THE RECENT DEVELOPMENT OF PHYSICAL SCIENCE
CONTENTS PHYSICAL SYSTEMS AND PHYSICAL THOUGHT INTRODUCTION QUANTUM MECHANICS AND PARTICULARISM STRUCTURAL ASSUMPTIONS AND CONSERVATION LAWS THE CRITERION OF ISOLATION THE RULE OF COMPOSITION STRUCTURAL DE?NITIONS CONCLUSION INTERPRETATIONS OF SPACETIME AND THE PRINCIPLE OF RELATIVITY THE RESTRICTED PRINCIPLE OF RELATIVITY CONVENTIONALISM THE GEOMETRIC APPROACH TO SPACETIME THE DYNAMIC APPROACH TO SPACETIME PRIMITIVE MOTION RELATIONALISM A GEOMETRY OF PUMS GALILEAN SPACETIME RECONSTRUCTING GALILEAN SPACETIME GALILEAN TRANSFORMATIONS FLAT RELATIVISTIC SPACETIME RECONSTRUCTING FLAT RELATIVISTIC SPACETIME THE LORENTZ TRANSFORMATIONS PRIMITIVE MOTION RELATIONALISM VS STANDARD INTERPRETATIONS OF SPACETIME THE METAPHYSICS OF TIME THE FLOW OF TIME AND MOTION THE CON?ICT BETWEEN PRESENTISM AND RELATIVITY BUT ETERNALISM IS FALSE TOO PRIMITIVE MOTION RELATIONALISM AND THE METAPHYSICS OF TIME THE HISTORY OF NEWTONIAN MASS THE GEOMETRIC CONCEPTION OF MASS THE DYNAMIC CONCEPTION OF MASS MACH’S CRITIQUE OF NEWTONIAN MASS PHYSICAL SYSTEMS AND MASS PRIMITIVE MOTION RELATIONALISM AND THE EXPANDED REFERENCE FRAMES THE STRETCHING PARAMETER ?0 AND NEWTONIAN MASS THE QUANTITY OF MATTER INERTIAL MASS STRUCTURAL ASSUMPTIONS, NEWTON’S SCIENTI?C METHOD, AND THE UNIVERSAL LAW OF GRAVITATION HYPOTHESES AND SCIENTI?C PROPOSITIONS STRUCTURAL ASSUMPTIONS AND THEIR ROLE IN INDUCTIVE REASONING NEWTON’S ARGUMENT FOR THE UNIVERSAL LAW OF GRAVITATION FROM THE AREA LAW TO THE CENTRIPETAL NATURE OF THE FORCE OF GRAVITY THE HARMONIC RULE AND THE INVERSE SQUARED DISTANCE NATURE OF THE GRAVITATIONAL FORCE DERIVING THE UNIVERSAL NATURE OF LAW OF GRAVITATION NEWTON’S SCIENTI?C METHOD THE SPECIAL THEORY OF RELATIVITY THE EXPANSION FACTOR ?0 AND MASS IN STR A NEW INTERPRETATION OF MASS IN STR KUHN’S THESIS OF INCOMMENSURABILITY FIELD’S INDETERMINACY OF REFERENCE INVARIANCE AS A MARK OF OBJECTIVITY EINSTEIN’S MASS AND ENERGY AS TWO MANIFESTATIONS OF SUBSTANCE SPACETIME MASS CHAPTER PHYSICAL SYSTEMS AND PHYSICAL THOUGHT 1 1 INTRODUCTION THE NOTION OF PHYSICAL SYSTEM IS SO UBIQUITOUS IT IS MENTIONED IN ALMOST EVERY WORK IN PHYSICS SCIENTISTS USE THE TERM, WITHOUT MUCH RE?ECTION, TO REFER TO AN AGGREGATE OF PHYSICAL OBJECTS ATTENTION IS SOMETIMES DIRECTED TO A SYSTEM WHEN ONE IS INTER- ESTED IN THE SYSTEM’S COMPONENTS AND THEIR DISTINCT STATES AND PROPERTIES BUT MORE OFTEN, PHYSICISTS ARE CONCERNED WITH THE ARRANGEMENT OF THE PARTS AND INTERACTIONS BETWEEN THE PARTS THEY USE VARIOUS THEORETICAL