## Posts

## Comments

**johnsidles**on Cambridge Meetup: Talk by Eliezer Yudkowsky: Recursion in rational agents · 2013-10-15T21:37:05.648Z · score: 0 (0 votes) · LW · GW

A preprint would be terrific too.

**A tough(?) question and a tougher(?) question:** When self-modifying AI's are citizens of Terry Tao's Island of the Blue-Eyed People/AIs, can the AIs trust one another to keep the customs of the Island? On this same AI-island, when the AI's play the Newcomb's Paradox Game, according to the rules of balanced advantage, can the PredictorAIs outwit the ChooserAIs, and still satisfy the island's ProctorAIs?

Questions in this class are tough (as they seem to me), and it is good to see that they are being creatively formalized.

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-07-08T14:09:51.742Z · score: 0 (0 votes) · LW · GW

Goodbye, gjm. The impetus that your posts provided to post thought-provoking mathematical links will be missed. :)

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-07-07T23:00:35.263Z · score: -2 (2 votes) · LW · GW

gjmasserts "Of the various ways to understand the quantum mechanics involved in the Standard Model, the clear winner is "many worlds"

LOL ... by that lenient standard, the first racehorse out of the gate, or the first sprinter out of the blocks, can reasonably be proclaimed "the clear winner" ... before the race is even finished!

That's a rational announcement only for very short races. Surely there is very little evidence that the course that finishes at comprehensive understanding of Nature's dynamics ... is a short course?

As for my own opinions in regard to quantum dynamical systems, they are more along the lines of **here are some questions that are mathematically well-posed and are interesting to engineers and scientists alike** ... and definitely *not* along the lines of "here are the answers to those questions"!

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-07-07T22:04:22.148Z · score: 0 (0 votes) · LW · GW

gjm avers: 'When Eliezer says that QM is "non-mysterious' ... He's arguing against a particular sort of mysterianism"

That may or may not be the case, but there is zero doubt that this assertion provides rhetorical foundations for the essay ** And the Winner is... Many-Worlds!**.

A valuable service of the mathematical literature relating to geometric mechanics is that it instills a prudent humility regarding assertions like "the Winner is... Many-Worlds!" A celebrated meditation of Alexander Grothendieck expresses this humility:

"A different image came to me a few weeks ago. The unknown thing to be known appeared to me as some stretch of earth or hard marl, resisting penetration ... the sea advances insensibly in silence, nothing seems to happen, nothing moves, the water is so far off you hardly hear it ... yet it finally surrounds the resistant substance."

Surely in regard quantum mechanics, the water of our understanding is far from covering the rocks of our ignorance!

As for the tone of my posts, the intent is that people who enjoy references and quotations will take no offense, and people who do *not* enjoy them can simply pass by.

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-07-07T16:49:36.937Z · score: 1 (1 votes) · LW · GW

gjmavers "Landsberg that has a section headed "Clash of cultures" but it could not by any reasonable stretch be called an essay. It's only a few paragraphs long."

LOL ... gjm, you must *really* dislike Lincoln's ultra-short *Gettysburg Address!*

More seriously, isn't the key question whether Landsberg's essay is *correct* to assert that "there are language and even philosophical barriers to be overcome", in communicating modern geometric insights to STEM researchers trained in older mathematical techniques?

Most seriously of all, gjm, please let me express the hope that the various references that you have pursued have helped to awaken an appreciation of the severe and regrettable mathematical limitations that are inherent in the essays of *Less Wrong's* **Quantum Physics Sequence**, including in particular Eliezer_Yudkowsky's essay *Quantum Physics Revealed As Non-Mysterious*.

The burgeoning 21st century literature of geometric dynamics helps us to appreciate that the the 20th century mathematical toolkit of *Less Wrong's* quantum essays perhaps will turn out to be not so much "less wrong" as "not even wrong," in the sense that *Less Wrong*'s quantum essays are devoid of the geometric dynamical ideas that are flowering so vigorously in the contemporary STEM literature.

This is of course very good news for young researchers! :)

**johnsidles**on Harry Potter and the Methods of Rationality discussion thread, part 21, chapters 91 & 92 · 2013-07-05T23:20:09.973Z · score: 2 (2 votes) · LW · GW

**Edit 1:** Kudos to "gjm" (see above) for pointing to Spivak's page on Amazon!

**Edit 2:** Spivak's *Hogwarts* proof implicitly uses a fundamental theorem in differential geometry that is called **Cartan's Magic Formula** ... this oblique magical reference is Spivak's joke ... as with many magical formulas, the origins of Cartan's formula are obscure.

