Newton's law of universal gravitation. Newton's law of universal gravitation states that any two bodies in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. (Separately it was shown that large spherically symmetrical masses attract and are attracted as if all their mass were concentrated at their centers.) This is a general physical law derived from empirical observations by what Isaac Newton called induction.[2] It is a part of classical mechanics and was formulated in Newton's work Philosophiæ Naturalis Principia Mathematica ("the Principia"), first published on 5 July 1687. (When Newton's book was presented in 1686 to the Royal Society, Robert Hooke made a claim that Newton had obtained the inverse square law from him – see History section below.)
In modern language, the law states the following: History[edit] Early History[edit] Plagiarism dispute[edit] Hooke's work and claims[edit] Vector form[edit] General relativity. General relativity, or the general theory of relativity, is the geometric theory of gravitation published by Albert Einstein in 1916[1] and the current description of gravitation in modern physics. General relativity generalizes special relativity and Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of partial differential equations. Some predictions of general relativity differ significantly from those of classical physics, especially concerning the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light.
Einstein's theory has important astrophysical implications. History[edit] Albert Einstein developed the theories of special and general relativity. Inflation (cosmology) In physical cosmology, cosmic inflation, cosmological inflation, or just inflation is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from 10−36 seconds after the Big Bang to sometime between 10−33 and 10−32 seconds. Following the inflationary period, the Universe continues to expand, but at a less rapid rate.[1] Inflation was developed in the early 1980s. It explains the origin of the large-scale structure of the cosmos.
Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the Universe (see galaxy formation and evolution and structure formation).[2] Many physicists also believe that inflation explains why the Universe appears to be the same in all directions (isotropic), why the cosmic microwave background radiation is distributed evenly, why the Universe is flat, and why no magnetic monopoles have been observed.
Overview Space expands . . Duration Reheating. Lambda-CDM model. The ΛCDM or Lambda-CDM model is a parametrization of the Big Bang cosmological model in which the universe contains a cosmological constant, denoted by Lambda (Greek Λ), and cold dark matter (abbreviated CDM). It is frequently referred to as the standard model of Big Bang cosmology, since it is the simplest model that provides a reasonably good account of the following properties of the cosmos: the existence and structure of the cosmic microwave backgroundthe large-scale structure in the distribution of galaxiesthe abundances of hydrogen (including deuterium), helium, and lithiumthe accelerating expansion of the universe observed in the light from distant galaxies and supernovae The model assumes that general relativity is the correct theory of gravity on cosmological scales. Some alternative models challenge the assumptions of the ΛCDM model. Overview[edit] Lambda-CDM, Accelerated Expansion of the Universe.
. , is currently [2013] estimated to be 68.3%. History[edit] Successes[edit] Big Bang. According to the Big Bang model, the universe expanded from an extremely dense and hot state and continues to expand today. The graphic scheme above is an artist's concept illustrating the expansion of a portion of a flat universe. The Big Bang is the scientific theory that is most consistent with observations of the past and present states of the universe, and it is widely accepted within the scientific community. It offers a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background, large scale structure, and the Hubble diagram.[3] The core ideas of the Big Bang—the expansion, the early hot state, the formation of light elements, and the formation of galaxies—are derived from these and other observations. As the distance between galaxies increases today, in the past galaxies were closer together.
Overview Timeline of the Big Bang The earliest phases of the Big Bang are subject to much speculation.