The Future of our Universe: From the 21st Century to the End

Abstract

This talk describes our current picture for the long term fate of the cosmos. We discuss the evolution of planets, stars, galaxies, and the universe itself over time scales that greatly exceed the current age of the universe. The story begins with the effects of accelerated cosmic expansion, which causes every galaxy cluster to become its own island universe in the ``near'' future. Next we discuss stellar evolution with a focus on the development of the most common, low mass stars. After accounting for the end of conventional star formation, we find the distribution of stellar remnants -- the neutron stars, white dwarfs, and brown dwarfs remaining after stellar evolution has run its course. In the resulting darkness, star formation continues at a highly attenuated rate through brown dwarf collisions. This process tapers off as the galaxy loses its stars, primarily by ejection through scattering encounters. As the galaxy disperses, weakly interacting dark matter particles are accreted by white dwarfs, where they annihilate and keep the old stellar remnants ``warm.” After the demise of the galaxy, the expelled degenerate objects (primarily white dwarfs) evaporate through the decay of their constituent nucleons. After these stellar remnants have disappeared, the black holes are the brightest astrophysical objects, slowly losing their mass as they emit Hawking radiation. After the largest black holes have evaporated, the universe slowly slides into darkness. Or does it?