I'm currently reading Dodelson's "Modern Cosmology" where he in Chapter 4.2 discuss the Boltzmann equation for photons and consider a perturbed FRW spacetime for which ##g_{00} = -1 - 2 \Psi## and ##g_{ij} = a^2 \delta_{ij}(1+2\Phi)##. At page 90 he states that "in an overdense region we have ##\Psi <0## and ##\Phi >0##. Why is this true?(adsbygoogle = window.adsbygoogle || []).push({});

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# FRW pertubations in overdense and underdense regions

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