In Hawking’s A Brief History of Time, Hawking writes, “As philosopher of science Karl Popper has emphasised,” a good theory is characterised by the fact that it makes a number of predictions that could in principle be disproved or falsified by observation….but if ever a new observation is found to disagree, we have to abandon or modify the theory.
Then immediately adds: “At least that is what is supposed to happen, but you can always question the competence of the person who carried out the observation.” Taking the example of Newton and Einstein’s theories of gravity, Hawking goes on to show how, “in practice” falsified theories tend to be modified or “extended” rather than abandoned.
Roger Penrose, in his 2004 The Road to Reality (not 2005 as I thought) says that Popper has “too stringent a criterion, and definitely too idealistic a view of science in this modern world of ‘Big science’.” (p1020).