Philosophical Questions

Cosmology considers the problem of the universe taken as a whole and ponders questions such as the origin of the world and its evolution in time. The logical and basic nature of cosmology means that philosophical questions arise here more than they tend to do in other branches of physical science. It is common to distinguish in science between fundamental laws, such as the law of gravity or the law of valences, and laws that apply to special systems or objects, such as Kepler's law of planetary orbits or the principle of natural selection in biology. Hubble's law combines characteristics of both types of law. It concerns the particular configuration of gravitating matter as it happens to exist in nature. On the other hand, because it describes the universe as a whole, it is about everything that ever was and ever will be.

The cosmological principle provides an example of how philosophical views have influenced scientific theorizing about the universe. The adoption of the principle by Einstein and Milne was based on what appeared to be a reasonable a priori assumption about the relationship of the observer to the universe at large. It turned out that geometric world-building starting with the principle conformed with the exciting discoveries in extragalactic astronomy. By extending the principle to include time as well as space, the steady state theorists obtained the perfect cosmological principle and cited philosophical reasons in support of it. Philosophical issues have also arisen in attempts to justify the general theory of relativity as the necessary framework to describe the universe.

A different sort of question has been raised by the philosopher Ian Hacking (1989) and concerns the essentially passive character of extragalactic astronomy. Hacking has staked out a position in the philosophy of science according to which a theoretical entity in physics is said to be real if it is possible to manipulate this entity in some way. Although electrons and other subatomic particles are not directly observable in the same sense as are macroscopic entities such as colliding balls, electrical sparks, or glowing gases, they are nonetheless just as real because we are able to interfere with them: to eject them from instruments, to change their path by means of magnetic fields, or to accelerate them in particle accelerators. Not even in the boldest visions of science fiction does there seem any prospect of interacting actively with the objects located in the universe beyond our galaxy. The study of the distant universe is destined to be a passive science, and for this reason—according to Hacking—extragalactic objects are deprived of an essential characteristic of what it means for something to be real to us.

The philosophical doctrine advanced by Hacking is related to the more general point concerning the irrelevance of extragalactic astronomy to our daily lives. Concerns about the value of the new science of astrophysics were already raised in the nineteenth century by the pioneer of stellar spectroscopy, William Huggins: "The new astronomy, unlike the old astronomy to which we are indebted for skill in the navigation of the seas, the calculation of the tides, and the daily regulation of the time, can lay no claim to afford us material help in the routine of daily life" (Meadows 1984, 70). More recently, commentators such as journalist John Horgan (1996) have cast a skeptical eye at discussions of the early universe, suggesting that they are part of what he calls "ironic science," science that is subject to multiple interpretations. Entities postulated in cosmology such as monopoles or dark energy are more tentative and theoretical than researchers would sometimes lead one to believe. This conclusion is related to the contrast between the highly technical and specialized character of professional research in cosmology and the descriptive and unrigorous character of popular expositions of the subject.

There is no doubt that large parts of cosmology are bound to remain theoretical. Speculations about the inflationary character of the early universe or the creation of small black holes after the big bang will never be subject to direct confirmation. The goal of theoretical work can only be to find a picture of the primordial universe that is plausible and consistent with what is observed to have occurred from the moment that matter decoupled from radiation. It remains the case that the emergence and subsequent verification of big bang cosmology constitutes one of the most substantial and unexpected develop ments of modern science. We can now make scientific statements about the origin and evolution of the whole universe, something that only a century ago would have seemed inconceivable.

A consequence of the revolution of the past century has been that cosmology has become an essentially historical science. In order to understand the universe as we see it today, it is necessary from observation and theory to reconstruct one singular event, the primordial big bang 13 or 14 billion years ago, and to trace the subsequent evolution of the universe. Final questions traditionally understood to lie within the domain of religion have become part of science. It is worth noting that the father of the big bang theory, the Abbé Lemaître, became a scientific advisor to the Vatican in the later part of his career. In a 1951 address Pope Pius XII cited big bang cosmology in support of the Christian conception of a Creator and the beginning of the world in a creation event. Lemaître himself had reservations about mixing science and religion, believing that matters of religious faith depend in the final analysis on considerations whose validity is independent of the results of science. Modern cosmology has become a kind of secular theology, coming as close as rational investigation ever can to uncovering the ultimate mysteries of the universe.

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