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).
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;
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).