Editing Physical cosmology (section)

===Cosmic microwave background===
{{Main|Cosmic microwave background}}
The cosmic microwave background is radiation left over from [[Decoupling (cosmology)|decoupling]] after the epoch of [[recombination (cosmology)|recombination]] when neutral atoms first formed. At this point, radiation produced in the Big Bang stopped [[Thomson scattering]] from charged ions. The radiation, first observed in 1965 by [[Arno Penzias]] and [[Robert Woodrow Wilson]], has a perfect thermal [[black body|black-body]] spectrum. It has a temperature of 2.7 [[kelvin]]s today and is isotropic to one part in 10<sup>5</sup>. [[Cosmological perturbation theory]], which describes the evolution of slight inhomogeneities in the early universe, has allowed cosmologists to precisely calculate the angular [[power spectrum]] of the radiation, and it has been measured by the recent satellite experiments ([[Cosmic Background Explorer|COBE]] and [[WMAP]])<ref name=Lamarre2010>{{cite book | chapter=The Cosmic Microwave Background | last1=Lamarre | first1=Jean-Michel | title=Observing Photons in Space | volume=9 | editor1-first=M. C. E. | editor1-last=Huber | editor2-first=A. | editor2-last=Pauluhn | editor3-first=J. L. | editor3-last=Culhane | editor4-first=J. G. | editor4-last=Timothy | editor5-first=K. | editor5-last=Wilhelm | editor6-first=A. | editor6-last=Zehnder | series=ISSI Scientific Reports Series | year=2010 | pages=149–162 | bibcode=2010ISSIR...9..149L }}</ref> and many ground and balloon-based experiments (such as [[Degree Angular Scale Interferometer]], [[Cosmic Background Imager]], and [[BOOMERanG experiment|Boomerang]]).<ref name=Sievers2003>{{cite journal | title=Cosmological Parameters from Cosmic Background Imager Observations and Comparisons with BOOMERANG, DASI, and MAXIMA | display-authors=1 | last1=Sievers | first1=J. L. | last2=Bond | first2=J. R. | last3=Cartwright | first3=J. K. | last4=Contaldi | first4=C. R. | last5=Mason | first5=B. S. | last6=Myers | first6=S. T. | last7=Padin | first7=S. | last8=Pearson | first8=T. J. | last9=Pen | first9=U.-L. | last10=Pogosyan | first10=D. | last11=Prunet | first11=S. | last12=Readhead | first12=A. C. S. | last13=Shepherd | first13=M. C. | last14=Udomprasert | first14=P. S. | last15=Bronfman | first15=L. | last16=Holzapfel | first16=W. L. | last17=May | first17=J. | journal=The Astrophysical Journal | volume=591 | issue=2 | pages=599–622 | year=2003 | doi=10.1086/375510 | bibcode=2003ApJ...591..599S | arxiv=astro-ph/0205387 | s2cid=14939106 }}</ref> One of the goals of these efforts is to measure the basic parameters of the Lambda-CDM model with increasing accuracy, as well as to test the predictions of the Big Bang model and look for new physics. The results of measurements made by WMAP, for example, have placed limits on the neutrino masses.<ref name=Hinshaw2013>{{cite journal | title=Nine-year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Parameter Results | display-authors=1 | last1=Hinshaw | first1=G. | last2=Larson | first2=D. | last3=Komatsu | first3=E. | last4=Spergel | first4=D. N. | last5=Bennett | first5=C. L. | last6=Dunkley | first6=J. | last7=Nolta | first7=M. R. | last8=Halpern | first8=M. | last9=Hill | first9=R. S. | last10=Odegard | first10=N. | last11=Page | first11=L. | last12=Smith | first12=K. M. | last13=Weiland | first13=J. L. | last14=Gold | first14=B. | last15=Jarosik | first15=N. | last16=Kogut | first16=A. | last17=Limon | first17=M. | last18=Meyer | first18=S. S. | last19=Tucker | first19=G. S. | last20=Wollack | first20=E. | last21=Wright | first21=E. L. | journal=The Astrophysical Journal Supplement | volume=208 | issue=2 | page=19 | date=October 2013 | doi=10.1088/0067-0049/208/2/19 | bibcode=2013ApJS..208...19H | arxiv=1212.5226 | s2cid=37132863 }}</ref>

