Science vs. Wishful Thinking

"Absence of evidence is not evidence of absence." —Traditional

It seems that there is some distance between most people's understanding of this traditional aphorism, often mistakenly attributed in origin to Carl Sagan, and its meaning. The cause in most cases may be found in the nuance of its usage, but I'd like to explain another principle which is likely leaking into its meaning: the impossibility of induction.

Scientific knowledge is based on inductive reasoning; you take a small sample and infer the larger result. This is actually a very bad way of proving things! Imagine being asked to prove that there are infinitely many prime numbers and responding by listing all the prime numbers you can think of, noting that there are more than you can count, and pointing to a bunch of other problems in math that would be solved if there were an infinity of primes. You'd be laughed out of the room if you claimed this was proof of anything in front of a  mathematician! Mathematicians use this kind of reasoning to make conjectures and hypotheses, but since math is based on a set of axioms (facts that are considered true by definition), any claim in mathematics ought to be able to be proven deductively and inarguably (there are some complicated caveats to this, but for the kinds of math useful in practical problems, this is fair to say. Before anyone goes all Gödel on me, consider that you may be being an asshole, you know what I mean.)

In scientific study, however, we do not have the luxury of getting to state things that are true by definition. We must synthesize rules for the way nature behaves from observations, which always means there is a chance of error. Once we are reasonably sure that we've got some new rule right, then we can use that rule as an axiom and deduce its consequences, which would be conditionally true dependent upon the validity of our new rule. So even though scientists often use deduction, it's all based on inductive reasoning. This is why scientists are constantly repeating experiments and testing the reproducibility of results. Each independent confirmation of a hypothesis increases our confidence in the validity of that hypothesis, but we can never really be mathematically sure of anything. Bummer!

This kind of reasoning, phrased less fairly, is often used by groups with some anti-science agenda to cast doubt and generally take up time that could be used learning things that science can teach us. Think of the "teach the controversy" movement among evolution deniers, or the classic dodge of "Science can't prove God doesn't exist", or even "We shouldn't do anything to upset the economy over global warming when science can't even prove it's our fault." The real reason that people are resistant to the scientific sides of these debates is because they are heavily invested (usually emotionally, but sometimes financially) in the other side; the fact that science can't prove its claims the way mathematics can is the desperate handhold of the terrified, cliffhanging apologist, futilely clinging with eyes closed and feet six inches off the ground.

The fact is: There are certain things that science has taught us that we are so incredibly confident are true, they are practically certain, e.g., stuff is made of atoms, all life on Earth evolves, the Sun will rise tomorrow (actually, this is probably the least certain example I've chosen!). We can essentially say that all legitimate uncertainty in such supremely evident facts boils down to this: What if the Universe is playing tricks on us? The only possible explanation for a world in which we have such strong evidence for things that aren't true would be that the laws of physics are not only violable, but being used to confuse us, probably by some god that doesn't want us to know that it exists. This explanation is itself unfalsifiable, and therefore doesn't explain or answer anything, even if it were true. (I should point out that this does not fit with the description of the Abrahamic God, who, while often a dick, isn't described as actively engaged in concealing himself from reasonable inquiry. Sorry Christians, this doesn't get you off the hook.).

So if we don't live in the fief of Puck, the trickster god, the Universe makes sense, and while science may not be able to mathematically prove claims, it has been given a pretty thorough vetting (we would notice if electricity suddenly started obeying different laws, for example). In a sensible universe, crossing your fingers, hoping, or just believing as hard as you can that science is wrong for some ulterior reason is betting against the house.

Given that science, reason, and rational thought are the only ways to actually understand things about reality, we can return to the initial quote and append to it for emphasis: "Absence of evidence is not evidence of absence necessarily." The difference can be fleshed out with two examples: the case for alien life and the case for the truth of religion.

In the case for alien life, we have a good understanding of how intelligent life evolved on this planet, and a plausible explanation of how life arose from chemistry. We expect these principles to apply everywhere in the Universe (again, it isn't playing tricks on us), and so it wouldn't surprise us to find intelligent life elsewhere. The fact that we see no evidence for life elsewhere yet doesn't imply that there is none, there are many reasons that we may not detect intelligent life, so non-detection is compatible with its existence. The absence of evidence is not evidence of absence.

In the case for religion, specifically the belief that a supernatural entity has ordered the Universe with us somehow in mind, you must explain the lack of evidence provided by an omnipotent deity which is invested in our acceptance of its existence. To take the example of Christianity, one must somehow accept the fact that God created the Universe, the concepts of sin and salvation, and the consequences for sin without salvation, all the while intentionally omitting from Creation the least shred of evidence that anything supernatural exists whatsoever. The only way to avoid eternal torment in this Universe is to believe in one particular religion out of thousands of equally unsupported mythologies for no good reason at all. If an omnipotent being truly cared about the souls of those at risk of torment, He would have supplied not just a hint of evidence, but an unavoidable, constant, and significant demonstration of all of the important principles required for a person to avoid a horrible fate. I think this is the root of the double standard applied to reality by the religious, where every beautiful story or landscape is evidence of God's goodness, and every horrible outcome is evidence of the Fall of Man; the religious know that if God is hiding His existence from human beings and causing them to enter Hell, He is indeed a more vile monster than any man. In this case, the lack of evidence for God flies in the face of what we would expect from such a being, and so we can say in this case that absence of divine evidence is indeed evidence of divine absence.

Don't waste your time hiding from the scientific explanation; science seeks only the truth, and if your particular favorite idea is found to be true, then it will become a part of our scientific understanding of the world. Time spent wishing reality were otherwise is time we should be spending using science to understand how to bring about a better reality.

"All our science, measured against reality, is primitive and childlike — and yet it is the most precious thing we have." —Albert Einstein