GRAVITY’S KISS GRAVITY’S KISS THE DETECTION OF GRAVITATIONAL WAVES HARRY COLLINS The MIT Press Cambridge, Massachusetts London, England © 2017 Massachusetts Institute of Technology All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means (including photocopying, recording, or information storage and retrieval) without permission in writing from the publisher. This book was set in Adobe Garamond and Berthold Akzidenz Grotesk by The MIT Press. Printed and bound in the United States of America. Library of Congress Cataloging-in-Publication Data Names: Collins, H. M. (Harry M.), 1943- Title: Gravity’s kiss : the detection of gravitational waves / Harry Collins. Other titles: Detection of gravitational waves Description: Cambridge, MA : The MIT Press, [2017] | Includes bibliographical references and index. Identifiers: LCCN 2016035193 | ISBN 9780262036184 (hardcover : alk. paper) Subjects: LCSH: Gravitational waves--Research. | General relativity (Physics) Classification: LCC QC179 .C647 2017 | DDC 539.7/54--dc23 LC record available at https://lccn.loc.gov/2016035193 10 9 8 7 6 5 4 3 2 1 For Osh and Elsa CONTENTS 1 The First Week: We Have Coherence 1 2 Reservations and Complications: Malicious Injections? 17 3 Half a Century of Gravitational Wave Detection 49 4 Weeks 2 and 3: The Freeze, Rumors 57 5 Week 4: The Box Is Opened 75 6 Week 5 to the End of October: Directness, Black Holes 87 7 November: Ripples, Belief, and Second Monday 113 8 November: Writing the Discovery Paper 131 9 December, Weeks 12–16: The Proof Regress, Relentless Professionalism, and the Third Event 173 10 January and February: The LVC-Wide Meetings and the Submission 195 11 The Last Ripples: From the Press Conferences to the American Physical Society and the Rest of the World 225 12 Changing Order: The Long Aha! 255 13 On the Nature of Science 289 14 The Book, the Author, the Community, and Expertise 313 Postscript: The Beginning of Gravitational Wave Astronomy 325 How the Book Was Written and Those Who Helped 343 Sociological and Philosophical Notes 349 Appendix 1: Procedure for Making a First Discovery 377 Appendix 2: First Draft of the Discovery Paper without Author List or Bibliography 383 Appendix 3: Rules for Author Lists 395 References 397 Index 403 vi Contents 1 THE FIRST WEEK We Have Coherence It is September 14, 2015, and I am in my study sitting on the sofa with my laptop on my knees—the way I spend most of my waking life these days, as I prefer to work from home. It’s evening and I am idly reading the subject lines of the dozens of emails that come in every day. The largest number come from the gravitational wave community, and I usually delete them without reading. I’ve been working with this community for over four decades now, longer than all the active gravitational wave scientists except one. Once every six months or so I might save a short string of these Chapter 1 emails in a folder, in case they turn out later to be of interest. I study how science is actually done in real time. One email catches my eye. The subject line is “Very interesting event on ER8.” It had come in around noon, British Summer Time. The email First eek says that the interesting event has been seen by the c B analysis “pipeline.” The abbreviation “cB ” stands for “coherent wave burst” and the “Burst Group,” which developed the pipeline and is tasked with finding bursts of gravitational waves without basing the search on preconceived wave- forms. The cB pipeline, then, has just detected something that looks like an interesting burst of waves. A pipeline is a mathematical/statistical procedure that is applied to the torrent of data that pours out of the inter- ferometric detectors; different groups operate different pipelines based on different principles—they may have more than one each—to monitor the data streams and automatically search for anything that looks like a gravi- tational wave signal. hen the machines are running smoothly there could be a few alerts per week. The email I have noticed is addressed primarily to the CBC Group but also to other groups. “CBC” stands for “compact binary coalescence.” This is the group tasked with analyzing gravitational wave signals that come from binary stars at the end of their lives—the signals emitted in the last mad second or so of“ inspiral,” when the pair of stars, as with a skater drawing in her arms, start to rotate faster and faster around each other until they merge into one heavier star. The theory says these systems will emit a burst of gravitational waves that, in the last moments of rotation, as the new star that is born out of the merger reverberates with cosmic passion, might be strong enough to have a chance of being sensed by the exquisite machines that humans have placed on Earth to catch