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Cormac O'Raifeartaigh

Publications and source records attributed to Cormac O'Raifeartaigh.

14 recordsLinked to original sources
arXiv2022

Einstein's Oxford Blackboard: A Unique Historical Artefact

Einstein's blackboard is a well-known exhibit at the History of Science Museum at Oxford University. However, it is much less well known that the writing on the board provides a neat summary of a work of historic importance, Einstein's 1931 model of the expanding universe. As a visual representation of one of the earliest models of the universe to be proposed in the wake of Hubble's observations of the nebulae, the blackboard provides an intriguing snapshot of a key moment in modern astronomy and cosmology. In addition, one line on the blackboard that is not in Einstein's 1931 paper casts useful light on some anomalies in the calculations of that paper.

physics.hist-ph↗
arXiv2022

Testing General Relativity on the Largest Scales in the Years 1915-1955: the Dawning of Modern Cosmology

Soon after he proposed three classic observational tests for the general theory of relativity, Einstein realised that a consistent description of the universe as a whole provided another important challenge for the theory. In this essay, we recall how general relativity found important application in the nascent field of cosmology, from the static models of Einstein and de Sitter to the expanding cosmologies of Friedmann and Lemaitre. By the early 1930s, the first tentative astronomical evidence of cosmic expansion had trigged a paradigm shift to dynamic cosmologies, almost all of which were couched firmly within the framework of general relativity. However, further progress was impeded for some years by a paucity of observational data. In the 1950s, the debate between steady-state and big bang models of the universe provided a new stimulus for the quest to determine key parameters of relativistic models of the cosmos by astronomical observation, setting the stage for today's precision cosmology.

physics.hist-ph↗
arXiv2021

Historical and philosophical reflections on the Einstein-de Sitter model

We present some historical and philosophical reflections on the paper "On the Relation Between the Expansion and the Mean Density of the Universe", published by Albert Einstein and Willem de Sitter in 1932. In this famous work, Einstein and de Sitter considered a relativistic model of the expanding universe with both the cosmological constant and the curvature of space set to zero. Although the Einstein-deSitter model went on to serve as a standard model in 'big bang' cosmology for many years, we note that the authors do not explicitly consider the evolution of the cosmos in the paper. Indeed, the mathematics of the article are quite puzzling to modern eyes. We consider claims that the paper was neither original nor important; we find that, by providing the first specific analysis of the case of a dynamic cosmology without a cosmological constant or spatial curvature, the authors delivered a unique, simple model with a straightforward relation between cosmic expansion and the mean density of matter that set an important benchmark for both theorists and observers. We consider some philosophical aspects of the model and provide a brief review of its use as a prototype 'big bang' model over much of the 20th century.

physics.hist-ph↗
arXiv2020

Redshifts versus paradigm shifts; against renaming Hubble's Law

We consider the proposal by many scholars and by the International Astronomical Union to rename Hubble's law as the Hubble-Lemaitre law. We find the renaming questionable on historic, scientific and philosophical grounds. From a historical perspective, we argue that the renaming presents an anachronistic interpretation of a law originally understood as an empirical relation between two observables. From a scientific perspective, we argue that the renaming conflates the redshift/distance relation of the spiral nebulae with a universal law of spatial expansion derived from the general theory of relativity. We note that the first of these phenomena is merely one manifestation of the second, an important distinction that may be relevant to contemporary puzzles concerning the current rate of cosmic expansion. From a philosophical perspective, we note that many of the named laws of science are empirical relations between observables, limited in range, rather than laws of universal application derived from theory.

physics.hist-ph↗
arXiv2020

Eddington, Lemaitre and the hypothesis of cosmic expansion

Arthur Stanley Eddington was one of the leading astronomers and theorists of his generation and a prominent proponent of the general theory of relativity. Yet when his former assistant Georges Lemaitre sent him a paper in 1927 suggesting that the well-known redshifts of the spiral nebulae might be a manifestation of a cosmic expansion predicted by relativity, Eddington paid no attention for three years. In this paper, we consider the reasons for this oversight. We find that conventional explanations (such as Lemaitre's status as a relatively junior researcher and his decision to publish in a lesser-known Belgian journal) do not convince. We propose an alternative explanation that has not been considered in the literature - namely that the observational data cited by Lemaitre in support of his model were of a preliminary nature and would not have been sufficiently convincing for Eddington and others to consider non-static cosmologies.

physics.hist-ph↗
arXiv2019

Historical and Philosophical Aspects of the Einstein World

This article presents a brief review of some historical and philosophical aspects of Einstein's 1917 paper 'Cosmological Considerations in the General Theory of Relativity', a landmark work that denoted the starting point of modern theoretical cosmology. Our presentation includes a discussion of Einstein's early views of issues such as the relativity of inertia, the curvature of space and the cosmological constant. Particular attention is paid to lesser-known aspects of Einstein's paper such as his failure to test his model against observation, his failure to consider the stability of the model and a slight mathematical confusion concerning the introduction of the cosmological constant term. Taken in conjunction with his later cosmological works, we find that Einstein's approach to cosmology was characterized by a pragmatic search for the simplest model of the universe that was consistent with the principles of relativity and with contemporaneous astronomical observation.

physics.hist-ph↗
arXiv2019

Interrogating the legend of Einstein's "Biggest Blunder"

It is well known that, following the emergence of the first evidence for an expanding universe, Albert Einstein banished the cosmological constant term from his cosmology. Indeed, he is reputed to have labelled the term, originally introduced to the field equations of general relativity in 1917 in order to predict a static universe, his "biggest blunder". However serious doubts about this reported statement have been raised in recent years. In this paper, we interrogate the legend of Einstein's "biggest blunder" statement in the context of our recent studies of Einstein's cosmology in his later years. We find that the remark is highly compatible with Einstein's cosmic models of the 1930s, with his later writings on cosmology, and with independent reports by at least three physicists. We conclude that there is little doubt that Einstein came to view the introduction of the cosmological constant term a serious error and that it is very likely that he labelled the term his "biggest blunder" on at least one occasion. This finding may be of some relevance for those theoreticians today who seek to describe the recently-discovered acceleration in cosmic expansion without the use of a cosmological constant term.

