Bibliography on Philosophy of Cosmology

 Review of the original motivation for inflation (in terms of solving fine-tuning problems) in relation to the problem of time’s arrow and Penrose’s objection.

Concise overview of foundational questions facing early universe theories, including inflation and several alternative approaches.

Detailed critical analysis of the case for inflationary cosmology at the time (late 90s). Identifies and criticizes implicit philosophical assumptions made by cosmologists.

Enormously influential case in favor of “inflationary cosmology,” based on its ability to solve the horizon, flatness, and monopole problems. Identifies the transition from an inflationary stage back to ordinary expansion as a major unresolved problem.

A defense of inflation, following the Planck observational results, in reply to criticisms by Ijjas, Steinhardt, and Loeb.

In this paper, the authors argue that there are two distinct versions of inflation: the “classical” version, while appealing, is strongly disfavored by observations. The “post-modern” version faces more profound problems related to whether it is testable in principle.

Textbook treatment focusing on how inflation generates initial perturbations that serve as the seeds for the formation of later structures through gravitational enhancement.

Wonderfully clear survey of a variety of topics in physics and mathematics at intermediate level.  Unabashedly idiosyncratic approach to some topics in physics.  Discussion of cosmology and objections to inflation appear in Chapters 27-28.

This article uses the case of inflation to argue that modern cosmology does not need a new methodology or standard of evidence distinct from other domains of physics. Smeenk argues that evidential support for aspects of theories in physics falls into the broad categories of consilience of multiple lines of evidence, and the successive refinement of evidential support guided by a theory-governed research program. Though inflation has not adequately fulfilled either of these lines of evidential support, it should be held to these standards in order to be said to have been empirically confirmed.

What is the impact of a cosmological perspective on philosophical debates regarding the nature of laws?  Balashov analyzes the views about modality of the steady state advocates in detail. Their arguments, along with reflections on symmetry breaking, suggest the possibility that local physical laws evolve on cosmic scales.

In part a review of the state of the field at the time, but Bondi also clearly formulates challenges regarding the contrast between laws and initial conditions in cosmology.  These challenges would subsequently motivate his formulation of the steady state theory.

Ellis explores how the uniqueness of the universe creates specific challenges for understanding the relation between data and models in cosmology, validating and verifying models, and accounting for their explanatory role.

Kragh argues that although cosmology is clearly a nomological science, there are many aspects that are clearly historical in nature, akin to archaeology or geochemistry. The article briefly traces the historical development of isotopic measurements through to Gamow’s groundbreaking work on big bang nucleosynthesis. Kragh argues that this is an example of nuclear archaeology, showing how the abundances and distribution of elements in the Universe undermined the Steady State model.

Why do the expanding universe models work as well as they do? McCrea argues that dynamical processes after the big bang lead to a uniform universe (well described by these models), and that successful inferences of this type count as a valid response to the problem of uniqueness.

Munitz discusses why the scientific methodology of cosmology must be re-thought in light of the uniqueness of its object. If a law expresses the common features that can be found among a variety of instances of some phenomenon, then the uniqueness of the universe seriously challenges the idea that the aim of a scientific theory is to discover laws and to use them to explain and predict.

Philosophical discussion of how to formulate the common assumption that physical laws express regularities evident in subsystems of the universe, while acknowledging that these subsystems are all parts of the universe.

This book features separate arguments by each author, who together advocate for a strikingly new, and controversial, approach to cosmology, based on:  (i) the uniqueness of the universe, (ii) the reality of time, taken to imply that the laws of physics evolve, and (iii) anti-Platonism with regard to mathematics, and its consequences regarding applicability of mathematics.

Toulmin argues that many of the debates in cosmology have analogs in the debates that occurred in the early development of geology. He shows, for example, that the various attempts to both justify and undermine the assumption of homogeneity and isotropy in cosmology have strikingly similar character to the debates in the 19th century concerning the proper formulation and interpretation of the principle of uniformitarianism.

Interesting discussion between Bondi and Whitrow on the nature of cosmology, prompted by Whitrow’s BBC review of Bondi’s book.  Reflects the mid-century debate between the big bang and steady state theories, but also touches on many more general methodological questions.

A detailed account of the cosmological parameters determined or constrained by the Planck 2018 measurements of cosmic microwave background anisotropies. The Hubble constant is inferred from this data assuming ΛCDM cosmology. Significantly, this paper highlights a 3.6σ tension with local measurements of the Hubble constant, with the local measurements preferring a higher value.

