ABSTRACT
In this chapter we discuss a general procedure to solve the Friedmann equation, finding a general integral expression for the age of the universe, depending on the observable cosmological parameters, in particular https://www.w3.org/1998/Math/MathML"> H 0 $ H_0 $ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781138496903/9a8e923c-4fb7-4659-9b6c-a1dea75201d9/content/inline-math9_1.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> and https://www.w3.org/1998/Math/MathML"> Ω 0 $ \Omega _0 $ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781138496903/9a8e923c-4fb7-4659-9b6c-a1dea75201d9/content/inline-math9_2.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> . In this way we manage to identify two different solutions to the age problem: the first one is an open universe without cosmological constant (i.e., a purely matter model), the second one is a flat Lemaitre model with an admixture of matter and https://www.w3.org/1998/Math/MathML"> Λ $ \Lambda $ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781138496903/9a8e923c-4fb7-4659-9b6c-a1dea75201d9/content/inline-math9_3.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> -like fluid. 1