Newer experiments, such as [[QUIET]] and the [[Atacama Cosmology Telescope]], are trying to measure the [[polarization (waves)|polarization]] of the cosmic microwave background.<ref name=Naess2014>{{cite journal | title=The Atacama Cosmology Telescope: CMB polarization at 200 < l < 9000 | display-authors=4 | last1=Naess | first1=Sigurd | last2=Hasselfield | first2=Matthew | last3=McMahon | first3=Jeff | last4=Niemack | first4=Michael D. | last5=Addison | first5=Graeme E. | last6=Ade | first6=Peter A. R. | last7=Allison | first7=Rupert | last8=Amiri | first8=Mandana | last9=Battaglia | first9=Nick | last10=Beall | first10=James A. | last11=de Bernardis | first11=Francesco | last12=Bond | first12=J. Richard | last13=Britton | first13=Joe | last14=Calabrese | first14=Erminia | last15=Cho | first15=Hsiao-mei | last16=Coughlin | first16=Kevin | last17=Crichton | first17=Devin | last18=Das | first18=Sudeep | last19=Datta | first19=Rahul | last20=Devlin | first20=Mark J. | last21=Dicker | first21=Simon R. | last22=Dunkley | first22=Joanna | last23=Dünner | first23=Rolando | last24=Fowler | first24=Joseph W. | last25=Fox | first25=Anna E. | last26=Gallardo | first26=Patricio | last27=Grace | first27=Emily | last28=Gralla | first28=Megan | last29=Hajian | first29=Amir | last30=Halpern | first30=Mark | last31=Henderson | first31=Shawn | last32=Hill | first32=J. Colin | last33=Hilton | first33=Gene C. | last34=Hilton | first34=Matt | last35=Hincks | first35=Adam D. | last36=Hlozek | first36=Renée | last37=Ho | first37=Patty | last38=Hubmayr | first38=Johannes | last39=Huffenberger | first39=Kevin M. | last40=Hughes | first40=John P. | last41=Infante | first41=Leopoldo | last42=Irwin | first42=Kent | last43=Jackson | first43=Rebecca | last44=Muya Kasanda | first44=Simon | last45=Klein | first45=Jeff | last46=Koopman | first46=Brian | last47=Kosowsky | first47=Arthur | last48=Li | first48=Dale | last49=Louis | first49=Thibaut | last50=Lungu | first50=Marius | last51=Madhavacheril | first51=Mathew | last52=Marriage | first52=Tobias A. | last53=Maurin | first53=Loïc | last54=Menanteau | first54=Felipe | last55=Moodley | first55=Kavilan | last56=Munson | first56=Charles | last57=Newburgh | first57=Laura | last58=Nibarger | first58=John | last59=Nolta | first59=Michael R. | last60=Page | first60=Lyman A. | last61=Pappas | first61=Christine | last62=Partridge | first62=Bruce | last63=Rojas | first63=Felipe | last64=Schmitt | first64=Benjamin L. | last65=Sehgal | first65=Neelima | last66=Sherwin | first66=Blake D. | last67=Sievers | first67=Jon | last68=Simon | first68=Sara | last69=Spergel | first69=David N. | last70=Staggs | first70=Suzanne T. | last71=Switzer | first71=Eric R. | last72=Thornton | first72=Robert | last73=Trac | first73=Hy | last74=Tucker | first74=Carole | last75=Uehara | first75=Masao | last76=Van Engelen | first76=Alexander | last77=Ward | first77=Jonathan T. | last78=Wollack | first78=Edward J. | journal=Journal of Cosmology and Astroparticle Physics | volume=2014 | issue=10 | pages=007 | date=October 2014 | doi=10.1088/1475-7516/2014/10/007 | bibcode=2014JCAP...10..007N | arxiv=1405.5524 | s2cid=118593572 }}</ref> These measurements are expected to provide further confirmation of the theory as well as information about cosmic inflation, and the