ECHOES

After the Big Bang, the Universe was an incredibly hot fireball, expanding to create the Universe we see around us today. In the beginning though, space was jam-packed full of tiny particles. Light couldn't travel anywhere: it was immediately halted by all the particles that were flying around. So space was completely opaque, a concept which is very hard for us to imagine, as we are used to being able to see everything around us.

But after 300,000 years, the Universe had cooled to about the same temperature as the surface of the Sun. This was when particles began to join to form atoms. Atoms don't interfere with light, letting it travel by unimpeded. So gradually light began to pour through the Universe.

The afterglow from this momentous event formed a bright halo, whose light then began gradually to filter down through space and time. As we look out into space we also look back into time. If it were possible to see out this far, this cosmic halo would form the furthest visible point in the Universe. Everything beyond this, from the birth of the Universe until this epoch of 'first light' will be invisible to us forever.

But if we can't see it then how do we know that it's there? In 1963, two astronomers, Arno Penzias and Robert Wilson, chanced across a mysterious signal, later called 'the cosmic microwave background', or CMB for short. This signal is the leftover energy from this historic cosmic event. An event so powerful that its effects filtered all the way through space and time and can still be detected today. You can even see it for yourself - the fuzzy interference that appears on your untuned TV set is the signature from the early Universe.

When astronomers measured this signal in different directions, they saw that it was stronger in some areas than others. This is due to the fact that in the early Universe atoms weren't spread out evenly, so light flooded across the Universe in uneven ripples. There have been many recent projects, such as BOOMERanG and MAXIMA, which involved sending balloons above the Earth's atmosphere to measure these ripples in the CMB. Astronomers can then create a map of the early Universe and see how matter evolved into galaxies. Not only that, but by measuring this pattern across all of the sky, astronomers can calculate the shape and size of the whole Universe. Doing this will help to crack one of the greatest mysteries of all time - the fate of the Universe.