In many ways, physics stems from ancient Greek philosophy. From Thales' first attempt to characterize matter, to Democritus' deduction that matter ought to reduce to an invariant state, the Ptolemaic astronomy of a crystalline firmament, and Aristotle's book Physics (an early book on physics, which attempted to analyze and define motion from a philosophical point of view), various Greek philosophers advanced their own theories of nature. Physics was known as natural philosophy until the late 18th century.
By the 19th century physics was realized as a discipline distinct from philosophy and the other sciences. Physics, as with the rest of science, relies on philosophy of science to give an adequate description of the scientific method.[13] The scientific method employs a priori reasoning as well as a posteriori reasoning and the use of Bayesian inference to measure the validity of a given theory.[14]
The development of physics has answered many questions of early philosophers, but has also raised new questions. Study of the philosophical issues surrounding physics, the philosophy of physics, involves issues such as the nature of space and time, determinism, and metaphysical outlooks such as empiricism, naturalism and realism.[15]
Many physicists have written about the philosophical implications of their work, for instance Laplace, who championed causal determinism,[16] and Erwin Schrödinger, who wrote on quantum mechanics.[17] The mathematical physicist Roger Penrose has been called a Platonist by Stephen Hawking,[18] a view Penrose discusses in his book, The Road to Reality.[19] Hawking refers to himself as an "unashamed reductionist" and takes issue with Penrose's views.[20]