"This talk will mostly be stories... I want to tell you about Albert Einstein, and about his theory of relativity - what it is, why he was thinking about it and also about some of the very latest developments that have happened just this year."
Albert Einstein is one of the most famous scientists in history. His greatest achievement is the general theory of relativity, which describes how the force of gravity works. It is the theory which explains why apples fall from trees, why we are all stuck to the Earth, why the Moon orbits the Earth, and the Earth orbits the Sun.
This talk by Professor David Tong from the University of Cambridge was originally given to an audience of 16-17 year olds. You can read a simpler article about how Einstein developed his theory of relativity here.