NOTES ON METAPHYSICS OF SPACE AND SPACETIME Contents Metaphysics of Physics. 1 Motion 1 Space. 3 Substantivalism. 6 Time. 8 Geometry 9 THE THEORY OF RELATIVITY. 11 Metaphysics of Physics · Epistemology o How is metaphysical knowledge possible? o Can non-empirical methods tell us anything about the world? " Hume: synthetic truths are only knowable a priori (unlike Kant) " Carnap/logical positivists: metaphysical statements are not empirically verifiable and therefore meaningless " Underdetermination of theory by evidence = requires metaphysical clarification · Methodology: o Is physics prior to metaphysics? " Realism = yes, therefore can read metaphysics off the physics " Anti-realism = no, cant do this Motion · Key question: does absolute motion exist? · Key thought experiment to conceptualise this issue = Galilleo's ship: o Imagine you are inside a ship, with not portholes. o You do not know whether the ship is stationary or in motion o Is there an experiment you could do from in the cabin to tell if the ship is moving or stationery? " If yes, motion = absolute · If no, motion = relative · 2 types of relativity: o Dynamical = there is no dynamically distinguishable state of motion o Kinematical = there is no privileged body of reference with respect to which we can make absolute claims re motion Newton argues for absolute motion: Page 1 of 14
o Scholium: "we have some arguments to guide us, partly from the apparent motions, which are the differences of true motionsff partly from the forces which are the causes and effects of the true motions" · What is 'apparent motions, which are the differences of true motion'? o If A and B are in relative motion with respect to each other, then there can be nothing with respect to which both A and B are at rest. o But we can't conclude from this that either A or B is then in motion with respect to absolute space, unless we first assume absolute space exists. o Within Newton's theory this follows, but is circular if used as an argument for absolute space. . What about 'forces which are the causes and effects of the true motions'? o = concerns accelerated motion o For Newton's laws say that a body not subject to forces persists in whatever state of motion (uniform, rectilinear) it has, but that (absolute) accelerations are caused by forces o Thus, the second argument is apparently that if two bodies accelerate relative to each other, this is caused by a force acting on at least one of the bodies and that body is also accelerating relative to absolute space. o Assertion in question is 'absolute acceleration is caused by a force' " Leibniz failed entirely to see any cogency in this argument because of his different evaluation of the status of that principle. " For him, it was an assertion in Newtonian terms of a fact that could be stated, insofar as it had any empirical relevance, also in his