Introduction

Attitudes were very different in 1632 when Galileo introduced the idea of Relativity. Almost everybody knows that Albert Einstein was a famous scientist, and most people know that he put forward a theory involving something called Relativity. One argument that people used, was to say that if the Earth were really hurtling though space we would feel its motion. Galileo introduced the idea of Relativity to counter that argument. Isaac Newton’s laws, and his theory of gravity, are therefore consistent with the Principle of Relativity. Special Relativity ignores gravity. After Einstein had formulated Special Relativity he thought a lot about the nature of gravity. General Relativity is directly relevant for our lives, because it is used by satellite navigation systems such as the American Global Positioning System. A satnav uses radio signals from three or more satellites to determine its position, and General Relativity is needed to interpret those signals.