Weyl symmetry of the classical bosonic string Lagrangian is broken by quantization, with profound consequences described here. Reimposing symmetry requires that the background space-time satisfy the equations of general relativity: general relativity, hence classical space-time as we know it, arises from string theory. We investigate the logical role of Weyl symmetry in this explanation of general relativity: it is not an independent physical postulate but required in quantum string theory, so from a certain point of view it plays only a (...) formal role in the explanation. (shrink)
Quantum gravity--the marriage of quantum physics with general relativity--is bound to contain deep and important lessons for the nature of physical time. Some of these lessons shall be canvassed here, particularly as they arise from quantum general relativity and string theory and related approaches. Of particular interest is the question of which of the intuitive aspects of time will turn out to be fundamental, and which 'emergent' in some sense.
The nature of space and time is one of the most fascinating and fundamental areas of the philosophy of physics. This study aims to provide a complete account of current debates in the application of spacetime to string theory. String theory has been an important discipline within physics for many years but is only now being applied to the problems faced by philosophers of science. This emerging area of physics is discussed in relation to a number of theories including general (...) relativity, T-duality and moduli space, and set in the context of current and future research. (shrink)
Physical time plays a different role in general relativity than in quantum mechanics and the particle physics based on it. The first section of this chapter provides a brief survey of the main approaches to quantum gravity and then proceeds to consider the lessons that can be drawn from two distinct strategies for discovering a theory of quantum gravity. In the next section, the chapter first explicates the fate of time in approaches to quantum gravity that start with general relativity (...) (GR) and attempt to quantize it. Second, it investigates approaches to quantum gravity that start from quantum particle physics. The third and fourth sections respectively offer an assessment of time as understood in string theory and 'non‐commutative' field theory. One of the important possibilities for time in quantum gravity is that it might fail to commute with space. (shrink)
_Abstract_: In this paper we carve out a _reformist_ agenda within the debate on the foundations of cognitive science, incorporating some important ideas from the 4E cognition literature into the computational-representational framework. We are deeply sympathetic to this reformist program since we think that, despite strong criticism of the concept of computation and the related notion of representation, computational models should still be at the core of the study of mind. At the same time, we recognize the need for a (...) liberalization of the computational and representational framework that can address deep dissatisfaction with the anti-biologism and radical internalism of classical cognitive science. However, reform is a difficult task, so in this article we focus on two open questions within the reformist agenda. The first concerns the possibility of combining mechanistic-computational and dynamical explanations. The second concerns related changes in the notion of representation and its use (with special attention to Andy Clark’s radical predictive processing). _Keywords_: Continuum of Representational Genera;_ _Enactivism; Predictive Processing; Radical Embodied Cognition Thesis; Representationalism _ Due problemi aperti nell’agenda riformista della filosofia della scienza cognitiva _ _Riassunto_: In questo lavoro identifichiamo un’agenda _riformista_ nel dibattito sui fondamenti della scienza cognitiva che incorpora alcune idee centrali provenienti dalla letteratura sulla cognizione 4E all’interno di una cornice computazionalista e rappresentazionalista. Tale agenda considera il quadro computazionalista e rappresentazionalista ancora imprescindibile ai fini dello studio integrato della mente e del cervello, ma ne persegue una liberalizzazione nell’intento di renderlo idoneo ad accogliere alcuni importanti spunti emersi dalla letteratura sulla cognizione delle 4E. Tuttavia, riformare è un compito difficile. In questo articolo ci concentriamo su due problemi aperti nell’agenda riformista. Il primo riguarda la possibilità di mettere assieme le spiegazioni meccaniciste e computazionaliste con quelle dinamiche. Il secondo riguarda i cambiamenti relativi alla nozione di rappresentazione e al suo impiego (con particolare attenzione all’elaborazione predittiva radicale di Andy Clark). _Parole chiave_: Continuum dei generi rappresentazionali;_ _Elaborazione predittiva; Enattivismo; Tesi della cognizione incarnata radicale; Rappresentazionalismo. (shrink)
This paper explains the phenomenon of `entanglement exchange' within the Bohmian approach to quantum mechanics. After explaining Bohmian mechanics and entanglement exchange, in which pairs of particles become entangled without ever interacting causally in the usual, unitary sense, our aim is to use this example, to illustrate how the `pilot wave' mediates non-local correlations. The discussion thus gives a useful new way to think about entanglement exchange, and clarifies the structure of Bohmian mechanics.
