|A diagram of the separation of powers theory of government, developed by French political philosophy theorist Charles Montesquieu, showing the power of the government divide between the executive (law initiating), legislative (law passing), and judicial branches (law judging), who are kept checked in balance, via some type of two way exchange force arrows, so that no one branch becomes all powerful, and hence unstable.|
The separation of power theories, supposedly, was first discussed by Aristotle, who, in his Politics, discussed the concept of “mixed government”.
In 1748, Charles Montesquieu, in his The Spirit of the Laws, deeply influenced by the celestial mechanics work of Isaac Newton, supposedly, introduced a tripartite political power.
In c.1760, Scottish-born American John Witherspoon, student of the Montesquieu, a signatory of the Declaration of Independence, supposedly, began teaching some type of separation of powers politics in America.
In 1769, American political theorist James Madison (1751-1836), the so-called “father of the constitution”, and America’s fourth president, was said to be studying a primitive form of social physics a Princeton (see: political physics) under Witherspoon.
“To prevent these abuses, it is requisite society should set bounds to its confidence; should limit the power which it delegates to its chiefs; should reserve to itself a sufficient portion of authority to prevent them from injuring it; it must establish prudent checks; it must cautiously divide the powers it confers, because united it will be infallibly oppressed.”
— Baron d’Holbach (1770), The System of Nature (pg. 71)
In 1787, James Madison, the so-called "father of the Constitution", wrote the US Constitution, wherein the separation of powers based government is found. 
In 1919, American 28th president Woodrow Wilson, at some point, supposedly, challenged Madison’s Newtonian-based version of the Constitution, arguing to the effect that it wasn’t Darwinian enough and sought to overcome the “friction” of the separation of powers. The following is Wilson’s concluding argument: 
“The Constitution was founded on the law of gravitation. The government was to exist and move by virtue of the efficacy of ‘checks and balances.’ The trouble with the theory is that government is not a machine, but a living thing. It falls, not under the theory of the universe, but under the theory of organic life. It is accountable to Darwin, not to Newton. It is modified by its environment, necessitated by its tasks, shaped by the sheer pressure of life.”
In 2013, Romanian physicist Radu Chisleag, in his "Newtonian Mechanics and Romanian Constitution Reform", grappled with separation of power issues, in physics terms, in respect to how the new post-socialism constitution was formulated by politicians with no fundamental physical science training, thereby producing some kind of precariously balanced "four powers" constitution model. 
1. Connelly, William F. (2010). James Madison Rules America: the Constitutional Originals of Congressional Partisanship (§: Wilson versus Madison: The Separation of Powers, pgs. 119-). Rowman & Littlefield Publishers.
2. (a) Wilson, Woodrow. (1912). “What is Progress?”, Campaign speech; in: The New Freedom (§2). Publisher, 1913.
(b) Connelly, William F. (2010). James Madison Rules America: the Constitutional Originals of Congressional Partisanship (§: Wilson versus Madison: The Separation of Powers, pgs. 119-). Rowman & Littlefield Publishers.
2. Chisleag, Radu. (2013). "Newtonian Mechanics and Romanian Constitution Reform" (video, 49:19-min) (PowerPoint, 78-slides), talk delivered at the University of Pitesti Econophysics and Sociophysics Workshop (UPESW) / Exploratory Domains of Econophysics News (EDEN V). University of Pitesti, Pitesti, Romania, Jun 29.
● Separation of powers – Wikipedia.