The notion that scientific theories must be tested experimentally is fundamental to the doctrine of positivism, which also requires that theories must always deal with quantities that are observable.
But Steven Weinberg, a Nobel Laureate and one of the greatest living physicists, asserts that "positivism has done as much harm as good". To make this point, which he develops at length in his excellent book "Dreams of a Final Theory", he argues that it was positivism that kept a number of scientists from believing in atoms, in electrons and much later in quarks.
Weinberg supports his claim with a comparison of two scientists. The British physicist J.J. Thomson is credited with the discovery of the electron, but Walter Kaufman in Germany performed the same experiment independently at the same time, and even managed a more precise measurement of the electron's properties. While Thomson reported the discovery of a new particle, which he named the electron, Kaufman merely reported the phenomenon he had observed (the bending of cathode rays). Exercising a positivist's restraint, he did not assume it corresponded to a new particle.
The harm caused by a positivist approach, in Weinberg's view, is this: unless one is willing to make - and believe - a hypothesis based on the limited information available, there tends to be a lack of direction in one's subsequent research. Only if one makes a conjecture about what is happening, defying positivism at least temporarily, is one motivated to perform experiments that can confirm or deny the conjecture.
Should we take positivism seriously/ or can it be a guiding principle ??