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This metric has only two undetermined parameters. An overall dimensionless length scale factor R describes the size scale of the universe as a function of time (an increase in R is the expansion of the universe), [152] and a curvature index k describes the geometry.
where t is the age of the universe, is the speed of light and r e is the classical electron radius. Hence, in units where c = 1 and r e = 1, the age of the universe is about 10 40 units of time. This is the same order of magnitude as the ratio of the electrical to the gravitational forces between a proton and an electron:
The Big Crunch is a hypothetical scenario for the ultimate fate of the universe, in which the expansion of the universe eventually reverses and the universe recollapses, ultimately causing the cosmic scale factor to reach absolute zero, an event potentially followed by a reformation of the universe starting with another Big Bang.
The theory explains that the universe will expand until all matter decays and ultimately turns to light. Since nothing in the universe would have any time or distance scale associated with it, the universe becomes identical with the Big Bang, resulting in a type of Big Crunch that becomes the next Big Bang, thus perpetuating the next cycle. [21]
Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate. [1]
A cosmological horizon is a measure of the distance from which one could possibly retrieve information. [1] This observable constraint is due to various properties of general relativity, the expanding universe, and the physics of Big Bang cosmology.
In cosmology, the steady-state model or steady-state theory is an alternative to the Big Bang theory. In the steady-state model, the density of matter in the expanding universe remains unchanged due to a continuous creation of matter, thus adhering to the perfect cosmological principle , a principle that says that the observable universe is ...
In modern physical cosmology, the cosmological principle is the notion that the spatial distribution of matter in the universe is uniformly isotropic and homogeneous when viewed on a large enough scale, since the forces are expected to act equally throughout the universe on a large scale, and should, therefore, produce no observable inequalities in the large-scale structuring over the course ...