I am reading a book by Sir Arthur Eddington, published in 1935, called New Pathways in Science. Eddington was a great populariser of science in the 1930s, and he was writing only a few years after science was turned completely on its head by the discovery (or invention) of Relativity and Quantum Mechanics. Even though the book is 80 years old and science has moved on, much of it is still relevant, and it has the exciting revolutionary freshness of a master of his field explaining modern fantastical ideas.
One of the philosophical and scientific issues of the 18th and 19th century was the concept of free will. Newtonian mechanics had shown that both the orbits of the planets and the path of a billiard ball could be predicted with complete mathematical precision. Questions arose. If every effect has a cause, and those effects can be calculated (determined) from the cause, does anyone truly possess free will? Surely, it was said, our lives are preordained, and what will be, will be, regardless of any human intervention. The idea was called Determinism.
Quantum Mechanics and thermodynamics replaced certainty with probability. The Uncertainty Principle sets a limit to the predictability of any system. In the sub-microscopic world of the atom, the ‘billiard ball’ does not necessarily go in the direction expected from classical mechanics.
Eddington produced three definitions of determinism, one from Laplace (1749 – 1827), one from Omar Khayyam and one from a philosopher, C D Broad (1787 – 1971). I had never heard of Broad, and perhaps his definition of determinism explains why:
“Determinism” is the name given to the following doctrine. Let S be any substance, ψ any characteristic, and t any moment. Suppose that S is in fact in the state σ with respect to ψ at t. Then the compound supposition that everything else in the world should have been exactly as it in fact was, and that S should instead have been in one of the other two alternative states with respect to ψ is an impossible one. [The three alternative states (of which σ is one) are: to have the characteristic ψ, not to have it, and to be changing.]
I have read this statement a dozen times. I think I understand the point, but is it clear? Is it necessary to resort to Greek letters and compound brackets to express the simple idea of cause and effect? Should one have to read a sentence many times in order to understand it? I think not.