Sunday, May 29, 2005

Judaism, Physics, and God

I recently read Judaism, Physics, and God: Searching for Sacred Metaphors in a Post-Einstein World (the Harvard comma in the title is my defiant insertion) by Rabbi David W. Nelson (not to be confused with this David Nelson).

The subject matter was right up my alley -- I taught a four-day course on "Playing Dice with the Universe: Rabbinic Literature, Quantum Mechanics, and Indeterminacy" at last year's NHC Summer Institute, and I'm teaching a one-hour excerpt on the Shavuot Retreat this year. So my first reaction to seeing the book was "Cool! Someone else is putting my shtick in print!". (Not at all "That bastard stole my idea", because I'm too lazy to write a book anyway, so I was glad someone else was taking care of it.) Then I started reading and got annoyed because Nelson wasn't dealing with quantum mechanics the way I do. Then I read further and realized that we were approaching the interface between Judaism and physics from very different perspectives (a physics teacher with an extracurricular interest in Jewish texts vs. a rabbi with an extracurricular interest in physics) and had very different objectives in putting Judaism and physics together, so it didn't make sense to criticize the book for failing to achieve my objectives, because he had his own objectives and the book should be viewed in that light. Then I was at peace.

My course starts with an introduction to quantum mechanics, focusing on the Einstein/Bohr debate over the interpretation of the wavefunction, then the bulk of the course is a close reading of rabbinic texts dealing with indeterminacy (generally in some physical quantity, and things like "Shabbat" and "tamei" are physical properties in the Talmud's physics, but also indeterminacy in truth toward the end), reading the texts through the lens of quantum mechanics and inserting the rabbis into the Einstein/Bohr debate. The purposes include 1) an intellectual meditation on how different "approaches to knowledge" address the questions on indeterminacy ("If a tree falls in the woods and no one is there to hear it, does it make a sound?"), 2) shedding light on the strand of indeterminacy running through Jewish tradition, contrary to the idea that religious traditions (or science, for that matter) represent certainty, 3) puzzling through the rabbis' logic puzzles for their own sake. Many people enjoyed the course, but some criticized it for not really having a point. And it's true -- the fuzzy ethical message at the end was a bit tacked-on. I was really focusing more on process and exploration.

At first Nelson's book seems superficially similar. Each chapter addresses a different topic in modern physics (cosmology, quantum mechanics, chaos theory, special relativity, general relativity, and string theory) and begins with an overview of the physics topic and then connects it to Jewish texts and concepts. However, Nelson's approach and goal are completely different from mine. His goal is to find new metaphors for God using concepts in contemporary physics. Nelson makes no claims that the new physics actually describes God (who can know this anyway?), but suggests that these metaphors may represent new meaningful ways for us to relate to God. He writes "So it seems that metaphors for God are not properly metaphors for God at all, but rather metaphors for our beliefs about God. The difference is a crucial one. For although I do not think we can have direct experience of God, we do have direct experience of our beliefs."(p. 234) Some of the metaphors work for me and others don't, and that's ok, these other metaphors may work for someone else. There is no end to the metaphors we can devise in our ultimately futile attempts to describe God. ("Asaperah chevodecha v'lo re'iticha, adamecha achanecha v'lo yeda'ticha." "I will tell of your glory though I have not seen you; I will analogize and describe you though I have not known you.")

One of the most meaningful (for me) connections between physics and God in this book (though not a metaphor per se) is in the chapter on string theory. Nelson discusses the incompatibility between quantum mechanics and general relativity and the search for a unified theory. He writes:
Most of the physicists whose works I have read appear to need to find a unity among the forces of nature and the different theories that describe and explain them. This word need ought not be taken lightly. This deep need is rooted in a fervent belief -- likewise a word to be taken seriously -- that the whole universe operates with a single set of principles, rather than with multiple sets. [...]
It seems to be based not in any empirical observation that everything in nature functions according to a single set of rules, for in fact, casual observation suggests just the opposite. Rather, it is based in a fundamental conviction that there must be a single set of rules, perhaps even a single rule, at the root of everything. [...] (p. 183-84)

