Looking back in time
Brian Cox explains why light from stars and galaxies takes time to travel to Earth.
Light is the fastest thing in the Universe, but it’s not infinitely fast; so the further an object is from us, the further back in time we see it. The light we see from the Sun left its surface 8 minutes ago, and the light from our nearest galaxy, Andromeda, is 2.5 million years old. The Hubble Ultra Deep Field space telescope has taken pictures of a piece of space which is so far away the light has taken 13 billion years to reach us.