Is supernovae data in favour of isotropic cosmologies?
نویسنده
چکیده
Most of the observational claims in cosmology are based on the assumption that the universe is isotropic and homogeneous so they essentially test different types of Friedmann models. This also refers to recent observations of supernovae Ia, which, within the framework of Friedmann cosmologies give strong support to negative pressure matter and also weaken the age conflict. In this essay we drop the assumption of homogeneity, though temporarily leaving the assumption of isotropy with respect to one point, and show that supernovae data can be consistent with a model of the universe with inhomogeneous pressure known as the Stephani model. Being consistent with supernovae data we are able to get the age of the universe in this model to be about 3.8 Gyr more than in its Friedmann counterpart. An essay presented for Gravity Research Foundation Essay Competition ’99. ∗email:[email protected]
منابع مشابه
Isotropic singularities in shear-free perfect fluid cosmologies
We investigate barotropic perfect fluid cosmologies which admit an isotropic singularity. From the General Vorticity Result of Scott, it is known that these cosmologies must be irrotational. In this paper we prove, using two different methods, that if we make the additional assumption that the perfect fluid is shear-free, then the fluid flow must be geodesic. This then implies that the only she...
متن کاملIsotropic Cosmological Singularities Ii. the Einstein-vlasov System
We consider the conformal Einstein equations for massless colli-sionless gas cosmologies which admit an isotropic singularity. After developing the general theory, we restrict to spatially-homogeneous cosmologies. We show that the Cauchy problem for these equations is well-posed with data consisting of the limiting particle distribution function at the singularity.
متن کاملIsotropic cosmologies in Weyl geometry
We study homogeneous and isotropic cosmologies in a Weyl spacetime. We show that for homogeneous and isotropic spacetimes, the field equations can be reduced to the Einstein equations with a twofluid source. We write the equations as a two-dimensional dynamical system and analyze the qualitative, asymptotic behavior of the models. We examine the possibility that in certain theories the Weyl 1-f...
متن کاملIsotropic Cosmological Singularities I. Polytropic Perfect Fluid Spacetimes
We consider the conformal Einstein equations for 1 ≤ γ ≤ 2 poly-tropic perfect fluid cosmologies which admit an isotropic singularity. For 1 < γ ≤ 2 it is shown that the Cauchy problem for these equations is well-posed, that is to say that solutions exist, are unique and depend smoothly on the data, with data consisting of simply the 3-metric of the singularity. The analogous result for γ = 1 (...
متن کاملIsotropic and Anisotropic Bouncing Cosmologies in Palatini Gravity
We study isotropic and anisotropic (Bianchi I) cosmologies in Palatini f(R) and f(R,RμνR μν) theories of gravity and consider the existence of non-singular bouncing solutions in the early universe. We find that all f(R) models with isotropic bouncing solutions develop shear singularities in the anisotropic case. On the contrary, the simple quadratic model R+ aR/RP +RμνR /RP exhibits regular bou...
متن کامل