Seminarium KMMF "Teoria Dwoistości"

1. The Friedmann-Lemaitre (FL) cosmological models and their basicimplications. In this part of the talk will I show how the FL models follow from symmetry assumptions imposed on the Einstein equations, and will briefly explain their relation to observational cosmology. Emphasis will be put on dubious claims based on these models, such as the cosmological principle and the hypothesis of accelerated expansion of the Universe. 2. The Lemaitre-Tolman (LT) models and their relation to some of thecosmological observations. These models are the simplest known generalisation of the FL models. In spite of being spherically symmetric, they allow for several interesting insights, within the exact theory, into the consequences of existence of matter condensations and voids in the Universe. In this part of the talk I will show how spatial variations in the expansion pattern can mimic the accelerated expansion of the Universe without the need to introduce "dark energy". 3. The Szekeres (Sz) models and their observational implicationsThese models are fully nonsymmetric generalisations of the LT models. They arise by making the spheres, invariantly defined in the LT geometry, non-concentric. This allows for describing still more observable phenomena. One of them is the direction drift of light rays propagating through mass inhomogeneities (this effect is also present for nonradial rays in LT models). This will signal inhomogeneity in large-scale matter distribution when the observations become sufficiently precise. 4. If time permits: In the LT and Sz models some of the light rays emitted soon after the Big Bang get blue-shifted rather than redshifted, i. e. their observed frequency is higher than at the emission point. Possible observational signatures of such rays will be discussed.