physics.hist-ph↗
arXiv2017

One Hundred Years of the Cosmological Constant: from 'Superfluous Stunt' to Dark Energy

We present a centennial review of the history of the term known as the cosmological constant. First introduced to the general theory of relativity by Einstein in 1917 in order to describe a universe that was assumed to be static, the term fell from favour in the wake of the discovery of the expanding universe, only to make a dramatic return in recent times. We consider historical and philosophical aspects of the cosmological constant over four main epochs: (i) the use of the term in static cosmologies (both Newtonian and relativistic); (ii) the marginalization of the term following the discovery of cosmic expansion; (iii) the use of the term to address specific cosmic puzzles such as the timespan of expansion, the formation of galaxies and the redshifts of the quasars; (iv) the re-emergence of the term in today's Lamda-CDM cosmology. We find that the cosmological constant was never truly banished from theoretical models of the universe, but was sidelined by astronomers for reasons of convenience. We also find that the return of the term to the forefront of modern cosmology did not occur as an abrupt paradigm shift due to one particular set of observations, but as the result of a number of empirical advances such as the measurement of present cosmic expansion using the Hubble Space Telescope, the measurement of past expansion using type SN 1a supernovae as standard candles, and the measurement of perturbations in the cosmic microwave background by balloon and satellite. We give a brief overview of contemporary interpretations of the physics underlying the cosmic constant and conclude with a synopsis of the famous cosmological constant problem.

physics.hist-ph↗
arXiv2017

Einstein's 1917 Static Model of the Universe: A Centennial Review

We present a historical review of Einstein's 1917 paper 'Cosmological Considerations in the General Theory of Relativity' to mark the centenary of a key work that set the foundations of modern cosmology. We find that the paper followed as a natural next step after Einstein's development of the general theory of relativity and that the work offers many insights into his thoughts on relativity, astronomy and cosmology. Our review includes a description of the observational and theoretical background to the paper; a paragraph-by-paragraph guided tour of the work; a discussion of Einstein's views of issues such as the relativity of inertia, the curvature of space and the cosmological constant. Particular attention is paid to little-known aspects of the paper such as Einstein's failure to test his model against observation, his failure to consider the stability of the model and a mathematical oversight concerning his interpretation of the role of the cosmological constant. We recall the response of theorists and astronomers to Einstein's cosmology in the context of the alternate models of the universe proposed by Willem de Sitter, Alexander Friedman and Georges Lemaitre. Finally, we describe the relevance of the Einstein World in today's 'emergent' cosmologies.

physics.hist-ph↗
arXiv2015

A new perspective on steady-state cosmology: from Einstein to Hoyle

We recently reported the discovery of an unpublished manuscript by Albert Einstein in which he attempted a 'steady-state' model of the universe, i.e., a cosmic model in which the expanding universe remains essentially unchanged due to a continuous formation of matter from empty space. The manuscript was apparently written in early 1931, many years before the steady-state models of Fred Hoyle, Hermann Bondi and Thomas Gold. We compare Einstein's steady-state cosmology with that of Hoyle, Bondi and Gold and consider the reasons Einstein abandoned his model. The relevance of steady-state models for today's cosmology is briefly reviewed.

physics.hist-ph↗
arXiv2015

Einstein's cosmology review of 1933: a new perspective on the Einstein-de Sitter model of the cosmos

We present a first English translation and analysis of a little-known review of relativistic cosmology written by Albert Einstein in late 1932. The article, which was published in 1933 in a book of Einstein papers translated into French, contains a substantial review of static and dynamic relativistic models of the cosmos, culminating in a discussion of the Einstein-de Sitter model. The article offers a valuable contemporaneous insight into Einstein's cosmology in the 1930s and confirms that his interest lay in the development of the simplest model of the cosmos that could account for observation, rather than an exploration of all possible cosmic models. The article also confirms that Einstein did not believe that simplistic relativistic models could give an accurate description of the early universe.

physics.hist-ph↗
arXiv2014

Einstein's steady-state theory: an abandoned model of the cosmos

We present a translation and analysis of an unpublished manuscript by Albert Einstein in which he attempted to construct a 'steady-state' model of the universe. The manuscript, which appears to have been written in early 1931, demonstrates that Einstein once explored a cosmic model in which the mean density of matter in an expanding universe is maintained constant by the continuous formation of matter from empty space. This model is very different to previously known Einsteinian models of the cosmos (both static and dynamic) but anticipates the later steady-state cosmology of Hoyle, Bondi and Gold in some ways. We find that Einstein's steady-state model contains a fundamental flaw and suggest that it was abandoned for this reason. We also suggest that he declined to explore a more sophisticated version because he found such theories rather contrived. The manuscript is of historical interest because it reveals that Einstein debated between steady-state and evolving models of the cosmos decades before a similar debate took place in the cosmological community.

physics.hist-ph↗
arXiv2013

The contribution of VM Slipher to the discovery of the expanding universe

A brief history of the discovery of the expanding universe is presented, with an emphasis on the seminal contribution of VM Slipher. It is suggested that the well-known Hubble graph of 1929 could also be known as the Hubble-Slipher graph. It is also argued that the discovery of the expanding universe matches the traditional view of scientific advance as a gradual process of discovery and acceptance, and does not concur with the Kuhnian view of science progressing via abrupt paradigm shifts.

physics.hist-ph↗