Motivated by the conceptual problems concerning the quantisation of gravity, the Dutch theoretical physicist G. 't Hooft (1999 Nobel prize in physics) put forward the notion that quantum mechanics must be the emergent theory of some underlying, deterministic theory. This proposal usually goes by the name quantum mechanics as an emergent phenomenon. This research line, initiated by 't Hooft in the late 1990's, has been the subject of intense research over the last 15 years, by 't Hooft himself as well as by many other researchers. In this PhD thesis we present our own approach to quantum mechanics as an emergent phenomenon.According to the emergence paradigm for quantum mechanics, information-loss effects in the underlying deterministic theory lead to the arrangement of states of the latter into equivalence classes, that one identifies as quantum states of the emergent quantum mechanics. In brief, quantisation is dissipation, according to 't Hooft.Moreover it has been argued in the literature that, in the presence of weak gravitational fields, quantum effects must be indistinguishable from thermal effects. Since the latter are typically dissipative in nature, the presence of a weak gravitational field should provide a framework in which quantum effects can be explained as due to thermal, dissipative fluctuations. Furthermore, since gravitational effects can be locally gauged away (thanks to the equivalence principle), there should exist some kind of equivalence principle for quantum effects, i.e., some kind of relativity principle for the notion of quantumness as opposed to the notion of classicality. In this PhD thesis we elaborate on this idea.Once a reference frame is fixed, however, quantum effects cannot be gauged away, and the statement quantisation is dissipation lends itself to a thermodynamical treatment. In this thesis we also present one mechanism whereby quantum mechanics is seen to emerge, thus explicitly realising 't Hooft's proposal. This mechanism is based on a dictionary between semiclassical quantum mechanics, on the one hand, and the classical theory of irreversible thermodynamics in the linear regime, on the other. This thermodynamical formalism, developed by Nobel prize winners Onsager and Prigogine, can be easily mapped into that of semiclassical quantum mechanics.
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ResumenMotivado por los problemas conceptuales relativos a la cuantización de la gravedad, el físico teórico holandés G. 't Hooft (premio Nobel de física en 1999) sugirió la noción de que la mecánica cuántica pudiera ser la teoría emergente de alguna otra teoría determinista subyacente. Dicha propuesta se conoce como la mecánica cuántica en tanto que teoría emergente. Esta línea de investigación, iniciada por 't Hooft a finales de los años 90, ha sido objeto de intenso estudio a lo largo de losúltimos 15 años, tanto por el mismo 't Hooft como por numerosos otros investigadores. En esta tesis doctoral presentamos nuestra propia aproximación a la mecánica cuántica como fenómeno emergente.De acuerdo con este paradigma emerg...