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Tue, 30 Aug 2016

An extra Gigayear for the Universe?

Popular science descriptions of our present understanding of observational cosmology tend to say that we know the age of the Universe to be 13.80 gigayears, with an uncertainty of just 0.02 gigayears (20 megayears). But some of the oldest microlensed stars in the Galactic Bulge, within the central kiloparsec or so of our Galaxy, have best estimated ages of about 14.7 gigayears!. In the figure at left, our analysis of the probability distribution of the most likely age of the oldest of these stars is shown. The thin curves show probability densities for the ages of individual stars—several of these peak between about 14.5 and 15 gigayears. The thick curve shows the age of the oldest of these stars, supposing that we choose the individual star ages randomly according to their probability distributions. (This includes possible ages much lower than in the figure; we take the full asymmetric distributions into account.) So could the Universe be a gigayear older than is generally thought? The uncertainties are still big, but this is certainly an exciting prospect for shifting towards a more physically motivated cosmological model.

The more careful descriptions of the age of the Universe give a caveat—a warning of how or why the standard estimate might be wrong—the age estimate depends on fitting observations by using the standard ΛCDM model. Which is the standard model of cosmology. Meaning that it makes a non-standard assumption about gravity. Instead of allowing space to curve differently in regions where matter collapses into galaxies versus places where the Universe becomes more empty, which is what Einstein's general relativity says, the standard model is rigid (apart from uniform expansion). It doesn't allow general relativity to apply properly.

Several of us have been working on theoretical tools and observational analysis to see if we can apply general relativity better than in the standard model. At least so far, we generally find that doing our homework tells us that the would-be mysterious "dark energy" is really, until or unless proven otherwise, just a misinterpretation of space recently becoming negatively curved (on average) as voids and galaxies have formed during the most recent several gigayears.

This is where the age of the Universe comes in. In our new paper, arXiv:1608.06004, my colleagues and I summarise some key numbers that we argue are needed by any of the "backreaction" models similar to ours, which allow space to curve as galaxies and voids form, as required by the Einstein equation of general relativity. These simple constraints show that by fitting a no-dark-energy flat model (the Einstein–de Sitter model) at early times, the age of the Universe should be somewhat less than 17.3 gigayears, and quite likely somewhat more than the ΛCDM estimate of 13.8 gigayears. So we looked at published observations of stellar ages, which individually still have big uncertainties, but together favour the oldest stars having ages of around 14.7 gigayears. As expected, this is somewhere in between the two limits of 13.8 and 17.3 gigayears.

So will there be a race between detailed "backreaction" models versus stellar observers to get tight cosmological predictions of the age of the Universe versus accurate spectrosopic measurements of the oldest Galactic stars's ages (which have to be younger than the Universe, of course!)?

Barely had our paper become public on ArXiv, that we were reminded by colleagues studying cosmic microwave background (CMB) observations using the Einstein–de Sitter, no-dark-energy, flat cosmological model at early times that they also found an age of the Universe of something like 14.5 gigayears! Figure 4 bottom-right of arXiv:1012.3460 (PRD) shows our colleagues' estimates of the age of the Universe using the CMB and type Ia supernovae observations. Their most likely age is about 14.5 gigayears, give or take about half a gigayear. This is not so very different from the Galactic Bulge star best estimate! So we have very different, independent methods tending to give similar results. The uncertainties are still big. This story is not closed. But an extra Gigayear for the age of the Universe may be a clue that helps shift from the precise ΛCDM cosmology to the upcoming generation of accurate cosmology...

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Sat, 13 Feb 2016

New Windows on the Universe

David Wiltshire from Roy Kerr's institute at the University of Canterbury describes the LIGO discovery of a beautiful gravitational wave signal of a binary black hole merger:

As researchers with the Laser Interferometer Gravitational-Wave Observatory (LIGO) announce they have spotted gravitational waves – ripples in space itself set off by violent astrophysical events – University of Canterbury Professor of Physics Dr David Wiltshire discusses what it means.

The announcement that gravitational waves have been directly captured for the first time ever, from the collision of two black holes, opens a new age of astronomy. From now on we will be able to “listen” to the Universe with “ears” that are not limited by the electromagnetic spectrum, completely changing our understanding. It is a moment in history every bit as important as when Galileo first pointed his telescope at the stars and planets, or when the first radio, X-ray, infrared or gamma ray telescopes were first turned on by 20th century astronomers.

... more at Reflections on Science.