them. These inspirals and mergers can be modeled, though the exact waveform depends on the mass of each component in the inspiral and the way they are spinning; there is an almost infinite number of possible combinations, and when the CBC pipeline, as opposed to the Bc pipeline, looks for a gravitational wave it looks for close similarity to one of the 250,000 possible models in its “template bank.” The template bank divides the indefinite world of potential into detectable actuality. Here is that first email, which comes from Marco Drago: Mon., Sept. 14, 2015, 11:56 (all times are British Summer Time until October 25, when they move to Greenwich Mean Time) Hi all, cWB has put on gracedb a very interesting event in the last hour. https://gracedb.ligo.org/events/view/G184098 This is the CED: https://ldas-jobs.ligo.caltech.edu/~waveburst/online/ER8_LH _ONLINE/JOBS/112625/1126259540-1126259600/OUTPUT _CED/ced_1126259420_180_1126259540-1126259600 _slag0_lag0_1_job1/L1H1_1126259461.750_1126259461.750/ Qscan made by Andy: https://ldas-jobs.ligo.caltech.edu/~lundgren/wdq/L1_1126259462.3910/ https://ldas-jobs.ligo.caltech.edu/~lundgren/wdq/H1_1126259462.3910/ 2 Chapter 1 It is not flag as an hardware injection, as we understand after some fast investigation. Someone can confirm that is not an hardware injection? “GraceDB,” by the way, is the “Gravitational wave candidate database.” It is the web page that shows events of potential interest, and it mostly logs things automatically so long as it is triggered by the events extracted from the pipelines that surpass a certain threshold. But it logs a lot of events, none of which has ever turned out to be a genuine gravitational wave. To be reading these emails you need to be part of a select group, and to access theURL s you need a password, which, as far as I know, outside of the scientists, only I possess. The select group is known as the “LIGO–Virgo collaboration” or “LVC.” It is the group based around the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo. LIGO has two four-kilometer interferometers in the United States, while Virgo is a French–Italian collaboration with one three-kilometer interfer- ometer near Pisa (which was not online at the time of the putative signal). But there are 1,000 or more scientists involved located all over the world.1 I look at the websites and see certain traces that appear to be large and 1. Actually, about 1,250, but I’ll use the round figure of 1,000 throughout the text. The LIGO–Virgo collaboration contains within itself elements of competition. Virgo was originally an entirely independent operation intended to compete with the US effort but it has been less well funded and, as a multicountry consortium (initially Italy and France), has more organizational difficulties to overcome. Perhaps as a result of these problems its interferometer has always lagged behind LIGO in terms of sensitivity, and Virgo scientists will be very disappointed that they were not able to contribute to the first detection of gravitational waves. The British-German GEO600 was also first conceived as a competi- tive instrument, but it was relatively starved of funds and it soon became clear that its most important role would be to contribute technically toLIGO , which it has done very suc- cessfully. That said, the scientists from all groups have worked as a seamless and pretty well frictionless team when it comes to analyzing the meaning of the signal detected byLIGO and writing up the results. So they are a fairly solidaristic group when it comes to handling and presenting the data (with some residual rivalry between LIGO and Virgo that seemed to show itself occasionally in the Big Dog incident (see chapter 2) but is nowhere in evi- dence in respect of the event. hen it comes to building apparatus, they are much more independent and competitive. 3 First eek appear to coincide in time on the two great interferometric detectors—L1 and H1—located 2,000 miles apart in Louisiana and ashington State, L1 therefore being southeast of H1. But I’m not that excited, because stuff like this comes up all the time: the detectors are so sensitive that they are always jiggling about and creating false alarms. e’ve been waiting fifty years to see a gravitational wave and it is pretty unlikely that this is it. The next email, which comes twenty minutes later, though it again does not get me very excited, at least makes me think I probably will save this string of emails in its own folder. This email says: “this is a nice inspiral with Mchirp = 27 Mo.” The implication is that the analysis of the shape of the waveform—its relatively low frequency and “ringdown” profile—indi- cates that combined objects with a total mass of considerably more than 27 of our suns have been involved.