The Future of Spacetime [Anglais] [Relié]

Put Stephen Hawking, Kip Thorne, Igor Novikov, Timothy Ferris and Alan Lightman in a room together, and I would imagine that the intellectual sparks would fly lively and thick. The five essays collected in this book are adapted from those sparks, talks given at the California Institute of Technology in June 2000 to honor the 60th birthday of physicist Kip Thorne. If there is a unifying theme to the essays, it is the possibility of time travel, one of Thorne's obsessions as a theoretician of general relativity and, of course, a topic of perennial popular interest. None of the authors was paid for his contribution, and royalties will go to a Caltech scholarship fund in Thorne's name. Theoretical physicist Igor Novikov starts by asking, "Can we change the past?" He shows how curious foldings and warpings of spacetime apparently allow the possibility of traveling back in time and considers the so-called grandfather paradox: What if I travel back in time and kill my grandfather? Then, logically, I would never have been born to make my journey into the past. Novikov argues that the laws of nature would prevent such logical paradoxes from happening. Stephen Hawking is perhaps the world's most famous theorist of spacetime. He is less sanguine than Novikov that time travel is possible, except on the scale of individual atomic particles, which is not of much use for science-fiction fantasies. If Hawking's take on the physics is correct, grandfather is doubly safe. Thorne uses his commanding presence at the heart of the book to address the question implicit in the title: How will our understanding of spacetime evolve in the near future, theoretically and experimentally? The final two essays, by writers Timothy Ferris and Alan Lightman, though excellent in themselves, have nothing directly to do with the topic at hand. Ferris considers how science is communicated to the general public, and Lightman muses on relations between science and art. It all adds up to less than the sum of its parts. The word "hodgepodge" comes to mind, and the fact that the editors decided the book needed a long preparatory introduction (longer than all but one of the five contributions) and a puffed-up glossary suggests that the problems were apparent from the beginning. Anyone who wants the skinny on time travel and the future of spacetime would do well to go directly to Thorne's excellent popular book Black Holes and Time Warps: Einstein's Outrageous Legacy (W. W. Norton, 1994). Still, there is a terrific story lurking among the disparate parts of the present volume, but readers will have to dig it out for themselves. I would suggest skipping the introduction and going straight to Lightman's piece on science and art. He was trained as a physicist and has transformed himself into a successful novelist, so he knows both sides of which he speaks. He takes us to the heart of the creative process and shows us what physicists and novelists have in common. For one thing, they both make up stories, and they both want their stories to be true. Ferris tells us why scientific story making is essential to a healthy and free body politic. "Technologically, intellectually, and even politically, science resides somewhere near the center of our culture, by which I mean the society of all those persons who value their freedom, honor their responsibilities, appreciate their ignorance, and are willing to keep learning," he writes. Now go to the essays by Novikov and Hawking and watch two outrageously clever minds at play in the fields of knowledge and ignorance. They take Einstein's supreme story--his theory of gravity and spacetime, called general relativity--and make delightful riffs on the theme. What if? they ask. They agree on this: even if it turns out that time travel is impossible, it is important that we understand why it is impossible. Finally, turn to Thorne's central essay, where it all comes together. We have in Einstein's legacy a fabulously inventive story: black holes, time travel, ripples in spacetime, the big bang--stuff any novelist would have been proud to invent. But the story must be put to the experimental test, and so far general relativity has passed muster. Soon new tests of a most exquisite sensitivity will come on line, and these are the focus of Thorne's crystal-ball gazing. The Laser Interferometer Gravitational Wave Observatory (LIGO)--three huge instruments at Hanford, Wash., and Livingston, La.--and similar devices in Italy, Germany and Japan promise the possibility of detecting gravitational waves rippling through spacetime from colossal events (imploding stars, colliding black holes, even the big bang itself) unfolding across the universe. Then, sometime around 2010 if physicists get their way, the Laser Interferometer Space Antenna (LISA) will be launched into space. Three intercommunicating spacecraft arrayed across millions of kilometers of the solar system, bobbing like corks in water as gravitational waves roll by, will map in fine detail the bending of space, the warping of time, and the whirl of spacetime around distant black holes. LISA will detect ripples in spacetime as small as one hundredth the diameter of an atom. What a story! What a test! This is story making that lifts the human spirit out of our sometimes petty terrestrial concerns and places us among the stars.

Chet Raymo is emeritus professor at Stonehill College in Massachusetts and a science columnist for the Boston Globe.

Caltech physicist Kip Thorne's sixtieth birthday was celebrated in essay form by fellow relativists interested not only in space-time but also in explaining it to nonscientists. Collected in this volume, these pieces feature Thorne's predictions about imminent discoveries of space-time gravity waves; Stephen Hawking's sporting arguments against certain of Thorne's ideas about black holes and wormholes; and two views by popular writers (Timothy Ferris and Alan Lightman) on making such subjects accessible. If accessibility is the book's underlying task, its first two essays may well be the most effective. In one, a physicist equips the reader with the elements of space-time concepts and terminology, such as world lines, rotational transformation, and frames of reference. The other examines whether Einstein's equations allow for the existence of time machines by examining the paradoxes about causality that arise if they do. Exuding a lighthearted tone, these pieces will appeal especially to those who enjoyed Thorne's Black Holes and Time Warps: Einstein's Outrageous Legacy (1994). Gilbert Taylor
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