Regrettably, tgb, even the redoubtable

Google Booksdoes not provide page-images for Spivak'sPhysics for Mathematicians: Mechanics I. The best advice I can give is to seek this book within a university library system.

**johnsidles**on Harry Potter and the Methods of Rationality discussion thread, part 21, chapters 91 & 92 · 2013-07-05T12:59:28.101Z · score: 1 (1 votes) · LW · GW

LOL --- perhaps a chief objective of the Ministry of Magic is to conceive and require obfuscating interfaces to magic! That would explain a lot!

Parallels to real-world high-school and/or undergraduate mathematical education ... are left as an exercise. :)

**johnsidles**on Harry Potter and the Methods of Rationality discussion thread, part 21, chapters 91 & 92 · 2013-07-05T12:56:28.014Z · score: 1 (1 votes) · LW · GW

For a professional-grade comment on "muggle math" versus "Hogwarts math", see Michael Spivak's *Physics for Mathematicians: Mechanics I*.

To express this point another way ... how likely is it, that Harry's final understanding of magic will be *non*-mathematical? What grade of mathematical abstraction capabilities will Harry need to acquire?

**johnsidles**on Harry Potter and the Methods of Rationality discussion thread, part 21, chapters 91 & 92 · 2013-07-05T11:50:32.114Z · score: -1 (7 votes) · LW · GW

Conspicuously absent from the canon, and from *Methods of Rationality* (so far) --- and absent entirely from the Hogwarts curriculum --- are two fundamental elements of rational cognition:

- mathematics, and
- artificial intelligences (AIs)

Therefore

Postulate 1"Magic" is the name that witches, wizards, and muggles alike give to the practice of manipulating physical reality by negotiation with agents that are (artificial? primordial? evolved? accidentally created?) intelligences.

Postulate 2"Magical Spells" is the name that witches, wizards, and muggles alike give to an evolving set of protocols for negotiating with an existing community of (mysterious) intelligences. These protocols are designed to minimize the risks and harms associated to the practice of magic, by concealing the physical origins of magic.

Postulate 3The chief organizing objective of the Hogwarts curriculum is to preserve the social fictions that are associated to Postulates 1 and 2.

Postulate 4Harry Potter is regarded as dangerous because he seeks to evade the restrictions associated to Postulates 1, 2, and 3, by inquiring into the true nature of magic and its actions.

**Literary Remark** Harry Potter would do well to reflect upon the words and fate of Captain Ahab:

"All visible objects, man, are but as pasteboard masks. But in each event — in the living act, the undoubted deed — there, some unknown but still reasoning thing puts forth the mouldings of its features from behind the unreasoning mask. If man will strike, strike through the mask! How can the prisoner reach outside except by thrusting through the wall? To me, the white whale is that wall, shoved near to me. Sometimes I think there's naught beyond. But 'tis enough. He tasks me; he heaps me; I see in him outrageous strength, with an inscrutable malice sinewing it. That inscrutable thing is chiefly what I hate; and be the white whale agent, or be the white whale principal, I will wreak that hate upon him. Talk not to me of blasphemy, man; I'd strike the sun if it insulted me. For could the sun do that, then could I do the other; since there is ever a sort of fair play herein, jealousy presiding over all creations. Ohg abg zl znfgre, zna, vf rira gung snve cynl. Jub'f bire zr? Gehgu ungu ab pbasvarf."

**Conclusion** Harry Potter's quest to restore Hermione Granger may be leading him and the Hogwarts crew to a similarly disastrous fate as Ahab and the Pequod crew.

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-22T23:13:21.533Z · score: 0 (0 votes) · LW · GW

An elaboration of the above argument now appears on *Shtetl Optimized*, essentially as a meditation on the question: What strictly *mathematical* proposition would comprise *rationally* convincing evidence that the key linear-quantum postulates of "One Ghost in the Quantum Turing Machine* amount to “an unredeemed claim [that has] become a roadblock rather than an inspiration” (to borrow an apt phrase from Jaffe and Quinn's arXiv:math/9307227).

