79 research outputs found
Skeptical Notes on a Physics of Passage
This paper investigates the mathematical representation of time in physics.
In existing theories time is represented by the real numbers, hence their
formal properties represent properties of time: these are surveyed. The central
question of the paper is whether the existing representation of time is
adequate, or whether it can or should be supplemented: especially, do we need a
physics incorporating some kind of `dynamical passage' of time? The paper
argues that the existing mathematical framework is resistant to such changes,
and might have to be rejected by anyone seeking a physics of passage. Then it
rebuts two common arguments for incorporating passage into physics, especially
the claim that it is an element of experience. Finally the paper investigates
whether, as has been claimed, `causal set theory' provides a physics of
passage.Comment: 14 page
The (A)temporal Emergence of Spacetime
This paper examines two cosmological models of quantum gravity (from string
theory and loop quantum gravity) to investigate the foundational and conceptual
issues arising from quantum treatments of the big bang. While the classical
singularity is erased, the quantum evolution that replaces it may not
correspond to classical spacetime: it may instead be a non-spatiotemporal
region, which somehow transitions to a spatiotemporal state. The different
kinds of transition involved are partially characterized, the concept of a
physical transition without time is investigated, and the problem of empirical
incoherence for regions without spacetime is discussed.Comment: Forthcoming in Philosophy of Science; 13 page
Out of Nowhere: Spacetime from causality: causal set theory
This is a chapter of the planned monograph "Out of Nowhere: The Emergence of
Spacetime in Quantum Theories of Gravity", co-authored by Nick Huggett and
Christian W\"uthrich and under contract with Oxford University Press. (More
information at www.beyondspacetime.net.) This chapter introduces causal set
theory and identifies and articulates a 'problem of space' in this theory.Comment: 29 pages, 5 figure
Emergent spacetime and empirical (in)coherence
Numerous approaches to a quantum theory of gravity posit fundamental
ontologies that exclude spacetime, either partially or wholly. This situation
raises deep questions about how such theories could relate to the empirical
realm, since arguably only entities localized in spacetime can ever be
observed. Are such entities even possible in a theory without fundamental
spacetime? How might they be derived, formally speaking? Moreover, since by
assumption the fundamental entities can't be smaller than the derived (since
relative size is a spatiotemporal notion) and so can't 'compose' them in any
ordinary sense, would a formal derivation actually show the physical reality of
localized entities? We address these questions via a survey of a range of
theories of quantum gravity, and generally sketch how they may be answered
positively.Comment: 18 pages, 1 figure, accepted for publication in Studies in History
and Philosophy of Modern Physic
Out of Nowhere: The 'emergence' of spacetime in string theory
This is a chapter of the planned monograph "Out of Nowhere: The Emergence of
Spacetime in Quantum Theories of Gravity", co-authored by Nick Huggett and
Christian W\"uthrich and under contract with Oxford University Press. (More
information at www.beyondspacetime.net.) This chapter analyses the nature and
derivation of spacetime topology and geometry according to string theory.Comment: 40 pages, 2 figure
Spacetime 'Emergence'
Could spacetime be derived rather than fundamental? The question is pressing because attempts to quantize gravity have led to theories in which (arguably) there are either no, or only extremely thin, spacetime structures. Moreover, recent proposals for the interpretation of quantum mechanics have suggested that 3-dimensional space may be an ‘appearance’ derived from the 3N-dimensional space in which an N-particle wavefunction lives (cross- reference). In fact, I will largely assume a positive answer, and investigate how it could be; in particular, I want to explicate the role of philosophy in producing a satisfactory explanation of spacetime, providing a roadmap for philosophical engagement with quantum gravity
Missing the point in noncommutative geometry
Noncommutative geometries generalize standard smooth geometries, parametrizing the noncommutativity of dimensions with a fundamental quantity with the dimensions of area. The question arises then of whether the concept of a region smaller than the scale - and ultimately the concept of a point - makes sense in such a theory. We argue that it does not, in two interrelated ways. In the context of Connes’ spectral triple approach, we show that arbitrarily small regions are not definable in the formal sense. While in the scalar field Moyal-Weyl approach, we show that they cannot be given an operational definition. We conclude that points do not exist in such geometries. We therefore investigate (a) the metaphysics of such a geometry, and (b) how the appearance of smooth manifold might be recovered as an approximation to a fundamental noncommutative geometry
Reading the Past in the Present
In this paper I challenge David Albert's account of the knowledge asymmetry, arguing that an information gathering and utilizing system (IGUS) could know more of the past than can be inferred from Albert's system of Past Hypothesis, laws, and initial measure. To do so I provide a general physical/computational account of our knowledge of the past, based on the IGUS, and draw various conclusions about our limitations
Reading the Past in the Present
In this paper I challenge David Albert's account of the knowledge asymmetry, arguing that an information gathering and utilizing system (IGUS) could know more of the past than can be inferred from Albert's system of Past Hypothesis, laws, and initial measure. To do so I provide a general physical/computational account of our knowledge of the past, based on the IGUS, and draw various conclusions about our limitations
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