It is well known that Niels Bohr insisted on the necessity of classical concepts in the account of quantum phenomena. But there is little consensus concerning his reasons, and what he exactly meant by this. In this paper, I re-examine Bohr’s interpretation of quantum mechanics, and argue that the necessity of the classical can be seen as part of his response to the measurement problem. More generally, I attempt to clarify Bohr’s view on the classical/quantum divide, arguing that the relation (...) between the two theories is that of mutual dependence. An important element in this clarification consists in distinguishing Bohr’s idea of the wave function as symbolic from both a purely epistemic and an ontological interpretation. Together with new evidence concerning Bohr’s conception of the wave function collapse, this sets his interpretation apart from both standard versions of the Copenhagen interpretation, and from some of the reconstructions of his view found in the literature. I conclude with a few remarks on how Bohr’s ideas make much sense also when modern developments in quantum gravity and early universe cosmology are taken into account. (shrink)

Inflationary cosmology has been widely accepted due to its successful predictions: for a “generic” initial state, inflation produces a homogeneous, flat, bubble with an appropriate spectrum of density perturbations. However, the discovery that inflation is “generically eternal,” leading to a vast multiverse of inflationary bubbles with different low-energy physics, threatens to undermine this account. There is a “predictability crisis” in eternal inflation, because extracting predictions apparently requires a well-defined measure over the multiverse. This has led to discussions of anthropic predictions (...) based on a measure over the multiverse, and an assumption that we are typical observers. I will give a pessimistic assessment of attempts to make predictions in this sense, emphasizing in particular problems that arise even if a unique measure can be found. (shrink)

The present article discusses shared epistemological characteristics of two distinct areas of research: the field of first-person inquiry and the field of quantum mechanics. We outline certain philosophical challenges that arise in each of the two lines of inquiry, and point towards the central similarity of their observational situation: the impossibility of disregarding the interrelatedness of the observed phenomena with the act of observation. We argue that this observational feature delineates a specific category of research that we call the non-trivial (...) domain. Unlike the trivial domain, non-trivial research cannot assume the view from nowhere on which the observed phenomena could be regarded as existing independently of the process of observation. Presenting first-person inquiry and quantum mechanics as two of its examples, we show that non-trivial research violates several fundamental observational presuppositions of the trivial domain, exemplified in the principles of classical physics. Drawing on Niels Bohr’s philosophy of quantum mechanics and the constructivist notion of enaction, we stress the constructive, participatory, and irreversible nature of observation in the non-trivial domain. We discuss the possibility of developing a non-representationalist epistemology of the non-trivial, and consider the implications of our discussion for research in the non-trivial domain, as well as for the general understanding of the scientific inquiry. (shrink)

Theological engagement with quantum physics has, to this day, been dominated by the Copenhagen interpretation. However, philosophers and physicists working in the “quantum foundations” field have largely abandoned the Copenhagen view on account of what is widely seen as its troublesome antirealism. Other metaphysical approaches have come to the fore instead, which often take a strongly realist flavor, such as de Broglie-Bohm, or Everett's “Many-Worlds” interpretation. In the spirit of recent quantum foundations work, this article introduces a collection of studies (...) aimed at taking quantum theology “beyond Copenhagen.” The present article advocates a commitment to “quantum fundamentalism,” which could resolve some of the enduring ontological problems faced by existing theological work with quantum mechanics, especially in discussions of quantum special divine action. Taking quantum fundamentalism literally would mean a departure from the Copenhagen interpretation, and the article suggests the need for a new research program to lay the groundwork in the natural theology of quantum foundations. (shrink)

This paper gives an overview of significant issues in the philosophy of cosmology, starting off by emphasizing the uniqueness of the universe and the way models are used in description and explanation. It then considers, basic limits on observations; the need to test alternatives; ways to test consistency; and implications of the uniqueness of the universe as regards distinguishing laws of physics from contingent conditions. It goes on to look at the idea of a multiverse as a scientific explanation of (...) facts about fine-tuning, in particular considering criteria for a scientific theory and for justifying unseen entities. It considers the relation between physical laws and the natures of existence, and emphasizes limits on our knowledge of the physics relevant to the early universe, and the non-physical nature of some claimed infinities. The final section looks briefly at deeper issues, commenting on the scope of enquiry of cosmological theory and the limits of science in relation to the creation of the universe. (shrink)