Readers of *Not Even Wrong* seeking further (strictly mathematical) mathematical illumination in regard to these issues may wish to consult Arnold Neumaier and Dennis Westra's textbook-in-progress *Classical and Quantum Mechanics via Lie Algebras* (arXiv:0810.1019, 2011), whose Introduction states:

"The book should serve as an appetizer, inviting the reader to go more deeply into these fascinating, interdisciplinary fields of science. ... [We] focus attention on the simplicity and beauty of theoretical physics, which is often hidden in a jungle of techniques for estimating or calculating quantities of interest."

That the Neumaier/Westra textbook is an unfinished work-in-progress constitutes proof *prima facie* that the final *tractatus* upon these much-discussed *logico-physico-philosophicus* issues has yet to be written! :)

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-21T12:03:54.283Z · score: -1 (1 votes) · LW · GW

Shminux, it may be that you will find that your concerns are substantially addressed by Joshua Landsberg's *Clash of Cultures* essay (2012), which is **cited above**.

"These conversations [are] very stressful to all involved ... there are language and even philosophical barriers to be overcome."

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-21T11:30:28.980Z · score: 1 (3 votes) · LW · GW

The entanglement(s) of hot-noisy-evolved biological cognition with abstract ideals of cognition that Eliezer Yudkowsky vividly describes in *Harry Potter and the Methods of Rationality*, and the quantum entanglement(s) of dynamical flow with the physical processes of cognition that Scott Aaronson vividly describes in *Ghost in the Quantum Turing Machine*, both find further mathematical/social/philosophical echoes in Joshua Landsberg's *Tensors: Geometry and Applications* (2012), specifically in Landsberg's thought-provoking introductory section **Section 0.3: Clash of Cultures** (this introduction is available as **PDF on-line**).

*E.g.*, the above discussions above relating to "map versus object" distinctions can be summarized by:

Aaronson's Law of Ontic Mixing"We can't always draw as sharp a line as we'd like betweenmapandterritory".

as contrasted with the opposing assertion

Landsberg's No-Mixing Principle"Don’t use coordinates unless someone holds a pickle to your head"

As Landsberg remarks

"These conversations [are] very stressful to all involved ... there are language and even philosophical barriers to be overcome."

The Yudkowsky/Aaronson philosophical divide is vividly mirrored in the various divides that Landsberg describes between geometers and algebraists, and mathematicians and engineers.

**Question** Has it happened before, that philosophical conundrums have arisen in the course of STEM investigation, then been largely or even entirely resolved by further STEM progress?

**Answer** Yes of course (beginning for example with Isaac Newton's obvious-yet-wrong notion that "absolute, true and mathematical time, of itself, and from its own nature flows equably without regard to anything external").

**Conclusion** It may be that, in coming decades, the philosophical debate(s) between Yudkowsky and Aaronson will be largely or even entirely resolved by mathematical discourse following the roadmap laid down by Landsberg's outstanding text.

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-20T19:00:58.753Z · score: 1 (3 votes) · LW · GW

Quantum aficionados in the mold of **Eliezer Yudkowsky** will have fun looking up "Noether's Theorem" in the index to Michael Spivak's **well-regarded** *Physics for Mathematicians: Mechanics I*, because near to it we notice an irresistible index entry "Muggles, 576", which turns out to be a link to:

TheoremThe flow of any Hamiltonian vector field consists of canonical transformations

Proof(Hogwarts version) ...

Proof(Muggles version) ...

**Remark** It is striking that Dirac's *The Principles of Quantum Mechanics* (1930), Feynman's *Lectures on Physics* (1965), Nielsen and Chuang's *Quantum Computation and Quantum Information* (2000)---and Scott Aaronson's essay *The Ghost in the Turing Machine* (2013) too---all frame their analysis exclusively in terms of (what Michael Spivak aptly calls) Muggle mathematic methods! :)

**Observation** Joshua Landsberg has written an essay **Clash of Cultures** (2012) that discusses the sustained tension between Michael Spivak's "Hogwarts math versus Muggle math". The tension has historical roots that extent at least as far back as Karl Gauss' celebrated apprehension regarding the "**the clamor of the Boeotians**" (aka Muggles).

**Conclusion** Michael Spivak's wry mathematical jokes and Eliezer Yudkowsky's wonderfully funny *Harry Potter and the Methods of Rationality* both help us to appreciate that outdated Muggle-mathematical idioms of standard textbooks and philosophical analysis are a substantial impediment to 21st Century learning and rational discourse of all varieties---including philosophical discourse.

