Reference: A Logical Approach to Theoretical Physics
Here is an interesting commentary on the logical framework of physics [“Continuity and the Void” by Kevin Brown].
Several early Greek philosophers, including Democritus, imagined the universe as consisting of a multitude of irreducible particles moving in an empty void. On the other hand, Aristotle (c. 350 BC) denied the existence of a “void” (a region of space containing no substance), believing instead that the universe is filled continuously with substance… From this point of view it’s possible for a continuous substance to possess variable density, so the compressibility of air does not imply the existence of empty spaces.
The modern physics is based on the “particles in void” framework. It does not believe that the universe is filled continuously with substance.
“Particles” represent isolated bits of matter that are separated by void. Therefore, there is no continuity among the particles. They are never directly in contact.
Particles have properties that we may perceive. But void is perceived only as a gap among particles. Void has no properties of its own that may be perceived.
There is nothing that continues across the boundary between a particle and void except for geometry. The measures of geometry exist even when there is no substance to measure. Therefore, any possibility of continuum of substance is replaced by geometry in the “particles in void” framework.
Common to particles and void is the mathematical abstraction of geometry.
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Geometry
Astronomy considers stars and planets as point particles in the sky separated by vast distances. The obvious relationship among them is provided by Geometry. The other consideration is the motion of the moon around the earth, and planets around the sun, which requires the presence of some kind of force between them.
The success of Newton’s universal law of gravity raised the importance of geometry and mathematics, and established “particles in void” as the logical framework of physics. But with this framework arose the problem of “action at a distance”. It required the presence of some mechanism in the void.
This revived the concept of aether as the substance, which permeated the void. Newton wrote [“Newton’s Principia” (1686) Translation by Andrew Motte, American edition of 1846, p. 26]:
A most subtle spirit which pervades all bodies…by the force and action of which spirit the particles of bodies mutually attract one another, at near distances, and cohere, if contiguous; and electric bodies operate at greater distances, as well repelling as attracting the neighbouring corpuscles; and light is emitted, reflected, refracted, inflected and heats bodies; and all sensation is excited, and the members of animal bodies move at the command of the will, namely, by the vibrations of this spirit, mutually propagated along the solid filaments of the nerves, from the outward organs of sense to the brain, and from the brain into the muscles.
But the possibility of aether and its actual nature was yet to be corroborated with reality.
Geometry alone could not explain how force got communicated across the void. It then led to the postulate of aether as a substance permeating the void.
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Electricity and Magnetism
The phenomena of electricity and magnetism were being studied extensively during the 18th and 19th centuries. During this period the atomic theory was being used to explain the chemical structure of matter. The phenomena of electricity and magnetism seemed to explain how force was communicated through the void between atoms.
From his experimental investigation into electricity and magnetism, Faraday formed the view [“A speculation touching Electrical Conduction and the Nature of Matter” by Michael Faraday (1844), Philosophical Magazine and Journal of Science, Vol. XXIV, p. 136] that an atom is not a supposed little hard particle separate from the powers around it. An atom is constituted of the powers it has, and it extends as far as its powers extend.
… where is there the least ground (except in a gratuitous assumption) for imagining a difference in kind between the nature of that space midway between the centres of two contiguous atoms and any other spot between these centres? a difference in degree, or even in the nature of the power consistent with the law of continuity, I can admit, but the difference between a supposed little hard particle and the powers around it I cannot imagine…
Hence matter will be continuous throughout, and in considering a mass of it we have not to suppose a distinction between its atoms and any intervening space. The powers around the centres give these centres the properties of atoms of matter; and these powers again, when many centres by their conjoint forces are grouped into a mass, give to every part of that mass the properties of matter. In such a view all the contradiction resulting from the consideration of electric insulation and conduction disappears.
Thus, in matter the atoms touch each other and there is no void among them.
But is there a similar situation with the bodies in the heavens? Do these bodies touch each other with their power of gravity that is extended as aether?
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Light and Gravity
The phenomena of light and gravity were studied extensively by Newton himself in the 17th century. This study was carried forward in 18th and 19th centuries, but no connection was ever made between light and gravity.
Faraday, however, stated the following [“Thoughts on Ray Vibrations”, Lecture by Michael Faraday (1846), Experimental Researches in Electricity, Vol III, M. Faraday, p447-452]:
The view which I am so bold to put forth considers, therefore, radiation as a kind of species of vibration in the lines of force which are known to connect particles and also masses of matter together. It endeavors to dismiss the aether, but not the vibration …
The aether is assumed as pervading all bodies as well as space: in the view now set forth, it is the forces of the atomic centres which pervade (and make) all bodies, and also penetrate all space. As regards space, the difference is, that the aether presents successive parts of centres of action, and the present supposition only lines of action; as regards matter, the difference is, that the aether lies between the particles and so carries on the vibrations, whilst as respects the supposition, it is by the lines of force between the centres of the particles that the vibration is continued.
According to Faraday, there was no separate substance, such as, aether. Matter itself extended as lines of force filling all space between the material bodies. Radiation was the vibrations in these lines of force.
Faraday looked at radiation, such as, light, to be the extension that carried the force of matter.
In short, the idea of “void” was unsustainable. First, the theoretical concept of “aether”, and then, a more realistic idea of “force carrying radiation” were simply the attempts to discover the nature of “space”, which was thought to be void of matter.
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