Q: How big is space?
A: 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 at UW-Madison. 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.