How big is space?
Space is probably infinite, but we can see only the part that contains stars or galaxies whose light has been able to reach us, says Francis Halzen, a professor of physics.
The universe originated about 13.7 billion years ago with the Big Bang, so light cannot have been traveling for more than 13.7 billion years. “Since we know how old the universe is,” Halzen says, “and the speed of light, we can calculate the size of space we can see.”
Halzen, who directs a giant telescope in Antarctica that is designed to see neutrinos spewed by titanic explosions in the distant universe, says we can theoretically see about 13.7 billion light years in any direction. Because light travels almost 6 trillion miles in a year, it can “only” have traveled about 80 billion trillion miles since the Big Bang.
Practically, astronomers struggle mightily to see objects at these astounding distances. It’s likely that the extremely distant objects that created this ancient light have since blown themselves to bits, but the light from those explosions has not yet reached Earth.