couldn't exist!"

• If we find over and over again that our part of the multiverse appears to us, given the way we describe parameter values, to be remarkably close to a knife-edge of fundamental change and disruption is an empirical prediction of the anthropic cosmological principle.

• Thus it is testable, and we are testing it.

An Economist Reads Jane Austenania

Tyler Cowen's screws seem considerably looser than usual this morning:

Marginal Revolution: Confessions of a Jane Austen Addict: That's the title of Laurie Viera Rigler's new and fun book.  The basic premise is that a pouty L.A. girl "wakes up" in the body of a character in a Jane Austen novel; here is the book's website.  She also finds herself courted by an ardent suitor, Edgeworth, who wants an answer to his marriage proposal and soon.  My wonderings were skewed as usual:

1. Would I, at first, have to act sick and crazy so as to cover up what are in fact more systematic lapses from accepted codes of social behavior?
2. If I am a rational Bayesian, what percentage of "transported people" should I expect to find in my new world?  (It is indicative that our heroine thinks she is very special and isn't much concerned with this question.)  Would such people be natural allies or enemies?
3. If I met another transported person, could I figure this fact out?  How long would it take and what are the best hints to drop?  Should I just mention "the Boston Red Sox" and see what happens?
4. Living in such a world, how useful is it to know how the novel ends?  (This is a theme in the story.)  Could such knowledge compensate for not understanding the non-articulated rules of this world very well?  What rate of interest should I pay on borrowed money, given the presence of speculative opportunities?
5. Being a rational Bayesian, how should I revise upwards my estimates that the world is ruled by an evil Demi-Urge, and what does this imply for the optimal degree of ethical behavior? It is a sad commentary on our educational system that Courtney, the heroine of the novel, never ponders such a question.
6. At what percentage of "transported people" would we expect to see an impact on real GDP, and would this impact be positive or negative?

Readers, what other questions should I be asking?

Of course, the biggest question of all, IMHO, is not asked. It is:

Just how confident can I be that I should buy British long-term Treasuries on June 15, 1815?

Michael O'Hare Praises Robert Frank's Economic Naturalist

Michael O'Hare writes:

The Reality-Based Community: Serve fewer courses to nourish more; let the diners in the kitchen and give them aprons.: Bob Frank exhibits the factor most highly correlated with student evaluations of teaching, which is manifest enthusiasm for his subject matter.... Modern psychology has boiled down being really smart to a couple of core traits. One is knowing a lot about a lot of different things; the other is being wired up so these different things jump out of their usual cognitive boxes and connect in unusual ways. Frank is smart in this way, so his exploration connected his experience with learning languages and his general education knowledge of why male and female albatrosses look alike while bull and cow seals don't.

The result is three very solid insights, consistent with a lot of what others are discovering about how people learn. The first is the difference between (i) recall and repetition of a recipe, formula or fact on cue and (ii) really knowing something. The second is the principle articulated by Bob Behn thus: "If you're teaching someone to use a computer, you should never touch the computer." The third is the difference between the few important basic principles that experts use all the time without realizing it, and the many abstruse and frontier-pushing results they get with them.

Put these together and you get a teaching model with:

1. A few big ideas, looked at from many directions and dressed up (but not hidden) in many guises.
2. Students getting their hands dirty using these ideas to solve problems they know they have (this is always better than letting the ideas look like new problems they didn't want).
3. Displacement of the concept of being right by the concept of being useful (Nelson Goodman explains this in Ways of Worldmaking).

The central exercise of such a course is to assign the students the role of naturalist (this is where the birds and seals come in): Find a situation that surprises you, that you can understand better (or even explain completely) using the core concepts of economics. Your explanation doesn't have to be complete, or even right, but it has to be interesting and reasonable. Five hundred words, once in the middle of the semester and again at the end.

I have generalized his exercise this spring in my introduction to public policy course to a "policy naturalist" assignment with excellent results (though I'm not sure I did such a good job of distilling the course down to fewer big ideas and less showoffy arcana), and I intend to do the same next fall in an introductory probability and statistics course. This model really has legs.

