There has been an interesting discussion in the comments on my post When can we conclude that dark matter does not exist? with commenter Establishment Liberal taking strong exception to my statement that one cannot prove the non-existence of entities. I started posting my response in the comments but it got rather long and I thought, what the hell, why not make it into a separate post? All these are things that I go into in some detail in my forthcoming book The Paradox of Science but I will sketch out my response here.
EL has made many postings in that thread and John Morales has responded to some of the points but the main one that I will respond to is this one and my comments will be in response to points made there.
EL is correct that I am saying that “one cannot prove that there are no immaterial human souls”, or “one cannot prove that there are no unicorns”.
The point I am making is that questions of the non-existence of entities are arrived at using reasoned judgments based on a preponderance of evidence, not on proof, because determined believers in the existence of anything can always add ad hoc explanations for the lack of positive evidence. This is why, for example, conspiracy theories never die and people continue to believe in all manner of superstitions. I am saying that we cannot prove with 100% certainty that there are no unicorns (or T rexes or whatever) because believers can always posit explanations for the lack of evidence, which is why the Loch Ness monster still has its supporters. This is why arguments with people who believe in ghosts and immaterial souls rarely convince them that they are wrong. If such arguments are so definitive, how come we still have believers? As the TV character House said, “Rational arguments don’t usually work on religious people. Otherwise there would be no religious people.” At some point, some of us people come to the conclusion that these proposed escape clauses are preposterous and that it is not reasonable to believe in them and proceed to live their lives as if they do not exist. They leave the believers to their own devices.
EL does define the word ‘prove’ to mean “demonstrate the truth of the claim beyond all reasonable doubt, but not all possible doubt”, but the key word in that definition is ‘reasonable’, because getting agreement on what is reasonable to believe and what is not is the sticking point. It requires making a judgment and getting agreement on judgments depends on many factors that do not command universal acceptance.
EL’s argument using the Standard Model in particle physics is interesting but unconvincing because it posits a certainty about it that is not held even by physicists. For one thing, while the SM is the best one we have for sub-atomic particle physics, it is by no means considered the last word by all physicists. The SM is a composite of all manner of theories, including QCD and electroweak theories, that are patched together with and gravity tacked on. It is by no means a complete, closed system even within the realm of particle physics that has answered all the questions. And it comes nowhere close to addressing, let alone answering, the questions in chemistry, biology, geology, and other areas of science. It is only the extreme reductionists who argue that the SM has ‘solved’ the problems in other areas.
Furthermore, take EL’s statements.
The Standard Model is now a complete and accurate theory of every single experiment that has ever been done on Earth.
There is new physics to be discovered, but none of that physics is happening on Earth, and we know this because the math of Quantum Field Theory says so and because of our experiments with particle accelerators.
In order to entertain the epistemic possibility that supernatural stuff exists, you also have to entertain the epistemic possibility that the Standard Model is very, very wrong, and that is not a reasonable thing to do in light of the incredible evidence that we have in favor of the Standard Model.
These statements are so strong and sweeping that I suspect that few physicists would accept them. The idea that the SM is the last word in science that pretty much has explained everything that happens on Earth is simply wrong. No scientific theory has ever explained all the phenomena that fall under its purview. There are always things it does not explain and the SM is no exception. Furthermore, all scientific theories are underdetermined by the data, in the sense that no set of data, however large, uniquely determines a scientific theory. It can never be shown that SM is the only theory that we can construct to explain the data.
The SM does not require anything supernatural as part of its explanatory structure but that is different from saying that it leaves no room for their existence. Furthermore, EL is saying that it is not reasonable to reject that SM. The use of that word supports my contention that accepting SM is a judgment based on evidence, not on proof. EL makes that same point about reasonableness again later:
For angels and gods that actually do something, they cannot exist, because by definition they are something above materialism, and the Standard Model and the evidence for it leave no room for such things. If some thing exists and obeys the Standard Model, then it’s probably not reasonable to use the word “supernatural” to describe it, and for postulates that there exists something that has effect on our material world in a way that does not conform to the Standard Model, we can be sure that such things do not exist because of the overwhelming evidence in favor of the near universal applicability of the Standard Model.
Again, to repeat my main points, no scientific theory has ever explained all the data that falls under its purview. Furthermore, no set of data ever uniquely determines a theory. This is why believers in the supernatural can always find reasons for belief. In fact, that is the whole basis for Intelligent Design. The best we can say is that it is not reasonable to hold those beliefs. So while I agree with EL’s concluding statement that “the evidence strongly supports an impersonal, material world that evolves according to simple, impersonal, material, mathematical laws”, it is quite a different matter to go from there to argue that therefore we have proved it to be so with any sense of certainty.
As I said, establishing these points involve looking in depth at the history and philosophy of science as well as the field of epistemology, and I can at best sketch the main outlines of the argument here. I hope those who are interested in exploring such questions more deeply will read the book when it comes out, possibly later this year.