PROGRAMMING THE UNIVERSE:
A Quantum Computer Scientist Takes On the Cosmos.
By Seth Lloyd.
Knopf. 221 pp. $25.95
Some 14 billion years ago, just after the Big Bang, the universe was a strange but fundamentally simple place, a hot dense blob of stuff teeming with elementary particles. So how did we get from there to here? How did that mostly featureless goo evolve into the universe we find today, with its galaxies and stars, planets and rocks, oceans and weather, bacteria, beetles, and, of course, our own estimable selves?
Seth Lloyd, a professor of mechanical engineering at MIT, would like us to think he has the answer, or at least the beginnings of one. Lloyd does not build bridges or design power stations. His interest is in computing, specifically the novel discipline of quantum computing. A conventional computer operates on classical bits—the familiar ones and zeroes of binary arithmetic. The “qubits” of a quantum computer, by contrast, can exist in several states at once—superpositions, to use the official word—that resolve into particular outcomes only when some suitable measurement is made. What this means in principle, as Lloyd explains, is that a quantum computer—if it can ever be made to work—is just the thing for doing massively parallel calculations, where you want to perform the same operations on lots of data at once.
Lloyd’s cosmic ambitions hinge on two points. First, in a precise sense, the whole universe is a quantum computer. That is, it’s a physical system running according to the rules of quantum mechanics and generating an observable outcome. Second, the complexity of the universe today, as contrasted with its simpler origins, can be thought of as an increase in information content. You need more data to describe a motley collection of stars and planets and animals than you do to describe a uniform blob of hot particles.
Connecting these two points is the marvelous fact that a quantum computer can actually generate information. Because quantum events are only partially predictable, and can lead to a range of possible outcomes, a quantum system can grow in information content as it evolves. By thinking in these terms, Lloyd asserts, we can get a handle on how the universe came into its present state.
Lloyd’s writing is engaging but not always easy. Following his explanations is sometimes like trying to solve horrible chess problems in one’s head. Still, the general idea comes across.
Yet I read this book with mounting skepticism. Is Lloyd offering an explanation of the universe, or merely a new description? In the 19th century, at the peak of the industrial age, it was commonplace to regard the world as a giant machine. Now, in the information age, the universe has apparently become a giant computer. Lloyd’s argument is that describing the universe in terms of quantum computations provides a new way to tackle pressing theoretical problems in physics.
But a chicken-and-egg question arises: Can the informational approach lead to new physics, or do we need to understand the physics in order to work out the evolution of information? On this crucial point, Lloyd’s eager presentation falls short. It’s nice to know, in a broad sense, that the growing complexity of our cosmic habitat does not contravene any basic laws. But what we really want to know, surely, is not just how any old complex universe came into being, but how this particular universe and our cozy planet, with its odd collection of life forms, came to pass.