CONSTRUCTS TO SINGLE OUT STATES AND PROPERTIES OF THE COMPOSITE SYSTEM; STATES AND PROPERTIES THAT EITHER SUPERVENE ON THE PARTICULAR CON?GURATION OF THE PARTS OR CONSTITUTE NON-SUPERVENING, EMERGENT FEATURES EVEN THOUGH THE NOTION OF PHYSICAL SYSTEM DOES NOT NECESSARILY PRESUPPOSE ANY METAPHYSICAL STANCE, PHYSICISTS OFTEN THINK THAT PROPERTIES OF COMPOSITE SYSTEMS ARE REDUCIBLE TO THE PROPERTIES OF THEIR PARTS TAKE FOR EXAMPLE A NEUTRON COMPRISED OF ONE “UP” QUARK AND TWO “DOWN” QUARKS ONE WAY OF DESCRIBING THE NEUTRON IS TO THINK OF IT AS A PHYSICAL SYSTEM COMPRISED OF DISTINCT COMPONENTS THE STATES AND PROPERTIES ATTRIBUTED TO THE NEUTRON AS A WHOLE ARE DETERMINED BY THE STATES AND PROP- ERTIES OF THE QUARKS AND THE STRONG INTERACTION BETWEEN THEM THE ZERO NET CHARGE OF THE NEUTRON, FOR EXAMPLE, ARISES FROM THE + 3E CHARGES OF EACH OF THE “DOWN” QUARKS THE NEUTRON’S DESCRIPTION, ACCORDING TO THIS VIEW, IS MERELY AN ECONOMIC REPRESENTATION OF THE QUARKS WHEN DETAILS CONCERNING THE QUARKS ARE NOT RELEVANT TO THE PROBLEM AT HAND THE NEUTRON’S INTERNAL STRUCTURE IS IGNORED, AND THE NEUTRON IS TREATED AS A SINGLE ENTITY WITH ITS DISTINCT STATES AND PROPERTIES EVEN THOUGH STATES AND PROPERTIES OF COMPOSITE SYSTEMS ARE INDISPENSABLE TO PHYSICS, THE TENDENCY IS TO THINK OF COMPOSITE BODIES AS NON-EXISTING A PERFECT THEORY WOULD THEN INCLUDE NO COMPOSITE OBJECTS AND WOULD ADMIT ONLY COMPLEX DESCRIPTIONS OF SIMPLE PARTS ONE WAY TO MAKE THIS APPROACH TENABLE IS TO ASSUME THAT MATERIAL OBJECTS HAVE ULTIMATE PARTS AND THAT THESE ULTIMATE CONSTITUENTS OF MAT- TER HAVE MATERIAL PROPERTIES AND ARE LOCATED IN PARTICULAR POINTS IN SPACETIME AN AGGREGATE OF SUCH LOCALIZED PARTS MAY THEN BE DESCRIBED WITH THE HELP OF COMPOSITE ARE SUMMED UP TO YIELD THE VOLUME OF THE COMPOSITE OBJECT ORDINARILY, INTEGRATION OVER VOLUMES APPEARS IN THE FORMALISM AS A MERE MATHEMATICAL DEVICE, A STANDARD RULE IN WHICH NUMBERS ARE ADDED UP NEVERTHELESS, A BRIEF RE?ECTION WILL DEMON- STRATE THAT INTEGRATION OVER VOLUME RE?ECTS A PHYSICAL ASSUMPTION ABOUT THE NATURE OF SPACE: VIZ , THAT THE VOLUME OF A COMPOSITE BODY IS THE SUM OF THE VOLUMES OF THE PARTS IT IS SUCH AN INTUITIVE ASSUMPTION UNDERLYING OUR CONCEPT OF SPACE THAT ONE BECOMES UNAWARE OF THE PHYSICAL ORIGIN OF THIS RULE AND THINKS OF IT AS A FORMAL DEVICE BUT THE RULE FOR INTEGRATING OVER VOLUMES OF SPACE IS NOT MERELY A FORMAL RULE, RE?ECTING THE MATHEMATICAL FUNCTION OF ADDITION; RATHER, IT IS A MATHEMATICAL RULE REPRESENTING A STRUCTURAL ASSUMPTION ABOUT THE