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In the same way that the ''[[Moon]]'' refers to our ([[Earth]]'s) moon, ''the Universe'' is used by some cosmologists to refer to our universe. In this article, ''the Universe'' is equivalent to ''our observable universe''.
In the same way that the ''[[Moon]]'' refers to our ([[Earth]]'s) moon, ''the Universe'' is used by some cosmologists to refer to our universe. In this article, ''the Universe'' is equivalent to ''our observable universe''.
Theoretical and [[Physical cosmology|observational cosmologists]] vary in their usage of the term ''the Universe'' to mean either this whole system or just a part of this system. [http://links.jstor.org/sici?sici=0022-5037 JSTOR: One Universe or Many?]
As used by observational cosmologists, ''the Universe'' most frequently refers to the finite part of space-time. The Universe is directly observable by making [[discovery (observation)|observation]]s using [[telescope]]s 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 coordinates|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.
As used by observational cosmologists, ''[[the Universe]]'' most frequently refers to the [[finite]] part of [[space-time]]. The Universe is directly observable by making [[observation]]s using [[telescope]]s 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 ([http://en.wikipedia.org/wiki/Comoving_distance 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.
In order to [[clarify]] terminology, [http://en.wikipedia.org/wiki/George_Ellis 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 [http://en.wikipedia.org/wiki/Chaotic_inflation chaotic inflation] models.
==Observable portion==
==Observable portion==
