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'''Physical cosmology''', as a branch of [[astronomy]], is the study of the large-scale structure of the [[universe]] and is concerned with fundamental questions about its formation and evolution. Cosmology involves itself with studying the motions of the celestial bodies and the [[first cause]]. For most of human history, it has been a branch of [[metaphysics]]. Cosmology as a [[science]] originates with the [[Copernican principle]], which implies that celestial bodies obey identical [[physical law]]s to those on earth, and [[Newtonian mechanics]], which first allowed us to understand those motions. This is now called [[celestial mechanics]]. Physical cosmology, as it is now understood, began with the twentieth century development of [[Albert Einstein]]'s theory of [[general relativity]] and better [[astronomy|astronomical]] observations of extremely distant objects.  

'''Physical cosmology''', as a branch of [[astronomy]], is the study of the large-scale structure of the [[universe]] and is concerned with fundamental questions about its formation and evolution. Cosmology involves itself with studying the motions of the celestial bodies and the [[first cause]]. For most of human history, it has been a branch of [[metaphysics]]. Cosmology as a [[science]] originates with the [[Copernican principle]], which implies that celestial bodies obey identical [[physical law]]s to those on earth, and [[Newtonian mechanics]], which first allowed us to understand those motions. This is now called [[celestial mechanics]]. Physical cosmology, as it is now understood, began with the twentieth century development of [[Albert Einstein]]'s theory of [[general relativity]] and better [[astronomy|astronomical]] observations of extremely distant objects.  

Light elements, primarily hydrogen and helium, were created in the [[Big Bang]]. These light elements were spread too fast and too thinly in the Big Bang process (see [[nucleosynthesis]]) to form the most stable medium-sized atomic nuclei, like iron and nickel. This fact allows for later energy release, as such intermediate-sized elements are formed in our era. The formation of such atoms powers the steady energy-releasing reactions in [[star]]s, and also contributes to sudden energy releases, such as in [[nova]]e. Gravitational collapse of matter into black holes is also thought to power the most energetic processes, generally seen at the centers of galaxies (see [[quasar]]s and in general [[active galaxies]]).

Light elements, primarily hydrogen and helium, were created in the [[Big Bang]]. These light elements were spread too fast and too thinly in the Big Bang process (see [[nucleosynthesis]]) to form the most stable medium-sized atomic nuclei, like iron and nickel. This fact allows for later energy release, as such intermediate-sized elements are formed in our era. The formation of such atoms powers the steady energy-releasing reactions in [[star]]s, and also contributes to sudden energy releases, such as in [[nova]]e. Gravitational collapse of matter into black holes is also thought to power the most energetic processes, generally seen at the centers of galaxies (see [[quasar]]s and in general [[active galaxies]]).

Cosmologists are still unable to explain all cosmological phenomena purely on the basis of known conventional [[Energy forms|forms of energy]], for example those related to the [[Accelerating universe|accelerating expansion of the universe]], and therefore invoke a yet unexplored form of energy called [[dark energy]][http://www.sciencemag.org/cgi/content/abstract/300/5627/1914?siteid=sci&ijkey=eJV6VmToFgZIE&keytype=ref Science 20 June 2003:Vol. 300. no. 5627, pp. 1914 - 1918] Throwing Light on Dark Energy, Robert P. Kirshner. Accessed December 2006 to account for certain cosmological observations. One hypothesis is that dark energy is the energy of [[virtual particle]]s (which mathematically must exist in vacuum due to the [[uncertainty principle]]).

Cosmologists are still unable to explain all cosmological phenomena purely on the basis of known conventional [[Energy forms|forms of energy]], for example those related to the [[Accelerating universe|accelerating expansion of the universe]], and therefore invoke a yet unexplored form of energy called [[dark energy]][https://www.sciencemag.org/cgi/content/abstract/300/5627/1914?siteid=sci&ijkey=eJV6VmToFgZIE&keytype=ref Science 20 June 2003:Vol. 300. no. 5627, pp. 1914 - 1918] Throwing Light on Dark Energy, Robert P. Kirshner. Accessed December 2006 to account for certain cosmological observations. One hypothesis is that dark energy is the energy of [[virtual particle]]s (which mathematically must exist in vacuum due to the [[uncertainty principle]]).

There is no unambiguous way to define the total energy of the universe in the current best theory of gravity, [[general relativity]]. As a result it remains controversial whether one can meaningfully say that total energy is conserved in an expanding universe. For instance, each [[photon]] that travels through intergalactic space loses energy due to the [[redshift]] effect. This energy is not obviously transferred to any other system, so seems to be permanently lost. Nevertheless some cosmologists insist that energy is conserved in some sense. e.g. An Introduction to Modern Cosmology ISBN 0-470-84835-9 . This argues cogently "Energy is always, always, always conserved."

