According to General Relativity, curvature is dynamical: what then dictates its almost exact flatness in the early universe?

Flatness Problem

Image: According to General Relativity, curvature is dynamical: what then dictates its almost exact flatness in the early universe?


The flatness problem is an example of fine-tuning, noticed by Dicke in 1969. In Friedmann's equation the expansion of the universe is controlled by two factors: the total energy density and the curvature. Today we find from supernova observations that these two numbers cancel almost exactly, yielding a universe which is very close to being flat. When extrapolated backwards the difference between these two numbers shrinks down rapidly, with there difference being less than one part in 10^62.

Proposed solutions to the flatness problem include anthropic reasoning – that we could not observe a universe which was not close to being flat as galaxies would not persist long enough for life to evolve, and cosmic inflation.

Links

Ned Wright on the nature of curvature >

Cormac O’Rafferty : the flatness problem >

Wikipedia: the flatness problem >

Author: David Sloan >

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