Starost univerzuma — разлика између измена
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{{Short description|Vreme je proteklo od Velikog praska}}{{rut}}
{{Космологија}}
U [[fizička kosmologija|fizičkoj kosmologiji]], '''starost univerzuma''' je [[Космолошка доба|vreme ]] proteklo od [[Велики прасак|Velikog praska]]. Today, astronomers have derived two different measurements of the age of the [[universe]]:<ref>
{{cite news
|publisher=[[European Space Agency]]
|date=17 July 2018
|title=From an almost perfect Universe to the best of both worlds
|department=Planck mission
|at=last paragraphs
|website=sci.esa.int
|url=https://sci.esa.int/s/wRe24lA |url-status=live
|archive-url=https://web.archive.org/web/20200413085647/https://sci.esa.int/web/planck/-/60499-from-an-almost-perfect-universe-to-the-best-of-both-worlds
|archive-date=13 April 2020
}} </ref> a measurement based on direct observations of an early state of the universe, which indicate an age of {{val|13.787|.020}} [[1,000,000,000|billion]] years as interpreted with the [[Lambda-CDM model|Lambda-CDM concordance model]] as of 2018;<ref name="Planck 2018">
{{cite journal
|author=Planck Collaboration
|year=2020
|title=Planck 2018 results. VI. Cosmological parameters
|journal=Astronomy & Astrophysics
|volume=641 |at=page A6 (see PDF page 15, Table 2: "Age/Gyr", last column)
|doi=10.1051/0004-6361/201833910
|arxiv=1807.06209 |s2cid=119335614
}}
</ref>
and a measurement based on the observations of the local, modern universe, which suggest a younger age.<ref>
{{cite journal
|last1=Riess |first1=Adam G. |last2=Casertano |first2=Stefano
|last3=Yuan |first3=Wenlong |last4=Macri |first4=Lucas
|last5=Bucciarelli |first5=Beatrice |last6=Lattanzi |first6=Mario G.
|last7=MacKenty |first7=John W. |last8=Bowers |first8=J. Bradley
|last9=Zheng |first9=Weikang |last10=Filippenko |first10=Alexei V.
|last11=Huang |first11=Caroline |display-authors=6
|date=2018-07-12
|title=Milky Way cepheid standards for measuring cosmic distances and application to Gaia DR2: Implications for the Hubble constant
|journal=The Astrophysical Journal
|volume=861 |issue=2 |pages=126
|issn=1538-4357 |doi=10.3847/1538-4357/aac82e
|arxiv=1804.10655 <!-- |url=http://arxiv.org/abs/1804.10655 --- redundant -->
|bibcode=2018ApJ...861..126R |s2cid=55643027
}}
</ref><ref>
{{cite web
|author=ESA/Planck Collaboration
|date=17 July 2018
|title=Measurements of the Hubble constant
|website=sci.esa.int
|publisher=[[European Space Agency]]
|url=https://sci.esa.int/s/W3kNpXW |url-status=live
|archive-url=https://web.archive.org/web/20201006231013/https://sci.esa.int/web/planck/-/60504-measurements-of-the-hubble-constant
|archive-date=7 October 2020
}}
</ref><ref>
{{cite journal
|last1=Freedman |first1=Wendy L. |last2=Madore |first2=Barry F.
|last3=Hatt |first3=Dylan |last4=Hoyt |first4=Taylor J.
|last5=Jang |first5=In-Sung |last6=Beaton |first6=Rachael L.
|last7=Burns |first7=Christopher R. |last8=Lee |first8=Myung Gyoon
|last9=Monson |first9=Andrew J. |last10=Neeley |first10=Jillian R.
|last11=Phillips |first11=Mark M. |display-authors=6
|date=2019-08-29
|title=The Carnegie-Chicago Hubble Program. VIII. An independent determination of the Hubble constant based on the tip of the red giant branch
|journal=The Astrophysical Journal
|volume=882 |issue=1 |pages=34
|issn=1538-4357 |doi=10.3847/1538-4357/ab2f73
|arxiv=1907.05922 <!-- |url=http://arxiv.org/abs/1907.05922 --- redundant -->
|bibcode=2019ApJ...882...34F |s2cid=196623652
}}
</ref>
The [[measurement uncertainty|uncertainty]] of the first kind of measurement has been narrowed down to 20 million years, based on a number of studies which all gave extremely similar figures for the age. These include studies of the [[microwave background radiation]] by the [[Planck (spacecraft)|''Planck'' spacecraft]], the [[Wilkinson Microwave Anisotropy Probe]] and other space probes. Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang,<ref name="arxiv-20121220">
{{cite journal
|last1=Bennett |first1=C.L.