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Sat, 06 Feb 2016

Inhomogeneous relativistic cosmology ADS links

A mix of some recent and some older articles on inhomogeneous relativistic cosmology—especially cosmological backreaction—is available at: ADS inhomogeneous cosmology. This list is not complete!

For selecting a subset of the above:

  1. click on the ADS URL above;
  2. in the ADS interface, Select All Records;
  3. Get form to query selected articles only;
  4. enter normal ADS query parameters, e.g. author, year, and/or words in title or abstract;
  5. Send Query;

The bibcode list is here:

    2017arXiv170100819S 2016arXiv161209309C 2016arXiv161208222B 2016arXiv161203726F 2016arXiv161109275B 2016arXiv161105447M 2016arXiv161103437D 2016arXiv161102139P 2016arXiv161101885S 2016arXiv160904081E 2016arXiv160903724F 2016arXiv160902061C 2016arXiv160806004R 2016arXiv160804403G 2016arXiv160800534M 2016arXiv160800452C 2016arXiv160708797R 2016arXiv160707377K 2016arXiv160705677L 2016arXiv160403503W 2016arXiv160307837T 2016arXiv160301479L 2016arXiv160200302O 2016arXiv160200121R 2016arXiv160107362B 2016arXiv160107356O 2016arXiv160107030S 2016arXiv160100110K 2016PhRvL.116y1301G 2016MNRAS.457.3285M 2016MNRAS.456L..45R 2016JCAP...06..035B 2016JCAP...01..009K 2016IJMPD..2530007B 2016GReGr..48...51B 2015mgm..conf..922K 2015arXiv151209348R 2015arXiv151207869C 2015arXiv151202947O 2015arXiv151105124B 2015arXiv150906316K 2015arXiv150200506K 2015PhRvD..92f9904K 2015PhRvD..92b3532K 2015PhRvD..92b3512A 2015PhRvD..91f3534W 2015PhRvD..91f3519N 2015PhRvD..91f3512S 2015PhRvD..91d3508K 2015MNRAS.453.2364B 2015MNRAS.448.1660R 2015JCAP...08..025K 2015CQGra..32u5021B 2015CQGra..32u5013K 2015CQGra..32p5012S 2015CQGra..32m5007V 2014PhRvD..90l3536P 2014PhRvD..90j3525K 2014PhRvD..90f4021K 2014PhRvD..90b3524K 2014PhRvD..89h9901K 2014PhRvD..89b3520K 2014MNRAS.437.1096R 2014JCAP...12..049C 2014JCAP...05..031B 2014JCAP...02..009B 2014EPJC...74.2786F 2014CQGra..31i5012K 2014CQGra..31h5002K 2014CQGra..31g5021S 2013arXiv1311.5402O 2013arXiv1311.3787W 2013PhRvL.111y1302I 2013PhRvD..88h3529W 2013PhRvD..88d3004F 2013PhRvD..87l3503B 2013JCAP...10..043R 2013JCAP...09..003B 2013IJMPD..2230013K 2013GReGr..45.2529R 2013GReGr..45.1971B 2013GReGr..45.1515R 2013CQGra..30w5008B 2013CQGra..30q5006D 2013CQGra..30f5016S 2013CQGra..30f5015S 2013CQGra..30b5002B 2012dsu..workE..18S 2012arXiv1210.2161L 2012arXiv1206.6164E 2012arXiv1202.0430M 2012PhRvD..86l3508P 2012PhRvD..86j4036K 2012PhRvD..86h3539L 2012PhRvD..86h3520M 2012PhRvD..86f4001K 2012PhRvD..86b3520B 2012PhRvD..85l4016K 2012PhRvD..85j3512B 2012PhRvD..85h3528R 2012PhRvD..85h3502I 2012PhRvD..85d3506C 2012PhRvD..85b3510F 2012GReGr..44..353R 2012GReGr..44..239K 2012GReGr..44...81J 2012EPJC...72.2242R 2012CQGra..29p5007B 2012CQGra..29o5001B 2012CQGra..29k5004R 2012ARNPS..62...57B 2011arXiv1110.1828K 2011arXiv1109.2314C 2011arXiv1105.1864E 2011PhRvD..84l3001D 2011PhRvD..84b3510K 2011PhRvD..83h4020G 2011PhRvD..83h3503K 2011PhRvD..83f3506N 