The ontology of spacetime
In his 1915 paper, the one in which Einstein asserted the 4-dimensionality of spacetime, he drew upon prior work of Hermann Minkowski and Henri Poincaré, both mathematicians, as authorities supporting his use of the term. At that time, there was no consensus as to the structure of what appeared to be an empty domain, the vast container in which our universe lies suspended, resting on no floor nor touching any boundary. Space was an apparently empty vessel, in which by some mysterious force or suspension, the earth, the moon, the stars and planets moved in a great, harmonious dance, The relationships of these entities were governed by an equally mysterious attraction, called gravity, which in opposition to the centrifugal force embodied in their orbits, maintained, over billions of years, this precarious balance.
Now, Einstein must have known in his innermost understanding, that space, empty, formless, having no sensible reality in and of itself, was not a thing, a real physical entity. And he must have also, this mathematical genius, known that its fellow concept, time, shared that condition, being unseen, not tangible, and incapable of modification. Still, the conceptual notion was broadly accepted that three dimensions were the minimum requirement for location and describing objects’ relative character and position. It was also broadly understood that an object’s persistence, it’s existential duration, could be measured in units of time.
In ordinary space, a position is(can be) specified by three numbers, known as dimensions. In the Cartesian coordinate system, these are called x, y, and z. A position in spacetime is called an event, and requires four numbers to be specified: the three-dimensional location in space, plus the position in time. Spacetime is thus four dimensional. An event is something that happens instantaneously at a single point in spacetime, represented by a set of coordinates x, y, z and t.
The other prime benefit of adopting this four-dimensional construct, spacetime, was that it can be used directly in mathematics, the essential symbolic language of physics, and that that lent validity to his theory.
So, in the end, Albert Einstein’s Theory of General Relativity was developed, published, and became, ultimately, the standard methodology for the description and explanation of the mystery of this wonderful aggregation of billons of stars planets, galaxies. This beautiful (self described by its author) mathematical construct, defining the relationships between two purely mathematical (not real) concepts became accepted as the ultimate description of something that is actuallyreal, the universe itself.
How explain this? No one at the time seemed to question the essential, physical reality of the purely mathematical elements of the theory, that is, that space and time were, at best, only real as symbols of something else. There were and had been only hints and assertions that space was more than just an empty vessel. Faraday knew it as a field or collection of fields, of pure energy, Maxwell and Lorenz put forth the notion that it (space) might be a vessel but a filled one, hosting an as yet undetectable ether which provided a medium to explain the transmission of electromagnetic forces, light, and the like., but basically most physicists even to this day, have been lured into seeing space as an object in and of itself, capable of being bent, curved, distorted, and hence explaining gravity and other effects, all derived from and conflated with Einstein’s mathematical conceptualization
What of Einstein himself? Did he believe in space as a true medium? Did he see it as an elastic solid, deformable by outside forces and objects? Or was his use of the word purely metaphorical, in service of his mathematical ambitions. He was a questioning man, perhaps he felt that reducing the word to a set of equations was enough. At any rate, we never learned what he saw in his imagination when he thought of the German word Raum, or the word Zeit, combining them into his essentially Germanic neologism Raumzeit, translated into the English word, spacetime.
I’d like to add here one more cautionary assertion. A dimensionis not real either, in the sense that it exists on its own, mysteriously inhabiting space, giving it a structure or form. Dimensions are human symbolic constructs, invented for a particular purpose, to describe and communicate certain attributes of real objects, events sand phenomena, to tell us their location relative to reference points, to describe their size or extent, to give conceptual form to instructions. All those and more. I have written about this elsewhere, in a piece entitled “How many dimensions make a universe?” The answer is: as many as you need, to adequately establish the location of a post, or a galaxy, to communicate essential information about its size, extent motion, velocity. It amazes me to hear otherwise rational, intelligent scientists use these terms as if they referred to some real thing, one which no one has ever seen felt, tasted, touched or experienced in any other way. 9Now you know some of my sensitivity buttons.)
So, let’s back up a little bit.
If what we call space were real, substantive, a thing in and of itself, we could say it could be bent, curved, distorted, by the presence of a large mass, and that if smaller (or larger) masses drew near, they would be drawn together by that distortion, what Newton called a force, as in the famous elastic sheet metaphor. (If you look carefully at those illustrations, you may wonder what gravitational force existed below the sheet to draw those masses down). There is no explanation in General Relativity as to what force causes the distortion of spacetime, only that distortion occurs. No causality explanation is offered, by Einstein or any later specialist. Only that “space” is distorted by the presence of a mass. Aristotle thought that objects fell to earth because of an “affinity” is felt, perhaps like the “chemistry that draws two lovers. But no further explanation is offered by General Relativity, only that attraction occurs
We are left with only one answer that makes sense. That “spacetime” was offered as a metaphor for an as yet (in 1915) unknown medium, or flexible solid, that is still not visible but might be, perhaps detectable by other means at our disposal. Michelson and Morley basically disproved that a particulate ether existed that all of these “real” things of the universe are passing through, planets, stars, light, magnetic fields, and the like. But the idea that “spacetime” is a metaphor for a field, probably an electromagnetic one, is a real possibility. If we extend that thought to what I have proposed, that is, that all of our detectable objects events, and phenomena are organized distortions of that field becomes a real possibility
Truly this is revolutionary. Not only is General Relativity overthrown, but also quantum mechanics, most of particle physics and their related fields. Hence, every particle does not have a field , but is a concentration of energy that distorts its region of the only real field, the primal measureless electromagnetic cosmos. As large masses (very high concentrations of energy) exist, they generate equivalent distortions of the field, explaining apparent attraction and effects at a distance, what we now call gravitation. One field, an elastic solid, bearing within it and of it organized distortions we know as our perceptible universe, truly simple.