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The Cosmological Pinciples 1 The Cosmological Principles by Konrad Rudnicki A Southern Cross Review E-book www.SouthernCrossReview.org 2 Foreword Cosmology deals with the whole universe, both observable and unobservable, while astronomy deals with the observable part. Cosmological principles are the assumptions which allow us to deduce the nature of the whole on the basis of the observable. Not surprisingly, any study of cosmological principles must combine elements of astronomy, physics, and philosophy. Therein lies not only a fascinating challenge but also a problem for the author of a book on this subject. For astronomers usually do not know philosophy very well; physicists often do not know much of astronomy and philosophy, and most philosophers are not adept in astronomy and physics. In writing a book to be read by all three groups of scholars - as well as by serious amateurs in these fields - I have attempted to avoid mathematical formulae and sophisticated terms. Instead, I have referred to original papers and professional books when appropriate. I presume the reader to be familiar with at least one of these three areas and to be acquainted with at least the basic facts and notions from the others. A book about the development of the human approach to so basic a scientific and philosophical problem as the structure of the Universe has to deal with yet another domain of human knowledge: the history of science. History is not the subject of this book, so I have taken the liberty to simplify, even to schematize, my account of various historical epochs and the outlooks of various scholars and philosophers. I beg my historian colleagues to pardon me for all these simplifications which were necessary to prevent the book from growing too large. It was not my primary intent to write a popular book on science, but I will be glad if it turns out that for the most part it can be also read and comprehended by amateurs of astronomy, physics, or philosophy. I completed the manuscript at my home in Cracow, but the main conceptual work was done earlier, in 1988/89, during my sabbatical year at the Department of Space Physics and Astronomy of Rice University in Houston, Texas. I owe cordial thanks to the people who invited me and made my stay there possible, particularly to Professor Alexander Dessler and to the late Professor Konstantin Kolenda, as well as to my son Anthony and his wife María. Furthermore, I am indebted to Rev. Professor Michael Heller for his systematic reading of the text and for his valuable comments. My friends Marek Krosniak and Andrea Karpoff have corrected my English and contributed greatly to its readability. Clopper Almon assisted on the American end of invaluable email communication between America and Poland. During my visit to Tucson, Arizona in 1989, I discussed some philosophical matters with Professor Andrzej Pacholczyk; this conversation was an important turning point in my work. It was he who drew my attention to the fact that there was no book devoted specifically to the issue of cosmological principles. Thus, instead of taking up some particular problems in the form of contributions to professional journals, I made up my mind to prepare such a book. I am aware that this is but a first attempt to discuss in depth this rather peculiar field of human activity. Future authors will surely find many ways to improve on it. Cracow, October 1992 Konrad Rudnicki 3 About the author Konrad Rudnicki is professor of astronomy at the Jagiellonian University in Poland. He was formally director on the University Observatory in Cracow. He is a member-participant of the Free European Academy of Science (Holland), member of the Commission of Galaxies of the International Astronomical Union and member of the Mathematical-Astronomical Section at the Goetheanum (Switzerland). Prof. Rudnicki has been Senior Research Fellow at the California Institute of Technology (1965-1967), visiting professor at Rice Institute (USA). The areas of his interest are: extragalactic astronomy, cosmology, philosophy of science and the methodology of science. “The Cosmological Principles” was originally published in a print edition by the Jagiellonian University in 1995. (ISBN 83-233-0898-5) It was also serialized in SouthernCrossReview.org. © Konrad Rudnicki 4 Introduction 0.01. Astronomy and cosmology Cosmology is a science concerned with the Universe as a whole, while astronomy deals with celestial bodies, their systems and all related phenomena. If the entire Universe were observable, cosmology could be considered as just the most general section of astronomy. But it may well be that the entire Universe is not observable. If so, then we may well ask if its possible to extrapolate from the observable to the unobservable. Simple philosophical statements that make it possible to make this step are called cosmological principles and are the subject of this book. There are cosmological theories and even strict mathematical models, so- called small universe models (Dyer 1987, Ellis 1987a), which represent the Universe as fully accessible to our observations. But most cosmologists and astronomers do not believe in their validity. Moreover, they would be rather difficult to verify and do not belong to the mainstream of contemporary cosmology. Were it to be proved at some future time that the Universe is ultimately observable, then this book will lose its point. But as long as this is not the case, the profound question of bringing the unobservable parts of the Universe under investigation remains a central problem in contemporary cosmology. While the ancient thinkers believed in the existence of non-observable parts of our universe consisting of imponderable, sublime, and invisible matter, according to most contemporary astronomers and cosmologists there is a surface called the "cosmological horizon." No physical signal, no information can reach us from beyond this horizon. Thus there are two possibilities. One is to consider cosmology as not belonging to the exact sciences but rather as a domain of metaphysics1. One can say: it is not a task of any experimental or observational science to form statements about the Universe in general, i.e. referring also to its parts that cannot be observed. After all, the unobservable belongs to the domain of metaphysics1. But again it might be said that any exact science involves statements that are not directly related to observations. In mathematics, for example, no geometrical figure can be seen or measured by physical devices. All that can be constructed in the physical world can be but a representation of mathematical entities; yet mathematical reality in itself can be accessed only through our minds. The laws of physics as such are also not observable; only their consequences can be observed. Should this mean that they belong to the realm of metaphysics? Accordingly, nobody has any right to demand that everything has to be observable in cosmology. In that domain also, the human mind can supplement what cannot be accessed by sensory perception or physical instruments. Sometimes cosmology, along with its cosmological principles, is considered to be not metaphysics but metascience (e.g. Kaz-yutinskiy 1981), which 5 amounts to the same thing but sounds better. The above considerations are based on a specific concept of the Universe, which will be explicitly explained and used further in this book. But this understanding is not the only one possible. For one, George W. Collins II (1988) defines the Universe in following way 'The Universe is all what was, is, and will be accessible to observation". In such a sense only those regions situated beyond the horizon belong to the Universe which in future (or past) cosmological epochs will (did) cross the horizon surface and enter (leave) "the observable part of the Universe." Another plausible concept of the Universe, exploiting the difference between the notions "Universe" and "Cosmos" is brought up in Section 6.12. The problem consists in how to augment the existing body of evidence about the observable parts of the Universe so as to encompass its unobservable parts too. One possible way of doing this, perhaps the simplest one, consists in extrapolating the avail-able results of astronomy to the whole of the Universe. As we have noted, simple philosophical statements instrumental in accomplishing such an extrapolation are now called cosmological principles General propositions stating the impossibility of such an extrapolation should also be included among cosmological principles, if they include some idea about the overall structure of the Universe. 0.02. Philosophy, physics, astronomy and cosmology Cosmology, if we do accept it as a science and not as metaphysics, is a discipline standing right at the meeting point of three areas of human knowledge: astronomy, theoretical physics, and philosophy. All the three are of equal significance for cosmology. Astronomy determines which kind of celestial bodies or their aggregates are the "building stones," basic elements in the construction of the Universe. Theoretical physics shows us what laws govern or may govern in various parts of the Universe and in various times past, contemporary, and future. Philosophy (particularly the branch called methodology of science or theory of knowledge) instructs us how to use our mental capacity to grasp the entire Universe, even though we do observe just a part of it and can experiment only within a very limited range of conditions, the Earth and its immediate environment (not possibly further than within in the Solar system). 0.03. Philosophy in cosmology The role of philosophy in cosmology is sometimes underestimated. It is said that the impact of an overall manner of thinking, specific individual philosophy, is to be found in every science. This causes the same data to be interpreted quite differently by various researchers according to their respective world views.
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