In an effort to resolve the increasingly significant discrepancy between local measurements of the Hubble constant and the global value inferred from the cosmic microwave background and ΛCDM, this paper proposes changes to the ΛCDM model. They allow for separate variations of late or early time cosmology, and develop a model-independent reconstruction of late time expansion history. Studying how these changes would alter directly measured quantities, the authors place constraints on possible deviations from ΛCDM at early times.

This paper presents a new local method for measuring the Hubble constant, based on a calibration of the tip of the red giant branch, applied to Type Ia supernovae. The new measured value splits the difference between the Planck-inferred value and previous local measurements, falling within 1.2σ of the former and 1.7σ of the latter. The authors argue that calibrating via the tip of the giant red branch leads to more accurate local measurements, indicating that the Hubble constant discrepancy may disappear after all.

The standard for local determinations of the Hubble constant, this paper details the use of Cepheid distance calibration for Type Ia supernovae. Makes a case that the older Planck CMB-inferred value of H₀ may contain systematic errors, since the deviation is more significant there than with the WMAP combined data. However, further CMB measurements have only increased the significance of the discrepancy.

Bertone and Hooper provide a broad historical perspective on the problematic observations and the theoretical arguments that led to accepting the dark matter model. They also review the possible candidates for dark matter particles, and the challenges that the dark matter model currently faces. This paper constitutes an excellent introduction to the topic.

This classic overview of the evidence for the dark matter model, that includes a presentation of its rival MOND, constitutes a nice complement to the paper by Bertone and Hooper, especially for philosophers with no-background in physics.

This paper introduces the term ‘dark matter’ for the first time to refer to the possible unseen matter that could explain the discrepancy between the observed mass and the predicted mass within the Coma Cluster. This paper also pioneers the application of the Virial Theorem to calculate the mass of celestial objects.

This paper is a complement to the one above, and provides a thorough critical analysis of the implicit assumptions required to apply the Virial Theorem.

Rubin et al. use the recently developed 21cm technique to measure the orbital velocity of galaxies. They observed that the rotational velocity of the set of galaxies they studied did not decline beyond the radial distance, as expected if most mass is contained within this distance. Their results suggest that galaxies rotate faster than what their observed mass accounts for and constitute a second source of evidence for dark matter.

This paper provides a third line of evidence for missing matter, based on N-body simulations. Simulations seemed to indicate that disk galaxies are very unstable systems, in contradiction with the observations of galaxies with circular orbits. This problem was later solved in Ostriker and Peebles, 1973 by the introduction of additional matter in the form of a dark matter halo.

This paper marks the birth of the dark matter halos model. Ostriker and Peebles suggest that galaxies are embedded in a dark spheroidal halo, whose gravitational effect would explain both the dynamical anomalies observed and the numerical instability of disk galaxies.

This very accessible paper does a good job at showing where MOND does better than ΛCDM, and the challenges it faces.

This paper constitutes a great starting point for those interested in the question of how quantum fluctuations in the early universe provide the seeds for galaxies, thereby constraining the nature and properties of dark matter. It also emphasizes the crucial role of simulations in contrasting the distribution and growth of cosmic structure for hot, warm and cold dark matter.

A recollection by Peebles of how he came to introduce the CDM model, a model where the mass of the universe is dominated by weakly interacting but massive particles, as a way to account for the anisotropies observed in the cosmic background microwave. This paper is a very nice complement to Frenk and White 2012 on how the CMB constrains the ΛCDM model.

This short paper provides a good summary of how unevenly well the ΛCDM model fares when contrasting the large, the medium and the small scales.

This article insists on the institutional changes, i.e., putting together physics and astronomy, that were needed in the field of cosmology to turn problematic observations into evidence for dark matter. In particular, it emphasizes how the quest for extra matter that could close the Universe – i.e., compensate its expansion rate – played a crucial role in reuniting the two lines of arguments for missing matter coming from rotation curves and galaxies clusters.

The author argues that dark matter detection through gravitational lensing should not be used as a test of General Relativity. Since dark matter can only be detected through its gravitational effects, then its detection requires a theory of gravity. Thus, discrepancies between observed and predicted mass of galaxies can be interpreted either as evidence of missing matter or as evidence that we need to revise our theory of gravity.

