A little while ago I went to see Zizek!, a new documentary about charismatic and controversial Slovenian philosopher and cultural critic Slavoj Zizek. Part of the Zizekian controversy can be traced straightforwardly to his celebrity — not hard to get fellow academics ornery when you’re greeted by admiring throngs at each of your talks (let me tell you) — but there is also his propensity for acting in ways that are judged to be somewhat frivolous: frequent references to pop culture, an unrestrained delight in telling jokes. I was fortunate enough to see Zizek in person, as part of a panel discussion following the film. He is a compelling figure, effortlessly outshining the two standard-issue academics flanking him on the panel. He adamantly insisted that he had no control over the documentary of which he was the subject, indeed that he hasn’t even seen it, but then reveals that a number of important scenes were admittedly his idea. In one example, the camera lingers on a striking portrait of Stalin in his apartment, which the cinematic Zizek explains as a litmus test, a way of interrogating the bourgeois sensibilities of his visitors. The flesh-and-blood Zizek, meanwhile, points out that it was just a joke, and that he would never have something so horrible as a portrait of Stalin on his wall. It ties into his notion that a film will never reveal the true person behind the scholar or public figure, nor should it; the ideas will stand or fall by themselves, separate from their personification in an actual human. I have no educated opinion about his standing as a thinker; see John Holbo, Adam Kotsko (and here), or Kieran Healy for some opinions, or read this interview in The Believer and judge for yourself.
The movie opens with a Zizek monologue on the origin of the universe and the meaning of life. We can talk all we like, he says, about love and meaning and so on, but that’s not what is real. The universe is “monstrous” (one of his favorite words), a mere accident. “It means something went terribly wrong,” as you can hear him say through a distinctive lisp in this clip from the movie. He even invokes quantum fluctuations, proclaiming that the universe arose as a “cosmic catastrophe” out of nothing.
I naturally cringed a little at the mention of quantum mechanics, but his description ultimately got it right. Our universe probably did originate as a quantum fluctuation, either “from nothing” or within a pre-existing background spacetime. Mostly, to be honest, I was just jealous. As a philosopher and cultural critic, Zizek gets not only to bandy about bits of quantum cosmology, but is permitted (even encouraged) to connect them to questions of love and meaning and so on. As professional physicists, we’re not allowed to talk about those questions — referees at the Physical Review would not approve. But it’s worth interrogating this intellectual leap, from the accidental birth of the universe to the richness of meaning we see around us. How did we get there from here, and why?
It’s the possibility of addressing this question that I take to be the most significant aspect of the “computational quantum universe” idea advocated by Seth Lloyd in his new book Programming the Universe. Lloyd is a somewhat controversial figure in his own right, but undoubtedly an influential physicist; he was the first to propose a plausible design for a quantum computer. I.e., a computer that takes advantage of the full quantum-mechanical wavefunction of its elements, rather than being content with the ordinary classical states.
To Lloyd, quantum computation is a hammer, and it’s tempting to see everything interesting as a nail — from black holes to quantum gravity to the whole universe. The frustrating aspect of his book is the frequency with which he insists that “the universe is a quantum computer,” without always making it clear just what that means or why we should care. What is the universe supposed to be computing, anyway? Its own evolution, apparently. And what good is that, exactly? It’s hard to tell at first whether the entire idea is merely a particular language in which we are free to talk about good old-fashioned physics and cosmology, or whether it’s a profound change of perspective that can be put to good use. What physicists would really like to know is, does thinking of the universe as a quantum computer actually help us solve any problems?
Well, maybe. My own personal reconstruction of the problem that Lloyd is suggesting we might be able to solve by thinking of the universe as a quantum computer, although in slightly different words, is precisely that raised by Zizek’s monologue: Why, in the course of evolving from the early universe to the end of time, do we pass through a phase featuring the fascinating and delightful complexity we see all around us?
