If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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I know what SI is. I'm not even pushing the point that SI not always the best thing to do - I'm not sure if it is, as it's certainly not free of assumptions (such as the choice of the programming language / Turing machine), but let's not go into that discussion.
The point I'm making is different. Imagine a world / universe where nobody has any idea what SI is. Would you be prepared to speak to them, all their scientists, empiricists and thinkers and say that "all your knowledge is purely accidental, you unfortunately have absolutely no methods for determining what the truth is, no reliable methods to sort out unlikely hypotheses from likely ones - while we, incidentally, do have the method and it's called Solomonoff induction"? Because it looks like what iarwain1 is saying implies that. I'm sceptical of this claim.
You can have more to it than the complexity penalty, but you need a complexity penalty. The number of possibilities increases exponentially with the complexity. If the probability didn't go down faster, the total probability would be infinite. But that's impossible. It has to add to one.