Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory.

Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory. On the other hand, you can disprove a theory by finding even a single observation that disagrees with the predictions of the theory. As philosopher of science Karl Popper has emphasized, a good theory is characterized by the fact that it makes a number of predictions that could in principle be disproved or falsified by observation. Each time new experiments are observed to agree with the predictions the theory survives, and our confidence in it is increased; but if ever a new observation is found to disagree, we have to abandon or modify the theory.

A theory is only as good as its assumptions. If the premises are false, the theory has no real scientific value. The only scientific criterion for judging the validity of a scientific theory is a confrontation with the data of experience.

[T]heories are only hypotheses, verified by more or less numerous facts. Those verified by the most facts are the best; but even then they are never final, never to be absolutely believed.

A theory can never be proven absolutely true, therefore there is no end to scientific endeavor. A true scientific theory is always open to be disproved, and the burden of proof is continually placed on the scientist.

Even a scientist is a human being. So it is natural for him, like others, to hate the things he cannot explain. It is a common illusion to believe that what we know today is all we ever can know. Nothing is more vulnerable than scientific theory, which is an ephemeral attempt to explain facts and not an everlasting truth in itself.

It should be clear by now that there are people who can, in fact, be reasonably considered experts; that it is rational to rely, within limits, on expert opinion; and that it is possible, by exercising relatively simple criteria, to gain insight into whether a particular expert is reliable or not. It is also true that experts, of course, do make mistakes, and that even the agreement of a large majority of experts in a field does not guarantee that they got it right. That’s the nature of scientific truth, as we have seen throughout this book: it is tentative, because it is the result of a human endeavor that is limited both by the type and amount of available evidence and by humans’ finite mental powers and emotional reactions. But the examples above show how you can, with a little bit of practice, tell science from bunk!

I claim that the success of current scientific theories is no miracle. It is not even surprising to the scientific (Darwinist) mind. For any scientific theory is born into a life of fierce competition, a jungle red in tooth and claw. Only the successful theories survive—the ones which in fact latched onto the actual regularities in nature.

There never comes a point where a theory can be said to be true. The most that one can claim for any theory is that it has shared the successes of all its rivals and that it has passed at least one test which they have failed.

Everything transitory--the knower and the known.

The theory of universal gravitation is not cast-iron. No theory is, and there is always room for improvement. Isn't that so? Science is constructed out of approximations that gradually approach the truth. . . Well, that means all theories are subject to constant testing and modification, doesn't it? And if it eventually turns out that they're not quite close enough to the truth, they need to be replaced by something that's closer. Right?

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.

A theory, to scientists, means something rather different from its popular use, which suggests something speculative or untested. A scientific theory is a cohesive body of knowledge, an explanation that is consistent among a range of cases and can allow you to predict what might happen in unknown situations.

Well, we haven’t learnt yet to live together peacefully... But I don’t know what progress really means. Anyway, I think we need to have faith in the fact that there is more out there to be explained. Even the paradigms that we now have, including subjective value theory, for example, are only provisional. Some physicist might believe that ultimately, we will be able to explain everything. To me, that is utterly stupid, just like saying that an atheist is equally dogmatic as a Texas Baptist. It seems to me that, if you accept evolution, you can still not expect your dog to get up and start talking German. And that’s because your dog is not genetically programmed to do that. We are human animals, and we are equally bound. There are whole realms of discourse out there that we cannot reach, by definition. There are always going to be limits beyond which we cannot go. Knowing that they are there, you can always hope to move a little closer – but that’s all.