This document is the first installment of three in the Cerro Grande Fire Series. The Cerro Grande Fire left many in the Los Alamos community acutely aware of the importance of backing up the hard drive. I could think of no better instrument for the process than Los Alamos National Laboratory itself. This is a collection of letters written to various friends and colleagues (several of whom regularly circuit this archive), including Howard Barnum, Paul Benioff, Charles Bennett, Herbert Bernstein, Doug Bilodeau, Gilles Brassard, Jeffrey Bub, Carlton Caves, Gregory Comer, Robert Griffiths, Adrian Kent, Rolf Landauer, Hideo Mabuchi, David Mermin, David Meyer, Michael Nielsen, Asher Peres, John Preskill, Joseph Renes, Mary Beth Ruskai, Rüdiger Schack, Robert Schumann, Abner Shimony, William Wootters, Anton Zeilinger, and many others.

In a way, I hope this book evokes images of the kind of dusty, pipe-smoke infused gems one sometimes finds in the far corner of a used bookstore – something not unlike the copy of William James' collected letters I once owned. It takes a funny person to read such a book: one who is willing to dig in the far corner. But I would not want that imagery taken too far. For despite its nod to the happenstance that brought it about, this is not a book about the past, but about our open future. Its singular theme is the quantum.

14 February 1995, “Turtle Wax”

Let me wax just a little. A few quotes by Wolfgang Pauli on quantum mechanical randomness and objective reality. (Taken from the English translation of a paper titled “Matter.”)

09 April 1996, “Randomness”

I don't know if you remember me, but we met at the Santa Fe Institute Workshop on the Physics of Information two summers ago. I spoke to you about your old papers on randomness and quantum mechanics.

In any case, I am very much interested in them again. (Presently, in particular, the ones titled “Finite and Infinite Measurement Sequences in Quantum Mechanics and Randomness: The Everett Interpretation” JMP18 (1977) 2289, and “A Note on the Everett Interpretation of Quantum Mechanics” Found. Phys. 8 (1978) 709.) Carl Caves and I are writing a book on Quantum Information and are trying to get a feel for how far these sorts of considerations really go toward deriving the standard probability expression of quantum theory.

Last night I reread the latter of the two papers mentioned above. The main question on my mind now is about Section 4 “The Asymptotic Description.” At the end you state, “Thus it is an open question whether or not there is any possible state description of the asymptotic situation that includes component states each corresponding to a possible universe as perceived by an observer with memory trace ν.” Has there been any progress in this direction since then?? If there has, could you please send me a reference or outline the solution?

10 February 1997, “Sunday Afternoons and Consistent Histories”

I've finally completed to my satisfaction your challenge of taking a plunge into “consistent histories.” And I've had great fun! In particular, I read all or most of each of the following:

1. “Consistent Histories and the Interpretation of Quantum Mechanics,”

2. “Quantum Interpretation Using Consistent Histories,”

3. “Correlations in separated quantum systems: A consistent history analysis of the EPR problem,”

4. “The Consistency of Consistent Histories: A Reply to d'Espagnat,”

5. “A Consistent History Approach to the Logic of Quantum Mechanics,”

6. “Consistent Histories and Quantum Reasoning.”

I don't think I've read everything, but I'll trust that I haven't missed anything too significant – at least for a novice education in the subject.

I say I had great fun because, before this, my only introduction to consistent histories had been through various talks by Gell-Mann, Hartle, and Zurek. And, I can't say I ever found any of those satisfactory – they all made it a very confusing muddle to me. I never could figure out the point, i.e., what actually was being proposed as a “solution” to the quantum interpretation problem. Consequently, I often just fell asleep or thought about other things or both. In contrast, I found all your papers logically crisp.

22 July 1996, “Noodles of Nothing”

How's your academic life? Have you been reading any? Do you still subscribe to Texas Monthly? Or was it The Smithsonian, I forget which? Right now, in my spare time, I'm reading Robert Oppenheimer: Letters and Recollections. Mostly it's a collection of letters from when he was in college and graduate school. The fellow was an amazing writer: it would be hard to tell he was a scientist if you didn't know otherwise. Of course, my real interest is in peering into his thoughts as he was learning quantum mechanics; that's why I'm putting time into the book. But it is always good to absorb something of someone else's style.

Have you ever read anything by William James (the psychologist and philosopher – not to be confused with Henry James)? For some reason I'm just fascinated with his writing style; I would love to be able to pull the same tricks, and have it acceptable to do so. If you get a chance, take a look at the first few pages of his essay “The Dilemma of Determinism” just for the style. (You'll be able to find it in the library in any collection of his essays, probably with titles like The Will to Believe; the one I have at home is a Dover edition.)

There's a new phenomenon going on in my field: we've apparently reached the level where it's time for some books on the subject.

October 1997, and to Asher Peres, “Premonition?”

I was awakened this morning just in the middle of a complicated dream. I only remember very fuzzy fragments, but there is one in particular that I thought you two would enjoy hearing about. Someone walked up and handed me a newspaper clipping. The headline read, “Bill Wootters and World Renowned Teleporter Asher Peres Attain New Heights.” I didn't see the article, but the headline was accompanied by a picture of you two both wearing lederhosen and Alpine hats, smiling at the camera!!