There is no unambiguous way to define the total energy of the universe in the current best theory of gravity, [[general relativity]]. As a result it remains controversial whether one can meaningfully say that total energy is conserved in an expanding universe. For instance, each [[photon]] that travels through intergalactic space loses energy due to the [[redshift]] effect. This energy is not obviously transferred to any other system, so seems to be permanently lost. Nevertheless some cosmologists insist that energy is conserved in some sense. e.g. An Introduction to Modern Cosmology ISBN 0-470-84835-9 . This argues cogently "Energy is always, always, always conserved."

===Textbooks===

===Textbooks===

*{{cite book | author=Cheng, Ta-Pei | title=Relativity, Gravitation and Cosmology: a Basic Introduction | location=Oxford and New York| publisher=Oxford University Press| year=2005 | id=ISBN 0-19-852957-0}} Cosmology is introduced in the framework of general relativity -- but without the full tensor apparatus, which is presented in the last part of the book. Particularly suitable for an introductory GR course with an emphasis on cosmology.

* Cheng, Ta-Pei, Relativity, Gravitation and Cosmology: a Basic Introduction ISBN 0-19-852957-0  Cosmology is introduced in the framework of general relativity -- but without the full tensor apparatus, which is presented in the last part of the book. Particularly suitable for an introductory GR course with an emphasis on cosmology.

* {{cite book | first = Scott | last = Dodelson | year = 2003 | title = Modern Cosmology | publisher = Academic Press | id = ISBN 0-12-219141-2 }} Released slightly before the [[Wilkinson Microwave Anisotropy Probe|WMAP]] results, this is the most modern introductory textbook.

* Scott Dodelson, Modern Cosmology ISBN 0-12-219141-2 Released slightly before the [[Wilkinson Microwave Anisotropy Probe|WMAP]] results, this is the most modern introductory textbook.

* {{cite book | last = Grøn | first = Øyvind | coauthors = Hervik, Sigbjørn | title = Einstein's General Theory of Relativity with Modern Applications in Cosmology | location = New York | publisher = Springer | year = 2007 | id = ISBN 978-0-387-69199-2}}

* Grøn Øyvind, Einstein's General Theory of Relativity with Modern Applications in Cosmology ISBN 978-0-387-69199-2  

* {{cite book | first = Edward | last = Harrison | year = 2000 | title = Cosmology: the science of the universe | publisher = Cambridge University Press | id = ISBN 0-521-66148-X }} A relatively unmathematical textbook.

* Edward Harrison, Cosmology: the science of the universe ISBN 0-521-66148-X A relatively unmathematical textbook.

* {{cite book | first = Marc | last = Kutner | title = Astronomy: A Physical Perspective | publisher = Cambridge University Press | year = 2003 | id = ISBN 0-521-52927-1 }} An introductory astronomy textbook.

* Marc Kutner, Astronomy: A Physical Perspective ISBN 0-521-52927-1 An introductory astronomy textbook.

* {{cite book | first = Edward | last = Kolb | coauthors = Michael Turner | title = The Early Universe | publisher = Addison-Wesley | year = 1988 | id = ISBN 0-201-11604-9 }} This is the classic reference for cosmologists.

* Edward Kolb, The Early Universe ISBN 0-201-11604-9 This is the classic reference for cosmologists.

* {{cite book | first = Andrew | last = Liddle | title = An Introduction to Modern Cosmology | publisher = John Wiley | year = 2003 | id = ISBN 0-470-84835-9 }} An introduction to cosmology without General Relativity

* Andrew Liddle, An Introduction to Modern Cosmology ISBN 0-470-84835-9 An introduction to cosmology without General Relativity

* {{cite book | first = Andrew | last = Liddle | coauthors = David Lyth | title = Cosmological Inflation and Large-Scale Structure | publisher = Cambridge | year = 2000 | id = ISBN 0-521-57598-2 }} An introduction to cosmology with a thorough discussion of inflation.

* Andrew Liddle, Cosmological Inflation and Large-Scale Structure ISBN 0-521-57598-2 An introduction to cosmology with a thorough discussion of inflation.

* {{cite book | first = Viatcheslav | last = Mukhanov | title = Physical Foundations of Cosmology | publisher = Cambridge University Press | year = 2005 | id = ISBN 0-521-56398-4 }}

* Viatcheslav Mukhanov, Physical Foundations of Cosmology ISBN 0-521-56398-4  

* {{cite book | author = Padmanabhan, T. | title = Structure formation in the universe | publisher = Cambridge University Press | year = 1993 | id = ISBN 0-521-42486-0 }} Describes the formation of large-scale structures in detail.

* Padmanabhan, T., Structure formation in the universe,  ISBN 0-521-42486-0 }} Describes the formation of large-scale structures in detail.

