Saturday, January 22, 2011


Yesterday's post was but a long-winded introduction to the idea of prior probability and how even after seeing a piece of evidence that, by itself, favours one hypothesis, you can still prefer another one. I promised I'd get to the point today, and I occasionally keep my promises, so...

The point is thus. A few weeks ago, I came across a paper on ESP, which can learn more about here or read here. Now, I don't believe in ESP. In fact, I find the idea ridiculous. But I also find the idea of dismissing an idea due to its apparent ridiculousness without considering the evidence ridiculous. I do try to be rational, and recently, as you may have read about in older posts, I've realised that I'm not as rational as I thought. And learnt quite a few new things relevant to that, including the concept of Bayesian probability which is rather central to this series of posts.

When first faced with this paper, I'm ashamed to admit I lapsed into old ways of thinking, fell right into the grip of confirmation bias, and started to poke this paper in ways I wouldn't poke one that agreed with me. Not because of any real reason, just because it disagreed with me. That lead me to some rather idiotic conclusions which I, fortunately, decided not to share with the world. 

Later, thinking more clearly and reminded of my commitment to question ideas equally whether they agree with me or not, I basically slapped myself in the face (metaphorically) and said, ok, let's stop for a second and think. Am I really proceeding with this the right way? No.

And thus I now accept the reality of psychic powers.

Nah, of course not. ESP is still bullshit. And the concept of prior probability is quite relevant as to why.

This is actually touched upon in the article I linked, one that I hadn't really taken a good look at before today. Basically, after I sat down, stopped try to rationalise, and cleared my thinking, I remembered what little I know about prior probability, and the concept is quite relevant. Given what we know about how the human brain and the laws of physics work, it is absurdly improbable for information to travel backwards in time in the manner proposed by the paper's author. Special relativity says that it is impossible for information to travel faster than the speed of light. Physics is not complete, of course, so it's not impossible that new quantum effects will show some minor possibility of time-travelling information. But it is very unlikely, and it is incredibly unlikely that the first piece of evidence for that would come from human brains looking at pictures and not, say, particle accelerators. Human brains are hardly ideal environments for quantum experimentation.

The article brings up the example of casinos which is less compelling but more approachable. Basically, if ESP worked as reliably as the paper indicates, it'd be trivial to beat the house, and yet casinos make a profit. There's also the fact that James Randi still has his million dollars. And many other things you could probably think of on your own. Before reading the paper, the prior probability of the ESP hypothesis was so low that basically any hypothesis that fit the data and wasn't ESP would have a huge advantage. Not because of bias, but because of the fact that, based on virtually every observation, reality doesn't seem to work that way.

In fact, based on that knowledge, I made an advance note to myself. I should have taken the effort to write down a proper prediction and test my beliefs, and I did not, but, when considering what the new evidence would led me to believe my conclusion was that ESP was almost certainly not the correct answer, and very probably it would be some methodological error in the experiment. I could not clarify which one, I am not strong enough in the ways of science yet. But, if you trust the rationality of the author of this, they can.

So, I was right, somewhat, which makes me feel a little better over my irrational collapse. I still need to watch out more carefully. But that is not the conclusion I had in mind, since I only read that today and the series was started yesterday. 

Some accuse science of limiting itself to naturalistic explanations, or say that science requires an assumption of naturalism to work. They are wrong. Naturalism is not an assumption, it's a result. Richard Carrier defines naturalism as the idea that every mental phenomenon can be reduced to entirely nonmental ones. I agree with him on this, and it underlies my point. There's nothing preventing science from working if, in fact, nonreducible mental phenomena exist. If there is actually some sort of fact about the human mind that makes it defy physics, that is not beyond the purview of science. Science has pretty convincingly piled the evidence in favour of naturalism, giving it an enormous prior probability. That is why science prefers natural hypotheses to supernatural ones. Not bias, simply Bayesian probability.

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