I discuss how modern cosmology illustrates under-determination of theoretical hypotheses by data, in ways that are different from most philosophical discussions. I emphasise cosmology's concern with what data could in principle be collected by a single observer ; and I give a broadly sceptical discussion of cosmology's appeal to the cosmological principle as a way of breaking the under-determination.I confine most of the discussion to the history of the observable universe from about one second after the Big Bang, as described (...) by the mainstream cosmological model: in effect, what cosmologists in the early 1970s dubbed the ‘standard model’, as elaborated since then. But in the closing Section 4, I broach some questions about times earlier than one second. (shrink)

The inflationary scenario has become the paradigm of early universe cosmology, and – in conjunction with ideas from superstring theory—has led to speculations about an “inflationary multiverse”. From a point of view of phenomenology, the inflationary universe scenario has been very successful. However, the scenario suffers from some conceptual problems, and thus it does not have the status of a solid theory. There are alternative ideas for the evolution of the very early universe which do not involve inflation but which (...) agree with most current cosmological observations as well as inflation does. In this lecture I will outline the conceptual problems of inflation and introduce two alternative pictures - the “matter bounce” and “string gas cosmology”, the latter being a realization of the “emergent universe” scenario based on some key principles of superstring theory. I will demonstrate that these two alternative pictures lead to the same predictions for the power spectrum of the observed large-scale structure and for the angular power spectrum of cosmic microwave background anisotropies as the inflationary scenario, and I will mention predictions for future observations with which the three scenarios can be observationally teased apart. (shrink)

In Every Thing Must Go James Ladyman and Don Ross argue for a radical version of naturalistic metaphysics and propose that contemporary analytic metaphysics is detached from science and should be discontinued. The present article addresses the issues of whether science and metaphysics are separable, intuitions and understanding should be excluded from scientific theory, and Ontic Structural Realism satisfies the criteria of the radical version of naturalism advanced by Ladyman and Ross. The point underlying those topics is that successful scientific (...) research presupposes metaphysics, and that basic epistemic virtues common to metaphysics and science may allow us—as opposed to what Ladyman and Ross suggest—to increase our understanding of the world and to put constraints on allowable metaphysical theories. (shrink)

This paper analyzes two different proposals, one by Ellis and Brundrit, based on classical relativistic cosmology, the other by Garriga and Vilenkin, based on the DH interpretation of quantum mechanics, both concluding that, in an infinite universe, planets and beings must be repeated an infinite number of times. We point to possible shortcomings in these arguments. We conclude that the idea of an infinite repetition of histories in space cannot be considered strictly speaking a consequence of current physics and cosmology. (...) Such ideas should be seen rather as examples of «ironic science» in the terminology of John Horgan. (shrink)

As the theory of the atom, quantum mechanics is perhaps the most successful theory in the history of science. It enables physicists, chemists, and technicians to calculate and predict the outcome of a vast number of experiments and to create new and advanced technology based on the insight into the behavior of atomic objects. But it is also a theory that challenges our imagination. It seems to violate some fundamental principles of classical physics, principles that eventually have become a part (...) of western common sense since the rise of the modern worldview in the Renaissance. So the aim of any metaphysical interpretation of quantum mechanics is to account for these violations. (shrink)

We provide a discussion of some main ideas in our project about the physical foundation of the time concept in cosmology. It is standard to point to the Planck scale as a limit for how far back we may extrapolate the standard cosmological model. In our work we have suggested that there are several other interesting limits -- located at least thirty orders of magnitude before the Planck time -- where the physical basis of the cosmological model and its time (...) concept is progressively weakened. Some of these limits are connected to phase transitions in the early universe which gradually undermine the notion of 'standard clocks' widely employed in cosmology. Such considerations lead to a 'scale problem' for time which becomes particularly acute above the electroweak phase transition. Other limits are due to problems of building up a cosmological reference frame, or even contemplating a sensible notion of proper time, if the early universe constituents become too quantum. This 'quantum problem' for time arises e.g. if a pure quantum phase is contemplated at the beginning of inflation at, say, $\sim 10^{-34}$ seconds. (shrink)

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. (shrink)

The spectacular successes of quantum physics have made it a commonplace to assert that we live in a quantum world. This idea seems to imply a kind of “quantum fundamentalism” according to which everything in the universe is fundamentally of a quantum nature and ultimately describable in quantum-mechanical terms. Bohr’s conception of quantum mechanics has traditionally been seen as opposed to such a view, not least because of his insistence on the necessity of the concepts of classical physics in the (...) account of quantum phenomena. Recently, however, a consensus seems to be emerging among careful commentators on Bohr to the effect that he, after all, did subscribe to some version of quantum fundamentalism. Against this consensus, and by re-examining the historical record, I will defend a variant of the traditional reading of Bohr in which the answer to what an object is depends on the experimental context; and in principle, any physical system can be treated quantum-mechanically but not all systems can be treated that way at the same time. (shrink)