1443:
563:
40:
654:, so the measured positions of the peaks in the Cosmic Microwave Background spectrum, integrated over the visible sky, are limited by the fact that only one spectrum is observable from Earth. The observable universe viewed from another galaxy will have the peaks in slightly different places, while remaining consistent with the same physical laws, inflation, etc. This second meaning may be regarded as a special case of the third meaning.
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still leaves considerable uncertainty about the underlying model. Variance is normally plotted separately from other sources of uncertainty. Because it is necessarily a large fraction of the signal, workers must be very careful in interpreting the statistical significance of measurements on scales
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In the case of only one realization it is difficult to draw statistical conclusions about its significance. For example, if the underlying model of a physical process implies that the observed property should occur only 1% of the time, does that really mean that the model is excluded? Consider the
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citizens, and so on. For an observer who has only one observation (of his/her own citizenship) and who happens to be French and cannot make any external observations, the model can be rejected at the 99% significance level. Yet the external observers with more information unavailable to the first
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The most widespread use, to which the rest of this article refers, reflects the fact that measurements are affected by cosmic large-scale structure, so a measurement of any region of sky (viewed from Earth) may differ from a measurement of a different region of sky (also viewed from Earth) by an
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In other words, even if the bit of the universe observed is the result of a statistical process, the observer can only view one realization of that process, so our observation is statistically insignificant for saying much about the model, unless the observer is careful to include the
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in density) that happens on the horizon scale only gives us one observable realization. A physical process on a larger scale gives us zero observable realizations. A physical process on a slightly smaller scale gives us a small number of realizations.
1351:
788:, the common way of dealing with this on the horizon scale and on slightly sub-horizon scales (where the number of occurrences is greater than one but still quite small), is to explicitly include the
662:
This most widespread use of the term is based on the idea that it is only possible to observe part of the universe at one particular time, so it is difficult to make statistical statements about
650:
It is sometimes used, mainly by cosmologists, to mean the uncertainty because we can only observe one realization of all the possible observable universes. For example, we can only observe one
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on spacing of satellites in an orbital system. Originally observed for the Solar System, the difficulty in observing other solar systems has limited data to test this.
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686:. In inflationary models, the observer only sees a tiny fraction of the whole universe, much less than a billionth (1/10) of the volume of the
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Somerville; Lee, Kyoungsoo; Ferguson, Henry C.; Gardner, Jonathan P.; Moustakas, Leonidas A.; Giavalisco, Mauro; et al. (2004).
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Portsmouth, Jamie (2004). "Analysis of the
Kamionkowski-Loeb method of reducing cosmic variance with CMB polarization".
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and is separate from other sources of experimental error: a very accurate measurement of only one value drawn from a
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inherent in observations of the universe at extreme distances. It has three different but closely related meanings:
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problems: suppose that random physical processes happen on length scales both smaller than and bigger than the
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of one universe, biologists have a sample size of one fossil record. The problem is closely related to the
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Another problem of limited sample sizes in astronomy, here practical rather than essential, is in the
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physical model of the citizenship of human beings in the early 21st century, where about 30% are
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929:"Quantifying the Effects of Cosmic Variance Using the NOAO Deep-Wide Field Survey"
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and has been the source of much controversy in the cosmology community since the
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Keremedjiev, M. S.; MacDonald, E. C.; Dey, A.; Jannuzi, B. T. (2005).
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of the universe) is the result of processes that follow some general
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postulated in inflation. So the observable universe (the so-called
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on the scale of the entire universe, as the number of observations (
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862:"Cosmic Variance in the Great Observatories Origins Deep Survey"
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amount that may be much greater than the sample variance.
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Stephen
Hawking (2003). Cosmology from the Top Down.
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Proceedings of the Davis
Meeting on Cosmic Inflation
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933:American Astronomical Society Meeting Abstracts
714:throughout the universe can only be described
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718:and cannot be derived from first principles.
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1076:Cosmic microwave background radiation (CMB)
635:It is sometimes used, incorrectly, to mean
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800:. This is important in describing the low
760:observer, know that the model is correct.
