Cosmology .:. The Universe
“Cosmology is defined as the branch of philosophy dealing with the origin and general structure of the universe, with it’s parts, elements, laws, and characteristics of space, time, causality, and freedom.”
“The study of the physical universe considered as a totality of phenomena in time and space.
a. The astrophysical study of the history, structure, and constituent dynamics of the universe.
b. A specific theory or model of this structure and these dynamics."
"Physical cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. Cosmology involves itself with studying the motions of the celestial bodies and the first cause. For most of human history, it has been a branch of metaphysics. Cosmology as a science originates with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on earth, and Newtonian mechanics, which first allowed us to understand those motions. This is now called celestial mechanics. Physical cosmology, as it is now understood, began with the twentieth century development of Albert Einstein's theory of general relativity and better astronomical observations of extremely distant objects."
"The twentieth century advances made it possible to speculate about the origins of the universe and allowed scientists to establish the Big Bang as the leading cosmological theory, which most cosmologists now accept as the basis for their theory and observations.(Some people still advocate alternative cosmologies such as the plasma cosmology and steady state theory, although professional cosmologists generally agree that the big bang best explains observations.) Physical cosmology, roughly speaking, deals with the very largest objects in the universe (galaxies, clusters and superclusters), the very earliest distinct objects to form (quasars) and the very early universe, when it was nearly homogeneous (hot big bang, cosmic inflation and the cosmic microwave background radiation)."
"The metric expansion of space is a key part of science's current understanding of the universe, whereby space itself is described by a metric which changes over time. It explains how the universe expands in the Big Bang model, a feature of our universe supported by all cosmological experiments, astrophysics calculations, and measurements to date."
"The expansion of space is conceptually different from other kinds of expansions and explosions that are seen in nature. Our understanding of the "fabric of the universe" (spacetime) requires that what we see normally as "space" and "distance" are not absolutes, but are determined by a metric that can change. In the metric expansion of space, rather than objects in a fixed "space" moving apart into "emptiness", it is the space that contains the objects which is itself changing. It is as if without objects themselves moving, space is somehow "growing" in between them."
"Because it is the metric defining distance that is changing rather than objects moving in space, this expansion (and the resultant movement apart of objects) is not restricted by the speed of light upper bound that results from special relativity."
"Theory and observations suggest that very early in the history of the universe, there was an "inflationary" phase where this metric changed very rapidly, and that the remaining time-dependence of this metric is what we observe as the so-called Hubble expansion, the moving apart of all gravitationally unbound objects in the universe. The expanding universe is therefore a fundamental feature of the universe we inhabit - a universe fundamentally different from the static universe Albert Einstein first considered when he developed his gravitational theory."
"The term universe has a variety of meanings based on the context in which it is described. In strictly physical terms the total universe is the summation of all matter that exists and the space in which all events occur. The part of the universe that can be seen or otherwise observed is usually called the known universe, observable universe, or visible universe. Because cosmic inflation removes vast parts of the total universe from our observable horizon, most cosmologists accept that it is impossible to observe the whole continuum and may use the expression our universe, referring only to that knowable by human beings in particular. In cosmological terms, the universe is thought to be a finite or infinite space -time continuum in which all matter and energy exist. It has been hypothesized by some scientists that the universe may be part of a system of many other universes, known as the multiverse."