July 1998, “Quantum Giggles”

I'm sitting at a little sidewalk cafe in Benasque, Spain thinking of you and all your efforts to find a compelling structure underneath quantum mechanics.

It's strange, but for me this has turned out to be a very foundation-oriented conference. Carl Caves and I have been working to construct a quantum version of de Finetti's theorem in classical probability theory. de Finetti's theorem gives the “subjectivist” a way to interpret an “unknown probability” within his framework: probability distributions over the probability simplex are nothing more than shorthand for a certain kind of probability assignment (called “exchangeable”) over a large multi-trial space. What is an unknown quantum state? If you take quantum states to be states of knowledge, as we do, then an unknown quantum state is a troublesome concept. We think that it can be fixed up in roughly the same way – one just has to identify the right notion of an “exchangeable density operator.”

I imagine it is hard to write a book; I am not sure I could ever do that. But since I discovered the medium of email in 1990, I have never stopped writing. I write, rewrite, and hone my ideas almost exclusively with the aid and clarifying influence of that wonderful tool. The influence may be subliminal, but it is there overpoweringly: if you really want to get an idea worked out for yourself, make it understandable to another mind through correspondence, where your face cannot be seen, but your voice must be heard – do it over and over again, gearing each presentation to each individual mind. Connect the idea to every aspect of life you can. If you stand the test, you are making progress, and often unbeknownst to yourself, transforming the initial seed of an idea into a more resilient and compelling structure. This collection of emails, graciously reprinted by Cambridge University Press with the encouragement of Simon Capelin, is predominantly a record of my honing one such idea – The Paulian Idea – as I came of age with the field of quantum information. If I can entertain the reader along the way, that is just as well too.

12 June 1999, “Interest in Pauli”

I have come across a reference to a paper of yours that I have not been able to obtain. May I ask of you to send me a reprint of it? The paper is:

I have read several of your other papers on Pauli's thought and have been uniformly pleased with each. I am especially interested in his ideas concerning the demise of the “detached-observer” notion within quantum theory. (I would also be interested in any of your other works on the subject that may have been written since your 1992 article, “Wolfgang Pauli between Quantum Reality and the Royal Path of Dreams.” This is the latest one that I am aware of.)

About myself, I am a theoretical physicist at Caltech who specializes in quantum information theory and quantum computing. I am well acquainted with your colleague Nicolas Gisin at the University of Geneva.

21 August 1999, “One More Article?”

Upon my return from Cambridge a couple of weeks ago, I found in my mailbox your package full of wonderful papers! Thank you so much.

29 September 1997, “Quantum Information Questions”

I think I'll answer your questions somewhat out of the order in which you asked them. I hope you don't mind: it may fit what I'm thinking more closely that way.

Bakercise 1:How important do you think these papers are to Quantum Information and the quantum technologies (computing, communication, cryptography and teleportation)? Are they a major step forward? And if so, why?

In my opinion, the Holevo–Schumacher–Westmoreland (HSW) result was the most technically difficult one in Quantum Information Theory to be proved last year. In the long run, the papers are certain to be classics. As far as importance goes, it was certainly one of the top two results (the other being a consortium of papers to do with fault-tolerant computation on quantum computers).

The HSW papers solve a long-standing problem that was on Holevo's mind as early as 1978. Holevo actually had a paper conjecturing this result in 1979, but somehow it escaped all of our attention until Richard Jozsa and I met him last September in Japan. He told us of the old paper then. (I've done a citation search since then, and, believe it or not, this paper had only been cited five times in its life.

February 1998, “Law Without Law…Or Something Like That”

This morning I read one of the papers you gave me last week (“Information is Inevitably Physical”) and was reminded of your interest in the idea that the laws of physics may not be written in stone once and for all…but instead may be contingent upon the particular details of the universe itself…and indeed may be evolutionary à la Peirce, Wheeler, Lee Smolin, etc. At least one version or other of this kind of thing has intrigued me for some time (essentially since meeting John Wheeler in 1985). It's been sort of a hidden hobby, somewhat connected with separating the wheat from the chaff in quantum mechanics. My personal writings on the subject are now pretty voluminous, though not yet tight enough in substance that I show them to too many: most are in the form of emails to colleagues such as you.

Anyway, if you're interested, perhaps I'll compile a small compendium and send it your way when I get back from Tokyo March 15 – I'm travelling essentially every moment until then. May be this will help us open a dialog to pinpoint where some real progress might be made.

In the meantime let me tip you off to another article on the subject that I ran across recently: S. S. Schweber: “The Metaphysics of Science at the End of a Heroic Age,” in Experimental Metaphysics, edited by R. S. Cohen, M. Horne, and J. Stachel (Kluwer, Dordrecht, 1997), pp. 171–198.

February 1996, “QM is a Law of Thought”

By the way, did you ever read the paper Carl and I wrote titled “Quantum Information: How Much Information in a State Vector?” In it we talk at some length about this idea of “Quantum Mechanics as a Law of Thought” and other Bayesian sounding things. (We even quote Gertrude Stein?!”!) Of course, all the ideas are loose now, but one day they'll be tight.

