It seems we live in a bizarre Universe. One of the greatest mysteries in the whole of science is the
prospect that 75% of the Universe is made up from a mysterious substance known as ‘Dark Energy’, which
causes an acceleration of the cosmic expansion. Since a further 21% of the Universe is made up from
invisible ‘Cold Dark Mater’ that can only be detected through its gravitational effects, the ordinary atomic
matter making up the rest is apparently only 4% of the total cosmic budget. These discoveries require a
shift in our perception as great as that made after Copernicus’s revelation that the Earth moves around
the Sun. This lecture will start by reviewing the checkered history of Dark Energy, not only since Einstein's
proposal for a similar entity in 1917, but by tracing the concept back to Newton's ideas. This lecture will
summarize the current evidence for Dark Energy and future surveys in which UCL is heavily involved: the
"Dark Energy Survey", the Hubble Space Telescope and the proposed Euclid space mission.