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2004/10/21 | 宇宙论[Cosmology]
类别(Ω〖物理〗)
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发表于 13:20
Cosmology is the study of the large-scale structure of the
universe
.It is concerned with fundamental questions about the formation, evolution, and future development of the
universe
. Specific cosmological questions of interest include the isotropy of the
universe
, the density of the
universe
, the equality of matter and anti-matter, and the origin of density fluctuations in galaxies. The most hotly sought after cosmological parameters of the present-day
universe
are the expansion rate, most commonly parameterized by the
Hubble constant
the
critical density
(the density required for the
universe
to stop expansion and eventually collapse back onto itself), the related quantity
, the
deceleration parameter
q
, the
cosmological constant
, the
curvature of the universe
, and the
expansion parameter
a
.Many of these quantities are related under the assumptions of a given cosmological model.
Different cosmological models give different evolutions and therefore different ages for the
universe
based on the current rate of expansion. Let
be the
curvature of the universe
,
the
critical density
, and
t
be the age of the
universe
. Then the following table summarizes the most common cosmological models.
<DIV ALIGN="CENTER"> <TABLE CELLPADDING=3 BORDER="1"> <TR><TD ALIGN="LEFT">closure</TD> <TD ALIGN="LEFT">model</TD> <TD ALIGN="LEFT"><IMG WIDTH="13" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" SRC="http://scienceworld.wolfram.com/physics/cimg1014.gif"></TD> <TD ALIGN="CENTER">volume</TD> <TD ALIGN="CENTER"><IMG WIDTH="12" HEIGHT="28" ALIGN="MIDDLE" BORDER="0" SRC="http://scienceworld.wolfram.com/physics/cimg96.gif"></TD> <TD ALIGN="LEFT">present age</TD> </TR> <TR><TD ALIGN="LEFT">closed</TD> <TD ALIGN="LEFT"><a href="Friedmann-LemaitreCosmologicalModel.html">Friedmann-Lemaître</a></TD> <TD ALIGN="LEFT"><IMG WIDTH="29" HEIGHT="28" ALIGN="MIDDLE" BORDER="0" SRC="http://scienceworld.wolfram.com/physics/cimg1015.gif"></TD> <TD ALIGN="CENTER">finite</TD> <TD ALIGN="CENTER"> <IMG WIDTH="49" HEIGHT="28" ALIGN="MIDDLE" BORDER="0" SRC="http://scienceworld.wolfram.com/physics/cimg1016.gif"></TD> <TD ALIGN="LEFT"> <IMG WIDTH="102" HEIGHT="34" ALIGN="MIDDLE" BORDER="0" SRC="http://scienceworld.wolfram.com/physics/cimg1017.gif"></TD> </TR> <TR><TD ALIGN="LEFT">flat</TD> <TD ALIGN="LEFT"><a href="Einstein-deSitterCosmologicalModel.html">Einstein-de Sitter</a></TD> <TD ALIGN="LEFT">0</TD> <TD ALIGN="CENTER">infinite</TD> <TD ALIGN="CENTER"> <IMG WIDTH="32" HEIGHT="28" ALIGN="MIDDLE" BORDER="0" SRC="http://scienceworld.wolfram.com/physics/cimg1012.gif"></TD> <TD ALIGN="LEFT">t = <IMG WIDTH="46" HEIGHT="34" ALIGN="MIDDLE" BORDER="0" SRC="http://scienceworld.wolfram.com/physics/cimg1018.gif"></TD> </TR> <TR><TD ALIGN="LEFT">open</TD> <TD ALIGN="LEFT"><a href="Friedmann-LemaitreCosmologicalModel.html">Friedmann-Lemaître</a></TD> <TD ALIGN="LEFT"><IMG WIDTH="29" HEIGHT="28" ALIGN="MIDDLE" BORDER="0" SRC="http://scienceworld.wolfram.com/physics/cimg1019.gif"></TD> <TD ALIGN="CENTER">infinite</TD> <TD ALIGN="CENTER"> <IMG WIDTH="49" HEIGHT="28" ALIGN="MIDDLE" BORDER="0" SRC="http://scienceworld.wolfram.com/physics/cimg1020.gif"></TD> <TD ALIGN="LEFT"> <IMG WIDTH="126" HEIGHT="34" ALIGN="MIDDLE" BORDER="0" SRC="http://scienceworld.wolfram.com/physics/cimg1021.gif"></TD> </TR> </TABLE> </DIV>
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