SPATIAL PROPERTIES OF PHYSICAL BODIES PARADOXICALLY, REDUCTIVE EXPLANATIONS ARE MADE POSSIBLE VIA ASSUMPTIONS ABOUT THE STRUCTURE OF PHYSICAL SYSTEMS FOR COMPOUND DESCRIPTIONS TO BE REDUCIBLE TO THEIR SIMPLER PARTS, ONE MUST HAVE AT ONE’S DISPOSAL VARIOUS MEASURES AND CALCULA- TIONAL DEVICES THAT SANCTION INFERENCES FROM THE SIMPLE TO THE COMPOUND AND VICE VERSA CONSIDER, FOR EXAMPLE, ADDITIVE PROPERTIES SUCH AS MASS AND CHARGE, WHICH UNDERWRITE THE SUMMATION OVER THE PROPERTIES OF THE PARTS THESE MEASURES ARE USED SO SEAMLESSLY THAT ONE FORGETS THAT THEY ARE MEASURES OF PHYSICAL FACTS DESCRIBING RELATIONS BETWEEN PARTS AND WHOLES FOR 200 YEARS MASS WAS THOUGHT TO BE AN ADDI- TIVE PROPERTY, BUT THE SPECIAL THEORY OF RELATIVITY DEMONSTRATES THAT REST MASS IS NOT AN ADDITIVE PROPERTY WHEN A SYSTEM DECOMPOSES INTO PARTS, THE REST MASS OF THE COMPOSITE SYSTEM IS NOT NECESSARILY THE SUM OF THE REST MASSES OF THE PRODUCTS OF DECAY THE STANDARD INTERPRETATION OF SUCH DECAYS IS THAT REST MASS WAS “CONVERTED” INTO ENERGY, BUT THE TRUTH OF THE MATTER IS THAT REST MASS IS SIMPLY NOT AN ADDITIVE PROPERTY 3 WHILE NEWTONIAN MASS IS ADDITIVE, THE REST MASS OF A COMPOSITE SYSTEM IN STR IS NOT THE SUM OF THE REST MASSES OF THE PARTS SIMILARLY, THERE IS A POSSIBLE WORLD IN WHICH THE VOLUME OF A COMPOSITE SYSTEM IS NOT THE SUM OF THE VOLUMES OF ITS COMPONENTS, ALTHOUGH SUCH A WORLD IS VERY DIF?CULT TO CONCEIVE THESE RE?EC- TIONS MAKE IT CLEAR THAT THE ABILITY TO SUM OVER PROPERTIES OF THE PARTS IN PRODUCING PROPERTIES OF COMPOSITE SYSTEMS RE?ECTS A PHYSICAL ASSUMPTION ANOTHER VERY IMPORTANT REDUCTIVE TOOL IS NEWTON’S PARALLELOGRAM LAW FOR THE COMPOSITION OF FORCES 4 ACCORDING TO THIS LAW, ONE CAN DERIVE THE COMPOSITE FORCE IMPINGING ON A BODY FROM THE COMPONENT FORCES THERE IS, HOWEVER, A POSSIBLE WORLD IN WHICH THE COMPOSITE FORCE IS NOT THE VECTORIAL SUM OF THE COMPONENT FORCES WHEN A COMPOSITE DESCRIPTION IS CONSTRUCTED FROM THE DESCRIPTION OF SIMPLER ELEMENTS, SUBSTANTIVE STRUCTURAL ASSUMPTIONS ABOUT PHYSICAL SYSTEMS ARE IMPLIC- ITLY EMPLOYED THE UNIVERSAL VALIDITY OF NEWTON’S PARALLELOGRAM LAW SEEMS NATURAL BECAUSE ONE OFTEN THINKS OF IT AS MERELY EXPRESSING A MATHEMATICAL RULE GOVERNING VECTORS HOWEVER, THE PHYSICAL CONTENT OF THE LAW IS STRIKING WHEN IT IS RECOGNIZED THAT THE LAW EXPRESSES A RULE OF COMPOSITION ASSUME BODIES A2 AND A3 EXERT FORCES ?F21 AND ?F31 OVER BODY A1 THE PARALLELOGRAM LAW ALLOWS US TO CALCULATE THE 3 SEE LANGE (2001) 4 COROLLARY 1 TO THE LAWS OF MOTION (NEWTON, 1999, P 417)