Inflationary Models

The Pre-inflation Era

Classical physics breaks down at the time when quantum mechanics and general relativity merge: i.e. when the Schwarzschild radius of a volume containing mass MP is on the same order as its Compton wavelength. This determines the size and density of the volume, and the density tells us when in the past history of the Universe this state was achieved: ∽ 5.4 × 10−44 s after the Big Bang. Clearly, physics at or around this time must be regarded as speculative, or simply unverifiable, though that does not stop theoretical physicists from writing papers about it!

If we look some time after the Planck era we are in the era of classical general relativity. During the 1960s, Moscow was a centre for studies of this very early phase of the cosmic expansion with the work of the Khalatnikov group. This culminated in important papers on models for the dynamic evolution of the Universe near the initial singularity by Belinskiǐ and Khalatnikov (1969) and Belinskiǐ, Khalatnikov and Lifshitz (1970, the BKL model). It was during that period that Sakharov wrote the first paper on quantum inhomogeneities in the very early Universe, Sakharov (1966a). In that paper Sakharov addressed the origin of density fluctuations in the framework of a cold Big Bang.