Thirteen billion years ago our universe was dark. There were neither stars nor galaxies; there was only hydrogen gas left over after the Big Bang. Eventually hydrogen atoms began to clump together to form stars—the very first ones to exist—initiating a major phase in the evolution of the universe, known as the Epoch of Reionization, or EoR.
“It boggles the mind that over 90% of the galaxies in the Universe have yet to be studied. Who knows what we will find when we observe these galaxies with the next generation of telescopes,” says astronomer Christopher Conselice, who led the 2016 team that discovered that there are ten times more galaxies in the universe than previously thought, and an even wider space to search for extraterrestrial life.
From our tiny blue dot, the universe appears inconceivably vast. In the grand cosmic scheme of things, all the light in the observable universe provides about as much illumination as a 60-watt bulb seen from 2.5 miles away, says Marco Ajello, an astrophysicist at Clemson University, who led a team in 2018 that has measured all of the starlight ever produced throughout the history of the observable universe.
Astronomers are confident that the volume of space-time within range of our telescopes—‘the universe’—is only a tiny fraction of the aftermath of the big bang. “We’d expect far more galaxies located beyond the horizon, unobservable,” says renowned astrophysicist Martin Rees, “each of which (along with any intelligences it hosts) will evolve rather like our own.”