It has been argued within some philosophy of quantum gravity circles that endorsing Lewisian modal metaphysics is incompatible with endorsing the fundamental physical ontology of any quantum gravity theory. Speaking concisely, the unsolvable tension would be between Lewis' metaphysical commitment to the fundamentality of space and time, and the physical lesson of quantum gravity about the disappearance of space and time from the fundamental structure of the world. In this essay I argue against the idea that the tension is unsolvable. (...) The analysis does not apply to quantum gravity in general, but only to the specific perspective delivered by quantum string theory. In the first two sections I describe what I think is the general formal payoff of Lewisian possible worlds semantics, and more importantly the general metaphysical payoff generated by some Lewisian metaphysical applications of that formal framework. Lewisian possible worlds semantics is not among the topics of this essay, still a concise presentation of its basic features is required for a more accurate description of the type of modal metaphysics Lewis delivers by applying that formal machinery. The moral of the story in the first two sections is that an attempt of preserving crucial features of Lewisian modal metaphysics, although endorsing the quantum string theory lesson on spacetime non fundamentality, would be not only possible, but also philosophically worthy in a general sense. Then, section three is divided in three parts. In the first part I summarize some formal tools of the methodology used elsewhere - (Vistarini, Routledge, 2019, chapter 6)- to argue for string theory background independence. More precisely, I briefly re-describe some crucial features of a topological-vector bundle structure there defined on a "space" associated to the theory. Such structure is there shown to carry physical and dynamical information about quantum strings systems supporting the thesis of background independence of quantum strings laws (string theory background independence is not a topic of this essay, and the construction of the full formal structure as well as the full argumentative line can be found in the work cited above). The rationale behind the choice of including these formal tools is explained in the second and third parts of section three: that very same topological-fiber bundle structure associated to string theory, if read differently, is shown to also carry structural properties of the Lewisian metaphysical scheme. More precisely, in the second part of section three I attempt to show that such topological-fiber bundle structure owns a topology which qualifies as a plausible accessibility structure extending the Lewisian similarity accessibility. To avoid confusion, I will denote the extended similarity order with S*, or S*-similarity. The latter has some interesting properties. It is quantitatively describable, and even more interestingly its spectrum of variation is a countable one. Then, insofar Lewisian similarity order can be regained from the S*-similarity, one might say that the latter is a metaphysical accessibility relation underlying the former because "more fundamental". As we will see, the explanation of what "more fundamental" means in this metaphysical context mainly involves the idea that the formal nature of S*-similarity, in particular its property of having a countable spectrum of variation, calibrates a metaphysical similarity that reflects the discreteness of the fundamental quantum nature of reality. The extended modal metaphysics with accessibility structure S*-similarity is informed by quantum string physics. Within the extended scheme, the Lewisian claim "things could have been different in countless ways" (Lewis 1973) is an approximate one because only permitted by ordinary language. As soon as one refines the accessibility structure by using the formal language of quantum string theory, it appears things could have been different in countable ways. But the Lewisian variety of alternative states of affairs can be regained from the underlying countable variety via a specific interpretation of the Humean supervenience thesis, one that changes the metaphysical status of the thesis' content and restricts the thesis' domain of application. Finally, in the third part of section three I attempt to show that the same topological-fiber bundle structure used to extend Lewisian similarity has a bundle component producing the formal scheme for a tentative extension of Lewisian nomological accessibility through the lens of string dualities. This will prove to be a non trivial task, and the Lewisian accessibility structure will be regained from the extended one only partially. Finally, the essay contains two short appendices summarizing two argumentative lines outside the main topic of the essay. They briefly describe different ways in which the non fundamentality of spatiotemporal structures can be found in quantum string theory. These sections can be skipped. Nevertheless, they might contribute to understand more robustly the general view endorsed by this essay, i.e. that there isn't any unsolvable tension between Lewis' commitment to the fundamentality of spatiotemporal relations and quantum gravity's lesson about their non fundamentality. -/- . (shrink)