so-called secondary anisotropies,<ref name=Jackson2009>{{Cite conference |title=Probing Inflation with CMB Polarization | display-authors=1 | last1=Baumann | first1=Daniel | last2=Jackson | first2=Mark G. | last3=Adshead | first3=Peter | last4=Amblard | first4=Alexandre | last5=Ashoorioon | first5=Amjad | last6=Bartolo | first6=Nicola | last7=Bean | first7=Rachel | last8=Beltrán | first8=Maria | last9=de Bernardis | first9=Francesco | last10=Bird | first10=Simeon | last11=Chen | first11=Xingang | last12=Chung | first12=Daniel J. H. | last13=Colombo | first13=Loris | last14=Cooray | first14=Asantha | last15=Creminelli | first15=Paolo | last16=Dodelson | first16=Scott | last17=Dunkley | first17=Joanna | last18=Dvorkin | first18=Cora | last19=Easther | first19=Richard | last20=Finelli | first20=Fabio | last21=Flauger | first21=Raphael | last22=Hertzberg | first22=Mark P. | last23=Jones-Smith | first23=Katherine | last24=Kachru | first24=Shamit | last25=Kadota | first25=Kenji | last26=Khoury | first26=Justin | last27=Kinney | first27=William H. | last28=Komatsu | first28=Eiichiro | last29=Krauss | first29=Lawrence M. | last30=Lesgourgues | first30=Julien | last31=Liddle | first31=Andrew | last32=Liguori | first32=Michele | last33=Lim | first33=Eugene | last34=Linde | first34=Andrei | last35=Matarrese | first35=Sabino | last36=Mathur | first36=Harsh | last37=McAllister | first37=Liam | last38=Melchiorri | first38=Alessandro | last39=Nicolis | first39=Alberto | last40=Pagano | first40=Luca | last41=Peiris | first41=Hiranya V. | last42=Peloso | first42=Marco | last43=Pogosian | first43=Levon | last44=Pierpaoli | first44=Elena | last45=Riotto | first45=Antonio | last46=Seljak | first46=Uroš | last47=Senatore | first47=Leonardo | last48=Shandera | first48=Sarah | last49=Silverstein | first49=Eva | last50=Smith | first50=Tristan | last51=Vaudrevange | first51=Pascal | last52=Verde | first52=Licia | last53=Wandelt | first53=Ben | last54=Wands | first54=David | last55=Watson | first55=Scott | last56=Wyman | first56=Mark | last57=Yadav | first57=Amit | last58=Valkenburg | first58=Wessel | last59=Zaldarriaga | first59=Matias |book-title=CMB Polarization Workshop: Theory and Foregrounds: CMBPol Mission Concept Study | volume=1141 | pages=10–120 | year=2009 | doi=10.1063/1.3160885 | bibcode=2009AIPC.1141...10B | arxiv=0811.3919 }}</ref> such as the [[Sunyaev-Zel'dovich effect]] and [[Sachs-Wolfe effect]], which are caused by interaction between [[galaxy|galaxies]] and [[galaxy cluster|clusters]] with the cosmic microwave background.<ref name=Scranton2003>{{cite arXiv | title=Physical Evidence for Dark Energy | display-authors=6 | last1=Scranton | first1=R. | last2=Connolly | first2=A. J. | last3=Nichol | first3=R. C. | last4=Stebbins | first4=A. | last5=Szapudi | first5=I. | last6=Eisenstein | first6=D. J. | last7=Afshordi | first7=N. | last8=Budavari | first8=T. | last9=Csabai | first9=I. | last10=Frieman | first10=J. A. | last11=Gunn | first11=J. E. | last12=Johnston | first12=D. | last13=Loh | first13=Y. | last14=Lupton | first14=R. H. | last15=Miller | first15=C. J. | last16=Sheldon | first16=E. S. | last17=Sheth | first17=R. S. | last18=Szalay | first18=A. S. | last19=Tegmark | first19=M. | last20=Xu | first20=Y. | eprint=astro-ph/0307335 | date=July 2003}}</ref><ref name=Refregier1999>{{cite book | chapter=Overview of Secondary Anisotropies of the CMB | last1=Refregier | first1=A. | title=Microwave Foregrounds | series=ASP Conference Series | volume=181 | editor1-first=A. | editor1-last=de Oliveira-Costa | editor2-first=M. | editor2-last=Tegmark | isbn=978-1-58381-006-4 | page=219 | year=1999 | bibcode=1999ASPC..181..219R | arxiv=astro-ph/9904235 }}</ref>