[After discussing the Standard Model and its zoo of particles:] Why should the universe, on its "simplest" level, be composed of so many different kinds of things? As I ponder the discomfort and dissatisfactions that physicists express when asking this critical question, I imagine they must mirror the feelings of the early monotheists many centuries ago. All around them were people whose best analysis of the world was that it was controlled, on its most basic level, by a panoply of gods. One controlled the sea, another the sun, another the mountains, and so on and on.
Each had its own characteristics, its own abode, and its own strengths and weaknesses. Each interested with the others in complex ways. But among the societies in which such views prevailed, there must have been some who intuitively felt that the world must be simpler. Eventually this intuition developed into a belief that there was just one god controlling the entire system. (p. 189)
The history of physics is filled with discoveries inspired by leaps of monotheistic faith like this. Newton showed that the force that makes apples fall to the ground is the same force that causes planetary orbits. If NAF is reading this, he can write in about the role of faith in fundamental symmetry and harmony in the development of the nebular hypothesis about the origin of the solar system. Electricity and magnetism were shown to be two manifestations of the electromagnetic interaction, first through the 19th-century work culminating in Maxwell's equations, then in Einstein's special relativity, which showed that the exact same force could be an "electric" force in one frame of reference and a "magnetic" force in another. And the discovery that all the elements on the periodic table (each thought to be a different fundamental particle) are just different permutations of the same three particles. Then Bohr's philosophy of complementarity: the wave nature of light and the particle nature of light are two manifestations of the same system. And then (as I told my students this week, freaking them out) De Broglie suggested (before any experimental confirmation of this absurd hypothesis) that the same is true for matter. And quarks, showing that the huge mess of particles found in accelerators was composed of a smaller mess of particles. (The road to the Standard Model was explicitly religious -- the Eightfold Way!) And then the electroweak unification theory, showing that the electromagnetic and weak force are unified at high energies, and the 1979 Nobel Prize press release also takes this historical view. And since then, everyone has been looking for a Grand Unified Theory (GUT), combining the electroweak and strong forces, and/or a Theory Of Everything (TOE), combining these with gravity. String theory is only one recent and well-publicized attempt; Einstein was looking unsuccessfully for a unified field theory for much of his later life. With each unification, we strive to move closer to the One that is the cause of everything in the universe.

Other highlights: "Listen, O Israel, Adonai is our God, Adonai, the Singularity!"(p. 19) A singularity is a point of infinite density like the center of a black hole, or the universe at the beginning of time according to the Big Bang model. The matter and energy present in this singularity at the beginning now comprise the entire universe; Nelson says that this is a way to read "m'lo chol ha'aretz k'vodo" ("the whole world is full of [God's] glory", Isaiah 6:3). Later, the singularity metaphor is also applied to black holes, saying that God is hidden, as by an event horizon.

I recommend this book to anyone who is interested in physics and Judaism. Beyond the actual content, the books provides new ways of thinking about physics and God.

Some of the flaws:
Rabbi Nelson states at the very beginning, "I am not a scientist. I have not taken a course in hard science or math since high school." (p. xxxvi) Therefore, all of the physics in the book is based on his extensive reading of "nontechnical, nonmathematical, purely descriptive books." As far as I can tell, the physics is correct for the most part -- there are minor errors, like mixing up "accuracy" and "precision", or "Grand Unified Theory" and "Theory Of Everything", but nothing major. The things that I find annoying would probably go unnoticed by someone encountering the physics content for the first time. However, the book still would have benefited from better editing by a physicist.

Nelson's sources include some of the same bestselling pop-physics books that I have read (Stephen Hawking, A Brief History of Time; Brian Greene, The Elegant Universe). But I read A Brief History of Time when I was much younger and learning about this stuff for the first time. I read The Elegant Universe when I was already a full-time physics teacher, and the details of string theory were certainly new to me, but even the topics that I already knew (intro to relativity and quantum mechanics) were worthwhile to read about because Greene presented them in innovative ways (now I finally have a way to explain Planck's solution to the ultraviolet catastrophe to high school students who don't know from stat mech without saying "Uh, but if the energy is quantized, the numbers magically work out! You'll learn why in college."). I don't think Nelson brought much added value to the physics parts (until the point in each chapter where he brought in the Jewish stuff); he is mostly restating what all the other pop-physics books already say. Which is completely fine if Judaism, Physics, and God is the first book you are reading about relativity or whatever, but I would still recommend Hawking and Greene as better physics-for-nonscientists books (though without the Judaism, of course). (While I'm recommending pop-physics books, throw in The God Particle by Leon Lederman.)

