Kerr-Schild geometry from cosmology to microworld and space-time structure

The Kerr-Schild (KS) geometry is linked tightly with the auxiliary flat Minkowski background. Nevertheless, it describes many curved spacetimes and the related physical models, starting from cosmology and black holes to the microworld of the spinning elementary particles and the prequantum structure of vacuum fluctuations. We consider here a KS model of the Bubble Universe – a semi-closed Universe with a rotating de Sitter (or anti-de Sitter) space embedded in an external flat space-time. When the solution has two horizons, it may also be interpreted as an Universe inside a black hole. In micro-world the KS geometry yields a model of the spinning particle consistent with gravity and describes a pre-quantum twistorial structure of space-time with the beam-like fluctuations of metric consistent with the beamlike fluctuations of electromagnetic vacuum. These light-like twistor-beams excitations are consistent with gravity and generalize the known pp-wave solutions. Following Wheeler’s estimations of the density of vacuum fluctuations we arrive at the general conclusion that Universe should be flat and have a zero cosmological constant. It contradicts predominant doctrine of the Big Bang and expanding Universe, and enforces us to return to an ‘effective flat geometry’ filled by the electromagnetic background radiation.