Transcendent Burn-out Theory
Theory that states that that Fermi's Paradox arises from civilisations transcending right out of the universe before they have a chance to expand across cosmologically significant distances.
According to Transcendent Burn-out Theory, the reason for the rarity of other intelligent races and the lack of an ancient, universe spanning, civilization is that as a civilization spreads across the stars and increases its population, the number of transcensions it experiences increases geometrically. With the spread of a civilization across the stars and the consequent increase in intra-civilization communications,knowledge and expertise, the paths to transcendence to SI:1 and higher levels and the number of safe techniques and methods to achieve these levels increases as a function of the number of communicating sites.
Eventually, virtually all parts of the civilization have transcended to a level that ceases to have any detectable interaction with the observable universe or else have gone extinct. Proponents of this theory point out that it took tens of thousands of years for terragens to achieve the first singularity level on a single world, but in the next few thousand years they achieved some five or more additional levels in thousands of locations.
Ultra-transcendent civilisations might be undetectable for a number of reasons; for instance they could create basement universes for computation that are more suitable for computation than our own universe, and choose to live there instead.