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-19T18:24:48.856Z · score: -1 (5 votes) · LW · GW

Shminux, perhaps some *Less Wrong* readers will enjoy the larger reflection of our differing perspectives that is provided by Arthur Jaffe and Frank Quinn’s *‘Theoretical mathematics’: Toward a cultural synthesis of mathematics and theoretical physics* (Bull. AMS 1993, arXiv:math/9307227, 188 citations); an article that was notable for its **biting criticism of Bill Thurston's geometrization program**.

Thurston's gentle, thoughtful, and scrupulously polite response *On proof and progress in mathematics* (Bull. AMS 1994, arXiv:math/9307227, 389 citations) has emerged as a classic of the mathematical literature, and is recommended to modern students by many mathematical luminaries (Terry Tao's weblog sidebar has a permanent link to it, for example).

**Conclusion** It is no bad thing for students to be familiar with this literature, which plainly shows us that it is neither necessary, nor feasible, nor desirable for everyone to think alike!

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-18T22:34:51.338Z · score: 0 (2 votes) · LW · GW

Thank you for your gracious remarks, Paper-Machine. Please let me add, that few (or possibly none) of the math/physics themes of the preceding posts are original to me (that's why I give so many references!)

Students of quantum history will find pulled-back/non-linear metric and symplectic quantum dynamical flows discussed as far back as Paul Dirac's seminal *Note on exchange phenomena in the Thomas atom* (1930); a free-as-in-freedom review of the nonlinear quantum dynamical frameworks that came from Dirac's work (nowadays called the "Dirac-Frenkel-McLachlan variational principle") is Christian Lubich's recent *On Variational Approximations In Quantum Molecular Dynamics* (*Math. Comp.*, 2004).

Shminux, perhaps your appetite for nonlinear quantum dynamical theories would be whetted by reading the most-cited article in the history of physics, which is Walter Kohn and Lu Jeu Sham's *Self-Consistent Equations Including Exchange and Correlation Effects* (1965, cited by 29670); a lively followup article is Walter Kohn's *Electronic Structure of Matter*, which can be read as a good-humored celebration of the practical merits of varietal pullbacks ... or as Walter Kohn calls them, *variational Ansatzes*, having a varietal product form.

There is a considerable overlap between Scott Aaronson's "freebit" hypothesis and the view of quantum mechanics that Walter Kohn's expresses in his *Electronic Structure of Matter* lecture (views whose origin Kohn ascribes to Van Vleck):

Kohn's Provocative StatementIn general the many-electron wavefunction ) for a system of electrons is not a legitimate scientific concept, when , where .

Scott's essay would (as it seems to me) be stronger if it referenced the views of Kohn (and Van Vleck too) ... especially given Walter Kohn's unique status as the most-cited quantum scientist in all of history!

Walter Kohn's vivid account of how his "magically" powerful quantum simulation formalism grew from strictly "muggle" roots---namely, the study of disordered intermetallic alloys---is plenty of fun too, and eerily foreshadows some of the hilarious scientific themes of Eliezer Yudkowsky's *Harry Potter and the Methods of Rationality*.

In view of these nonpareil theoretical, experimental, mathematical (and nowadays) engineering successes, sustained over many decades, it is implausible (as it seems to me) that the final word has been said in praise of nonlinear quantum dynamical flows! Happy reading Shminux (and everyone else too)!

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-18T15:25:26.783Z · score: 0 (2 votes) · LW · GW

Shminux, there are plenty of writers---mostly far more skilled than me!---who have attempted to connect our physical understanding of dynamics to our mathematical understanding of dynamical flows. So please don't let my turgid expository style needlessly deter you from reading this literature!

In this regard, Michael Spivak's works are widely acclaimed; in particular his early gem *Calculus on Manifolds: a Modern Approach to Classical Theorems of Advanced Calculus* (1965) and his recent tome *Physics for Mathematicians: Mechanics I* (2010) (and in a comment on *Shtetl Optimized* I have suggested some short articles by David Ruelle and Vladimir Arnold that address these same themes).

Lamentably, there are (at present) no texts that deploy this modern mathematical language in service of explaining the physical ideas of (say) Nielsen and Chuang's *Quantum Computation and Quantum Information* (2000). Such a text would (as it seems to me) very considerably help to upgrade the overall quality of discussion of quantum questions.