Let’s be more specific about what that means. The early universe — at least, the hot Big Bang with which our observable universe began — is a very low-entropy state. That is, it’s a very unlikely configuration in the space of all the ways one could arrange the universe — much like having all of the air molecules accidentally be located in one half of a room (although much worse). But entropy is increasing as the universe evolves, just like the Second Law of Thermodynamics says it should. The late universe will be very high entropy. In particular, if the universe continues to expand forever (which seems likely, although one never knows), we are evolving toward heat death, in which matter cools down and is dispersed thinly over space after black holes form and evaporate. This is a “natural” state for the universe, one which will essentially stay that way in perpetuity.
However. While the early universe is low-entropy and the late universe is high-entropy, both phases are simple. That is, their macrostates can be described in very few words (they have low Kolmogorov complexity): the early state was hot and dense and smoothly-distributed, while the final state will be cold and dilute and smoothly-distributed. But our current universe, replete as it is with galaxies and planets and blogospheres, isn’t at all simple, it’s remarkably complex. There are individual subsystems (like you and me) that would require quite a lengthy description to fully specify.
So: Why is it like that? Why, in the evolution from a simple low-entropy universe to a simple high-entropy universe, do we pass through a complex medium-entropy state?
Lloyd’s suggested answer, to the extent that I understand it, arises from the classic thought experiment of the randomly typing monkeys. A collection of monkeys, randomly pecking at keyboards, will eventually write the entire text of Hamlet — but it will take an extremely long time, much much longer than the age of the observable universe. For that matter, it will take a very long time to get any “interesting” string of characters. Lloyd argues that the situation is quite different if we allow the monkeys to randomly construct algorithms rather than mere strings of text; in particular, the likelihood that such an algorithm will produce interesting (complex) output is much greater than the chance of randomly generating an interesting string. This phenomenon is easily demonstrated in the context of cellular automata: it’s remarkably easy to find very simple rules for automata that generate extremely complex output from simple starting configurations.
So the force of the idea that “the universe is a quantum computer” lies in an understanding of the origin of complexity. Think of the different subsystems of the universe, existing in slightly different arrangements, running different quantum algorithms. It is much easier for such subsystems to generate complex output computationally than one might guess from an estimate of the likelihood of hitting upon complexity by randomly choosing configurations directly. There is an obvious connection to genetics and evolution; DNA sequences can be thought of as lines of computer code, and mutations and genetic drift allow organisms to sample different algorithms. It’s much easier for natural selection to hit upon interesting possibilities by acting on the underlying instruction set, rather than by acting on the (much larger) space of possible configurations of the pieces of an organism.
Of course I don’t really know if any of this is true or interesting. In particular, the role of the “quantum” nature of the computation seems rather unclear; at a glance, it would seem that much of the universe’s manifest complexity lies squarely in the classical regime. But big ideas are fun, and concepts like entropy and complexity are far from completely understood, so perhaps it’s permissible to let our imaginations run a little freely here.
The reason why this discussion of quantum computation and the complexity of the universe fits comfortably with the story of Zizek is that he should understand this (if he doesn’t already). Zizek is a Lacanian, a disciple of famous French psychoanalyst Jacques Lacan. Lacan was a similarly controversial figure, although his charisma manifested itself as taciturn impenetrability rather than voluble popular appeal. One of Lacan’s catchphrases was “the unconscious is structured like a language.” Which I take (not having any idea what I am talking about) as a claim that the unconscious is not simply a formless chaos of mysterious impulses; rather, it has an architecture, a grammar, rules of operation much like those of our higher-level consciousness.
One way of summarizing Lloyd’s explanation of the origin of complexity might be: the universe is structured like a language. It is not just a random configuration of particles typed out by tireless monkeys; it is a quantum computer, following the rules of its algorithms. And by following these rules the universe manages to generate configurations of enormous complexity. Examples of which include science, poetry, love, meaning, and all of those aspects of human life that lend it more interest than we attach to other chemical reactions.
Of course, it’s only a temporary condition. From featureless simplicity we came, and to featureless simplicity we will return. Like a skier riding the moguls, eventually we’ll reach the bottom of the hill, and dissolve into thermal equilibrium. It’s up to us to enjoy the ride.