This paper compares four techniques for measuring the masses of galaxies and larger astrophysical systems from their dynamics. The apparent agreement of these techniques is sometimes invoked as reason for hypothesizing the existence of huge quantities of “dark matter” as the best solution to “the dynamical discrepancy”, the 100-fold disparity between the amount of mass visible in large scale astrophysical systems and the amount calculated from dynamics. This paper argues that the agreement, though suggestive, is not definitive. The coincident measurements (...) remain the best reason for preferring dark matter over revisions to General Relativity for solving the dynamical discrepancy, but the resulting warrant for this preference is weak. (shrink)

The dark matter problem in astrophysics exposes an underappreciated weakness in the evidential warrant for General Relativity (GR). The "dark matter double bind" entails that GR gets no differential evidential support from dynamical phenomena occurring at scales larger than our solar system, as compared to members of a significant class of rival gravitation theories. These rivals are each empirically indistinguishable from GR for phenomena taking place at solar system scales, but make predictions that may differ radically from GR's at larger (...) scales. Thus the typical confidence in the universal applicability of GR is insufficiently warranted in the present evidential context. (shrink)

Dark matter is an essential ingredient of the present Standard Cosmological Model, according to which only 5% of the mass/energy content of our universe is made of ordinary matter. In recent times, it has been argued that certain cases of gravitational lensing represent a new type of evidence for the existence of DM. In a recent paper, Peter Kosso attempts to substantiate that claim. His argument is that, although in such cases DM is only detected by its gravitational effects, gravitational (...) lensing is a direct consequence of Einstein's Equivalence Principle and therefore the complete gravitational theory is not needed in order to derive such lensing effects. In this paper I critically examine Kosso's argument: I confront the notion of empirical evidence involved in the discussion and argue that EEP does not have enough power by itself to sustain the claim that gravitational lensing in the Bullet Cluster constitutes evidence for the DM Hypothesis. As a consequence of this, it is necessary to examine the details of alternative theories of gravity to decide whether certain empirical situations are indeed evidence for the existence of DM. It may well be correct that gravitational lensing does constitute evidence for the DM Hypothesis—at present it is controversial whether the proposed modifications of gravitation all need DM to account for the phenomenon of gravitational lensing and if so, of which kind—but this will not be a direct consequence of EEP. (shrink)

We review some recent developments in the conformal gravity theory that has been advanced as a candidate alternative to standard Einstein gravity. As a quantum theory the conformal theory is both renormalizable and unitary, with unitarity being obtained because the theory is a PT symmetric rather than a Hermitian theory. We show that in the theory there can be no a priori classical curvature, with all curvature having to result from quantization. In the conformal theory gravity requires no independent quantization (...) of its own, with it being quantized solely by virtue of its being coupled to a quantized matter source. Moreover, because it is this very coupling that fixes the strength of the gravitational field commutators, the gravity sector zero-point energy density and pressure fluctuations are then able to identically cancel the zero-point fluctuations associated with the matter sector. In addition, we show that when the conformal symmetry is spontaneously broken, the zero-point structure automatically readjusts so as to identically cancel the cosmological constant term that dynamical mass generation induces. We show that the macroscopic classical theory that results from the quantum conformal theory incorporates global physics effects that provide for a detailed accounting of a comprehensive set of 138 galactic rotation curves with no adjustable parameters other than the galactic mass to light ratios, and with the need for no dark matter whatsoever. With these global effects eliminating the need for dark matter, we see that invoking dark matter in galaxies could potentially be nothing more than an attempt to describe global physics effects in purely local galactic terms. Finally, we review some recent work by ’t Hooft in which a connection between conformal gravity and Einstein gravity has been found. (shrink)

I review some theoretical ideas in cosmology different from the standard “Big Bang”: the quasi-steady state model, the plasma cosmology model, non-cosmological redshifts, alternatives to non-baryonic dark matter and/or dark energy, and others. Cosmologists do not usually work within the framework of alternative cosmologies because they feel that these are not at present as competitive as the standard model. Certainly, they are not so developed, and they are not so developed because cosmologists do not work on them. It is a (...) vicious circle. The fact that most cosmologists do not pay them any attention and only dedicate their research time to the standard model is to a great extent due to a sociological phenomenon . We might well wonder whether cosmology, our knowledge of the Universe as a whole, is a science like other fields of physics or a predominant ideology. (shrink)

We review the observational foundations of the ΛCDMΛCDM model, considered by most cosmologists as the standard model of cosmology. The Cosmological Principle, a key assumption of the model is shown to be verified with increasing accuracy. The fact that the Universe seems to have expanded from a hot and dense past is supported by many independent probes . The explosion of detailed observations in the last few decades has allowed for precise measurements of the cosmological parameters within Friedman–Lemaître–Robertson–Walker cosmologies leading (...) to the ΛCDMΛCDM model: an apparently flat Universe, dominated by a cosmological constant, whose matter component is dominantly dark. We describe and discuss the various observational probes that led to this conclusion and conclude that the ΛCDMΛCDM model, although leaving a number of open questions concerning the deep nature of the constituents of the Universe, provides the best theoretical framework to explain the observations. (shrink)

Analytical reflections on tasks and functions of philosophy in the modern world, as well as, efforts deriving novel vision of practically all areas of the philosophical thought may become sound only after consideration of the innovations with which modern natural science has crossed the 20—21 centuries boundary. Discoveries in astrophysics at the end of the 20th century offer new and unprecedented perceptions of our world. In this world only 4% of the total Universe energy is attributed to the known forms (...) of the matter, 20% constitutes “dark matter” and 76% is in “dark energy”. The first decade of the 21st century will go on record inhistory of the civilization as the one associated with breakthrough experiments shedding light on the nature of the mysterious types of the matter, and construction of the unified theory of field. It is safe to regard modern science to be on the verge of profound transformations. These changes are bound to alter our outside world comprehension, redefining human being’s place in it. That advances a set of new serious requirements to philosophy as a science that must present ability to adapt to provide adequate and meaningful methodological interpretations to anticipated discoveries. This article addresses the characteristic features of modern conceptual knowledge of the world, with an attempt of offering their philosophical and methodological comprehension. (shrink)