Cosmology is the study of the cosmos, as well as the study of the origin, evolution, and eventual fate of the universe. All cosmologies have in common an attempt to understand the implicit order within the whole of being. In this way, most religions and philosophical systems have a cosmology.
Physical cosmology is the scholarly and scientific study of the origin, evolution, large-scale structures and dynamics, and ultimate fate of the universe, as well as the scientific laws that govern these realities. Religious cosmology (or mythological cosmology) is a body of beliefs based on the historical, mythological, religious, and literature and traditions of creation and eschatology.
Physical cosmology is studied by scientists, such as astronomers and theoretical physicists; and academic philosophers, such as metaphysicians, philosophers of physics and philosophers of space and time. Modern cosmology is dominated by the Big Bang theory, which attempts to bring together observational astronomy and particle physics
Although the word cosmology is recent, the study of the universe has a long history involving science, philosophy, esotericism and religion. Related studies include cosmogony, which focuses on the origin of the Universe, and cosmography, which maps the features of the Universe. Cosmology is also connected to astronomy, but while the former is concerned with the Universe as a whole, the latter deals with individual celestial objects.
Physics and astrophysics have played a central role in shaping the understanding of the universe through scientific observation and experiment. What is known as physical cosmology has been shaped through both mathematics and observation in an analysis of the whole universe. The universe is generally understood to have begun with the Big Bang, followed almost instantaneously by cosmic inflation; an expansion of space from which the universe is thought to have emerged 13.798 plus or minus 0.037 billion years ago.
Metaphysical cosmology has also been described as the placing of man in the universe in relationship to all other entities. This is exemplified by the observation made by Marcus Aurelius of a man’s place in that relationship: “He who does not know what the world is does not know where he is, and he who does not know for what purpose the world exists, does not know who he is, nor what the world is.”
Physical cosmology is the branch of physics and astrophysics that deals with the study of the physical origins and evolution of the Universe. It also includes the study of the nature of the Universe on its very largest scales. In its earliest form it was what is now known as celestial mechanics, the study of the heavens. The Greek philosophers Aristarchus of Samos, Aristotle and Ptolemy proposed different cosmological theories. In particular, the geocentric Ptolemaic system was the accepted theory to explain the motion of the heavens until Nicolaus Copernicus, and subsequently Johannes Kepler and Galileo Galilei proposed a heliocentric system in the 16th century. This is known as one of the most famous examples of epistemological rupture in physical cosmology.
With Isaac Newton, and the 1687 publication of Principia Mathematica, the problem of the motion of the heavens was finally solved. Newton provided a physical mechanism for Kepler’s laws and his law of universal gravitation allowed the anomalies in previous systems, caused by gravitational interaction between the planets, to be resolved. A fundamental difference between Newton’s cosmology and those preceding it was the Copernican principle that the bodies on earth obey the same physical laws as all the celestial bodies. This was a crucial philosophical advance in physical cosmology.
Modern scientific cosmology is usually considered to have begun in 1917 with Albert Einstein’s publication of his final modification of general relativity in the paper “Cosmological Considerations of the General Theory of Relativity” (although this paper was not widely available outside of Germany until the end of World War I). General relativity prompted cosmogonists explored the astronomical consequences of the theory, which enhanced the growing ability of astronomers to study very distant objects. Prior to this (and for some time afterwards), physicists assumed that the Universe was static and unchanging.
In parallel to this dynamic approach to cosmology, one long-standing debate about the structure of the cosmos was coming to a climax. A Mount Wilson astronomer had championed the model of a cosmos made up of the Milky Way star system only; while there were arguments for the idea that spiral nebulae were star systems in their own right – island universes. This difference of ideas came to a climax with the organization of the Great Debate at the meeting of the (US) National Academy of Sciences in Washington in April 1920. The resolution of this debate came with the detection of novae in the Andromeda galaxy by Edwin Hubble in 1923 and 1924. Their distance established spiral nebulae well beyond the edge of the Milky Way.
Subsequent modelling of the universe explored the possibility that the cosmological constant, introduced by Einstein in his 1917 paper, may result in an expanding universe, depending on its value. Thus the Big Bang model was proposed by the Belgian priest Georges Lemaitre in 1927 which was subsequently corroborated by Edwin Hubble’s discovery of the red shift in 1929 and later by the discovery of the cosmic microwave background radiation in 1964. These findings were a first step to rule out some of many alternative physical cosmologies.
Recent observations made by the COBE and WMAP satellites observing this background radiation have effectively, in many scientists’ eyes, transformed cosmology from a highly speculative science into a predictive science, as these observations matched predictions made by a theory called Cosmic inflation, which is a modification of the standard Big Bang model. This has led many to refer to modern times as the “Golden age of cosmology”.
In March 2014 astronomers at the Harvard-Smithsonian Center for Astrophysics announced the detection of gravitational waves, providing strong evidence for inflation and the Big Bang. However, in June 2014, lowered confidence in confirming the cosmic inflation findings was reported.
However, one should not assume that the current scientific conception of cosmology is correct. Although the general picture has remained the same since the 1920s, the specifics are often revised based on new observations and theories. Most notably in the history of cosmology, in 1964 the cosmic microwave background radiation was detected.
Modern cosmology has accumulated massive evidence, such as the cosmic microwave background radiation, that the universe began with a huge explosion known as the Big Bang. This occurred approximately 13.7 billion years ago. Starting from a singularity with zero volume and tremendous mass, the universe was born. Not only was matter ejected into space, but space itself originated with the Big Bang. Asked on a talk show “what came before the Big Bang”, the legendary physicist Stephen Hawking responded, “What lies north of the North Pole?” indicating that the question was meaningless. However, some physicists consider it likely that our universe is a baby universe of an earlier parent universe.
Our current observable universe is estimated to be about 90 billion light-years in diameter. This is only the observable universe, however, and the entirety of the universe may be much larger, or even infinite. Most physicists working in cosmology also argue that the universe is just one among many, embedded in a larger multiverse.
We find ourselves in a universe capable of sustaining life. Physicists have performed thought experiments where the fundamental physical constants have been modified by tiny increments, and they have concluded that many of these possible sets of physical law would preclude the formation of stable planets or other requirements for life. Rather than suggesting that the universe was fine-tuned by a deity, this indicates that our universe is likely one in a huge ensemble of largely lifeless universes.
Mythological cosmology deals with the world as the totality of space, time and all phenomena. Historically, it has had quite a broad scope, and in many cases was founded in religion. The ancient Greeks did not draw a distinction between this use and their model for the cosmos. However, in modern use it addresses questions about the Universe which are beyond the scope of science. It is distinguished from religious cosmology in that it approaches these questions using philosophical methods. Modern metaphysical cosmology tries to address questions such as:
- What is the origin of the Universe? What is its first cause? Is its existence necessary
- What are the ultimate material components of the Universe?
- What is the ultimate reason for the existence of the Universe? Does the cosmos have a purpose?
- Does the existence of consciousness have a purpose? How do we know what we know about the totality of the cosmos? Does cosmological reasoning reveal metaphysical truths?