The Principle of Relativity and the Origin of Inertia

After sketching the nature of the central problem in rapid spacetime transport – the manipulation of inertia – Mach’s ideas on the topic are mentioned. The origins of the concept of inertia and the principles of relativity and equivalence in the seventeenth century are outlined. But they did not lead to the theory of relativity, in no small part because of Newton’s adoption of absolute space and time. Special relativity theory is investigated, leading to Einstein’s discovery of the relationship between energy and inertial mass: \( m = E/{{c}^2} \), where E is the total non-gravitational energy of an isolated object at rest and c the speed of light in vacuum. How general relativity theory bears on this definition of inertial mass is then explored. The role of the Equivalence Principle – particularly, the prohibition of the localization of gravitational potential energy and the nature and role of “fictitious” forces – is examined, preparing the way for a discussion of Mach’s principle in Chap. 2. The behavior of light in the vicinity of negative mass matter is mentioned in anticipation of the third section of the book.