501264 - HISTORY OF PHYSICS

The course presents the broad lines of development of physics in the period from Galileo to the threshold of the great changes that Einstein introduced into the discipline with his famous articles of 1905 (special relativity, Brownian motion, light quantum). Galileo's work and other important seventeenth-century developments are contextualized in that fundamental stage of Western science which is called the "scientific revolution" and which is characterized overall by the abandonment of Aristotelian "qualities" in physics in favor of new explanatory schemes, such as abstract quantitative laws, corpuscularism, the mechanistic interpretation of natural processes and the use of variously conceived "forces". The positions taken on these fundamental questions by Descartes, Newton and Leibniz are examined specifically. The course proceeds sketching the structuring of physics during the eighteenth and nineteenth centuries in three large areas - mechanics, thermodynamics, electromagnetism - with the prevalence of reductionist approaches which attempted to ground the whole discipline on mechanical bases. The course focuses in particular on the kinetic-molecular interpretation of heat and on the unsuccessful attempts to extend the equipartition of energy to the elusive phenomenon of Brownian motion. The inability of physics to explain Brownian motion in this phase led to a crisis situation such as to call into question the kinetic interpretation of heat and the hypothesis of a real atomic-molecular constitution of matter, leading among other things to the re-emergence of forms of vitalism. The course continues by illustrating how, passing through van 't Hoff's results on osmotic pressure and Einstein's subsequent reinterpretation of Brownian motion, the kinetic-molecular explanation of heat and the real atomic-molecular constitution of matter were finally established, but by now on the threshold of a reorientation of physics along non-classical lines of development.
By focusing on some particularly significant "case studies", the course concretely shows how the history of physics can be used as an investigation methodology for conceptual clarification and for a better didactic transmission of contents currently present in physics texts. Galilean studies on the fall of bodies allow us to critically reconsider the notions of relativity of motion and undisturbed composition of motions in the same body. The difficult process through which Newton elaborates a quantitative dynamic treatment of uniform circular motion gives the opportunity to critically revisit this classic topic covered in mechanics courses. The Newtonian determination of the law of universal gravitation by combining the dynamics of circular motion with Kepler's laws is used to point out the characteristics of this law, removing conceptual confusions that sometimes remain in students, typical among all the lack of distinction between the fundamental gravitational law and the resulting action between extended spherical masses. The complex history of Brownian motion is exploited to recall and clarify various contents of the kinetic-molecular theory of heat. First of all, a method is proposed to obtain Brownian motion with the instrumentation usually available in school laboratories. Two cornerstones of the kinetic-molecular theory of heat, namely the kinetic-molecular modeling of the perfect gas and the equipartition of energy, are taken up and explored in depth starting from the first attempts to explain Brownian motion by directly applying the equipartition of energy to Brownian corpuscles. Of Einstein's subsequent approach, only the final formula for the mean square displacement of the Brownian corpuscles is considered, focusing however in detail on the experimental verification of the relationship. A comparison with the original memories makes it possible to appreciate the complexity of this verification and to identify various limitations in the usual educational presentations dedicated to the topic.