September 1996, “Silly Latin”

Allow me to continue my tradition of writing you only when I need something translated!! I've decided on an epithet for myself. Either:

What do you think? (…and don't tell me I'm plagiarizing Boole!) Anyway, the problem is that I would like to have these translated as closely as possible into Latin. Do you think you're up to the task? I would appreciate it so much.

I can't wait to see you in Japan; I really miss the old gang.

Rüdiger's First Reply: 19 September 1996

I like “Quantum Mechanics is a Law of Thought” better, but I can't give a good reason for that.

January 1999, “The (Un-)Detached Observer”

Yesterday I ran across your paper “On the Interpretation and Philosophical Foundation of Quantum Mechanics” posted on the web, and was very much impressed with its depth. Most importantly, however, I am sad to say, it reminded me that I still owe you some papers.

I have remedied that now by sending you a pile of things that I have written on the relation between information gain and quantum state disturbance. These are relevant to your request above, and, I think, even more relevant to the thoughts in your paper. I am in great agreement with the idea that there may be a deeper foundation to quantum mechanics, one along the lines that Pauli and Wheeler attempted to sketch. Quantum mechanics, it seems to me, is an expression of the best we can say in a world where the observer is not detached (to use Pauli's phrase). Recognizing and appreciating that lack of detachedness is the most exacting tool we have for peering into the greater future of quantum theory. This I think is the ultimate role of quantum information theory. (For the opposite point of view, however, you may be interested in having a look at John Preskill's paper “Quantum Information: Its Future Impact on Physics” at http://theory.caltech.edu/~preskill/.)

I hope you will enjoy the things I have sent you; it is always my attempt to be as clear as I possibly can be when I write.

May 2000, “History Reduced to Eight Pages”

Dear friends and family who have written or called with concern over the Los Alamos fires,

I apologize at the outset for sending a mass mailing like this. All of you hold a unique place in my mind, but time is scarce at the moment.

Sometime Wednesday or Thursday last week, the Cerro Grande fire invaded our home in Los Alamos and took essentially all that was in it. The only exceptions were our car, a couple of suitcases of clothes and memories, and most importantly, our lives. Kiki, Emma, and I are all physically well. So are our “boys,” the golden retrievers Albert and Wizzy. The last few days we have received shelter and comfort in Albuquerque in the home of Carl Caves and Karen Kahn. The boys have been in the foster care of Chris Hains (where they likely view themselves as having a resort vacation).

We saw the remains of our home Sunday: all that was left solid was the chimney. The thought of it makes us quite sad at times. I count as my greatest loss all the “intellectual property” that never made it or could not make it into my computer – my thousands of pages of meticulous calculation, my sad poems from sad times and my pre-electronic correspondence, my collection of over 700 physics, math, and philosophy books.

25 December 1996, “Reality Steaks”

Holiday cheers! I'm sitting in Geneva, connected to my machine at Caltech, thinking about an old fart in Massachusetts. I was just reading an article (in the New Yorker) about Woody Allen and came across the most wonderful quote: “I hate reality, but, you know, where else can you get a good steak dinner?” Like it? Quantum mechanics everywhere you turn.

17 February 1997, “Prophetic Herberts”

This is the second time you've intrigued me with a phrase or two: I'm not letting you off the hook this time. Please explain in more detail what you mean by the following. The first quote comes from 25 December 1996:

Herbal Treatment 1:Actually that Austrian reaction to enhancing classical communication was probably part of a reality-loving or at least a quantum-preferring inclination which is some-thing beneficial to the reality-seekers amongst us – if everyone were so crazed about measurement and what-all, Charlie would never have figured out that it wasn't the knowing of an answer which introduced the irreversibility; it was the erasure of the “garbage” produced in the calculation. And without all the fuss over reversible classical computation, we wouldn't have had so much fun with quantum comp.

The second quote comes from 12 February 1997:

Herbal Treatment 2:I was impressed similarly by Charlie's hint that thinking beyond the “big deal” everyone since Szilard seemed to make of measurements was crucial to his realization that the entropy generated by Maxwell's demon for a 1-molecule gas came from forgetting which side of the door it was on.

On 18 September 1996 I received email that began

Dear Dr. Mermin,

Although I didn't really know my correspondent, it was clear from what followed that he had thought hard – probably harder than I had – about many of the matters I was trying to address. His scholarship and intelligence were so evident that I started walking around with a nice feeling myself at having received unsolicited praise from so thoughtful a source.

Little did I know that those heartwarming words of appreciation were just bait to lure me into a long critical exchange which, to my pleasure and enlightenment, has been going on ever since. A part of my subsequent education (there have also been several invariably instructive and delightful real-life meetings) can be found in Chapter 18 below.

If Chris Fuchs (rhymes with “books”) did not exist then God would have been remiss in not inventing him. Foundations of quantum mechanics is a unique blend of poetry and analysis. Without the poetic vision the analysis tends to chase its own tail into more and more convoluted realms of intricate triviality. Without the analysis the poetry easily degenerates into self-indulgent doggerel.