|display-authors=etal
|date=2013
|title=Nine-year Wilkinson Microwave Anisotropy Probe (WMAP) observations: Final maps and results
|journal=The Astrophysical Journal Supplement Series
|volume=208 |issue=2 |page=20
|bibcode = 2013ApJS..208...20B |s2cid=119271232
|arxiv=1212.5225 |doi=10.1088/0067-0049/208/2/20
}}
</ref>
and measurements of the [[Red shift#Extragalactic observations|expansion rate]] of the universe can be used to calculate its approximate age by extrapolating backwards in time. The range of the estimate is also within the range of the estimate for the [[oldest star|oldest observed star]] in the universe.
== Objašnjenje ==
[[ Lambda-CMD model]] opisuje evoluciju univerzuma od veoma uniformnog, vrelog i gustog početnog stanja pa sve do danas, nekih 13.8 milijadi godina kasnije.<ref>{{cite web
|date=2 April 2013 |title=Cosmic Detectives |url=http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives |publisher=[[European Space Agency]] |access-date=2013-04-15 }} </ref> Ovaj model je veoma dobro razrađen u teoriji i snažno zasnovan u praksi skorašnjim visoko preciznim astronomskim posmatranjima kao sto je [[ WMAP]]. Međutim, teorije o poreklu početnog stanja ostaju na nivou spekulacija. Ukolio bi u Lambda-CDM modelu iz top početnog stanja pokušali da izvedemo neko prethodno stanje, veoma brzo (u deliću sekunde) bi došli do stanja singulariteta zvanog i "singularitet [[Велики прасак|Velikog praska]]". <span class="cx-segment" data-segmentid="337"></span> Iako bi univerzum, u teoriji, mogao da ima i dužu istoriju , [[Međunarodna astronomska unija]]<ref>{{cite news
|last = Chang|first = K.|date = 9. 03. 2008|title = Gauging Age of Universe Becomes More Precise|url = http://www.nytimes.com/2008/03/09/science/space/09cosmos.html?_r=1&oref=slogin|work = [[The New York Times]]|accessdate = }}</ref> trenutno koristi "starost univerzuma" u značenju trajanje Lambda-CDM ekspanzije, ili vreme proteklo od Velikog praska u [[Видљиви свемир|vidljivom univerzumu]].
==Ograničenja koja
Pošto univerzum mora biti star bar koliko i najstarija stvar u njemu, postoje brojnja posmatranja koja daju donju granicu starosti univerzuma.
{{cite journal
| last = Chaboyer | first = Brian
| title = The age of the universe
| date = 1 December 1998
| journal = Physics Reports
| volume = 307 | issue = 1–4 | pages = 23–30
| doi = 10.1016/S0370-1573(98)00054-4| arxiv = astro-ph/9808200
| bibcode = 1998PhR...307...23C | s2cid = 119491951
}}
</ref><ref>
{{cite journal
| last = Chaboyer | first = Brian
| title = A Lower Limit on the Age of the Universe
| date = 16 February 1996
| journal = Science
| volume = 271 | issue = 5251 | pages = 957–961
| doi = 10.1126/science.271.5251.957 | arxiv = astro-ph/9509115
| bibcode = 1996Sci...271..957C | s2cid = 952053
}}
</ref> U okviru njih imamo temperature najhladnijih [[beli patuljak|belih patuljaka]], koji se postepeno hlade kako stare.
==Cosmological parameters==
[[Image:Mplwp universe scale evolution.svg|thumb|left|upright=1.5|The age of the universe can be determined by measuring the [[Hubble constant]] today and extrapolating back in time with the observed value of density parameters (<math>~\Omega~</math>). Before the discovery of [[dark energy]], it was believed that the universe was matter-dominated ([[Einstein–de Sitter universe]], green curve). Note that the [[de Sitter universe]] has infinite age, while the [[Big Crunch|closed]] universe has the least age.]]
[[File:Age Universe Planck 2013.png|thumb|upright=1.5|The value of the age correction factor, <math>~F~,</math> is shown as a function of two [[cosmology|cosmological parameters]]: the current fractional matter density <math>~\Omega_\text{m}~</math> and cosmological constant density <math>~\Omega_\Lambda~.</math> The [[Lambda-CDM model|best-fit values]] of these parameters are shown by the box in the upper left; the matter-dominated universe is shown by the star in the lower right.]]
