INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the-deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. ProQuest Information and Learning 300 North Zeeb Road, Ann Arbor, Ml 48106-1346 USA 800-521-0600 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. National Library Bibliotheque nationale 1*1 of Canada du Canada Acquisitions and Acquisitions et Bibliographic Services services bibliographiques 395 Wellington Street 395, rue Wellington Ottawa ON K1A0N4 Ottawa ON K1A0N4 Canada Canada Your Votrw rite rw cm Out toe Nona ntirwnca The author has granted a non­ L’auteur a accorde une licence non exclusive licence allowing the exclusive pennettant a la National Library o f Canada to Bibliotheque nationale du Canada de reproduce, loan, distribute or sell reproduire, preter, distribuer ou copies of this thesis in microform, vendre des copies de cette these sous paper or electronic formats. la forme de microfiche/film, de reproduction sur papier ou sur format electronique. The author retains ownership of the L’auteur conserve la propriete du copyright in this thesis. Neither thedroit d’auteur qui protege cette these. thesis nor substantial extracts from Ni it la these ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent etre imprimes reproduced without the author’s ou autrement reproduits sans son permission. autorisation. 0-612-58243-4 Canada Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. The UNIVERSITYo/ WESTERN ONTARIO Faculty of Graduate Studies In the interests o f facilitating research by others at this institution and elsewhere, I hereby grant a licence to: THE UNIVERSITY OF WESTERN ONTARIO to make copies o f my thesis entitled DARK M A T T E R S /aJ Cq^ T £ -H ? o FARY A s T K qpHYSlCS '■ A CASE. SjUbY ,'M H 'irTr THfcOgy CHOICE AMP EVlDENTlAl- Rz ASoH /M k or substantial parts thereof, the copyright which is invested in me, provided that the licence is subject to the following conditions: 1. Only single copies shall be made or authorized to be made at any one time, and only in response to a written request from the library o f any University or similar institution on its own behalf or on behalf o f one o f its users. 2. This licence shall continue to the full term o f the copyright, or for so longs as may be legally permitted. 3. The Universal Copyright Notice shall appear on the title page o f all copies o f my thesis made under the authority o f the licence. 4. This licence does not permit the sale o f authorized copies at a profit, but does permit the collec­ tion by the institution or institutions concerned o f charges covering actual costs. 5. All copies made under the authority of this licence shall bear a statement to the effect that the copy in question "is being made available in this form by the authority o f the copyright owner solely for the purpose o f private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority ffom the copyright owner". 6. The foregoing shall in no way preclude my granting to the National Library o f Canada a licence to reproduce my thesis and to lend or sell copies o f the same. (signatureTSJwitness) (signature ofstudent) (date) (degree) (graduate program Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DARK MAHERS IN CONTEMPORARY ASTROPHYSICS: A CASE STUDY IN THEORY CHOICE AND EVIDENTIAL REASONING by W illiam L. Vanderburgh Graduate Program in Philosophy Submitted in partial fulfillment of the requirements for the degree o f Doctor of Philosophy Faculty o f Graduate Studies The University of Western Ontario London. Ontario December. 2000 © William L. Vanderburgh 2001 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. THE UNIVERSITY OF WESTERN ONTARIO FACULTY OF GRADUATE STUDIES CERTIFICATE OF EXAMINATION Chief Advisor Examining Board Advisory Committee The thesis by W illiam L. Vanderburgh entitled Dark Matters in Contemporary Astrophysics: A Case Study in Theory Choice and Evidential Reasoning is accepted in partial fulfillm ent o f the requirements for the degree o f Doctor o f Philosophy Date: w y /fa amining Board Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT AND KEYWORDS ABSTRACT: This dissertation examines the dynamical dark matter problem in twentieth century astrophysics from the point o f view o f History and Philosophy o f Science. The dynamical dark matter problem (which should be distinguished from the cosmological dark matter problem) describes the situation astronomers find themselves in with regard to the dynamics o f large scale astrophysical systems such as galaxies and galaxy clusters: The observed motions are incompatible with the visible distribution matter given the accepted law o f gravitation. This discrepancy has two classes o f possible solutions: either there exists copious amounts o f some kind o f matter that neither emits nor absorbs radiation (hence "dark” ), or the law o f gravitation must be revised. Chapter 2 describes the physical and philosophical foundations o f dynamical inferences— inferences from discrepancies between well-founded theoretical expectations and reliable observations to the characteristics o f candidate solutions. Chapter 3 discusses the history o f dark matter (beginning around 1930). Chapter 4 reviews the present evidence bearing on the dark matter problem. Chapter 5 evaluates the important candidate matter solutions in light o f the available evidence. Chapter 6 evaluates two candidate gravitational solutions on evidential and methodological grounds, and addresses the problem of theory choice. I do not try to solve the dark matter problem, but to uncover and evaluate patterns o f inference involved in evidential arguments for and against candidate solutions. I show that Newton's "Reasoning from Phenomena" is a good framework from which to understand what is going on in this field. I argue that "higher order" and especially non-dynamical evidence is the best hope for solving this problem in dynamics. This is so in part because o f ‘‘the dark matter double bind": the very' existence o f the dark matter problem means that we cannot be sure o f the overall matter distribution in astrophysical systems, and this in turn means that the observed motions by themselves cannot provide relative confirmation of any theory of gravitational interactions taking place at these scales. I use Newton's Rules o f Reasoning to argue that we should retain iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. General Relativity as our theory o f gravity at galactic and greater scales, despite the lack o f positive evidence to confirm it over its rivals at these scales. KEYWORDS: Philosophy o f Science. History o f Astronomy. History o f Physics. Twentieth Century Astrophysics. Newton. Duhem. Dark Matter. Gravitation. Dynamical Inferences. I ’nderdetermination o f Theory by Evidence. Theory Choice. Evidential Reasoning. Evidence. Methodology o f Science tv Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. EPIG RAPH And. hanging over it all. the brooding specter o f Rudolf Carnap and Hans Reichenbach. the Vienna Circle o f philosophy and the rise o f symbolic log A muddy world, in which he did not quite care to involve himself. — Philip K.. Dick. The Galactic Pot-Healer. 126. v Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS I am fortunate to have received assistance and support o f many kinds from many people during my graduate studies. The Department o f Philosophy at L'WO has been a wonderful and enriching place to be. My fellow graduate students over the years, though 1 cannot name them all here, have provided me with a community o f friends which I am going to miss terribly: thank you all for teaching me so much. I would like to give special mention to Gerry Calaghan. Todd Calder and Claire Nowlan. Tony Lariviere and Lyia Simon, and Aga Trojniak: their friendship has been very important to me. and I hope to be able to continue to lean on them. Professor Tracy Isaacs has also been a good friend, and a wonderful movie-going companion. I owe a great debt to Bonnie Mac Lachlan. John Gilbert Thorp and especially Professor John Thorp. Chair o f the Department. Their generosity and kindness in welcoming me into their family and providing me with a wonderful place to live (and eat!) for several important years o f my graduate career is something I w ill never forget.