Concordance cosmology without dark energy 3 the basis of other successful approximations, such as halo models and the Press{Schecter formalism The volumetric expansion of mini-universes is the cube of the linear expansion, assuming statistical isotropy Ignor-ing the boundary conditions and the local environment of
"Gravitation and Cosmology"), the Friedmann expansion for V can be denved without reference to anything outside of it so "Remove" the Exterior (same expansion behavior) When the universe becomes inhomogeneous, however, then individually-clustered & vorticity-stabilizedobjects become gravitational attractors, which pull on all other mass
2007b, 2008a), with the conclusion that a new concordance cosmology without ex-otic dark energy based on a realistic average of the observed structures is a likely possibility In this paper I will brie?y outline the key physical ingredients of the new interpretation 2 Geometrical Averaging and Geometrical Variance
universe without dark energy cosmology, which includes dark energy (top left panel, red), the new Avera model, that considers the structure Concordance cosmology without dark energy arxiv
On cosmic acceleration without dark energy View the table of contents for this issue, or go to the journal homepage for more Home Search Collections Journals About Contact us My IOPscience
Gravitational energy as “dark energy” Towards concordance cosmology without David L Wiltshire (University of Canterbury, NZ) DLW: New J Phys 9 (2007) 377
What kind of entities are dark matter and dark energy? What is Going back to cosmology What is The concordance model is empirically supported not just
We do not assume a flat universe in the fitting Our results show that the concordance cold dark matter (CDM) model remains the best model to explain the
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Philosophy and the Sciences
Introduction to the Philosophy of the Physical Sciences ?e 'concordance model' or ΛCD ?is asserts that we live in an in?nite universe, with approximately 5% ordinary matter (baryons), 25% Cold
Dark Matter, and 70% Dark Energy.
It builds on Einstein's general relativity (GR) and the so- called Friedmann-Lemaître-Robertson-Walker (FLRW) models.
Dark Matter and Dark Energy
What kind of entities are dark matter and dark energy? What is the rationale for choosing between rival research programs? ?omas Kuhn on the rationality of theory-choice In ?e Essential Tension (1977), Kuhn pointed out that theory choice seems governed by the following criteria: • accuracy (i.e. the theory is in agreement with experi - mental evidence); • consistency (i.e., the theory is consistent with other accepted scienti?c theories); • broad scope (i.e., the theory has to go beyond the origi- nal phenomena it was designed to explain); • simplicity (i.e., the theory should give a simple account of the phenomena); • fruitfulness (i.e., the theory should be able to predict
Novel phenomena).
• Kuhn: these criteria are either imprecise (e.g., how to de?ne 'simplicity'?); or they con?ict with one another (e.g., while Copernicanism seems preferable to Ptolemaic astronomy on the basis of accuracy; Ptolemaic astronomy fares better on the score of consistency with the Aristote - lian- Archimedean tradition of the time). • ?ese ?ve joint criteria are not su?cient to determine theory choice. • Instead, external, sociological factors seem to play a decisive role in how scientists gather consensus around a given theory.
Going back to cosmology...
What is the current evidence for the concordance model, with dark matter and dark energy? Are there viable alternatives to the concordance model? How do cosmologists make their rational decision of endorsing the concordance model?
Lambda-Cold Dark Matter
by Coldcreation (CC-BY SA 3.0)
What are dark matter and dark energy?
• Evidence from Supernova Ia shows that not only is the universe expanding but it is also accelerating in the ex - pansion. ?e currently most accepted hypothesis for this accelerated expansion is dark energy. • Dark energy means giving weight to the vacuum. If empty space can have density, it can also have anti-gravi - tational properties. • Why do galaxy clusters, and superclusters exist? ?e simplest answer is: because gravity can amplify density irregularities. • By mapping the three dimensional distribution of galax - ies, we're able to infer the density of the universe. • ?e majority of the clumpable matter in the universe is of a form that we only see through gravity. ?e matter we see from radiation is dark matter (DM). Evidence for Dark Matter comes from galaxies' ?at rotation curves.
Alternatives to ΛCDM
Going back to Duhem and the underdetermination prob - lem. Does underdetermination loom in contemporary cosmology?
Two possible rivals to Dark Energy
1. Inhomogeneous Lemaitre-Tolman-Bondi (or LTB) models (rather than the standard FLRW model, which assumes, with the Cosmological Principle, that the Uni - verse is roughly homogeneous and isotropic, namely it has the same uniform structure in all spatial positions and directions).
2. LTB denies homogeneity (but retains isotropy), and
assumes that there are spatial variations in the distri - bution of matter in the Universe, and that we live in an underdense or 'void' region of the Universe (a 'Hubble bubble'), which is expanding at a faster rate than the average. • Instead of modifying FLRW models, we could try to modify General Relativity itself (to avoid DE).
Possible rivals to Dark Matter:
Modi?ed Newtonian Dynamics
or MOND, ?rst pro - posed by Milgrom (1983), and in its relativistic form by
Bekenstein (2010).
Is theory-choice underdetermined in
cosmology? ?e underdetermination argument challenges the ration - ality of theory-choice. Was Kuhn right in claiming that neither simplicity, nor any of the other criteria, will ever be su?cient to deter- mine the rationality of theory choice? Philosophers of science have sometimes appealed to the notion of empir- ical support as a more promising way of thinking about theory choice. ?e concordance model is empirically supported not just when there is direct experimental evidence for some of its main theoretical assumptions, but when the model is inte - grated / embedded into a broader theoretical framework. In this way, the model receives indirect empirical support from any other piece of evidence, which although not a direct consequence of the model itself, are nonetheless consequences of the broader theoretical framework in which the model is embedded. Credit: Lahav, O., Massimi, M. "Dark Energy, Paradigm Shi?s, and the Role of
Evidence" (2014)
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