The problem of determining the age of the universe is closely tied to the problem of determining the values of the cosmological parameters. Today this is largely carried out in the context of the [[Lambda CDM model|ΛCDM]] model, where the universe is assumed to contain normal (baryonic) matter, cold [[dark matter]], radiation (including both [[photon]]s and [[neutrino]]s), and a [[cosmological constant]].
The fractional contribution of each to the current energy density of the universe is given by the [[density parameter]]s <math>~\Omega_\text{m}~,</math> <math>~\Omega_\text{r}~,</math> and <math>~\Omega_\Lambda~.</math>
The full [[ΛCDM]] model is described by a number of other parameters, but for the purpose of computing its age these three, along with the [[Hubble constant|Hubble parameter]] <math>~H_0~</math>, are the most important.
If one has accurate measurements of these parameters, then the age of the universe can be determined by using the [[Friedmann equations|Friedmann equation]]. This equation relates the rate of change in the [[scale factor (cosmology)|scale factor]] <math>~a(t)~</math> to the matter content of the universe. Turning this relation around, we can calculate the change in time per change in scale factor and thus calculate the total age of the universe by [[Integral|integrating]] this formula. The age <math>~t_0~</math> is then given by an expression of the form
:<math>t_0 = \frac{1}{H_0} \, F (\,\Omega_\text{r},\,\Omega_\text{m},\,\Omega_\Lambda,\,\dots\,)~</math>
where <math>~H_0~</math> is the [[Hubble's law|Hubble parameter]] and the function <math>~F~</math> depends only on the fractional contribution to the universe's energy content that comes from various components. The first observation that one can make from this formula is that it is the Hubble parameter that controls that age of the universe, with a correction arising from the matter and energy content. So a rough estimate of the age of the universe comes from the [[Hubble time]], the inverse of the Hubble parameter. With a value for <math>~H_0~</math> around {{val|69|u=km/s/Mpc}}, the Hubble time evaluates to <math>~1/H_0 =~</math>{{val|14.5}} billion years.<ref>
{{Cite book
|last=Liddle |first=A. R.
|date=2003
|title=An Introduction to Modern Cosmology |edition=2nd
|publisher=[[John Wiley & Sons|Wiley]]
|isbn=978-0-470-84835-7
|url=https://archive.org/details/introductiontomo00lidd_717
|url-access=limited
|page=[https://archive.org/details/introductiontomo00lidd_717/page/n73 57]
}}
</ref>
To get a more accurate number, the correction function <math>~F~</math> must be computed. In general this must be done numerically, and the results for a range of cosmological parameter values are shown in the figure. For the [[Lambda CDM model|Planck values]] <math>~(\Omega_\text{m}, \Omega_\Lambda) =~</math>(0.3086, 0.6914), shown by the box in the upper left corner of the figure, this correction factor is about <math>~F = 0.956 ~.</math> For a flat universe without any cosmological constant, shown by the star in the lower right corner, <math>~F = {2}/{3}~</math> is much smaller and thus the universe is younger for a fixed value of the Hubble parameter. To make this figure, <math>~\Omega_\text{r}~</math> is held constant (roughly equivalent to holding the [[Cosmic Microwave Background|CMB]] temperature constant) and the curvature density parameter is fixed by the value of the other three.
Apart from the Planck satellite, the Wilkinson Microwave Anisotropy Probe ([[WMAP]]) was instrumental in establishing an accurate age of the universe, though other measurements must be folded in to gain an accurate number. [[CMB]] measurements are very good at constraining the matter content <math>~\Omega_\text{m}~,</math><ref>
{{cite web
|last=Hu
|first=W.
|title=Animation: Matter Content Sensitivity. The matter-radiation ratio is raised while keeping all other parameters fixed.
|url=http://background.uchicago.edu/%7Ewhu/physics/anim2.html
|publisher=[[University of Chicago]]
|access-date=2008-02-23
|archive-url=https://web.archive.org/web/20080223184613/http://background.uchicago.edu/~whu/physics/anim2.html
|archive-date=23 February 2008
|url-status=live
}}
</ref>
and curvature parameter <math>~\Omega_\text{k}~.</math><ref name="anim3">
{{cite web
|last=Hu |first=W.
