roland comments on Causal Universes - Less Wrong

60 Post author: Eliezer_Yudkowsky 29 November 2012 04:08AM

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Comment author: roland 28 November 2012 08:22:51PM 1 point [-]

But if you were scared of being wrong, then assigning probability literally zero means you can't change your mind, ever,

Why can't you change your mind ever? Is this because of the conservation of expected evidence?

Comment author: JoshuaZ 28 November 2012 08:24:25PM 8 points [-]

No. This isn't conservation of expected evidence but a simple consequence of Bayes theorem. If your prior probability is zero, then you end up with a zero in the numerator of the theorem (since P(A) is zero). So your final result is still zero.

Comment author: evand 28 November 2012 09:48:35PM 0 points [-]

Of course, if you also assigned a probability of zero to the event you just observed, now you have 0/0 error, which is more awkward to deal with. The case of having a posterior probability of zero in contradiction to the evidence is not particularly problematic for the agent's thinking, it just isn't very useful. But a true 0/0 event might well cause serious issues.

Comment author: Eugine_Nier 29 November 2012 06:35:03AM 1 point [-]

In practice, you conclude you hallucinated the event.