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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
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. |
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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:
- click on the ADS URL above;
- in the ADS interface, Select All Records;
- Get form to query selected articles only;
- enter normal ADS query parameters, e.g. author, year, and/or words in title or abstract;
- Send Query;
The bibcode list is here:
-
2018arXiv180510455B
2018arXiv180108566B
2018arXiv180108362W
2018MNRAS.473L..46B
2018CQGra..35b4003B
2018AAS...23142005B
2017arXiv171204229T
2017arXiv171204041B
2017arXiv171202967B
2017arXiv171008804B
2017arXiv171002496G
2017arXiv171002451M
2017arXiv171002374D
2017arXiv170906022M
2017arXiv170809143B
2017arXiv170807769F
2017arXiv170801031H
2017arXiv170700191S
2017arXiv170700111Y
2017arXiv170609309A
2017arXiv170607236D
2017arXiv170606179R
2017arXiv170502328S
2017arXiv170408975L
2017arXiv170402810B
2017arXiv170401774C
2017arXiv170400703B
2017arXiv170308809K
2017arXiv170308552S
2017arXiv170304191R
2017arXiv170303572K
2017arXiv170100819S
2017PhRvD..95f3517S
2017JCAP...07..028S
2017A&A...598A.111R
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
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2015MNRAS.453.2364B
2015MNRAS.448.1660R
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2014MNRAS.437.1096R
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2014JCAP...05..031B
2014JCAP...02..009B
2014EPJC...74.2786F
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2013arXiv1311.5402O
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2013CQGra..30b5002B
2012igrc.book.....P
2012dsu..workE..18S
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2012EPJC...72.2242R
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2012ARNPS..62...57B
2011arXiv1110.1828K
2011arXiv1109.2314C
2011arXiv1105.1864E
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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
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2011CQGra..28p4001E
2011CQGra..28p2002B
2010arXiv1012.3084B
2010arXiv1012.3083B
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
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2010GReGr..42..567M
2010CQGra..27x5017C
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2010CQGra..27j9002C
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2010AIPC.1241.1146S
2010AIPC.1241.1074M
2010AIPC.1241..991L
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2010A&A...518A..21C
2009suem.book.....B
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2008wscm.conf..118C
2008mgm..conf.1837C
2008mgm..conf.1831L
2008mgm..conf..700K
2008dmap.conf..565W
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2006tmgm.meet...80K
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2006PhRvD..73b3518H
2006PhLA..354....8B
2006JCAP...11..003R
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2006CQGra..23..817B
2006CQGra..23..235I
2006A&A...454..415B
2005gr.qc.....7057N
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2005PhLA..347...38E
2005MNRAS.362..213B
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2002nmgm.meet..627K
2002grcg.conf...29B
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1978AcC.....7..101K
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