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1481:Statistical deviation and dispersion
1040:Cosmology from the Top Down (online)
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792:of very small statistical samples (
710:: for example, the distribution of
682:model is usually supplemented with
13:
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334:2dF Galaxy Redshift Survey ("2dF")
14:
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866:The Astrophysical Journal Letters
549:Timeline of cosmological theories
314:Cosmic Background Explorer (COBE)
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329:Sloan Digital Sky Survey (SDSS)
182:Future of an expanding universe
828:. Just as cosmologists have a
824:A similar problem is faced by
768:. This variance is called the
706:. Some of these processes are
544:History of the Big Bang theory
340:Wilkinson Microwave Anisotropy
1:
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536:Discovery of cosmic microwave
187:Ultimate fate of the universe
1282:Arcminute Microkelvin Imager
643:, and in this case the term
7:
1357:Mobile Anisotropy Telescope
1317:Cosmic Anisotropy Telescope
1277:Atacama Cosmology Telescope
806:cosmic microwave background
652:Cosmic Microwave Background
304:Black Hole Initiative (BHI)
10:
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1087:Discovery of CMB radiation
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1001:10.1103/PhysRevD.70.063504
67:Chronology of the universe
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1092:Timeline of CMB astronomy
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670:) must be not too small.
160:Expansion of the universe
1322:Cosmic Background Imager
1128:Sunyaev–Zeldovich effect
324:Planck space observatory
110:Gravitational wave (GWB)
826:evolutionary biologists
755:citizens, about 1% are
751:citizens, about 5% are
647:should be used instead.
177:Inhomogeneous cosmology
18:Cosmic Variance (blog)
268:Large-scale structure
246:Shape of the universe
1402:South Pole Telescope
1146:image (2018) of the
794:Poisson distribution
722:Philosophical issues
641:Poisson distribution
580:Astronomy portal
538:background radiation
515:List of cosmologists
16:For the weblog, see
1302:BICEP (1,2,3,Array)
993:2004PhRvD..70f3504P
945:2005AAS...20717006K
888:2004ApJ...600L.171S
834:anthropic principle
796:) when calculating
280:Structure formation
172:Friedmann equations
62:Age of the universe
26:Part of a series on
1476:Physical cosmology
1397:Simons Observatory
1133:Thomson scattering
1123:Sachs–Wolfe effect
786:physical cosmology
704:general relativity
319:Dark Energy Survey
263:Large quasar group
32:Physical cosmology
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1113:Diffusion damping
971:Physical Review D
700:quantum mechanics
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947:. Archived from
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879:astro-ph/0309071
872:(2): L171–L174.
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820:Similar problems
779:particle horizon
732:particle horizon
692:particle horizon
684:cosmic inflation
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258:Galaxy formation
218:Lambda-CDM model
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953:. Retrieved
949:the original
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823:
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774:distribution
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741:
736:perturbation
726:This raises
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698:, including
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619:
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342:Probe (WMAP)
276:
273:Reionization
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148:Hubble's law
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118:
90:
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1158:Experiments
830:sample size
668:sample size
629:uncertainty
626:statistical
297:Experiments
230:Dark matter
223:Dark energy
165:FLRW metric
102:Backgrounds
1470:Categories
1352:LSPE/STRIP
1347:Keck Array
1342:GroundBIRD
1332:COSMOSOMAS
1226:LSPE/SWIPE
955:2007-09-18
939:: 170.06.
847:References
802:multipoles
674:Background
377:Copernicus
355:Scientists
210:Components
1392:Saskatoon
1367:POLARBEAR
1221:BOOMERanG
1009:119349882
892:CiteSeerX
664:cosmology
618:The term
507:Zeldovich
407:Friedmann
382:de Sitter
309:BOOMERanG
238:Structure
203:Structure
87:Inflation
1412:Tenerife
1211:Archeops
1190:RELIKT-1
1178:LiteBIRD
914:16650601
790:variance
766:variance
753:American
712:galaxies
688:universe
680:Big Bang
568:Category
487:Suntzeff
447:Lemaître
397:Einstein
362:Aaronson
155:Redshift
57:Universe
50:Big Bang
1448:Physics
1434:Portals
1387:QUIJOTE
1204:Balloon
1142:4-year
1101:Effects
1020:Sources
989:Bibcode
941:Bibcode
884:Bibcode
804:of the
749:Chinese
624:is the
492:Sunyaev
477:Schmidt
467:Penzias
462:Penrose
437:Huygens
427:Hawking
412:Galileo
1312:CAPMAP
1260:Ground
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1246:Spider
1236:MAXIMA
1216:ARCADE
1184:Planck
1144:Planck
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457:Newton
452:Mather
442:Kepler
432:Hubble
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372:Alpher
367:Alfvén
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142:Future
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1460:Space
1382:QUIET
1377:QUBIC
1327:CLASS
1287:AMiBA
1272:ACBAR
1166:Space
1005:S2CID
979:arXiv
910:S2CID
874:arXiv
482:Smoot
472:Rubin
417:Gamow
402:Ellis
387:Dicke
1372:QUaD
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