Einstein's discovery of general relativity in the last century enabled us for the first time in history to come up with a compelling, testable theory of the Universe. There are two aspects of cosmology. First, there is an enormous amount of data today. The other aspect of modern cosmology is that we have developed a consistent theoretical framework which agrees quantitatively with data. These two features are the secret of the modern cosmology. The realisation that the Universe is expanding and was once much hotter and denser, can be tested against astronomical data. The theoretical and...