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Searching for the fingerprints of the Big Bang

According to modern cosmology the Universe was created 13.72 billion years ago from the massive expansion of an extremely dense ‘energy point’. Astronomers obtained confirmation of this with the discovery of cosmic background radiation (CBR), the radiation which pervades the entire Universe and which is regarded as the fossil of the Big Bang. Why are we still seeing the background radiation today if it was emitted 3.7 billion years ago? And why does it have a temperature of 2.7 Kelvin today if the Universe was 3000 Kelvin back then? Does radiation always cool down if it is travelling for a longer period of time? The Planck satellite will make it possible to measure very small temperature fluctuations in background radiation. Why are they so important, and what do they reveal to us about the primordial Universe? It is questions such as these that we want to look into in a way that we can visualise.