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The Generation of Knowledge Through Experimentation in Fundamental Physics: the Case of Gravity Probe B

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The Generation of Knowledge Through Experimentation in Fundamental Physics: the Case of Gravity Probe B ADVERTIMENT. Lʼaccés als continguts dʼaquesta tesi queda condicionat a lʼacceptació de les condicions dʼús establertes per la següent llicència Creative Commons: http://cat.creativecommons.org/?page_id=184 ADVERTENCIA. El acceso a los contenidos de esta tesis queda condicionado a la aceptación de las condiciones de uso establecidas por la siguiente licencia Creative Commons: http://es.creativecommons.org/blog/licencias/ WARNING. The access to the contents of this doctoral thesis it is limited to the acceptance of the use conditions set by the following Creative Commons license: https://creativecommons.org/licenses/?lang=en TESI DOCTORAL The Generation of Knowledge through Experimentation in Fundamental Physics: The Case of Gravity Probe B Autor: Director de Tesi: Christopher EVANS Dr. H Carl HOEFER Signat: Signat: Tutor: Dr. Thomas STURM Aquesta tesi es ofereix d’acord amb els requeriments del Doctorat en Filosofia del Departament de Filosofia de la Facultat de Filosofia i Lletres Setembre de 2016 iii CERTIFICADO DE DIRECCIÓN Título de la tesis doctoral: The Generation of Knowledge through Experimentation in Fundamental Physics: The Case of Gravity Probe B Director de la tesis: Dr. H Carl HOEFER Doctorando: Christopher EVANS Programa de doctorado: DOCTORADO EN FILOSOFÍA del DEPARTAMENTO DE FILOSOFÍA de la FACULTAD DE FILOSOFÍA Y LETRAS Universitat Autònoma de Barcelona Visto bueno del director de la tesis. Firmado en Barcelona, el 26 de septiembre de 2016: H Carl HOEFER v UNIVERSITAT AUTÒNOMA DE BARCELONA Resumen Facultat de Filosofia i Lletres Departament de Filosofia Doctorat en Filosofia La Generación de Conocimiento a través de la Experimentación en la Física Fundamental: El Caso de "Gravity Probe B" escrito por Christopher EVANS En el presente trabajo analizo desde un punto de vista crítico el episodio que representa “Gravity Probe B” (GP-B) (La Sonda de la Gravedad B) en la historia de la experimentación en la física fundamental. Anunciado como una “Prueba del Universo de Einstein”, GP-B fue un experimento para ex- aminar predicciones de la teoría general de la relatividad (TGR) que duró 50 años. GP-B nació en Stanford University, en el momento que el principio de la tecnología de satélites lo convirtió en una posibilidad y se convirtió en el proyecto más longevo de la NASA: los resultados finales se publicaron en el año 2011. Siguiendo el diseño original de 1960, GP-B pretendió medir el arrastramiento del marco espaciotemporal y el efecto geodésico sobre un giroscopio en órbita alrededor de la tierra en un satélite funcionando en modo “drag-free” (sin resistencia). Siguiendo una órbita puramente gravitacional, junto con el giroscopio y los magnetómetros formados por dispositivos super- conductores de interferencia cuántica, la nave espacial contenía un telescopio que rastreaba una estrella guía como punto de referencia. La misión espacial empezó en el 2004 y concluyó en el 2005 con el objetivo de medir el cambio en la orientación del eje de giro de los giroscopios, relativo al inmóvil espacio inercial, con una precisión de 0.5 milésimas de un segundo de arco (∼ 10−7 vi grados) a lo largo de un año. Para realizar el experimento fue necesario desar- rollar varias tecnologías completamente novedosas, y los sistemas de abordo diseñados establecieron varios récords por ser los sistemas más cerca de la perfección diseñados jamás. (GP-B) representa una oportunidad única para analizar cómo funcionan los experimentos científicos extremos y una gran oportunidad de estudiar los esfuerzos para generar conocimiento acerca de la TRG basado en la experimentación. GP-B se encontró con serias dificultades durante la ejecución, con importantes anomalías y un ruido excesivo en los datos. El equipo se vio obligado a desarrollar controvertidos métodos nuevos para analizar los datos que se obtuvieron. Inicialmente presento tanto la física relevante a la aproximación específica a la TRG apropiada para analizar la gravitación en el sistema solar (el marco posnewtoniano de parametrización) como la historia de la confirmación de TRG. Después de presentar GP-B y sus objetivos, introduzco el marco analítico que adopto para examinar los resultados y conclusiones que el equipo logró. Utilizo el trabajo de James Woodward y Deborah Mayo, combinándolo en una perspectiva basada en tres puntos: los datos observados pueden ser evidencia para fenómenos teóricos subyacentes; la experimentación hace lo posible para rastrear la veracidad de las hipótesis a través de la sensibilidad contrafáctica de los datos a las afirmaciones teóricas; y para que los datos valgan como evidencia a favor de un fenómeno, la prueba que represente el encaje de estos con las predicciones de las hipótesis examinadas debe ser severo, aunque no necesariamente rep- resente un uso novedoso de los datos. Destaco muchas preocupaciones con el análisis de los datos producidos por GP-B, pero a través de mi