Particle Physics: Ancient Greek Atomists

Physics - Atomism

Atomism arose as an explanatory scheme with the ancient Greeks (around 400BC), Leucippus and Democritus, and Epicurus, and the Roman poet, Lucretius. At the most fundamental level atomism is the belief that all phenomena are explicable in terms of the properties and behaviour of ultimate, elementary, localized entities (or 'fundamental particles'). Thus it prescribes a strategy for the construction of scientific theories in which the behaviour of complex bodies is to be explained in terms of their component parts. That strategy has led to many of the successes of modern physical science, though these do not prove that there actually are 'ultimate entities' of the type postulated by atomism.
Their (the atomists) analysis goes 'behind' the appearance of minute, unchangeable and indestructible 'atoms' separated by the emptiness of 'the void'. It is the void which is said to make change and movement possible. All apparent change is simply the result of rearrangements of the atoms as a consequence of collisions between them. This seems to lead to mechanical determinism, though, in an attempt to leave room for freewill, Epicurus and Lucretius postulated that atoms might 'deviate' in their courses. (For an explanation of Free Will see Philosophy/Free-Will-Determinism)
However if 'what exists' is 'atoms', what of the 'void'? In different ways both Aristotle and Descartes denied that there could be such a thing as literally 'empty space'. Physically therefore they saw the world as a plenum. Atomism was also associated with atheism, since as Lucretius put it, 'Nothing can ever be created out of nothing, even by divine power.' Conversely no thing can ever become nothing - so the atomists proposed a strict principle of conservation of matter.
The attempt of the ancient atomists to solve a metaphysical problem about the nature of change resulted in a brilliantly fruitful strategy for the construction of theories in the physical sciences. However there are unanswered philosophical objections to atomism and the very successes it has stimulated suggest that 'the stuff of the world' cannot ultimately be understood in terms of atomism. A thoroughgoing positivism will continue to hold that 'atomic theories' are simply devices for talking about observable phenomena. (The Concise Encyclopedia of Western Philosophy and Philosophers, 1991)

Particle Physics: Newton's Mechanics

Albert Einstein clearly understood the evolution and metaphysical foundations of physics, so it is interesting to consider his thoughts on Newton's Mechanics (which is founded on the motion of discrete particles in Absolute Space and Time).
Albert Einstein - Matter is not made of particles.The first attempt to lay a uniform theoretical foundation was the work of Newton. In his system everything is reduced to the following concepts:
i) Mass points with invariable mass
ii) Instant action-at-a-distance between any pair of mass points
iii) Law of motion for the mass point.
Physical events, in Newton's view, are to be regarded as the motions, governed by fixed laws, of material points in space. This theoretical scheme is in essence an atomistic and mechanistic one. There was not, strictly speaking, any all-embracing foundation, because an explicit law was only formulated for the actions-at-a-distance of gravitation; while for other actions-at-a-distance nothing was established a priori except the law of equality of actio and reactio. Moreover, Newton himself fully realized that time and space were essential elements, as physically effective factors, of his system. (Albert Einstein, 1940)

In Newtonian physics the elementary theoretical concept on which the theoretical description of material bodies is based is the material point, or particle. Thus matter is considered a priori to be discontinuous. This makes it necessary to consider the action of material points on one another as action-at-a-distance. Since the latter concept seems quite contrary to everyday experience, it is only natural that the contemporaries of Newton - and indeed Newton himself - found it difficult to accept. Owing to the almost miraculous success of the Newtonian system, however, the succeeding generations of physicists became used to the idea of action-at-a-distance. Any doubt was buried for a long time to come. (Albert Einstein, 1950)


As Einstein explains, the problem for the particle conception of matter has always been to explain how matter acts on other matter in the space around the particle. This caused Newton to assume instant action-at-a-distance (gravitational force), though Newton well realised this limitation of his Mechanics (which assumes the motion of particles in Space and Time). Newton simply assumed that discrete particles could act instantly on other particles at-a-distance in Space (Newton's instantaneous action-at-a-distance) though he was well aware of this problem as he explains in his famous letter to Bentley;
Sir Isaac Newton: Physics Famous Scientists - WSM Explains Newton's Three Laws of Motion. 'Absolute Space, in its own nature, without regard to any thing external, remains always similar and immovable' (Newton).It is inconceivable that inanimate brute matter should, without mediation of something else which is not matter, operate on and affect other matter without mutual contact. ... That gravity should be innate, inherent and essential to matter, so that one body may act upon another at-a-distance, through a vacuum, without the mediation of anything else by and through which their action may be conveyed from one to another, is to me so great an absurdity that I believe no man, who has in philosophical matters a competent faculty of thinking, can ever fall into it.
So far I have explained the phenomena by the force of gravity, but I have not yet ascertained the cause of gravity itself. ... and I do not arbitrarily invent hypotheses. (Newton. Letter to Richard Bentley 25 Feb. 1693)


Action-at-a-distance has puzzled philosophers and physicists since Newton first assumed instantaneous action-at-a-distance for gravitational Mass. For if matter is assumed to be a tiny particle, how could it interact (instantly!) with other matter at a distance in Space (across the entire universe)? For example, how do we, here on earth, sense the heat and light from the sun so distant in Space. We now realize that matter is not small, it is large.

Albert Einstein sought to solve this problem by completely rejecting the particle conception of matter, and instead replacing it with a pure field theory of matter (see Einstein Quotes below). Thus matter and space are united by a spherical field structure of matter, and instant action-at-a-distance is replaced with action limited by the velocity of light c (as an electromagnetic wave that changes the structure of the spherical fields that form matter).


Particle Physics: Einstein's Relativity

Albert Einstein - Matter is not made of particles.
The greatest change in the axiomatic basis of physics - in other words, of our conception of the structure of reality - since Newton laid the foundation of theoretical physics was brought about by Faraday's and Maxwell's work on electromagnetic field phenomena. (Albert Einstein, 1931)

The theory of relativity may indeed be said to have put a sort of finishing touch to the mighty intellectual edifice of Maxwell and Lorentz, inasmuch as it seeks to extend field physics to all phenomena, gravitation included. (Albert Einstein, 1934)

According to general relativity, the concept of space detached from any physical content (matter, objects) does not exist. The physical reality of space is represented by a field whose components are continuous functions of four independent variables - the co-ordinates of space and time. Since the theory of general relatively implies the representation of physical reality by a continuous field, the concept of particles or material points cannot play a fundamental part, nor can the concept of motion. The particle can only appear as a limited region in space in which the field strength or the energy density are particularly high. (Albert Einstein, 1954)

When forced to summarize the general theory of relativity in one sentence:
Time and space and gravitation have no separate existence from matter. (Albert Einstein))


Editor: Haselhurst


based

1. http://www.SpaceandMotion.com/Physics-Atom-Atoms-Particle.htm - Evolution of the Particle Concept in Physics. Ancient Greek Atomism, Newton's Mechanics, Einstein's Field Theory of Matter.