01 Front Matter (i-vi) 6/4/02 10:37 AM Page iii A B NTHROPIC IAS Observation Selection Effects in Science and Philosophy Nick Bostrom Routledge New York & London 01 Front Matter (i-vi) 6/4/02 10:37 AM Page iv Published in 2002 by Routledge 29 West 35th Street New York,NY10001 Published in Great Britain by Routledge 11 New Fetter Lane London EC4P 4EE Routledge is an imprint of the Taylor & Francis Group Printed in the United States of America on acid-free paper. Copyright © 2002 by Nick Bostrom All rights reserved.No part of this book may be reprinted or reproduced or utilized in any form or by any electronic,mechanical,or other means,now known or hereafter invented,including photocopying and recording,or in any information storage or retrieval system,without permission in writing from the publisher. 10 9 8 7 6 5 4 3 2 1 Library of Congress Cataloging-in-Publication Data Bostrom,Nick,1973– Anthropic bias :observation selection effects in science and philosophy / by Nick Bostrom. p.cm.— (Studies in philosophy) Includes bibliographical references and index. ISBN0-415-93858-9 1.Methodology. 2.Anthropic principle. 3.Selectivity (Psychology) 4.Observation (Scientific method) I.Title. II.Studies in philosophy (New York, N.Y.) BD241.B657 2002 121'.6—dc21 2001058887 01 Front Matter (i-vi) 6/4/02 10:37 AM Page v This book is dedicated to my father—tack pappa! 02 Contents (vii-x) 6/4/02 10:37 AM Page vii Contents ACKNOWLEDGEMENTS xi PREFACE xiii CHAPTER1 INTRODUCTION 1 Observation selection effects 1 A brief history of anthropic reasoning 5 Synopsis of this book 7 CHAPTER2 FINE-TUNING IN COSMOLOGY 11 Does fine-tuning need explaining? 13 No “Inverse Gambler’s Fallacy” 16 Roger White and Phil Dowe’s analysis 18 Surprising vs. unsurprising improbable events 23 Modeling observation selection effects: the angel parable 32 Preliminary conclusions 39 CHAPTER3 ANTHROPIC PRINCIPLES: THE MOTLEY FAMILY 43 The anthropic principle as expressing an observation selection effect 43 Anthropic hodgepodge 46 Freak observers and why earlier formulations are inadequate 51 The Self-Sampling Assumption 57 vii 02 Contents (vii-x) 6/4/02 10:37 AM Page viii viii Contents CHAPTER4 THOUGHT EXPERIMENTS SUPPORTING THE SELF-SAMPLING ASSUMPTION 59 The Dungeon gedanken 59 Two thought experiments by John Leslie 62 The Incubatorgedanken 64 The reference class problem 69 CHAPTER5 THE SELF-SAMPLING ASSUMPTION IN SCIENCE 73 SSA in cosmology 73 SSA in thermodynamics 76 SSA in evolutionary biology 78 SSA in traffic analysis 82 SSA in quantum physics 84 Summary of the case for SSA 86 CHAPTER6 THE DOOMSDAY ARGUMENT 89 Background 89 Doomsayer Gott 90 The incorrectness of Gott’s argument 92 Doomsayer Leslie 94 The premisses of DA, and the Old evidence problem 96 Leslie’s views on the reference class problem 104 Alternative conclusions of DA 107 CHAPTER7 INVALID OBJECTIONS AGAINST THE DOOMSDAY ARGUMENT 109 Doesn’t the Doomsday argument fail to “target the truth”? 109 The “baby-paradox” 111 Isn’t a sample size of one too small? 115 Couldn’t a Cro-Magnon man have used the Doomsday argument? 116 We can make the effect go away simply by considering a larger hypothesis space 116 Aren’t we necessarily alive now? 118 Sliding reference of “soon” and “late”? 119 How could I have been a 16th century human? 119 02 Contents (vii-x) 6/4/02 10:37 AM Page ix Contents ix Doesn’t your theory presuppose that what happens in causally disconnected regions affects what happens here? 120 But we know so much more about ourselves than our birth ranks! 120 The Self-Indication Assumption— Is there safety in numbers? 122 CHAPTER8 OBSERVER-RELATIVE CHANCES IN ANTHROPIC REASONING? 127 Leslie’s argument, and why it fails 127 Observer-relative chances: another go 130 Discussion: indexical facts—no conflict with physicalism 132 In conclusion 136 Appendix: the no-betting results 137 CHAPTER9 PARADOXES OF THE SELF-SAMPLING ASSUMPTION 141 The Adam & Eve experiments 142 Analysis of Lazy Adam: predictions and counterfactuals 144 ++ The UN gedanken: reasons and abilities 150 Quantum Joe: SSA and the Principal Principle 154 Upshot 156 Appendix: The Meta-Newcomb problem 157 CHAPTER10 OBSERVATION SELECTION THEORY: A METHODOLOGY FOR ANTHROPIC REASONING 159 Building blocks, theory constraints and desiderata 159 The outline of a solution 161 SSSA: Taking account of indexical information of observer- moments 162 Reassessing Incubator 165 How the reference class may be observer-moment relative 168 Formalizing the theory: the Observation Equation 172 A quantum generalization of OE 174 Non-triviality of the reference class: why (cid:1)0must be rejected 175 A subjective factor in the choice of reference class? 181 CHAPTER11 OBSERVATION SELECTION THEORY APPLIED 185 Cosmological theorizing: fine-tuning and freak observers 185 02 Contents (vii-x) 6/4/02 10:37 AM Page x x Contents The freak-observer problem places only lax demands on the reference class 193 The Sleeping Beauty problem: modeling imperfect recall 194 The case of no outsiders 195 The case with outsiders 196 Synthesis of the 1⁄- and the 1⁄-views 198 2 3 Observation selection theory applied to other scientific problems 198 Robustness of reference class and scientific solidity 202 Wrap-up 204 BIBLIOGRAPHY 207 INDEX 219