The view of physics that is most generally accepted at the moment is that one can divide the discussion of the universe into two parts. First, there is the question of the local laws satisfied by the various physical fields. These are usually expressed in the form of differential equations. Secondly, there is the problem of the boundary conditions for these equations, and the global nature of their solutions. This involves thinking about the edge of spacetime in some sense. These two parts may not be independent. Indeed it has been held that the local laws are determined by the large scale structure of the universe. This view is generally connected with the name of Mach, and has more recently been developed by Dirac (1938), Sciama (1953), Dicke (1964), Hoyle and Narlikar (1964), and others. We shall adopt a less ambitious approach: we shall take the local physical laws that have been experimentally determined, and shall see what these laws imply about the large scale structure of the universe.

This chapter guides the reader through three related enigmas of modern physics. The first is a mystery of quantum mechanics. Important aspects of quantum mechanics are still not truly understood, although competing theories have been proposed, including the Many-Worlds approach. The second enigma is the emergence of spacetime, and especially the way it interacts with gravity. Rather than following the traditional methodology of ‘quantising’ classical theories, the author proposes an alternative approach and instead seeks gravity within quantum mechanics. The chapter concludes with a discussion of the mystery of the arrow of time: what distinguishes the past from the future. Together, these three mysteries of modern physics serve as an important reminder of the endurance of enigmas in the very foundations of scholarly fields. Re-examining founding principles can provide a constructive alternative means of investigating mysteries, not only in modern science but also across other disciplines.

In this chapter, spacetime is identified as the empirical realm, to be understood in a relational sense. The spacetime construct emerges from the quantum substratum by way of actualized transactions, which establish spacetime events and their structural connections. This process is discussed in terms of causal set theory. The quantum substratum constitutes the reference for “absolute motion,” and rest-mass systems in the substratum define inertial frames. The transactional process breaks time symmetry, thus establishing an arrow of time and shedding light on the Second Law of Thermodynamics. Implications for free will are also discussed.

Introducing the Minkowski diagram and Minkowski space; how do we represent motion? And how can we represent the phenomena of length contraction and time dilation graphically?

We are now able to deduce the Lorentz transformation, relating two inertial frames. We examine three paradoxes, namely the famous twins paradox, the pole-in-the-barn paradox, and the so-called Bell's spaceships paradox. We also take another look at the relationship with electromagnetism.

This introductory chapter gives a brief survey of some of the phenomena for which classical general relativity is important, primarily at the largest scales, in astrophysics and cosmology. The origins of general relativity can be traced to the conceptual revolution that followed Einstein’s introduction of special relativity in 1905. Newton’s centuries-old gravitational force law is inconsistent with special relativity. Einstein’s quest for a relativistic theory of gravity resulted not in a new force law or a new theory of a relativistic gravitational field, but in a profound conceptual revolution in our views of space and time. Four facts explain a great deal about the role gravity plays in physical phenomena. Gravity is a universal interaction, in Newtonian theory, between all mass, and, in relativistic gravity, between all forms of energy. Gravity is always attractive. Gravity is a long-range interaction, with no scale length. Gravity is the weakest of the four fundamental interactions acting between individual elementary particles at accessible energy scales.