Engineering topics
Publications and source records attributed to Frieman, J. A..
It is shown that several schemes for compactification of the extra dimensions in Kaluza-Klein theories are unstable to a quantum gravitational process of barrier penetration: The universe can tunnel from a state with static extra dimensions to a de Sitter expansion of all dimensions. The tunneling rate is estimated, and it is found that the present state of the universe is probably long-lived (in good agreement with observation).
The evolution of inhomogeneous density perturbations in a model of the very early universe that is dominated for a time by a constant energy density of a false quantum-mechanical vacuum is analyzed. During this period, the universe inflates exponentially and supercools exponentially, until a phase transition back to the true vacuum reheats the matter and radiation. Focus is on the physically measurable, coordinate-independent modes of inhomogeneous perturbations of this model and it is found that all modes either are constant or are exponentially damped during the inflationary era.