Cosmology, Particles, and the Unity of Science

During the last three decades, there has been a growing realization among physicists and cosmologists that the relation between particle physics and cosmology may constitute yet another successful example of the unity of science. However, there are important conceptual problems in the unification of the two disciplines, e.g. in connection with the cosmological constant and the conjecture of inflation. The present article will outline some of these problems, and argue that the victory for the unity of science in the context of cosmology and particle physics is still far from obvious.Comment: 23 pages, no figures. To appear in Studies in History and Philosophy of Modern Physic

Weyl's principle, cosmic time and quantum fundamentalism

We examine the necessary physical underpinnings for setting up the cosmological standard model with a global cosmic time parameter. In particular, we discuss the role of Weyl's principle which asserts that cosmic matter moves according to certain regularity requirements. After a brief historical introduction to Weyl's principle we argue that although the principle is often not explicitly mentioned in modern standard texts on cosmology, it is implicitly assumed and is, in fact, necessary for a physically well-defined notion of cosmic time. We finally point out that Weyl's principle might be in conflict with the wide-spread idea that the universe at some very early stage can be described exclusively in terms of quantum theory.Comment: To appear in the section on "Physical and philosophical perspectives on probability and time" in S. Hartmann et al. (eds.) "Explanation, Prediction and Confirmation", Springer's The Philosophy of Science in a European Perspective book serie

The philosophy behind Quantum Gravity

This paper investigates some of the philosophical and conceptual issues raised by the search for a quantum theory of gravity. It is critically discussed wheter such a theory is necessary in the first place, and how much would be accomplished if it is eventually constructed. I argu that the motivations behind, and expectations to, a theory of quantum gravity are entangled with central themes in the philosophy of science, in particular unification, reductionism, and the interpretation of quantum mechanics. I further argue that there are - contrary to claims made on behalf of string theory - no good reasons to think that a quantum theory of gravity, if constructed, will provide a theory of everything, that is, a fundamental theory from which all physics ini principle can be derive

Some Trends in the Philosophy of Physics

A short review of some recent developments in the philosophy of physics is presented. I focus on themes which illustrate relations and points of common interest between philosophy of physics and three of its `neighboring' elds: Physics, metaphysics and general philosophy of science. The main examples discussed in these three `border areas' are (i) decoherence and the interpretation of quantum mechanics; (ii) time in physics and metaphysics; and (iii)methodological issues surrounding the multiverse idea in modern cosmology

Aesthetic Motivation in Quantum Physics: Past and Present

This essay explores the relations between aesthetics and motivation, primarily in quantum physics, focusing on the notions of play, beauty, and the joy of insight. The motivating role of these notions is examined both historically among the quantum pioneers and contemporarily, based on a series of interviews, among physicists associated with the Niels Bohr Institute in Copenhagen

Some trends in the philosophy of physics

A short review of some recent developments in the philosophy of physics is presented. I focus on themes which illustrate relations and points of common interest between philosophy of physics and three of its 'neighboring' fields: Physics, metaphysics and general philosophy of science. The main examples discussed in these three 'border areas' are (i) decoherence and the interpretation of quantum mechanics; (ii) time in physics and metaphysics; and (iii) methodological issues surrounding the multiverse idea in modern cosmology

Did time have a beginning?

By analyzing the meaning of time I argue, without endorsing operationalism, that time is necessarily related to physical systems which can serve as clocks. This leads to a version of relationism about time which entails that there is no time ‘before’ the universe. Three notions of metaphysical ‘time’ (associated, respectively, with time as a mathematical concept, substantivalism and modal relationism) which might support the idea of time ‘before’ the universe are discussed. I argue that there are no good reasons to believe that metaphysical ‘time’ can be identified with what we ordinarily call time. I also briefly review and criticize the idea of time ‘before’ the big bang associated with some recent speculative models in modern cosmology, and I argue that if the big bang model is a (roughly) correct description of our universe, then the best current answer to the question in the title is that time did have a beginning

The philosophy behind quantum gravity

This paper investigates some of the philosophical and conceptual issues raised by the search for a quantum theory of gravity. It is critically discussed whether such a theory is necessary in the first place, and how much would be accomplished if it is eventually constructed. I argue that the motivations behind, and expectations to, a theory of quantum gravity are entangled with central themes in the philosophy of science, in particular unification, reductionism, and the interpretation of quantum mechanics. I further argue that there are – contrary to claims made on behalf of string theory – no good reasons to think that a quantum theory of gravity, if constructed, will provide a theory of everything, that is, a fundamental theory from which all physics in principle can be derived

A critical note on time in the multiverse

In recent analyses of standard, single-universe, cosmology, it was pointed out that specific assumptions regarding the distribution and motion of matter must be made in order to set up the cosmological standard model with a global time parameter. Relying on these results, we critically examine the notion of time in the multiverse, and in particular the idea that some parts of the multiverse are older than others. By focusing on the most elaborated multiverse proposal in cosmology, the inflationary multiverse, we identify three problems for establishing a physically well-defined notion of global time; a quantum problem, a collision problem and a fractal problem. The quantum problem, and the closely related ``cosmic measurement problem", may even undermine the idea that parts of the multiverse causally and temporally precede our universe

The Quantum Vacuum and the Cosmological Constant Problem

The cosmological constant problem arises at the intersection between general relativity and quantum field theory, and is regarded as a fundamental problem in modern physics. In this paper we describe the historical and conceptual origin of the cosmological constant problem which is intimately connected to the vacuum concept in quantum field theory. We critically discuss how the problem rests on the notion of physically real vacuum energy, and which relations between general relativity and quantum field theory are assumed in order to make the problem well-defined