On the other hand, surely it is no bad thing for students to read these various works---each of them terrifically enjoyable in their own way---while wondering: How do these ideas fit together?

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-18T00:48:09.861Z · score: 4 (6 votes) · LW · GW

Gjmasks "Along what vector field V are you taking the Lie derivative?

The natural answer is, along a *Hamiltonian* vector field. Now you have all the pieces needed to ask (and even answer!) a broad class of questions like the following:

Alice possesses a computer of exponentially large memory and clock speed, upon which she unravels the Hilbert-space trajectories that are associated to the overall structure ), where is a Hilbert-space (considered as a manifold), is its metric, is its symplectic form, is the complex structure induced by ), and ) are the (stochastic,smooth) Lindblad and Hamiltonian potentials that are associated to a physical system that Alice is simulating. Alice thereby computes a (stochastic) classical data-record as the output of her unraveling.

Bob pulls-back ) onto his lower-dimension varietal manifold (per Joseph Landsberg's recipes), upon which he unravels the pulled-back trajectories, thus obtaining (like Alice) a classical data-record as the output of his unraveling (but using far-fewer computational resources).

Then It is natural to consider questions like the following:

QuestionFor hot noisy quantum dynamical systems (like brains), what is the lowest-dimension varietal state-space for which Bob's simulation data-record cannot be verifiably distinguished from Alice's simulation data-record? In particular, do polynomially-many varietal dimensions suffice for Bob's record to be indistinguishable from Alice's?

Is this a mathematically *well-posed* question? Definitely! Is it a scientifically *open* question? Yes! Does it have engineering consequences (and even medical consequences) that are *practical* and *immediate*? Absolutely!

What *philosophical* implications would a "yes" answer have for Scott's freebit thesis? Philosophical questions are of course tougher to answer than mathematical, scientific, or engineering questions, but one reasonable answer might be "The geometric foaminess of varietal state-spaces induces Knightian undertainty in quantum trajectory unravelings that is computationally indistinguishable from the Knightian uncertainty that, in Hilbert-space dynamical systems, can be ascribed to primordial freebits."

Are these questions *interesting*? Here it is neither feasible, nor necessary, nor desirable that everyone think alike!

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-17T22:36:15.800Z · score: 1 (3 votes) · LW · GW

JLM, the mathematically natural answer to your questions is:

• the quantum *dynamical* framework of (say) Abhay Ashtekar and Troy Schilling's *Geometrical Formulation of Quantum Mechanics* arXiv:gr-qc/9706069v1, and

• the quantum *measurement* framework of (say) Carlton Caves' on-line notes *Completely positive maps, positive maps, and the Lindblad form*, both pullback naturally onto

• the *varietal* frameworks of (say) Joseph Landsberg's *Tensors: Geometry and Applications*

Textbooks like Andrei Moroianu's *Lectures on Kahler Geometry* and Mikio Nakahara's *Geometry, Topology and Physics* are helpful in joining these pieces together, but definitely there is at present no single textbook (or article either) that grinds through all the details. It would have to be a long one.

For young researchers especially, the present literature gap is perhaps a good thing!

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-17T21:19:52.236Z · score: 2 (4 votes) · LW · GW

The dynamicist Vladimir Arnold had a wonderful saying:

"Every mathematician knows that it is impossible to understand any elementary course in thermodynamics."

This saying is doubly true of quantum mechanics. For example, the undergraduate quantum physics notion of "multiply a quantum vector by " is not so easy to convey without mentioning the number "." Here's how the trick is accomplished. We regard Hilbert space as a real manifold that is equipped with a symplectic form and a metric . Given an (arbitrary) vector field on , we can construct an endomorphism by first "flatting" with and then "sharping" with , that is . The physicist's equation thus is naturally instantiated as the endomorphic condition .

**The Point** To a geometer, the Lie derivative of has no very natural definition, but the Lie derivative of the endomorphism is both mathematically well-defined and (on non-flat quantum state-spaces) need not be zero. The resulting principle that " is not necessarily constant" thus is entirely natural to geometers, yet well-nigh inconceivable to physics students!

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-17T17:22:07.579Z · score: 2 (2 votes) · LW · GW

Thank you gjm. To the best of my understanding, (1) all markup glitches are fixed; (2) all links are live; and (3) an added paragraph (fourth-from-last) now explicitly links dynamic-J methods to Scott's notion of "freebits".

