age of the universe albert einstein arno allan penzias atom boomerang experiment back-of-the-envelope calculation big bang big bang nucleosynthesis cold dark matter comoving distance constellation cosmic gravitational wave background cosmic inflation cosmic microwave background radiation cosmic neutrino background cosmological principle cosmology dark energy diameter earth edwin hubble euclidean space fornax fred hoyle friedmann equations future of an expanding universe galaxy galaxy filament galaxy formation and evolution george gamow george smoot gould belt gravitational wave hubble ultra deep field hubble volume hydrogen information lambda-cdm model large-scale structure of the cosmos light-year local bubble local group local interstellar cloud metric expansion of space milky way multiverse observation observational cosmology orion arm outer space parsec particle horizon photon physical cosmology planck satellite radiation radius redshift robert woodrow wilson scale factor scientific american shape of the universe sloan digital sky survey solar system spacetime sphere star stephen hawking structure formation sun supercluster technology timeline of cosmology timeline of the big bang trillion ultimate fate of the universe universe vera rubin virgo supercluster wilkinson microwave anisotropy probe