Vesselin Petkov

There are two reasons for asking such an apparently unanswerable question. First, Max Born's recollections of what Minkowski had told him about his research on the physical meaning of the Lorentz transformations and the fact that Minkowski had created the full-blown four-dimensional mathematical formalism of spacetime physics before the end of 1907, both indicate that Minkowski might have arrived at the notion of spacetime independently of Poincare and at a deeper understanding of the basic ideas of special relativity independently of Einstein. So, had he lived longer, Minkowski might have employed successfully his program of regarding four-dimensional physics as spacetime geometry to gravitation as well. Moreover, Hilbert had derived the equations of general relativity simultaneously with Einstein. Second, even if Einstein had arrived at what is today called Einstein's general relativity before Minkowski, Minkowski would have certainly reformulated it in terms of his program of geometrizing physics and might have represented gravitation fully as the manifestation of the non-Euclidean geometry of spacetime exactly like he reformulated Einstein's special relativity in terms of spacetime. [NOTE: The text of two explanations was taken from my previous paper "Is Gravitation Interaction or just Curved-Spacetime Geometry?" because those explanations had to be repeated in the present paper anyway.]

As there have still been attempts to regard gravity, a 100 years after Einstein's general relativity, not as a manifestation of the non-Euclidean geometry of spacetime, but as a physical field, it is high time to face the ultimate judge -- the experimental evidence -- to settle this issue once and for all. Two rulings of the ultimate judge are reminded -- the experimental fact that falling particles do not resist their fall rules out the option that gravity may be a force, and the experiments that confirmed the relativistic effects are impossible in a three-dimensional world, which also implies that gravity is indeed manifestation of the geometry of the real spacetime. It is also stressed that not only are attempts to impose a kind of scientific democracy in physics doomed to failure, but such attempts might, in the end, hamper the advancement of fundamental physics.

This paper pursues two aims. First, to show that the block universe view, regarding the universe as a timelessly existing four-dimensional world, is the only one that is consistent with special relativity. Second, to argue that special relativity alone can resolve the debate on whether the world is three-dimensional or four-dimensional. The argument advanced in the paper is that if the world were three-dimensional the kinematic consequences of special relativity and more importantly the experiments confirming them would be impossible.

Over a hundred years ago in his paper "Space and Time" Hermann Minkowski demonstrated the profound meaning of the relativity postulate - the experimental fact that physical phenomena are the same in all inertial reference frames implies that the Universe is an absolute four-dimensional world in which all moments of time have equal existence due to their belonging to the fourth dimension. Since then there has been no consensus on the reality of this absolute world, which we now call Minkowski spacetime or simply spacetime. I will argue that facing the ultimate judge - the experimental evidence - allows us to settle this issue once and for all.

The present paper pursues two aims. First to show that the experiment proposed by Stolakis [1986] does not lead to absolute synchronization in a single frame of reference and therefore also to the measurement of one-way velocity of light. Second, by consecutively considering the problems of the conventionality of simultaneity and of existence to show that the simultaneity of distant events can be a matter of convention only in a four-dimensional world. * I am grateful to the anonymous referees for their useful suggestions on an earlier version of this paper.

The main purpose of this paper is to demonstrate that the analysis of the kinematical effects of special relativity holds the key to answering the question of the dimensionality of the world. It is shown that these effects and the experiments which confirmed them would be impossible if the world were three-dimensional. Section 2 shows that relativity of simultaneity, conventionality of simultaneity, and the existence of accelerated observers in special relativity would be impossible if the world were three-dimensional. Section 3 deals with the dimensionality of physical objects and demonstrates that the relativistic length contraction and the twin paradox would be impossible if the physical bodies involved in these relativistic effects were three-dimensional objects.