In the first two of these three posts on Young Earth Creationism I looked at how Young Earth Creationists are able to make their theory ‘fit’ the evidence, and how they suppose this ‘fit’ reveals their theory is confirmed – as well confirmed as the theory of evolution, say. We saw that for a theory to be strongly confirmed more is required than that sort of ’fit’, which even ludicrous theories can achieve.
But what more is required? When is a theory strongly confirmed by the evidence?
Consider this general rule of thumb: a theory is confirmed by a piece of evidence just in case the evidence is much more probable given the theory than it would be otherwise.
According to this rule, when considering whether a theory is confirmed by the evidence, you should consider how probable the evidence is given that theory.
Here’s an example. Suppose I see water droplets on the window and you come in wearing a wet shoes. Intuitively, that’s fairly good evidence it is raining. Why?
Part of the reason is that, if it were raining (my theory), those water droplets and wet shoes (the evidence) are just what I’d expect to see. If it’s raining, the probability I’d observe these things is high.
However, our rule of thumb says this isn’t the only probability we need to consider. For my theory to be confirmed, the evidence should also be rather less probable if the theory weren’t true.
To see why this second probability does seem to matter, let’s change my original example a bit. Suppose I know my neighbour has a powerful garden sprinkler that they use daily at around this time. It’s so powerful it sprays my windows and garden path. Given this background knowledge, the water on the window and your wet shoes are now much less good evidence it’s raining. For that’s the sort of thing I’d expect to observe even if it weren’t raining.
So it seems that the difference between these probabilities is important: the probability of the evidence if the theory were true, and also the probability of the evidence if the theory weren’t true. If the former probability is higher than the latter, then our theory may be significantly confirmed.
Notice both probabilities can be low and yet still the theory may be strongly confirmed if one probability is nevertheless much higher than the other. Here’s an example involving the theory of evolution. Every now and then a whale crops up with atavistic limbs – legs. Fish never display such limbs. This is considered powerful evidence for the theory that whales evolved from earlier land-dwelling mammals. Why so? Not because atavistic limbs are highly probable given that evolutionary theory. Perhaps the probability of such limbs showing up is fairly low even on that theory (maybe we would not predict atavistic limbs given the theory, say). But still, even if the probability of atavistic limbs is fairly low on that evolutionary theory, it’s still many, many times higher than on the view that whales did not evolve in that way. So those atavistic limbs do still strongly confirm that evolutionary theory about whales.
What about the fossil record? Why does that confirm evolutionary theory? As we dig down through the sedimentary layers, we find different species fossilized in a very specific order. For example we find only simple life forms in the lower layers, with higher layers revealing new species that appear as modifications of those below them. The fossil record reveals a tree-like structure of species emergence, with current species tracing back to a common ancestor. We never find fossils inconsistent with this theory: fossil rabbits or birds in those deposits classed as Pre Cambrian, for example (as JBS Haldane famously noted).
Now the fossils of different species being arranged through the sedimentary layers in this very specific way is exactly what we would expect on evolutionary theory (assuming we expect there to be any fossils at all). On the other hand, there’s little if any reason to expect this very specific arrangement if Young Earth Creationism is true. Indeed Young Earth Creationists wouldn’t be much surprised if fossil rabbits did start showing up in the Pre Cambrian layers. If the fossils were produced in the way most Young Earth Creationist now suggest – largely by those species being drowned and then buried in mud deposits created in just a few days or week during the flood on which Noah floated his Ark – then their being fossilized in that very specific order would be improbable. Indeed, that ordering would be the most extraordinary cosmic fluke. So, given that sort of arrangement of fossils is very probable on evolutionary theory and highly improbable on the alternative, the arrangement strongly confirms the theory of evolution.
So there are a couple of examples of how the theory of evolution is confirmed (by the fossil record and atavistic limbs). But we have barely scratched the surface: the evidence for evolution extends vastly beyond this.
Could Young Earth Creationism be strongly confirmed, at least in principle? Yes. If, on excavating the ground beneath our feet, we had discovered, not fossils, but a bottom layer clearly and repeatedly stamped ‘Made by God, 4004 BC’, that would provide a significant bit of evidence for Young Earth Creationism. Combined with other evidence, it might make Young Earth Creationism overwhelmingly confirmed.
Still, we’ve not entirely pinned down the conditions under which a theory is strongly confirmed. What we have said is that, as a rough rule of thumb, a theory is strongly confirmed when the evidence is much more probable given the theory than it is otherwise.
But that’s not quite right. Consider this. Anything that seems bafflingly improbable can always be explained by invoking some sort of hidden agent or being with both a desire that that state of affairs should exist and the magical ability to make it so.
Why do flowers grow in the Spring? Here’s my theory: Because there exist fairies who love flowers, like to see them bloom in Spring, and have the magical power to make them bloom at that time.
Why does the elephant have a long nose? Here’s my theory: Because an irritable nature spirit became annoyed by an elephant one day, and so decided to curse all elephants with a ridiculously long nose.
Why isn’t my car where I seem to remember having left it? Here’s my theory: mysterious car elves fell in love with it and moved it magically to their secret lair on Venus.
Now if I really can’t otherwise explain why flowers bloom in Spring, why elephants have such a long nose, or why I can’t find my car, should I conclude that these mysterious and magical beings are indeed in each case responsible? Surely not. Yet notice the probability of what is observed really is in each case much higher on the magical being theory than it is otherwise.
Clearly, something’s gone wrong here. It can’t be that easy to confirm the existence of fairies, irritable nature spirits and car stealing elves, can it? But what exactly has gone wrong?
I’ll leave that for you to think about. Feel free to make suggestions below…
Also consider: is there a moral to draw here when it comes to invoking that mysterious and magical being God to explain other things that strike us as bafflingly improbable?