We argue that computation via quantum mechanical processes is irrelevant to explaining how brains produce thought, contrary to the ongoing speculations of many theorists. First, quantum effects do not have the temporal properties required for neural information processing. Second, there are substantial physical obstacles to any organic instantiation of quantum computation. Third, there is no psychological evidence that such mental phenomena as consciousness and mathematical thinking require explanation via quantum theory. We conclude that understanding brain function is unlikely to require (...) quantum computation or similar mechanisms. (shrink)

Special relativity is said to prohibit faster-than-light (superluminal) signaling, yet controversy regularly arises as to whether this or that physical phenomenon violates the prohibition. I argue that the controversy is a result of a lack of clarity as to what it means to ‘signal’, and I propose a criterion. I show that according to this criterion, superluminal signaling is not prohibited by special relativity.

Bell’s theorem is purported to demonstrate the impossibility of a local “hidden variable” theory underpinning quantum mechanics. It relies on the well-known assumption of ‘locality’, and also on a little-examined assumption called ‘statistical independence’ (SI). Violations of this assumption have variously been thought to suggest “backward causation”, a “conspiracy” on the part of nature, or the denial of “free will”. It will be shown here that these are spurious worries, and that denial of SI simply implies nonlocal correlation between spacelike (...) degrees of freedom. Lorentz-invariant theories in which SI does not hold are easily constructed: two are exhibited here. It is conjectured, on this basis, that quantum-mechanical phenomena may be modeled by a local theory after all. (shrink)

Gauge theories are theories that are invariant under a characteristic group of "gauge" transformations. General relativity is invariant under transformations of the diffeomorphism group. This has prompted many philosophers and physicists to treat general relativity as a gauge theory, and diffeomorphisms as gauge transformations. I argue that this approach is misguided.

Whereas one can conceive of a relational classical mechanics in which absolute space and time do not play a fundamental role, quantum mechanics does not readily admit any such relational formulation.

This paper examines some common measures of complexity, structure, and information, with an eye toward understanding the extent to which complexity or information‐content may be regarded as objective properties of individual objects. A form of contextual objectivity is proposed which renders the measures objective, and which largely resolves the puzzle of Maxwell's Demon.

General relativity is commonly thought to imply the existence of a unique metric structure for space-time. A simple example is presented of a general relativistic theory with ambiguous metric structure. Brans-Dicke theory is then presented as a further example of a space-time theory in which the metric structure is ambiguous. Other examples of theories with ambiguous metrical structure are mentioned. Finally, it is suggested that several new and interesting philosophical questions arise from the sorts of theories discussed.

The quantization of gravity represents an important attempt at reconciling the two seemingly incompatible frameworks that lie at the base of modern physics, quantum theory and general relativity. The dissertation begins by looking at the incompatibilities between the two frameworks. The incompatibility with quantum theory, it is argued, is rooted in the profound differences between general relativity and ordinary field theories. The dissertation goes on to look at how, in practice, these incongruities are treated in the canonical quantization program, and (...) argues that their treatment is such that it is unlikely to lead to a satisfactory physical theory. The dissertation concludes by arguing that quantum theory only makes sense when embedded in a classical theory. Thus the reconciliation of quantum theory and general relativity suggests that we look outside the bounds of ordinary quantum theory for the proper theoretical framework. (shrink)

In this paper we consider a naive conception of what a quantum theory of gravity might entail: a quantum-mechanically fluctuating gravitational field at each spacetime point. We argue that this idea is problematic both conceptually and technically.

David Albert and Barry Loewer have proposed a new interpretation of quantum mechanics which they call the Many Minds interpretation, according to which there are infinitely many minds associated with a given (physical) state of a brain. This interpretation is related to the family of many worlds interpretations insofar as it assumes strictly unitary (Schrödinger) time-evolution of quantum-mechanical systems (no reduction of the wave-packet). The Many Minds interpretation itself is principally motivated by an argument which purports to show that the (...) assumption of unitary evolution, along with some common sense assumptions about mental states (specifically, beliefs) leads to a certain nonphysicalism, in which there is a many-to-one correspondence between minds and brains. In this paper, I critically examine this motivating argument, and show that it depends on a mistaken assumption regarding the correspondence between projection operators and yes/no questions. (shrink)

Anthropic arguments in multiverse cosmology and string theory rely on the weak anthropic principle (WAP). We show that the principle, though ultimately a tautology, is nevertheless ambiguous. It can be reformulated in one of two unambiguous ways, which we refer to as WAP_1 and WAP_2. We show that WAP_2, the version most commonly used in anthropic reasoning, makes no physical predictions unless supplemented by a further assumption of "typicality", and we argue that this assumption is both misguided and unjustified. WAP_1, (...) however, requires no such supplementation; it directly implies that any theory that assigns a non-zero probability to our universe predicts that we will observe our universe with probability one. We argue, therefore, that WAP_1 is preferable, and note that it has the benefit of avoiding the inductive overreach characteristic of much anthropic reasoning. (shrink)

From classical mechanics to quantum field theory, the physical facts at one point in space are held to be independent of those at other points in space. I propose that we can usefully challenge this orthodoxy in order to explain otherwise puzzling correlations at both cosmological and microscopic scales.

Special relativity is said to prohibit faster-than-light (superluminal) signalling, yet controversy regularly arises as to whether this or that physical phenomenon violates the prohibition. I argue that the controversy is a result of a lack of clarity as to what it means to `signal', and I propose a criterion. I show that although we have no reason to think that one can send signals faster than light, this is not prohibited by special relativity.

In 1949, Kurt Gödel found a solution to the field equations of general relativity that described a spacetime with some unusual properties. This “Gödel universe” permitted “closed timelike curves,” hence a kind of time travel, and it did not admit of decomposition into successive moments of time. In the same year, he published “A Remark about the Relationship between Relativity Theory and Idealistic Philosophy”, in which he used certain properties of this solution to argue for a kind of temporal idealism, (...) whereby “change [is] an illusion or an appearance due to our special mode of perception”. The paper is short and to the point, but the argument has usually been regarded as fatally flawed. In his Gödel Meets Einstein: Time Travel in the Gödel Universe, Palle Yourgrau makes a case for Gödel. (shrink)

This is a review of Yourgrau's book, the second edition of his "The Disappearance of Time.".

Review of "Space, Time, and Stuff" by Frank Arntzenius.