* {{cite book | first = John | last = Peacock | title = Cosmological Physics | publisher = Cambridge University Press | year = 1998 | id = ISBN 0-521-42270-1 }} An introduction with more background on general relativity and quantum field theory than most.

* John | last = Peacock, Cosmological Physics ISBN 0-521-42270-1 }} An introduction with more background on general relativity and quantum field theory than most.

* {{cite book | first = P. J. E. | last = Peebles | title = Principles of Physical Cosmology | publisher = Princeton University Press | year = 1993 | id = ISBN 0-691-01933-9 }} Peebles' book has a strong historical focus.

* P. J. E. Peebles, Principles of Physical Cosmology ISBN 0-691-01933-9 Peebles' book has a strong historical focus.

* {{cite book | first = P. J. E. | last = Peebles | title = The Large-Scale Structure of the Universe | publisher = Princeton University Press | year = 1980 | id = ISBN 0-691-08240-5 }} The classic work on large scale structure, in particular the discussion of correlation functions.

* P. J. E. Peebles, The Large-Scale Structure of the Universe ISBN 0-691-08240-5 The classic work on large scale structure, in particular the discussion of correlation functions.

* {{cite book | first = Martin | last = Rees | title = New Perspectives in Astrophysical Cosmology | publisher = Cambridge University Press | year = 2002 | id = ISBN 0-521-64544-1 }}

* Martin Rees, New Perspectives in Astrophysical Cosmology ISBN 0-521-64544-1

* {{cite book | first = Steven | last = Weinberg | title = Gravitation and Cosmology | publisher = John Wiley | year = 1971 | id = ISBN 0-471-92567-5 }} An older book, but still a standard reference for a lot of the mathematical formalism.

* Steven Weinberg,  Gravitation and Cosmology ISBN 0-471-92567-5 }} An older book, but still a standard reference for a lot of the mathematical formalism.

==See also==

==See also==

==External links==

==External links==

===From groups===

===From groups===

* [http://www.damtp.cam.ac.uk/user/gr/public/cos_home.html Cambridge Cosmology]- from Cambridge University (Public Home Page)

* [https://www.damtp.cam.ac.uk/user/gr/public/cos_home.html Cambridge Cosmology]- from Cambridge University (Public Home Page)

* [http://map.gsfc.nasa.gov/m_uni.html Cosmology 101] - from the [[NASA]] [[WMAP]] group

* [https://map.gsfc.nasa.gov/m_uni.html Cosmology 101] - from the [[NASA]] [[WMAP]] group

* [http://www.pbs.org/wgbh/nova/origins/ Origins, Nova Online] - Provided by ''[[Public Broadcasting Service|PBS]]''.

* [https://www.pbs.org/wgbh/nova/origins/ Origins, Nova Online] - Provided by ''[[Public Broadcasting Service|PBS]]''.

* [http://dhost.info/cosmology/ Cosmology] -- Cosmology Of The Universe.

* [https://dhost.info/cosmology/ Cosmology] -- Cosmology Of The Universe.

*[http://www.iasa.ir Iran Astronomy Sciences Academy] IASA

*[https://www.iasa.ir Iran Astronomy Sciences Academy] IASA

* [http://cfcp.uchicago.edu/ Center for Cosmological Physics]. [[University of Chicago]], [[Chicago|Chicago, Illinois]].

* [https://cfcp.uchicago.edu/ Center for Cosmological Physics]. [[University of Chicago]], [[Chicago|Chicago, Illinois]].

* ''Dictionary of the History of Ideas'':

* ''Dictionary of the History of Ideas'':

** [http://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-64 Cosmic Images]

** [https://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-64 Cosmic Images]

** [http://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-66 Cosmology from Antiquity to 1850]

** [https://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-66 Cosmology from Antiquity to 1850]

** [http://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-67 Cosmology  since 1850]

** [https://etext.lib.virginia.edu/cgi-local/DHI/dhi.cgi?id=dv1-67 Cosmology  since 1850]

* [http://www.shekpvar.net/~dennis/Elib/Astronomicon/Astronomicon/Cosmos/cosmos.html Cosmos - an Illustrated Dimensional Journey from microcosmos to macrocosmos] - from DNA Digital Nature Agency

* [https://www.shekpvar.net/~dennis/Elib/Astronomicon/Astronomicon/Cosmos/cosmos.html Cosmos - an Illustrated Dimensional Journey from microcosmos to macrocosmos] - from DNA Digital Nature Agency

* [http://www.astrofind.net/ AstroFind Search] - Search Engine for Cosmology and Astronomy

* [https://www.astrofind.net/ AstroFind Search] - Search Engine for Cosmology and Astronomy

* [http://www.vega.org.uk/video/programme/89 'The Mathematician Who Can't Add Up' Emma King Cosmologist]  Freeview 'Snapshot' video provided by the Vega Science Trust.

