June 02, 2006
Why scientific theories are more than explanations
(I will be traveling for a few weeks and rather than put this blog on hiatus, thought that I would continue with my weekday posting schedule by reposting some of the very early items, for those who might have missed them the first time around.)
At its heart, intelligent design creationism (IDC) advocates adopt as their main strategy that of finding phenomena that are not (at least in their eyes) satisfactorily explained by evolutionary theory and arguing that hence natural selection is a failed theory. They say that adding the postulate of an 'intelligent designer' (which is clearly a pseudonym for God) as the cause of these so-called unexplained phenomena means that they are no longer unexplained. This, they claim, makes IDC the better 'explanation.' Some (perhaps for tactical reasons) do not go so far and instead say that it is at least a competing explanation and thus on a par with evolution.
As I discussed in an earlier posting, science does purport to explain things. But a scientific explanation is more than that. The explanations also carry within themselves the seeds of new predictions, because whenever a scientist claims to explain something using a new theory, the first challenge that is thrown invariably takes the form "Ok, if your theory explains X under these conditions, then it should predict Y under those conditions. Is the prediction confirmed?"
If the prediction Y fails, then the theory is not necessarily rejected forever but the proponent has to work on it some more, explain the failure to predict Y, and come back with an improved theory that makes better predictions.
If the prediction Y is borne out, then the theory is still not automatically accepted but at least it gains a little bit of credibility and may succeed in attracting some people to work on it.
Theories become part of the scientific consensus when their credibility increases by these means until they are seen by the scientific community to be the exclusive framework for future investigations. A scientist who said things like "My new theory explains X but makes no predictions whatsoever" would be ignored or face ridicule. Such theories are of no use for science.
And yet this is precisely the kind of thing that IDC proponents are saying. To see why this cannot be taken seriously, here is something abridged from the book Physics for the Inquiring Mind by Eric Rogers (p. 343-345), written way back in 1960. In it Rogers looks at competing claims for why an object set in motion on a surface eventually comes to rest:
The Demon Theory of Friction
How do you know that it is friction that brings a rolling ball to a stop and not demons? Suppose you answer this, while a neighbor, Faustus, argues for demons. The discussion might run thus:
You: I don't believe in demons.
Faustus: I do.
You: Anyway, I don't see how demons can make friction.
Faustus: They just stand in front of things and push to stop them from moving.
You: I can't see any demons even on the roughest table.
Faustus: They are too small, also transparent.
You: But there is more friction on rough surfaces.
Faustus: More demons.
You: Oil helps.
Faustus: Oil drowns demons.
You: If I polish the table, there is less friction and the ball rolls further.
Faustus: You are wiping the demons off; there are fewer to push.
You: A heavier ball experiences more friction.
Faustus: More demons push it; and it crushes their bones more.
You: If I put a rough brick on the table I can push against friction with more and more force, up to a limit, and the block stays still, with friction just balancing my push.
Faustus: Of course, the demons push just hard enough to stop you moving the brick; but there is a limit to their strength beyond which they collapse.
You: But when I push hard enough and get the brick moving there is friction that drags the brick as it moves along.
Faustus: Yes, once they have collapsed the demons are crushed by the brick. It is their crackling bones that oppose the sliding.
You: I cannot feel them.
Faustus: Rub your finger along the table.
You: Friction follows definite laws. For example, experiment shows that a brick sliding along a table is dragged by friction with a force independent of velocity.
Faustus: Of course, the same number of demons to crush however fast you run over them.
You: If I slide a brick among a table again and again, the friction is the same each time. Demons would be crushed on the first trip.
Faustus: Yes, but they multiply incredibly fast.
You: There are other laws of friction: for example, the drag is proportional to the pressure holding the surfaces together.
Faustus: The demons live in the pores of the surface: more pressure makes more of them rush out and be crushed. Demons act in just the right way to push and drag with the forces you find in your experiments.
By this time Faustus' game is clear. Whatever properties you ascribe to friction he will claim, in some form, for demons. At first his demons appear arbitrary and unreliable; but when you produce regular laws of friction he produces a regular sociology of demons. At that point there is a deadlock, with demons and friction serving as alternative names for sets of properties - and each debater is back to his first remark.
Faustus's arguments are just like those of the IDC advocates, and the reason why they are consistently rejected by the scientific community. Scientists ask for more than just explanations from their theories. They also need mechanisms that make predictions. They know that that is the only way to prevent being drowned in an ocean of 'explanations' that are of no practical use whatsoever.
You can't really argue with people like Faustus who are willing to create ad hoc models that have no predictive power. Such explanations as he gives have no value to the practicing scientist. But when you walk away from this kind of fruitless pseudo-debate, you do allow the other side to charge that you are afraid to debate them, at which point, they may jump up and down and shout "See they cannot refute us. We win! We win!", however illogical the charge.
It reminds me of the duel scene in Monty Python and the Holy Grail in which King Arthur chops off the arms and legs of the Black Knight, leaving just his torso and attached head on the ground, totally defenceless. The Black Knight refuses however to concede defeat and offers a compromise: "Oh? All right, we'll call it a draw." When Arthur and his assistant walk away from this offer, the Black Knight starts taunting him saying "Oh. Oh, I see. Running away, eh? You yellow bastards! Come back here and take what's coming to you. I'll bite your legs off!"
At some point, in order to save your time (and your sanity) you have to simply walk away and ignore them. This explains why so many scientists refuse to get involved in the IDC battles.
POST SCRIPT: Unlearning ideas
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