If inflation occurred at a constant rate through the life of the universe, that same spot is 46 billion light-years away today according to Ethan Siegel, writing for Forbes (opens in new tab), making the diameter of the observable universe a sphere around 92 billion light-years. Thus, while scientists might see a spot that lay 13.8 billion light-years from Earth at the time of the Big Bang, the universe has continued to expand over its lifetime. Scientists know that the universe is expanding. The word "observable" is key the sphere limits what scientists can see but not what is there.īut though the sphere appears almost 28 billion light-years in diameter, it is far larger. Like a ship in the empty ocean, astronomers on Earth can turn their telescopes to peer 13.8 billion light-years in every direction, which puts Earth inside of an observable sphere with a radius of 13.8 billion light-years. "When it arrives, it tells us about the whole history of our universe."īecause of the connection between distance and the speed of light, this means scientists can look at a region of space that lies 13.8 billion light-years away. project scientist for the mission at NASA's Jet Propulsion Laboratory in Pasadena, California, in a statement (opens in new tab). "The cosmic microwave background light is a traveler from far away and long ago," said Charles Lawrence, the U.S.