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warpspeedpetey
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if there is no reason for them to be true, then how do we know they are true? Chaitin seems to take mathematical objects and their manipulation apart from reality as something more than machination, i wonder, do you think that it occured to him that there is no example of this in reality, yet there is an infinite set of RU? it shouldnt we have a universe full of sndwhiches popping into and out of existece?Consider arithmetic sentences of the form (Forall x, H(x)), where H() is an easily testable predicate, e.g., you can find out if H(17) is true or false just by pressing a few buttons on your calculator. Let U be the set of all such arithmetic sentences.
Chaitin is using the principle of the excluded middle here, so he is assuming that (Forall x, H(x)) is either true or false. If it is false, then there is a specific value n such that His false, and you can use your calculator to verify this. Call n a counter-example. Let CU be the subset of all sentences in U that have counter-examples.
Also consider proofs of (Forall x, H(x)). These are verifiable as well, because proofs must start from given axioms and must use sound rules of inference. Let PU be the subset of all sentences in U that have proofs, i.e., reasons.
What mathematicians have shown is that PU union CU is a proper subset of U, that is, there are an infinite number of arithmetic sentences in U that are neither in PU nor CU. Chaitin has some extension/variation of this result that I’m not really familiar with. I’ve seen his talk on Omega, but I haven’t really read his work.
Anyway, let RU = the rest of U, i.e., the subset of all sentences in U that are neither in PU nor CU. Mathematicians refer to sentences in RU as true because of the principle of the excluded middle, as we know that the sentences in RU have no counter-examples. In terms of the PSR, sentences in RU are true because they are true – there is no other reason for them being true other than that they are true.
It’s kind of like saying the reason there is a sandwich on my table is that, look and see, there is a sandwich on my table. It’s not lunch time, no one put it there, …, there are no reasons for the sandwich other than that it clearly exists because I can see it. Chaitin finds this to be a disproof of the PSR.