* [https://www.vega.org.uk/video/programme/89 'The Mathematician Who Can't Add Up' Emma King Cosmologist]  Freeview 'Snapshot' video provided by the Vega Science Trust.

===From individuals===

===From individuals===

*  [[Sean M. Carroll|Carroll, Sean]]. "''[http://preposterousuniverse.com/writings/cosmologyprimer/ Cosmology Primer]''". California Institute of Technology.

*  [[Sean M. Carroll|Carroll, Sean]]. "''[https://preposterousuniverse.com/writings/cosmologyprimer/ Cosmology Primer]''". California Institute of Technology.

*  Gale, George, "[http://plato.stanford.edu/entries/cosmology-30s/ Cosmology: Methodological Debates in the 1930s and 1940s]", ''The Stanford Encyclopedia of Philosophy'', Edward N. Zalta (ed.)

*  Gale, George, "[https://plato.stanford.edu/entries/cosmology-30s/ Cosmology: Methodological Debates in the 1930s and 1940s]", ''The Stanford Encyclopedia of Philosophy'', Edward N. Zalta (ed.)

* Hoiland, Paul, "''[http://cosmology.bravehost.com/ Modern Cosmology Examined]''"''[http://tprints.ecs.soton.ac.uk/archive/00000033/01/MUSINGS_ON_THE_EVOLUTION_OF_A_COSMOS.pdf Musing on the Evolution of a Cosmos]'' Gouldsboro, Maine.

* Hoiland, Paul, "''[https://cosmology.bravehost.com/ Modern Cosmology Examined]''"''[https://tprints.ecs.soton.ac.uk/archive/00000033/01/MUSINGS_ON_THE_EVOLUTION_OF_A_COSMOS.pdf Musing on the Evolution of a Cosmos]'' Gouldsboro, Maine.

*  Jordan, Thomas F., "''[http://arxiv.org/abs/astro-ph/0309756 Cosmology calculations almost without general relativity]''". ([[arXiv.org]])

*  Jordan, Thomas F., "''[https://arxiv.org/abs/astro-ph/0309756 Cosmology calculations almost without general relativity]''". ([[arXiv.org]])

* Madore, Barry F., "''[http://nedwww.ipac.caltech.edu/level5/ Level 5] : A Knowledgebase for Extragalactic Astronomy and Cosmology''". Caltech and Carnegie. Pasadena, California, USA.

* Madore, Barry F., "''[https://nedwww.ipac.caltech.edu/level5/ Level 5] : A Knowledgebase for Extragalactic Astronomy and Cosmology''". Caltech and Carnegie. Pasadena, California, USA.

* Smith, Tony, "''[http://www.innerx.net/personal/tsmith/cosm.html Cosmology] -- At the Millennium, Experimental Observations tell us a lot about Cosmology''".  

* Smith, Tony, "''[https://www.innerx.net/personal/tsmith/cosm.html Cosmology] -- At the Millennium, Experimental Observations tell us a lot about Cosmology''".  

* Tyler, Pat, and Phil Newman "''[http://universe.gsfc.nasa.gov/ Beyond Einstein]''". Laboratory for High Energy Astrophysics (LHEA) [[NASA]] [[Goddard Space Flight Center]].

* Tyler, Pat, and Phil Newman "''[https://universe.gsfc.nasa.gov/ Beyond Einstein]''". Laboratory for High Energy Astrophysics (LHEA) [[NASA]] [[Goddard Space Flight Center]].

*  [[Edward L. Wright|Wright, Ned]]. "''[http://www.astro.ucla.edu/~wright/cosmolog.htm Cosmology tutorial and FAQ]''". Division of Astronomy & Astrophysics, UCLA.

*  [[Edward L. Wright|Wright, Ned]]. "''[https://www.astro.ucla.edu/~wright/cosmolog.htm Cosmology tutorial and FAQ]''". Division of Astronomy & Astrophysics, UCLA.

* [http://www.sciam.com/article.cfm?chanID=sa006&articleID=0005DCFC-253F-1FFB-A53F83414B7F0000 Scientific American Magazine (February 2004 Issue) Four Keys to Cosmology] About acceleration.

* [https://www.sciam.com/article.cfm?chanID=sa006&articleID=0005DCFC-253F-1FFB-A53F83414B7F0000 Scientific American Magazine (February 2004 Issue) Four Keys to Cosmology] About acceleration.

* [http://www.asterdomus.com.br/Artigo_a_massa_do_Universo.htm The Mass of the Universe, in AsterDomus Planetarium site (portuguese)]

* [https://www.asterdomus.com.br/Artigo_a_massa_do_Universo.htm The Mass of the Universe, in AsterDomus Planetarium site (portuguese)]

[[Category: General Reference]]

[[Category: General Reference]]

[[Category: Physical Cosmology]]

[[Category: Physical Cosmology]]