The New York Times Book Review August 24, 2008 The Theory That Ate the World By GEORGE JOHNSON http://tinyurl.com/6zhyfl THE BLACK HOLE WAR My Battle With Stephen Hawking to Make the World Safe for Quantum Mechanics By Leonard Susskind 470 pp. Little, Brown & Company. $27.99 This is your universe on acid: 10 dimensions of space, seven of which we cannot see, filled almost entirely with dark matter and dark energy — invisible thought stuff that serves to make the cosmologists’ equations come out right. The cosmologists are stuck, with the rest of us, in Dimensions 1 through 3, and we are all made from what Earthlings quaintly regard as ordinary particles, the tiny fraction of matter that radiates and reflects mysterious waves called light. Compounding the indignity, this afterthought of an existence may be only an illusion — a holographic projection of some two-dimensional flatland that stretches like a timpani skin across the very edge of space. Plato had it backward. It’s the shadows on the wall that are real. At night when our brains are unplugged from our senses and error-correction is off, we dream furiously. And so it is with 21st-century physics. Undeterred by experimental data — it would take a particle accelerator as big as the galaxy to test some of the latest cosmological contrivances — theorists have found a new role as entertainers, scientific Scheherazades. Leonard Susskind, a professor of theoretical physics at Stanford, is one of the wiliest. Three years ago in “The Cosmic Landscape: String Theory and the Illusion of Intelligent Design,” he spun a tale of a multitude of different universes — nooks and crannies of a transcendent multiverse, or “landscape, ” each ruled by a different physics. This is probably the most controversial interpretation of superstring theory (some of Susskind’s colleagues absolutely hate the idea), but it has its appeal. With so many universes out there, the fact of our own existence need not inspire worship and awe. We just happen to occupy one of the niches where the laws are favorable to carbon-based life. In his new book, “The Black Hole War: My Battle With Stephen Hawking to Make the World Safe for Quantum Mechanics,” Susskind’s cosmos gets even weirder. Black holes already seemed scary enough, with their ability to swallow everything, including light. For a while, we learn, physicists were faced with the possibility that these cosmic vortexes might also be eaters of order, sucking up and destroying information. Like the Echthroi, the evil demons of entropy in Madeleine L’Engle’s novel “A Wind in the Door,” black holes might be chomping their way through the universe, ploughing sense into nonsense. The story of how Susskind and a colleague, the Dutch physicist Gerard ’t Hooft, disproved (or at least undermined) the theory begins in 1983 at a San Francisco mansion owned by, of all people, Werner Erhard, the New Age entrepreneur who had made his fortune with a profitable cult called EST. Erhard, we’re told, was also a “physics groupie,” and he presided over salons in which some of the world’s great theorists came to butt minds. The trouble began when Stephen Hawking made an astonishing prediction about what happens when information — a book, a painting, a musical recording or any pattern of matter or energy — falls into a black hole. Earlier, Hawking had proved that black holes eventually evaporate — at which point, he now claimed, everything inside them disappears from the universe. That might not sound like such a big deal. Just find another copy of whatever was lost. But that, Susskind realized, was not the point. Among the fundamentals of physics is that information must always be conserved. Even if you throw a DVD into a wood chipper, it is possible in theory (important weasel words) to chase down the splinters and recover the songs. Burned books can be reassembled from the smoke and ashes. Physics, in other words, dictates that everything that happens must be reversible. And that means information cannot be allowed simply to vanish. Even worse, quantum mechanics predicts that empty space seethes with tiny “ virtual black holes,” popping in and out of existence and gobbling up bits. If Hawking was right, Susskind concluded, “the foundations of our subject were destroyed.” Not everyone was quite so alarmed. But Hawking’s information paradox, as it came to be called, opened an arena in which two great theories of physics — general relativity, describing gravity, and quantum mechanics, describing everything else — duked it out. I was eager to learn how, in the end, Susskind and company showed that Hawking was probably wrong — that information is indeed conserved. But first I had to get through a 66-page crash course on relativity and quantum mechanics. Every book about contemporary physics seems to begin this way, which can be frustrating to anyone who reads more than one. (Imagine if every account of the 2008 presidential campaign had to begin with the roots of Athenian democracy and the heritage of the French Enlightenment.) Finally we get to the heart of the story, and it turns out to be a mind-bender. To make sense of Hawking’s paradox one must consider how much information, measured in bits, the 1s and 0s of binary code, can fit inside a black hole. The amount, it turns out, does not depend on the black hole’s volume, as one might expect, but on the area of its “horizon” — the flat, funnel-like mouth of the cosmic rabbit hole. Susskind explains this dizzying notion about as clearly as is probably possible. Every time a bit falls into a black hole, its opening expands by one square Planck length — an area billions and billions of times smaller than a proton. It is because of this phenomenon, Susskind contends, that the information isn’t lost. A description of everything that falls into a black hole, whether a book or an entire civilization, is recorded on the surface of its horizon and radiated back like imagery on a giant drive-in movie screen. As with a hologram, three dimensions are contained within two. Strangest of all, we learn, this holographic conjecture — elevated in the book, perhaps prematurely, to the holographic principle — may apply to the entire universe. Hence the notion of our own reality as an illusory projection of some flatlanders’ membrane world. It’s as though the pixilated people we see on television are real and the actors are only secondary manifestations. Or something like that. How this all fits together is still pretty murky. “ Getting our collective head around the holographic principle is probably the biggest challenge that we physicists have had since the discovery of quantum mechanics,” Susskind admits. He speculates at one point that our big bang of a universe is some kind of “inside-out black hole” — one that spews everything outward instead of sucking it in. But wait. Maybe it just looks that way because time is moving backward! Or — who knows? — maybe our universe is really a 3-D projection of a 4-D world falling through some hyperdimensional gullet! Toward the end of the book Susskind quotes Hawking: “We are just an advanced breed of monkeys on a minor planet of a very average star. But we can understand the universe.” Maybe. But not without a lot more data. George Johnson is the author of “Fire in the Mind: Science, Faith, and the Search for Order.” His most recent book is “The Ten Most Beautiful Experiments.” --

※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 219.70.176.25