The last two papers pursue the line opened by Vanderburgh on whether dark matter can be detected independently of general relativity. Kosso argues that the complete theory of general relativity is not needed for gravitational lensing, but only an assumption shared by all rivals: Einstein’s Equivalence Principle (EEP). In contrast, Sus argues against the sufficiency of the EEP.

This paper presents a review of the evidence for MOND and for dark matter and raises interesting philosophical questions about their relationship: if one model is impossible from the perspective of the other, but both models are needed in order to account for cosmological evidence and galaxy dynamics, how can scientists come up with a hybrid solution?

A review article that presents the shift from the “naturalness” to the “no stone left unturned” guiding principles underlying the search for dark matter candidates. This paper also suggests possible ways of diversifying the experimental search, notably by listing problematic astronomical observations that could be used to probe the ΛCDM model.

This paper provides an argument against taking the cosmological constant problem in cosmology as a serious problem. Bianchi and Rovelli argue that an additional constant multiple of the metric—the cosmological constant—arises naturally in the Einstein-Hilbert action for general relativity. Further, they clear up common misconceptions amongst physicists that they think contribute to an unreasonable focus on the cosmological constant problem.

A response to debates regarding the necessity of including dark energy in the standard model of cosmology to make sense of the supernovae redshift. Inhomogeneities are defined as deviations in the spatial average of gravitational properties of the actual spacetime from the assumed homogeneous properties. This nonperturbative treatment suggests that backreaction effects can be large, and might possibly account for accelerated expansion.

Provides an overview of work attempting to show that dark energy can be “explained away” by taking into account the back-reaction effects of small scale inhomogeneities on smoothed-over cosmological models of the universe. Ellis argues that new physics is not needed to explain accelerated expansion in the standard model of cosmology. The article is accessible to a broad audience, and references therein provide more detail for the interested reader.

This paper provides a heuristic discussion of Green and Wald’s previous theorems that prove that no small scale matter inhomogeneities can provide important backreaction effects in cosmology, provided that the energy density of the matter is positive in all frames. This is in relation to the Buchert et al. paper listed above. Their formalism assumes that backreaction effects would contribute a small tensorial correction to the Einstein field equations, in contrast to Buchert et al.

Explicates the steps required to formulate the cosmological constant problem, starting from quantum field theory and working up to coupling to the Einstein field equations in a semiclassical way. At each step, Koberinski argues that the step is not justified. The conclusion is that any solution will end up being a dissolutionof the problem.

A self-contained, highly comprehensive overview of the cosmological constant problem. Martin provides a pedagogical discussion of the problem, aimed at graduate level physics students. The paper discusses “classical” and “quantum” cosmological constant problems, and provides detailed calculations demonstrating the contributions to vacuum energy density from all types of quantum fields, using a dimensional regularization scheme. Evidence is reviewed for the presence of dark energy from within cosmology, as well as for vacuum energy in quantum theory.

A physics review article categorizing different approaches to understanding and solving the cosmological constant problem. Nobbenhuis breaks down the numerous approaches into five major categories: fine-tuning, symmetry principles, back-reaction mechanisms, violation of the equivalence principle, and statistical solutions.

This is the first systematic philosophical treatment of the cosmological constant problem. Rugh and Zinkernagel present the history of the cosmological constant problem, the various conceptual concerns about vacuum physics, and problems with merging quantum field theory and general relativity. The paper is written for a philosophy of physics audience, so greater attention is paid to issues that philosophers will find salient.

One of the first philosophical papers addressing issues of vacuum energy in quantum field theory and their relevance for the cosmological constant problem. Saunders argues that the vacuum energy in quantum field theory is a conceptual remnant that will be removed with more foundational work on quantum field theory. Saunders also examines the some of the barriers to doing away with vacuum energy.

Schneider argues that the cosmological constant problem is not, strictly speaking, a problem that falls within any of our current physical theories; rather, it is a problem within some future theory of quantum gravity. The role that the cosmological constant problem plays in contemporary physics is to make explicit the commitments from particle physics and general relativity that one thinks will be relevant for a correct theory of quantum gravity.

Spawned from focus on expansion energy from inflation—supposed to be contained in the potential of a scalar quantum field—physicists began to worry about the vacuum energy associated with all quantum fields, resulting in the cosmological constant problem. This review is often cited as the classic review on the supposed “crisis” of the cosmological constant problem and is an important read for anyone interested in the topic.