What is the “dark energy” behind the big crunch?
Dark energy and dark matter describe proposed solutions to as yet unresolved gravitational phenomena. So far as we know, the two are distinct. Dark matter originates from our efforts to explain the observed mismatch between the gravitational mass and the luminous mass of galaxies and clusters of galaxies. The gravitational mass of an object is determined by measuring the velocity and radius of the orbits of its satellites, just as we can measure the mass of the sun using the velocity and radial distance of its planets. The luminous mass is determined by adding up all the light and converting that number to a mass based on our understanding of how stars shine. This mass-to-light comparison indicates that luminous matter comprises less than 1 percent of the total mass in the universe. There is certainly more matter in our galaxy and other galaxies that we cannot see, but other evidence indicates that there is an upper limit to the total amount of normal matter present in the universe. By
