- a : a systematic whole held to arise by and persist through the direct intervention of divine power
- b : the world of human experience
- c (1) : the entire celestial cosmos (2) : milky way galaxy (3) : an aggregate of stars comparable to the Milky Way galaxy
- 2: a distinct field or province of thought or reality that forms a closed system or self-inclusive and independent organization
- 3: a set that contains all elements relevant to a particular discussion or problem
- 4: a great number or quantity <a large enough universe of stocks … to choose from — G. B. Clairmont>
The Universe is defined as the summation of all particles and energy that exist and the space-time in which all events occur. Based on observations of the portion of the universe that is observable, physicists attempt to describe the whole of space-time, including all matter and energy and events which occur, as a single system corresponding to a mathematical model.
The generally accepted scientific theory which describes the origin and evolution of the universe is Big Bang cosmology, which describes the expansion of space from an extremely hot and dense state of unknown characteristics. The universe underwent a rapid period of cosmic inflation that flattened out nearly all initial irregularities in the energy density; thereafter the universe expanded and became steadily cooler and less dense. Minor variations in the distribution of mass resulted in hierarchical segregation of the features that are found in the current universe; such as clusters and superclusters of galaxies. There are more than one hundred billion galaxies in the universe, To see the Universe in a Grain of Taranaki Sand, Swinburne University each containing hundreds of billions of stars, with each star containing about 10x57th power of atoms of hydrogen.
As used by observational cosmologists, the Universe most frequently refers to the finite part of space-time. The Universe is directly observable by making observations using telescopes and other detectors, and by using the methods of theoretical and empirical physics for studying its components. Physical cosmologists assume that the observable part of (comoving) space (also called our universe) corresponds to a part of a model of the whole of space, and usually not to the whole space. They use the term the Universe ambiguously to mean either the observable part of space, the observable part of space-time, or the entire space-time.
In order to clarify terminology, George Ellis, U. Kirchner and W.R. Stoeger recommend using the term the Universe for the theoretical model of all of the connected space-time in which we live, universe domain for the observable universe or a similar part of the same space-time, universe for a general space-time (either our own Universe or another one disconnected from our own), multiverse for a set of disconnected space-times, and multi-domain universe to refer to a model of the whole of a single connected space-time in the sense of chaotic inflation models.
- Stephen Hawking's Universe - why is the universe the way it is?
- Richard Powell: An Atlas of the Universe - images at various scales, with explanations.
- Logarithmic Maps of the Universe
- Seti@Home - the Search for Extraterrestrial Intelligence
- Number of Galaxies in the Universe
- Cosmology FAQ
If this were only a material universe, material man would never be able to arrive at the concept of the mechanistic character of such an exclusively material existence. This very mechanistic concept of the universe is in itself a nonmaterial phenomenon of mind, and all mind is of nonmaterial origin, no matter how thoroughly it may appear to be materially conditioned and mechanistically controlled. (195:7)