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-17T14:58:07.747Z · score: 0 (0 votes) · LW · GW

Gjm, after a round-of-suffering with the LaTeX equation editor, any-and-all markup glitches in the above comment now seem to be fixed (at least, the comment now parses OK on FireFox/OSX and Safari/OSX). Please let me know if you are encountering any remaining markup-relating problems, and if so, I will attempt to fix them.

**johnsidles**on Quotes and Notes on Scott Aaronson’s "The Ghost in the Quantum Turing Machine" · 2013-06-17T13:58:35.627Z · score: 2 (6 votes) · LW · GW

Rancor commonly arises when STEM discussions in general, and discussions of quantum mechanics in particular, focus upon personal beliefs and/or personal aesthetic sensibilities, as contrasted with verifiable mathematical arguments and/or experimental evidence and/or practical applications.

In this regard, a pertinent quotation is the self-proclaimed "personal belief" that Scott asserts on page 46:

"One obvious way to enforce a macro/micro distinction would be via a dynamical collapse theory. ... I personally cannot believe that Nature would solve the problem of the 'transition between microfacts and macrofacts' in such a seemingly ad hoc way, a way that does so much violence to the clean rules of linear quantum mechanics."

Scott's personal belief calls to mind Nature's solution to the problem of gravitation; a solution that (historically) has been alternatively regarded as both "clean" or "unclean". His quantum beliefs map onto general relativity as follows:

General relativity is "unclean""We can be confident that Nature will not do violence to the clean rules of linear Euclidean geometry; the notion is so repugnant that the ideas of general relativityCANNOTbe correct."

as contrasted with

General relativity is "clean""Matter tells space how to curve; space tells matter how to move; this principle is so natural and elegant that general relativityMUSTbe correct!"

Of course, nowadays we are mathematically comfortable with the latter point-of-view, in which Hamiltonian dynamical flows are naturally associated to non-vanishing Lie derivatives of metric structures , that is .

This same mathematical toolset allow us to frame the ongoing debate between Scott and his colleagues in mathematical terms, by focusing our attention not upon the metric structure , but similarly upon the complex structure .

In this regard a striking feature of Scott's essay is that it provides precisely *one* numbered equation (perhaps this a deliberate echo of Stephen Hawking's **A Brief History of Time**, which also has precisely one equation?). Fortunately, this lack is admirably remedied by the discussion in Section 8.2 "Holomorphic Objects" of Andrei Moroianu's textbook **Lectures on Kahler Geometry**. See in particular the proof arguments that are associated to Moroianu's Lemma 8.7, which conveniently is freely available as Lemma 2.7 of an early draft of the textbook, that is available on the arxiv server as **arXiv:math/0402223v1**. Moroianu's draft textbook is short and good, and his completed textbook is longer and better!

Scott's aesthetic personal beliefs naturally join with Moroianu's mathematical toolset to yield a crucial question: Should/will 21st Century STEM researchers embrace with enthusiasm, or reject with disdain, dynamical theories in which ?

Scott's essay is entirely correct to remind us that this crucial question is (in our present state-of-knowledge) not susceptible to *any* definitively verifiable arguments from mathematics, physical science, or philosophy (although plenty of arguments from plausibility have been set forth). But on the other hand, students of STEM history will appreciate that the community of *engineers* has rendered a unanimous verdict: in essentially all modern large-scale quantum simulation codes (matrix product-state calculations provide a prominent example).

So to the extent that biological systems (including brains) are accurately and efficiently simulable by these emerging dynamic-J methods, then Scott's *definition* of quantum dynamical systems may have only marginal relevance to the *practical* understanding of brain dynamics (and it is plausible AFAICT that this proposition is entirely consonant with Scott's notion of "freebits").

Here too there is ample precedent in history: early 19th Century textbooks like Nathaniel Bowditch's renowned *New American Practical Navigator* (1807) succinctly presented **the key mathematical elements of non-Euclidean geometry** (many decades in advance of Gauss, Riemann, and Einstein).

Will 21st Century adventurers learn to navigate nonlinear quantum state-spaces with the same exhilaration that adventurers of earlier centuries learned to navigate first the Earth's nonlinear oceanography, and later the nonlinear geometry of near-earth space-time (via **GPS satellites**, for example)?

