(For other posts in this series, see here.)
The previous post illustrated a crucial difference between science and religion that explains why scientists can resolve disagreements amongst themselves as to which theory should be considered true but religious people cannot agree as to which god is the one true god. In competition between scientific theories, after some time the weight of evidence is such that one side concedes that their theory should be rejected, resulting in a consensus verdict. In religion, since evidence plays no role, and reason and logic are invoked only when they support your own case and discarded by appealing to faith when reason goes against you, there is no basis for arriving at agreement. It would be unthinkable for a scientist to argue in favor of his or her theory by denying evidence and logic and telling people that they must have faith in the theory for it to work.
Science can come to a consensus not because all individual scientists on the losing side change their minds. Some of them can be as dogged as the most fervent believer in god in holding on to their beliefs, and as inventive in finding new reasons for belief, though they will never resort to appealing to supernatural forces or faith. The key difference is that over time, the advocates of a failing theory become less influential, more marginalized, and eventually die out. The next generation of research students chooses their areas of study when they are older and more aware of the field and tend to avoid signing on to failing theories, so that those declining theories eventually fade from the scene, to be found only in historical archives. Unlike in the case of religion, there is no institutional structure dedicated to perpetuating old theories, nor is there a sacred text that must be adhered to. As much as scientists admire the works of Isaac Newton and Albert Einstein and Charles Darwin, they do not treat them as divinely inspired. Science has moved on since they were written and their original theories have been modified and elaborated on, even if they still bear their names. Every generation of students is taught the current version of accepted theories, not the original ones.
In the case of religions, however, they are forced to conform to ancient texts. Furthermore, children are not allowed to choose their religious beliefs when they are of more mature age, the way that research scientists choose which theories they want to work with. Religions indoctrinate the next generation of impressionable children with those ancient beliefs when they are very young, thus ensuring that those beliefs persist. Furthermore, there is a vast industry (churches, priests, theologians, etc.) whose very livelihood depends on those ancient religious ideas being perpetuated. Scientists can shift their allegiance from one theory to another without losing their jobs. A theologian or priest cannot. Can you imagine a pope saying that after some thought he has come to the conclusion that there is no god or that Buddhism is the true religion? Hence even though the evidence against the existence of god is far more overwhelming than that against old and rejected scientific theories, theologians will cling on to their old ideas, never conceding that they are wrong, invoking more and more ad hoc hypotheses to justify their beliefs.
This is why science progresses but religions are stuck in a rut, the only progress in the latter being the new excuses that need to be invented to explain why there is no evidence for god, as science makes god increasingly unnecessary as an explanatory concept. In fact, the field of theology largely consists of explaining why there is no evidence for god. Religious believers have the wiggle room to do this because pure logic is never sufficient to eliminate a theory. This is why believers in god who claim that since logical or evidentiary arguments cannot disprove the existence of god, therefore it is reasonable to believe that god exists, are saying something meaningless.
In science too we cannot eliminate the phlogiston theory of combustion or the ether or the geocentric model of the solar system by logic or evidence. So how are scientists able to say with such confidence that some theories (like gravity) are true and that others (like ether or phlogiston) are false? Pierre Duhem (The Aim and Structure of Physical Theory, Pierre Duhem, 1906, translated by Philip P. Wiener, 1954) said that we have to appeal to the collective ‘good sense’ of the scientific community as a whole to arrive at a judgment of which theory is better. It is the community of professionals working in a given scientific area that is the best judge of how to weigh the evidence and decide whether a theory is right or wrong, true or false, rather than any individual member of that community, since scientists are like any other people and prone to personal failings that can cloud their judgment, unless they exercise great vigilance over themselves.
Next: How ‘good sense’ emerges in science