On 17 March 2014, astronomers of the [[BICEP and Keck Array#BICEP2|BICEP2 Collaboration]] announced the apparent detection of [[B-modes|''B''-mode]] polarization of the CMB, considered to be evidence of [[primordial gravitational wave]]s that are predicted by the theory of [[inflation (cosmology)|inflation]] to occur during the earliest phase of the Big Bang.<ref name="BICEP2-2014">{{cite web |title=BICEP2 2014 Results Release |url=http://bicepkeck.org/bicep2_2014_release.html |date=17 March 2014 |website=The BICEP / Keck CMB Experiments |access-date=18 March 2014 }}</ref><ref name="NASA-20140317">{{cite web |last=Clavin |first=Whitney |title=NASA Technology Views Birth of the Universe |url=http://www.jpl.nasa.gov/news/news.php?release=2014-082 |date=17 March 2014 |website=NASA |access-date=17 March 2014 }}</ref><ref name="NYT-20140317">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye
|title=Detection of Waves in Space Buttresses Landmark Theory of Big Bang
|url=https://www.nytimes.com/2014/03/18/science/space/detection-of-waves-in-space-buttresses-landmark-theory-of-big-bang.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2014/03/18/science/space/detection-of-waves-in-space-buttresses-landmark-theory-of-big-bang.html |archive-date=2022-01-01 |url-access=limited |date=17 March 2014 |work=[[The New York Times]] |access-date=17 March 2014 }}{{cbignore}}</ref><ref name="NYT-20140324">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |title=Ripples From the Big Bang |url=https://www.nytimes.com/2014/03/25/science/space/ripples-from-the-big-bang.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2014/03/25/science/space/ripples-from-the-big-bang.html |archive-date=2022-01-01 |url-access=limited |date=25 March 2014 |work=[[The New York Times]] |access-date=24 March 2014 }}{{cbignore}}</ref> However, later that year the [[Planck spacecraft|Planck]] collaboration provided a more accurate measurement of [[cosmic dust]], concluding that the B-mode signal from dust is the same strength as that reported from BICEP2.<ref name="AXV-20140919">{{cite journal
 |author=Planck Collaboration
 |year=2016
 |title=Planck intermediate results. XXX. The angular power spectrum of polarized dust emission at intermediate and high Galactic latitudes
 |arxiv=1409.5738
 |doi=10.1051/0004-6361/201425034
 |volume=586
 |issue=133
 |journal=Astronomy & Astrophysics
 |page=A133
|bibcode = 2016A&A...586A.133P |s2cid=9857299
 }}</ref><ref name="NYT-20140922">{{cite news |last=Overbye |first=Dennis |author-link=Dennis Overbye |date=22 September 2014 |title=Study Confirms Criticism of Big Bang Finding |url=https://www.nytimes.com/2014/09/23/science/space/study-confirms-criticism-of-big-bang-finding.html |url-access=limited |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2014/09/23/science/space/study-confirms-criticism-of-big-bang-finding.html |archive-date=2022-01-01 |access-date=2014-09-22 |work=[[The New York Times]]}}{{cbignore}}</ref> On 30 January 2015, a joint analysis of BICEP2 and [[Planck (spacecraft)|Planck]] data was published and the [[European Space Agency]] announced that the signal can be entirely attributed to interstellar dust in the Milky Way.<ref name="nature-20150130">{{cite news|last=Cowen|first=Ron|title=Gravitational waves discovery now officially dead|date=30 January 2015|newspaper=nature|doi=10.1038/nature.2015.16830}}<!--|access-date=2015-10-26--></ref>