**Conclusion** Scott's essay is right to remind us: *We don't know whether Nature's complex structure is comparably dynamic to Nature's metric structure, and finding out will be a great adventure!* Fortunately (for young people especially) textbooks like Moroianu's provide a well-posed roadmap for helping mathematicians, scientists, engineers --- and philosophers too --- in setting forth upon this great adventure. Good!

**johnsidles**on [link] Scott Aaronson on free will · 2013-06-15T19:32:06.976Z · score: 1 (5 votes) · LW · GW

Rancor commonly arises when STEM discussions in general, and discussions of quantum mechanics in particular, focus upon personal beliefs and/or personal aesthetic sensibilities, as contrasted with verifiable mathematical arguments and/or experimental evidence and/or practical applications.

In this regard, a pertinent quotation is the self-proclaimed "personal belief" that Scott asserts on page 46:

"One obvious way to enforce a macro/micro distinction would be via a dynamical collapse theory. ... I personally cannot believe that Nature would solve the problem of the 'transition between microfacts and macrofacts' in such a seemingly ad hoc way, a way that does so much violence to the clean rules of linear quantum mechanics."

Scott's personal belief calls to mind Nature's solution to the problem of gravitation; a solution that (historically) has been alternatively regarded as both "clean" or "unclean". His quantum beliefs map onto general relativity as follows:

General relativity is "unclean""We can be confident that Nature will not do violence to the clean rules of linear Euclidean geometry; the notion is so repugnant that the ideas of general relativityCANNOTbe correct."

as contrasted with

General relativity is "clean""Matter tells space how to curve; space tells matter how to move; this principle is so natural and elegant that general relativityMUSTbe correct!"

Of course, nowadays we are mathematically comfortable with the latter point-of-view, in which Hamiltonian dynamical flows are naturally associated to non-vanishing Lie derivatives of metric structures , that is .

This same mathematical toolset allow us to frame the ongoing debate between Scott and his colleagues in mathematical terms, by focusing our attention not upon the metric structure , but similarly upon the complex structure .

In this regard a striking feature of Scott's essay is that it provides precisely *one* numbered equation (perhaps this a deliberate echo of Stephen Hawking's **A Brief History of Time**, which also has precisely one equation?). Fortunately, this lack is admirably remedied by the discussion in Section 8.2 "Holomorphic Objects" of Andrei Moroianu's textbook **Lectures on Kahler Geometry**. See in particular the proof arguments that are associated to Moroianu's Lemma 8.7, which conveniently is freely available as Lemma 2.7 of an early draft of the textbook, that is available on the arxiv server as **arXiv:math/0402223v1**. Moroianu's draft textbook is short and good, and his completed textbook is longer and better!

Scott's aesthetic personal beliefs naturally join with Moroianu's mathematical toolset to yield a crucial question: Should/will 21st Century STEM researchers embrace with enthusiasm, or reject with disdain, dynamical theories in which ?

Scott's essay is entirely correct to remind us that this crucial question is (in our present state-of-knowledge) not susceptible to *any* definitively verifiable arguments from mathematics, physical science, or philosophy (although plenty of arguments from plausibility have been set forth). But on the other hand, students of STEM history will appreciate that the community of *engineers* has rendered a unanimous verdict: in essentially all modern large-scale quantum simulation codes (matrix product-state calculations provide a prominent example).

So to the extent that biological systems (including brains) are accurately and efficiently simulable by these emerging dynamic-J methods, then Scott's *definition* of quantum dynamical systems may have only marginal relevance to the *practical* understanding of brain dynamics (and it is plausible AFAICT that this proposition is entirely consonant with Scott's notion of "freebits").

Here too there is ample precedent in history: early 19th Century textbooks like Nathaniel Bowditch's renowned *New American Practical Navigator* (1807) succinctly presented **the key mathematical elements of non-Euclidean geometry** (many decades in advance of Gauss, Riemann, and Einstein).

Will 21st Century adventurers learn to navigate nonlinear quantum state-spaces with the same exhilaration that adventurers of earlier centuries learned to navigate first the Earth's nonlinear oceanography, and later the nonlinear geometry of near-earth space-time (via **GPS satellites**, for example)?

**Conclusion** Scott's essay is right to remind us: *We don't know whether Nature's complex structure is comparably dynamic to Nature's metric structure, and finding out will be a great adventure!* Fortunately (for young people especially) textbooks like Moroianu's provide a well-posed roadmap for helping mathematicians, scientists, engineers --- and philosophers too --- in setting forth upon this great adventure. Good!