análisis basada en este marco, mi conclusión es que las afirmaciones del equipo de GP-B son perfectamente válidas. También indico que este episodio demuestra que puede ser importante que los científicos adopten las perspectivas más sofisticadas propuestas por filósofos en lugar de contar con los más comunes acercamientos epistemológicos. Finalmente, indico que a pesar de la posi- bilidad de que el conocimiento generado no sea del todo sólido e inmóvil, y que algún día pueda revisarse, cumple con los requisitos más estrictos que la sociedad normalmente pide de las conclusiones de la investigación. vii UNIVERSITAT AUTÒNOMA DE BARCELONA Abstract Facultat de Filosofia i Lletres Departament de Filosofia Doctorat en Filosofia The Generation of Knowledge through Experimentation in Fundamental Physics: The Case of Gravity Probe B by Christopher EVANS In this thesis, I critically analyse Gravity Probe B (GP-B) as an extraordinary episode in the history of experimentation in fundamental physics. Billed as “Testing Einstein’s Universe,” GP-B was a 50-year-long experiment to test crucial predictions of the General Theory of Relativity (GTR). GP-B started life at Stanford University when satellite technology first made the “Relativity Gyroscope Experiment” feasible and it went on to become the longest running mission in NASA’s history; final results were published in 2011. Following the original design published in 1960, GP-B set out to measure frame dragging (also known as the Lense-Thirring effect) and the geodetic (or de Sitter) effect on a superconducting gyroscope orbiting the Earth in a “drag-free” satellite. Essentially executing a purely gravitational orbit, together with the science instrument assembly containing the (multiple) gyroscope(s) and supercon- ducting quantum interference devices used as magnetometers, the spacecraft housed a telescope trained on a reference “guide star”. The mission flew from 2004 to 2005 and aimed to measure the change in the orientation of the spin axis of the gyroscopes, relative to “fixed” inertial space identified using the guide star, to within 0.5 milliarcseconds (∼ 10−7 degrees) over the year-long experiment. The experiment required the development of several viii completely new technologies before it could be performed and the on-board systems broke numerous records as the most nearly perfect and most sensitive systems created. It represents a unique opportunity to analyse the workings of scientific experimentation taken to the extreme and a rare chance to examine efforts to generate knowledge based on experimental GTR: one of our two current fundamental physics theories. GP-B encountered serious problems during execution of the space mission with major anomalies and excessive noise in the data collected. The team was forced to develop controversial new data analysis methods to attempt to salvage meaningful results from the unexpected and unrepeatable dataset they retrieved. I initially present both the physics of GTR in the specific weak gravity approximation appropriate for analysing gravitational effects within the Solar System (the parametrised post-Newtonian framework) and the prior history of confirmation of GTR. After presenting GP-B and its aims, I then introduce the analytical framework that I adopt to examine the claims made by the team regarding their data analysis and eventual findings. I draw heavily on work by James Woodward and Deborah Mayo, among others, and combine this into a 3-point approach: observed data can act as evidence for underlying theoretical phenomena; experimentation contrives to track the truth of hypotheses via the counter- factual sensitivity of the data produced by the specific experimental set-up to those theoretical claims; and for data to count as evidence in favour of a phenomenon, the test that the match between them and the predictions of the hypothesis being examined represents must be severe, although not necessar- ily entail novel use of the data. I highlight many worries with the GP-B data analysis, but through analysing it within this framework, I conclude that the claims of the GP-B team are valid. I also indicate that the episode shows how it can be important for working scientists to adopt the more sophisticated approaches advocated by some philosophers rather than relying on more typical epistemological attitudes found in 20th century textbooks. I close by noting that although the knowledge gained may not be unshakeably solid and is open to future revision, it fulfils the strictest demands normally placed by society on the conclusions of investigation. ix Acknowledgements First and foremost I would like to thank my supervisor, Carl Hoefer, for his limitless help and encouragement, as well as his patience; I don’t feel I need to say that without him this project would never have got off the ground and much less have been brought to a satisfying close. Thanks also to Thomas Sturm for stepping in and agreeing to be my tutor over the last year of my work to produce this thesis; but maybe much more importantly, for encouraging me to continue with my research when I had almost abandoned it and always expressing his faith in me.
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