A theory of subatomic physics begun by Max Planck (1858-1947) and developed by Niels Bohr (1885-1962), Ernst Schrṭdinger (1887-1961), Werner Heisenberg (1901-1976), Paul Dirac (1902-1984) and others. In order to form an elementary understanding of quantum theory, it is useful to compare it to Newtonian and Einsteinian physics. In Newton's classical view, science defines the structure and movement of matter in a very fixed and real sense. Matter is composed of particles that move according to the same forces that govern the movement of billiard balls. Einstein argued that while the structure of matter ought to be considered definite, its movement is not. If particles are like billiard balls in motion, then the billiard table is also in motion. The billiard table is comprised of space and time, which are not two separate entitieshence the term spacetime in relativity theory. Even stranger, the movement of the billiard balls creates the spacetime billiard table that is the basis of the balls' movement. Einstein introduced into science the idea that the position of an observer contributes to the reality of the motion observed. When two observers, each in a different position, observe the same event differently, there is no way to determine whether one observation is right and the other wrong. If Newton's theory is compared to a tidy piece of realistic art, then Einstein's theory is more like a puzzle in which the objects look real enough, though their spatial relationships change before our eyes as in the case of a small circle drawn within a cube frame. As we gaze at it, the perspective shifts. The circle appears to be near the back left lower corner of the cube, then near the front left lower corner. But quantum theory can be compared only to an abstract yet suggestive art forma painting that at first glance appears to depict no subject at all, only chaos. Then, during closer scrutiny, forms are seen to emerge out of and merge back into the chaosa face, a hand, a bird or something else. Quantum theory gives no fixed and real definition of either the structure or the motion of matter. It predicts only where a quantum object may be found, or what state of motion it will be in. The where and what state of motion of that object are logically incompatible. Therefore quantum theory speaks of quantum objects as wave-particles. Ordinarily, the motion of objects through space is described in terms of four dimensions: length, breadth, height and duration of time. In quantum theory, as the number of quantum objects to be measured increases, more dimensions of space are added to account for them. But these dimensions are creations of the mind. This brings us to the problem of the interplay between mind and matter in quantum mechanics. There is no settled opinion as to where subjectivity ends and objectivity begins. Consequently, it has been remarked of quantum physics that there is no 'there' there. See Relativity theory.
American philosopher of great repute in the twentieth century (1908-1995). His argument that in scientific theory, any statement can be held true, come what may, if we make drastic enough adjustments elsewhere in the system, is often quoted.