Noun
a natural phenomenon involving the physical properties of matter and energy
Source: WordNetEmpirical evidence can never establish mathematical existence--nor can the mathematician's demand for existence be dismissed by the physicist as useless rigor. Only a mathematical existence proof can ensure that the mathematical description of a physical phenomenon is meaningful. Richard Courant
Since we seek to know what is the physical phenomenon we perceive, we must first enunciate this proposition, which will govern the whole of our discussion: to wit- Of the outer world we know nothing except our sensations. Alfred Binet