The problem with using pop physics books as primary sources is not that the physics is wrong (it isn't), but that there is a lack of perspective on what is common knowledge in the physics world and what is a particular author's idiosyncracy. For example, Nelson writes on p. 134, "As the object's speed approaches closer to light speed, its mass increases without limit, and thus, according to physicist Brian Greene,
it would require a push with an infinite amount of energy to reach or to cross the light barrier. This, of course, is impossible and hence absolutely nothing can travel faster than the speed of light."

This doesn't require a block quote, or even a citation! This is a core part of Einstein's special theory of relativity, and can be found in any introductory physics textbook. There is nothing extraordinary about Brian Greene's formulation of this idea. Likewise, Rabbi David Nelson wouldn't get a block quote and footnote if I wanted to say that
In Deuteronomy, as a part of the long series of speeches that Moses makes to the Israelites before his death, we find the following: "Hear O Israel! Adonai is our God, Adonai is One!" (Deut 6:4) This line, known as the Shema (from its first Hebrew word, shema, meaning "hear" or "listen"), is perhaps the best-known statement of Jewish faith. (Rabbi David W. Nelson, Judaism, Physics, and God, p.18)

since I think that idea has entered the public domain. Likewise, Greene gets credit for the light-clock thought experiment. ("Of all the explanations of this strange relationship between time and motion that I have read, that of Columbia University physicist Brian Greene has appealed to me most. He starts with a functional definition of time as that which is measured by the regular ticking of clocks...", p. 148) I think the light clock is a great thought experiment (I use it to derive time dilation when I teach relativity), but Greene didn't come up with it! Einstein himself was the one with the clock obsession. Meanwhile, other explanations attributed to Greene actually areare Greene originals, but it's hard to tell the difference here.

I think the quantum mechanics chapter misses a lot of opportunities. I would be biased and self-aggrandizing if I were to criticize it for failing to contrast the Copenhagen interpretation with hidden-variable theories, or failing to discuss the role of indeterminacy in rabbinic ontology, so I won't. But more objectively, I think the book misrepresents the Copenhagen interpretation. The main idea that he takes from it is that the observer's consciousness determines reality, and this is used as a jumping-off point to discuss the importance of consciousness and kavanah. He fails to note that the idea that human consciousness causes wavefunction collapse is very much a fringe version of the Copenhagen interpretation, and there are other explanations (e.g. decoherence) that don't depend on giving the human mind a special status and thus do better by Occam's Razor. The other interpretation of quantum mechanics discussed is the Many Worlds interpretation, which is a jumping-off point to talk about midrash ("what if?") and to reject ethnocentrism. These connections feel forced to me, and don't represent the most significant philosophical consequences of quantum mechanics.

The final chapter asks "Can a physicist pray?" (p. 259) More specifically, Nelson is asking whether it is possible to interact with an infinite God who spans the entire universe. His answer is "yes", but in a way that I don't find very satisfying. He refers to Hasidic meditative practices and proposes:
If we are willing to consider the Hasidic ploy of declaring the "plain meaning of the words" to be completely irrelevant, then we can even bring our sense of God in the universe, crafted as it is with metaphors from the world of physics, into the synagogue. There we can meditate on the unity of all matter, all space, all time, and all energy, while chanting the traditional prayer as a sort of mantra designed not to remind us of a particular message but to allow us to rise above all particular messages to focus on the one universal message: There is unity, structure, beauty, and meaning in the world. (p. 266)
So if prayer is a meditation on the whole universe, then why should we keep doing in the Jewish milieu? Nelson's answer is community and tradition (p. 267-68). I am not content with the idea of maintaining Jewish traditions because our parents did it and our friends are doing it, while holding our modern ideas about physics and the universe, and not forcing them to interact (and I am confused that Nelson appears to come to this conclusion after suggesting otherwise for the rest of the book). Our evolving interpretive tradition can and must be in dialogue with our scientific knowledge. Our classic texts cannot be merely mantras that we chant to maintain continuity with the past; we can read our newer understanding of the universe into the texts themselves.

Anyway, I'm sure all these issues will be worked out in the second edition. Go read the book, and then we can discuss it more.

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