The result of Bob's experiment is, obviously, a drawer full of these exercises, which he has assembled into a book... The Economic Naturalist, and if you're not putting on your coat to repair immediately to your local physical bookstore, or mousing over to your favorite online merchant to buy it, you are reading the wrong blog.

Matthew Yglesias Is Insecure!

Matthew Yglesias worries:

Matthew Yglesias: The Starbucks Factor: Is it a bad thing that Feist's The Reminder is on sale in Starbucks? I'll admit that when I saw the album there I was disturbed. Upon a moment's reflection, though, this is just snobbery. I don't like the idea that, in the future, if I praise Feist this may indicate to other people that I'm the sort of person who gets his music recommendations from Starbucks rather than the sort of person who knows a lot about Canadian indie music...

It's too late, Matt. You have revealed that you are the kind of person who fears that other people may think that you are the kind of person who gets his music recommendations from Starbucks.

It would be much better for you if you were to fear that you might be turning into the kind of person who fears that other people may think you are the kind of person who gets his music recommendations from Starbucks.

DeLong Sapience Watch...

Is Brad DeLong sapient? If so, how sapient? The evidence is mixed. Here is some more evidence:

There I was, procrastinating by looking at the iTunes music store, trying to figure out what my children had been buying. And I see a name? Aimee Mann. "That looks interesting," I think to myself. Why did it seem interesting? I didn't know. So I typed "Aimee Mann" into the search box, and...

...discovered that I had heard one of her songs, "Going Through the Motions," on the radio that day. Did I know that that song was sung by Aimee Mann? If you had asked me while I was listening to it if I knew who the singer was, I would have said no.

But something inside there did know.

Brad DeLong: sapient intellectual rational and reasonable being, or jumped-up East African plains ape running off a neural net and capable at times of putting forth an almost-convincing simulacrum of sapience?

Is Brad DeLong sapient? Express your opinion:

What Inside Here, Exactly, Knows the First Name of the Attorney General?

What Inside Here, Exactly, Knows the First Name of the Attorney General?

It was about a week ago. I was in a subway train underneath San Francisco Bay, writing a weblog post about Attorney General Alberto Gonzales. But I wrote not Alberto Gonzales but Henry Gonzales--and when I proofread it twice for typos, grammaros, and mindos, I decided both times that Henry Gonzales was correct, what I wanted to write.

So why did I think, while underneath San Francisco Bay, that Henry Gonzales was the name of the Attorney General?

The answer is in where I was going: I was going to a meeting at the Federal Reserve Bank of San Francisco. The late Henry Gonzalez (he died in 2000) was a congressman. He was one of the last honest Texas populists, and was chair of the House Banking Committee and a strident and effective critic of the Federal Reserve during the 1990s. Do any kind of concept search on "Federal Reserve" and "last name Gonzalez" and the first name "Henry" will pop up.

So there I was, underneath San Francisco Bay, trying to write about the U.S. attorney scandal and Alberto Gonzales while part of my brain is thinking about the fact that I am going to the Federal Reserve. When it comes time to tell my fingers whether to type A-l-b-e-r-t-o or H-e-n-r-y, that part of my brain that is thinking "Federal Reserve" votes that "Gonzales" goes with "Henry," while that part of my brain that is thinking "Bush administration" votes that "Gonzales" goes with "Alberto," and the first part of my brain is larger and stronger and remains larger and stronger as I proofread the post, come out of the subway, and stop off to borrow Starbucks's electrons to send the post out onto the internet...

The interesting thing, from my perspective at least, is that it doesn't seem like there was any thought going on here. I didn't (mistakenly) think that "Henry Gonzales is the Attorney General." I didn't think about it at all. There was just a bunch of neurons sending electrical signals to one another that culminate in impulses out to the fingers on the keyboard--a bunch of neurons that most of the time present a convincing simulacrum of sentient intelligence, until the mask slips.

