大象传媒

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鈥檚 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.