“One truth we have been able to count on concerning scientific persuit over the centuries has been that only testable theories survive the intense scrutiny of experimental science.”
Source: Reinventing Gravity (2008), Chapter 8, Strings And Quantum Gravity, p. 136
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John Moffat 22
British-Canadian physicist 1932Related quotes

“Darwinism is not a testable scientific theory, but a metaphysical research program.”
Unsourced variant: Evolution is not a fact. Evolution doesn't even qualify as a theory or as a hypothesis. It is a metaphysical research program, and it is not really testable science.
Popper later retracted his criticisms:
I have changed my mind about the testability and logical status of the theory of natural selection; and I am glad to have an opportunity to make a recantation.
:* "Natural selection and the emergence of mind" dialectica http://www.dialectica.ch/ Vol. 32 (1978), p. 339-355; republished in Evolutionary Epistemology, Rationality, and the Sociology of Knowledge (1987) edited by Gerard Radnitzky and W. W. Bartley, III
Unended Quest: An Intellectual Autobiography (1976)

Radio excerpt presented by Voice of America (17 January 2010) http://learningenglish.voanews.com/content/margaret-mead-1901-1978-one-of-the-most-famous-anthropologists-in-the-world-124869344/112571.html
2000s

Source: A Brief History of Time (1988), Ch. 1
Context: It has certainly been true in the past that what we call intelligence and scientific discovery have conveyed a survival advantage. It is not so clear that this is still the case: our scientific discoveries may well destroy us all, and even if they don’t, a complete unified theory may not make much difference to our chances of survival. However, provided the universe has evolved in a regular way, we might expect that the reasoning abilities that natural selection has given us would be valid also in our search for a complete unified theory, and so would not lead us to the wrong conclusions.

As quoted in Beyond Positivism and Relativism : Theory, Method, and Evidence (1996) by Larry Laudan, p. 259

New Pathways in Science: Messenger Lectures 1934 (1947), p. 211.
Power and Prosperity: Outgrowing Communist and Capitalist Dictatorships (2000), Ch. 1 The Logic of Power

Discours de réception de Louis Pasteur (1882)