p A PERIODICAL OF PARTICLE PHYSICS SUMMER 1994 VOL. 24, NUMBER 2 Editors RENE DONALDSON, MICHAEL RIORDAN Executive Editor BILL KIRK Editorial Advisory Board JAMES BJORKEN, ROBERT N. CAHN, DAVID HITLIN, JOEL PRIMACK, NATALIE ROE, HERMAN WINICK Illustrations page z TERRY ANDERSON Production VANI BUSTAMANTE RAY ISLE Photographic Services TOM NAKASHIMA Distribution CRYSTAL TILGHMAN page 21 The Beam Line is published quarterly by the Stanford Linear Accelerator Center, PO Box 4349, Stanford, CA 94309. Telephone: (415) 926-2585 INTERNET:
[email protected] BITNET: BEAMLINE@SLACVM FAX: (415) 926-4500 SLAC is operated by Stanford University under contract with the U.S. Department of Energy. The opinions of the authors do not necessarily reflect the policy of the Stanford Linear Accelerator Center. Cover: A transverse profile of an electron beam in the SLAC linac. Particle densities have been color coded. The bright, high-density core contains 3 x 1010 electrons. These elec- tron (and positron) beams are focused to diameters of less than a micron at their collision point, which is located at the center of the SLD detector. Printed on recycled paper As CONTENTS FEATURES 2 THE HEART OF A NEW MACHINE After years of effort, the world's first linear collider is producing exciting physics results at Stanford. Nan Phinney 12 WHATEVER HAPPENED TO THE THEORY OF EVERYTHING? A brief report on the current status of string theory. Lance Dixon 21 OPINIONS ABOUT EVERYTHING: EPAC '94 In which Werner tells about his summer vacation in London. Werner Joho -, -. I DEPARTMENTS 28 THE UNIVERSE AT LARGE Fossil Radioactivities & How We Knm .""''i 3 5 the Solar System Formed in a Hurry 10 m | Virginia Trimble 38 CONTRIBUTORS page 12 40 FROM THE EDITORS' DESK DATES TO REMEMBER page 28 The e0 New |yI .:, byNA...D :2:- i iE I I..- PHINNEY After-::IE:I:: years of effort, st linear collider is producinf results at Stanford.