Spacetime and Reality

Should physicists deal with the question of the reality of spacetime? It is argued that they should since this is a question about the dimensionality of the world and it is physics that should answer it. Almost a hundred years have passed since 1908 when Hermann Minkowski gave a fourdimensional formulation of special relativity according to which space and time are united into an inseparable four-dimensional entity – spacetime – and particles are represented by four-dimensional worldtubes. But so far physicists have not found it necessary to address the question of the reality of these worldtubes and spacetime itself. It seems most physicists assume that spacetime and the worldtubes of particles do not have counterparts in the external world since special relativity can be equally formulated in a three-dimensional and a four-dimensional language. However, while the two formulations of relativity are equivalent in a sense that they correctly describe the relativistic effects, they are diametrically different in terms of the dimensionality of the world. As the world is either three-dimensional or four-dimensional only one of the formulations of relativity adequately represents its dimensionality. For this reason it is a valid question to ask whether spacetime and the worldtubes of particles represent something real or they are just theoretical entities introduced to describe more concisely the relativistic effects that take place in a three-dimensional world. Put another way, the question is: “Does relativity describe a three-dimensional or fourdimensional world?” Many physicists appear to think that these are philosophical questions which they should not bother to answer. However, I doubt whether anyone would seriously argue that the dimensionality of the world is a philosophical question. Minkowski would certainly not. Dealing with the issue of the reality of worldtubes and spacetime is important for several reasons. It is natural to resolve this issue, i.e. the question of the dimensionality of the world according to relativity, first before dealing with the multi-dimensional spaces of more recent theories. Addressing the question of the nature of spacetime will provide us with a deeper understanding of what relativity tells us about the world. In particular, the question of the reality of worldtubes, as will be shown below, has immediate implications for the proper understanding of the physical meaning of the relativistic effects. And that is essential since there still exist misconceptions about the interpretation of some of these effects. For example, the temptation to interpret length contraction in terms of deformation forces is sometimes difficult to resist despite the fact that the muon experiment, for instance,