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Pablo_Stafforini comments on Parapsychology: the control group for science - Less Wrong
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My original comment was a reply to Mitchell Porter, who suggested that parapsychology would somehow receive support from the Matrix hypothesis. I replied by saying that this would not be true, or at least not clearly, if that hypothesis is understood as a claim about the ultimate nature of reality.
To take another example, suppose someone argued Berkeleyan idealists should be more open to psychic phenomena, since we are all ideas in the mind of God. I would reply that this is not so, since the fact that the world is ultimately made of mind has in itself no implications about whether certain kinds of mental phenomena take place within that world.
The ability of certain collections of atoms to communicate large amounts of information to other collections of atoms over vast distances without there being any detectable emissions is an incredibly complex power. Complex entities are a priori improbable compared to simple entities. You need some kind of creation mechanism to make them probable... with biological systems we have evolution, with pocket watches and jet planes you have human inventors. If you accept a metaphysical hypothesis that involves an intelligence creating the universe-- programmers or God-- you have a mechanism for making complex entities probable. That is why the Matrix hypothesis makes psychic phenomena more likely
This remains the case no matter what the universe is made of. All evidence suggests that psychic mechanisms are not available to us in our current mode of existence, whatever that may be. That evidence doesn't change until you get more.
At least, that seems to me to be the point ben is making.
Yes, but not no matter how the universe was created. The Matrix hypothesis includes a claim that the universe was created by some intelligence and that makes psychic phenomena substantially more plausible.
That doesn't mean all religious people have to believe in psychic phenomena or even that they should. If there is no evidence for psychic phenomena then there is not evidence for psychic phenomena. But if you think the universe was created claims of psychic phenomena should be less absurd on their face.
Another position that could be taken is "the evidence suggests that if we are living in a matrix scenario then it is probably one of the ones without matrix psychic powers". That is, assuming rational reasoning without granting a counter-factual premise. The evidence can then be considered to have a fixed effect on the probability of psychic powers. Whether it causes you to also lower your probability for a Matrix or to alter your description of probable Matrix type would be considered immaterial.
Again, this is just what my impression of Ben's position. He'll correct me if I'm wrong. For my part I don't care about Matrixes (especially No. 2. I walked out of that one in disgust! Actually, I do care about the 'dodge this!' line. It's infuriating.)
This all started when Michell Porter responded to Blueberry's claim that we know, intuitively, that psychic phenomena are just not possible. I'm not quite sure I know just what Blueberry was talking about. But his estimate of the existence of psychic phenomena was zero and not just because of parapsychology's failure to provide convincing evidence but because of our understanding of the world. Mitchell provides Blueberry with a hypothesis that is consistent with what we know about the world but under which the existence of psychic phenomena is not prohibitively improbable.
None of this changes the fact that finding evidence of psychic phenomenon should cause us to revise our probabilities of its existence up and that non finding evidence should cause us to revise our probabilities down. But if your probability is zero, and especially if your probability is zero for reasons other than the failure of parapsychology, a hypothesis with P>0 where P(psi) is >0 looks like information you needs to update on.
Ben says it isn't clear why this is so. Well creation makes complex, unselected entities more probable. But maybe I should wait to have this argument with him.
As far as the movie goes, it is all downhill right after Neo wakes up gooey pink tub and sees all the other people hooked into the Matrix. The whole movie should have taken place in the Matrix and kept us in the dark about what it really was until the very end. Would have been way cooler that way.
Once your probability is zero is it even possible to update away? That'd more be 'completely discarding your entire understanding of the universe for reasons that cannot be modelled within that understanding'. If something is impossible then something else, no matter how unlikely, must be the truth. This includes the hypothesis "every thought I have that suggests the p(0) hypothesis must be true is the product of cosmic rays messing with my brain."
I've always been really confused by this but it isn't clear that an event with P=0 is an impossible event unless we're talking about the probability of an event in a finite set of possible events. (Edit again: You can skip the rest of this paragraph and the next if you are smarter than me and already get continuous probability distributions. I'm obviously behind today.)This is how it was explained to me: Think of a dart board with a geometric line across it. That line represents probability space. An event with P=.5 is modeled by marking the middle of the line. If someone throws a dart at the line there is an equal chance that it lands at any point along the line. However, at any given point the probability that the dart lands there is zero.
I think the probability of any particular complex entity, event or law existing can be said to have a probability of zero absent a creator or natural selection or some other mechanism for enabling complexity. Of course this is really counterintuitive since our evolved understanding of probability deals with finite sets of possibilities. Also it means that 'impossible' can't be assigned a probability. (Edit: Also, the converse is true. The probability that the dart lands anywhere other than the spot you pick is 1 so certainty can't be mapped as 1 either.)
Also, imperfect Bayesians will sometimes assign less than ideal probabilities to things. A perfect Bayesian would presumably never wrongly declare something impossible because it could envision possible future evidence that would render the thing possible. But regular people are going to misinterpret evidence and fail to generate hypotheses so they might sometimes think something is impossible only to later have it's possibility thrown in their faces.
Interesting point. Since physics does appear on the surface to be continuous, I can't rule out continuous propositions. Perhaps the amended saying should read "0 and 1 are not probability masses, and 0 is not a probability density."
Oh. I was expecting your belief to be as with infinite-set atheism: that we never actually see an infinitely precise measurement.
And, having assigned p(A) = 0 to such an event A I will not be able to rationally update away from zero without completely discarding my former model. There is no evidence that can cause me to rationally update p(A) = 0 to something else ever. Discard it and overwrite with something completely unrelated perhaps, but never update. p(A) is right there as the numerator!
(But yes, I take your point and tentatively withdraw the use of 'impossible' to refer to p=0.)
ETA: Well, maybe you're allowed to use some mathematical magic to cancel out the 0 if p(B) = 0 too. But then, the chance of that ever happening is, well, 0.
Er, my bad. I missed your point. I see it now, duh.
So my friend thinks something S has a probability of zero but I know otherwise and point out that it is possible give assumption which I know my friend believes has a .1 chance of being true. He says "Oh right. I guess S is possible after all." What has just happened? What do we say when we see the dart land at a specific point on the line?
Well, if you believe in Cartesian skepticism (that is, that we might be in the Matrix), then your probability for anything can't ever be zero. Say the probability that this world is an illusion within another world is epsilon: in that case anything could be true. So the lowest probability we can assign to anything is epsilon. EY has a post on how 1 and 0 aren't probabilities.
If you observed psychic powers with no possibility of cheating, you should probably conclude that something metaphysically weird is going on: you're in a dream, you're insane, or there's a hole in the Matrix.
Find the probability p(A | B) where B = "nothing weird like what the Cartesian sceptics talk about is going on". That gets rid of the Matrix issue. Then it is just a matter of whether or not you want to let dart players divide by infinity all willy nilly.