2011MNRAS.418L..45B 2011MNRAS.418.2779S 2011MNRAS.413..367S 2011JCos...15.6100W 2011JCAP...10..016E 2011JCAP...10..002P 2011JCAP...05..028N 2011JCAP...05..003M 2011JCAP...03..029U 2011CQGra..28w5002S 2011CQGra..28p5004R 2011CQGra..28p4009K 2011CQGra..28p4008R 2011CQGra..28p4007B 2011CQGra..28p4006W 2011CQGra..28p4002B 2011CQGra..28p4001E 2011CQGra..28p2002B 2010arXiv1012.0784R 2010arXiv1003.4020V 2010arXiv1001.0904S 2010PhRvD..82l3528R 2010PhRvD..82b3523W 2010PhRvD..81j3512R 2010PhRvD..81b3501G 2010MNRAS.401..547H 2010JCAP...12..021M 2010JCAP...10..021M 2010JCAP...05..020E 2010JCAP...03..018R 2010JCAP...01..004E 2010IJMPD..19.1915B 2010GReGr..42.2813S 2010GReGr..42.2453K 2010GReGr..42.1399K 2010GReGr..42..567M 2010CQGra..27x5017C 2010CQGra..27q5013R 2010CQGra..27q5001S 2010CQGra..27j9002C 2010CQGra..27j5015K 2010AIPC.1241.1146S 2010AIPC.1241.1074M 2010AIPC.1241..991L 2010AIPC.1241..973K 2010A&A...518A..21C 2009arXiv0906.1325T 2009PhRvD..80l3512W 2009PhRvD..80h3525C 2009PhRvD..79h4006L 2009PhRvD..79h3011L 2009PhRvD..79b5009S 2009JCAP...02..011R 2009IJMPD..18.2121W 2009GReGr..41.2017B 2009GReGr..41.1585B 2009EAS....36...63R 2009EAS....36...57C 2008mgm..conf.1837C 2008mgm..conf.1831L 2008mgm..conf..700K 2008dmap.conf..565W 2008arXiv0811.3921E 2008arXiv0809.3314S 2008arXiv0807.1145S 2008PhRvD..78l3531I 2008PhRvD..78h4032W 2008PhRvD..78h3511V 2008PhRvD..78f4038K 2008PhRvD..78f3522P 2008PhRvD..77b3529H 2008PhRvD..77b3003M 2008PhDT.......344M 2008JCAP...10..003B 2008JCAP...04..026R 2008JCAP...02..004M 2008IJMPD..17..641W 2008CQGra..25s5001B 2008CQGra..25q5001C 2008ApJ...672L..91L 2007PhRvL..99y1101W 2007PhRvD..76l3004M 2007PhRvD..76h3504V 2007PhRvD..76d4006P 2007PhRvD..75d3509R 2007PThPh.117..229K 2007NJPh....9..377W 2007JPhA...40.7087K 2007JCAP...12..017B 2007JCAP...02..019E 2006tmpg.conf..279K 2006sf2a.conf..281L 2006PhRvD..74j3507C 2006PhRvD..73b3518H 2006JCAP...11..003R 2006CQGra..23.6379B 2006CQGra..23..235I 2006A&A...454..415B 2005gr.qc.....7057N 2005PhRvL..95o1102C 2005PhLA..347...38E 2005MNRAS.362..213B 2005CQGra..22L.113B 2004PhRvD..69d3502K 2004PhRvD..69b3502K 2004JCAP...02..003R 2003magr.workE..15K 2003PhRvL..90c1101B 2002gr.qc....12072Z 2002gr.qc....12070Z 2002PhRvD..66h4011H 2002PhRvD..65b3501K 2002CQGra..19.6109B 2001GReGr..33.1381B 2001ApJ...558L..79K 2000grg..conf..306B 2000PhRvD..62d3525B 2000GReGr..32..105B 2000A&A...353...63C 1998bhhe.conf..133K 1997JMP....38.4741M 1997BASI...25..401Z 1996rdgm.conf..163K 1995icm..conf...27K 1994CQGra..11.1373K 1994AcC....20...67K 1993PoAst..41...29K 1993GReGr..25..673Z 1992mgm..conf..642K 1992PoFiz..43..415K 1992GReGr..24.1015Z 1991RpMP...29..337K 1989grg..conf..341K 1989grg..conf..340K 1989JMP....30..433K 1987CQGra...4.1697E 1986mgm..conf..989K 1986gcr..conf..500K 1986AN....307..349K 1984grg..conf..215E 1984bbgl.symp...63K 1983grg1.conf..841K 1983GReGr..15..673K 1982botu.conf...15K 1981GReGr..13.1021K 1978AcC.....7..101K
(Last update: 2017-01-06.)

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