Legal Realism vs. Legal Formalism, William Douglas vs. Felix Frankfurter, Fred Rodell vs. Alex Bickel

I am told that somewhere in the back issues of the Yale Law Report there is a reminiscence of a dinner party conversation between Alex Bickel and Fred Rodell:

Alex: "Well, Fred, I may be naive, but I think that when the Supreme Court says something it means what it says."

Fred: "Well, Alex, we agree on this at least: you are naive..."

Does anyone have a more solid cite to this interaction between these two rare jackasses--from each of whom, however, one can learn a great deal?

The Meddling Idiot! As Though DeLong's Ape Brain Could Contain the Wisdom of the Krell!

Berkeley Letters and Science Faculty Forum. January 22, 2007. I always have problems understanding what John Campbell http://www.amazon.com/exec/obidos/asin/0199243816/braddelong00 is saying. He says that he is saying:

• There is an important and unbridgeable gulf between our notions of physical causation and our notions of psychological causation.
• Martian physicists--intelligences vast, cool, and unsympathetic with no notions of human psychology or psychological causation--could not understand why, could not put their finger on physical variables and factors explaining why, the fifty or so of us assemble in the Seaborg Room Monday at lunch time during the spring semester.

He says that he is not saying any of:

• The universe has a dual nature, in which mind is different from not-mind.
• Reductionism is wrong because there are important emergent properties of complicated systems, and reductionist and holistic explanations are quantitatively different.
• There is an important and unbridgeable gulf between understanding based on physical laws and understanding based on human empathy. Instead, Campbell says, there is only one kind of understanding and explanation, but it is applied to different sets of causal factors in different circumstances.

The word "supervenience" was not mentioned by anybody.

I had two questions for him. I think I would have understood him if I could have understood the answers to either of them:

• If I were a member of a team of tentacled Martian physicists (don't get me started on the image of mollusc-like Martians living on an essentially desert planet), my physical-description model of Berkeley would include a model of Assistant Dean Chuck Stroup's brain at the subatomic level. I would then be able to say: "Aha! Suppose we were to decrease the levels of serotonin in the particular half-cubic-foot of space that is Chuck Stroup's brain; then the email messages containing the string "L&S Faculty Forum today" don't get sent, and we don't assemble here for lunch. Wouldn't that be a way for Martian physicists with no concept of human psychology to begin to understand why we are all here in the Seaborg Room right now?

• Let me roughly quote from a lecture from a course, Physics 140, that I took as a junior from Ed Purcell: "How about the lithium atom? We can't calculate the joint orbitals of all three electrons--that's too hard. But we can get an approximate solution for the valence electron. It wants to be in the ground state, but the Pauli Exclusion Principle forbids it. So we can model the orbital of the third, valence electron as a single electron moving in the field of the nucleus partially shielded by the other two electrons in the next stable energy level above the ground state. The Schrodinger equation is... [Purcell starts doing math.]" Here we have a mixture of physical and psychological causation. The physical causation--the math driven by the physical laws of quantum mechanics--comes at the end. Before that comes psychological causation: Purcell attributes human-like intelligence to the electron that has desires and needs and to the brooding overall universal presence that is the Pauli Exclusion Principle, and so reduces the physical-causation problem to a simpler one that is approximately right and that he can solve. The resort to psychological causation is a way to get an answer even though the math for the three-electron problem is beyond our grasp. What is the difference between Ed Purcell's use of psychological causation here and your use of psychological causation as a factor in addition to serotonin levels in understanding human psychological depression?

But alas! I did not understand his answers--although I have no doubt that he did.

I can't help but think that the rhetorical trope of "Martian physicists" is a problem here. I take it for granted that "Martian physicists" have models of human brains at a subatomic level and understand the dynamic evolution of brain states and the connection of brain states to human actions, and do so at a level that makes "psychology" needless save as a shorthand way of dividing brain states into categories. Philosophers' "Martian physicists" don't seem to be able to do that.