|title=Animation: Angular diameter distance scaling with curvature and lambda
|publisher=[[University of Chicago]]
|url=http://background.uchicago.edu/%7Ewhu/physics/anim3.html
|url-status=live |access-date=2008-02-23
|archive-url=https://web.archive.org/web/20080223184618/http://background.uchicago.edu/~whu/physics/anim3.html
|archive-date=23 February 2008
}}
</ref>
It is not as sensitive to <math>~\Omega_\Lambda~</math> directly,<ref name="anim3"/> partly because the cosmological constant becomes important only at low redshift. The most accurate determinations of the Hubble parameter <math>~H_0~</math> are currently believed to come from measured brightnesses and redshifts of distant [[Type Ia supernova]]e. Combining these measurements leads to the generally accepted value for the age of the universe quoted above.
The cosmological constant makes the universe "older" for fixed values of the other parameters. This is significant, since before the cosmological constant became generally accepted, the Big Bang model had difficulty explaining why [[globular cluster]]s in the Milky Way appeared to be far older than the age of the universe as calculated from the Hubble parameter and a matter-only universe.<ref>
{{cite web
|title=Globular Star Clusters
|date=1 July 2011
|publisher=[[SEDS]]
|url=http://messier.seds.org/glob.html
|access-date=2013-07-19 |url-status=dead
|archive-url=https://web.archive.org/web/20080224064318/http://seds.org/messier/glob.html
|archive-date=24 February 2008
}}
</ref><ref>
{{cite web
|last=Iskander |first=E.
|date=11 January 2006
|title=Independent age estimates
|publisher=[[University of British Columbia]]
|url=http://www.astro.ubc.ca/people/scott/bbage.html
|access-date=2008-02-23 |url-status=live
|archive-url=https://web.archive.org/web/20080306024809/http://www.astro.ubc.ca/people/scott/bbage.html
|archive-date=6 March 2008
}}
</ref>
Introducing the cosmological constant allows the universe to be older than these clusters, as well as explaining other features that the matter-only cosmological model could not.<ref>
{{cite arXiv
|last1=Ostriker |first1=J.P.
|last2=Steinhardt |first2=P.J.
|year=1995
|title=Cosmic concordance
|eprint=astro-ph/9505066
}}
</ref>
==Vidi još==
Линија 18 ⟶ 208:
*[[Vidljivi svemir]]
*[[WMAP]]
== Reference ==
{{Reflist}}
== Spoljašnje veze ==
{{div col |colwidth=30em |content=
* {{cite web
|first=Ned |last=Wright
|title=Cosmology tutorial
|publisher=[[University of California, Los Angeles]]
|department=Division of Astronomy & Astrophysics
|type=academic personal site
|url=http://www.astro.ucla.edu/~wright/cosmolog.htm
}}
* {{cite web
| first = Edward L. | last = Wright
| date = 2 July 2005
| title = Age of the Universe
| publisher = [[University of California, Los Angeles]]
| department = Division of Astronomy & Astrophysics
| type = academic personal site
| url = http://www.astro.ucla.edu/~wright/age.html
}}
* {{cite web
|first=Wayne |last=Hu
|title=cosmological parameter animations
|publisher=[[University of Chicago|U. Chicago]]
|type=academic personal site
|url=http://background.uchicago.edu/~whu/metaanim.html
}}
* {{cite arXiv
|last1=Ostriker |first1=J.P.
|last2=Steinhardt |first2=P.J.
|year=1995
|title=Cosmic concordance
|eprint=astro-ph/9505066
}}
* {{cite web
|publisher=[[SEDS]]
|title=Globular star clusters
|url=http://messier.seds.org/glob.html
|url-status=dead <!-- presumed -->
|archive-url=https://web.archive.org/web/20150430163307/http://messier.seds.org/glob.html
|archive-date=2015-04-30
}}
* {{cite web
|first=Douglas |last=Scott
|title=Independent age estimates
|publisher=[[University of British Columbia]]
|place=Vancouver, BC
|type=academic personal site
|url=http://www.astro.ubc.ca/people/scott/bbage.html
}}
* {{cite web
|title=The scale of the universe
|website=KryssTal
|url=http://www.krysstal.com/scale.html
}} — Space and time set to scale for the beginner.
* {{cite web
|title=Cosmology calculator (with graph generation)
|website=iCosmos
|url=http://icosmos.co.uk/
}}
* {{cite web
|title=The Expanding Universe
|publisher=[[American Institute of Physics]]
|url=https://history.aip.org/history/exhibits/cosmology/ideas/expanding.htm
}}
}}
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