In this essay I claim that thought experiments have invariably been very important to inquire into the foundations of natural science (in particolar physics). In particular, they have proved essential to test the stability of allegedly clear but ultimately contradictory concepts, that were nonetheless at the basis of widely shared scientific theories. By quickly reviewing some famous Gedankenexperimenten proposed by Einstein against the completeness of (Bohr’s interpretation of) quantum mechanics, I will try to ask how could they possibly have the critical role that they always had.
In this essay I claim that thought experiments have invariably been very important to inquire into the foundations of natural science (in particolar physics). In particular, they have proved essential to test the stability of allegedly clear but ultimately contradictory concepts, that were nonetheless at the basis of widely shared scientific theories. By quickly reviewing some famous Gedankenexperimenten proposed by Einstein against the completeness of (Bohr’s interpretation of) quantum mechanics, I will try to ask how could they possibly have the critical role that they always had.
The author describes several thought experiments that are important in modern physics, by which he mean the physical theory and practice that developed explosively from the late 19th century onwards. Some thought experiments provide the basis for rigorous arguments with clear conclusions; others seem to work simply by drawing attention to an important question that otherwise might not have been apparent. While the thought experiments to be discussed here are key turning points in the history of modern physical theory, in several cases their full implications remain to be plumbed. It is an extraordinary fact that most of the decisive thought experiments in 20th-century physics were born from the fertile imagination of one person, Albert Einstein. This forces to ponder the importance of individual creativity in the advancement of science. The Einstein-Podolsky-Rosen (EPR) thought experiment dominates investigations of the foundations of quantum mechanics and plays a defining role in quantum information theory.
La metafisica studia l’essenza delle entità, lasciando alle scienze particolari lo studio degli aspetti empirici, specifici, mutevoli ed instabili. In questo senso essa è vicina all’ontologia, in relazione a problemi come l’esistenza di Dio, l’essere “in sè”, l’immortalità della coscienza, l’origine e il significato dell’universo. Anche la fisica speculativa spinge il suo interesse verso le questioni metafisiche, a livello tecnico (matematico) e a livello di pensiero (in relazione alla filosofia).Negli ultimi anni la fisica speculativa ha studiato e sviluppato interessanti concetti e idee, che coinvolgono le ultime teorie quantistico-relativistiche unificate. La ricerca di un significato della vita trova fermento nella ricerca di un significato circa l’esistenza del nostro universo, anche come possibile parte di un multiverso che lo contiene.Ci sono aspetti controversi sul ruolo della coscienza nel processo di riduzione della funzione d’onda in meccanica quantistica; ciò restringe il campo di validità di alcuni principi fondamentali durante l’interazione tra microsistemi e macrosistemi, con conseguente diversificazione della definizione dello stato ontologico di coscienza e realtà.Dalle risposte di Wittgenstein ai paradossi della comunicazione e del relativismo concettuale emerge una tensione nella sua visione dei giochi linguistici e nei suoi esperimenti mentali, che può essere meglio compresa attraverso alcune riflessioni di Wittgenstein su Einstein e la sua teoria della relatività.
My theme is thought experiment in natural science, and its relation to real experiment. I shall defend the thesis that thought experiments that do not lead to theorizing and to a real experiment are generally of much less value that those that do so. To illustrate this thesis I refer to three examples, from three very different periods, and with three very different kinds of status. The first is the classic thought experiment in which Galileo imagined that he had, by pure thought, demolished Aristoteles' dogma that heavier bodies fall more quickly than light ones. I will show that he was mistaken. The second is the Einstein-Podolsky-Rosen paper purporting to show that quantum mechanics must be incomplete in its domain of application. This thought experiment is a very good one, not because its conclusions are correct, but precisely because it was fruitful, leading to theory and, above all, to a real experiment. Finally I discuss the modern string theory of everything, which, while it is regarded as a physical theory by its instigators, shares some properties of the least successful sort of thought experiment.
The founding fathers of quantum mechanics had already perceived the essence of the difficulties of quantum mechanics; today, after almost a century, the discussions are still lively and, if some very interesting new aspects have emerged, at a deeper level the questions have not changed so much. What is more recent, nevertheless, is a general change of attitude among physicists: until about 1970 or 1980, most physicists thought that the essential questions had been settled, and that “Bohr was right and proved his opponents to be wrong”. This was probably a consequence of the famous discussions between Bohr, Einstein, Schrödinger, Heisenberg, Pauli, de Broglie, and others (in particular at the Solvay meetings [1–3], where Bohr's point of view had successfully resisted Einstein's extremely clever attacks). The majority of physicists did not know the details of the arguments. They nevertheless thought that the standard “Copenhagen interpretation” had clearly emerged from the infancy of quantum mechanics as the only sensible attitude for good scientists. This interpretation includes the idea that modern physics must contain indeterminacy as an essential ingredient: it is fundamentally impossible to predict the outcome of single microscopical events; it is impossible to go beyond the formalism of the wave function (or its generalization, the state vector ∣ψ) and complete it.
As Quine wrote in 1961, what strikes us in a paradox is its initial air of absurdity, which develops into a sort of psychological discomfort when we compare the conclusions of the reasoning with the apparently irrefutable arguments on which it is based. However, as he went on to observe, ‘More than once in history the discovery of paradox has been the occasion for major reconstruction at the foundations of thought’. Catastrophe may therefore lurk even in the most innocent-seeming of paradoxes and force us to recognize the arbitrary nature ‘of a buried premise or of some preconception previously reckoned as central to physical theory, to mathematics or to the thinking process’. More recently, ideas of this kind have been used to assert in general that the role of paradox in the growth of knowledge is to generate category switches and to construct new universes of discourse. It could also be argued that paradoxes constitute elements of the logic of discovery capable of amplifying and thus making intelligible the still obscure phases accompanying paradigm shifts. Paradoxes would thus represent points of accumulation for the tension created between a given system of conceptual representation and a theory or empirical discovery that violates it. Historians of science have tried different interpretative approaches in their attempts to unravel the thought process that was to lead Einstein in 1905 to the formulation of special relativity and the simultaneous demolition of the classical conception of space and time.
Il tema di questo articolo riguarda i rapporti controversi tra Einstein e altri due padri della meccanica quantistica, Bohr e Schroedinger. Innanzitutto esporrò i principi fondamentali di questa discplina. Poi parlerò dell'esperiemento mentale di Einstein, Podolsky e Rosen e mostrerò che questi fisici hanno fatto uso nel loro articolo di una precisa forma di inferenza. Di seguito vedremo le risposte di Bohr e Schrödinger, e come esse siano paradigmatiche di altre due forme di inferenza. Infine cercherò di trarra qualche piccola conclusione.