From: Eliezer Yudkowsky (sentience@pobox.com)
Date: Wed Jan 19 2005 - 12:48:01 MST
attached mail follows:
[I'm back from holidays having done some reading relevant to some
recent discussion on this list. Along with part of Popper's _Realism
and the Aim of Science_, I reread a little Penguin book on some of
Feynman's lectures entitled _The Meaning of It All_ containing a
chapter entitled the Uncertainty of Science.
In his, imo, well written, and enjoyable essay A Technical Explanation
of Technical Explanation, http://yudkowsky.net/bayes/technical.html
Eliezer writes (page 32 of 36 when I printed it out) :
"Imagine that you wake up one morning and your left arm
has been replaced by a blue tentacle. The blue tentacle
obeys your motor commands - you can use it to pick up
glasses, drive a car, etc. How would you explain this
hypothetical scenario? Take a moment to ponder this
puzzle before continuing."
So I did imagine it. I imagined it in good faith, and I imagined it
consistent with a spirit of exploration and good will built that Eliezer
had established through the early part of his essay.
Where Eliezer had placed "spoiler space", I stopped reading and I
wrote down my explanation. (I'd been reading with pen in hand and
making critical notes in the margin.) It seemed to be fair and
scientific to provide an answer *before* reading on so as not to
contaminate the experiment. )
I wrote (and I quote):
"I'd "explain" it provisionally as some surprising organisation
of people had entered my house and replaced my arm whilst
I slept with technology I didn't know existed.
I'd be bewildered. Frightened even. But I'd not think "magic"
had occurred".
And then, with the heightened curiosity of one who has escalated
their commitment I went back to see what Eliezer the Bayesian,
Eliezer the spreader-of-analogical-probability-clay-mass would have
done.
And he'd written this.
"How would I explain the event of my left arm being replaced
by a blue tentacle? The answer is that I wouldn't. It isn't going
to happen."
Email perhaps can't convey my exact reaction to that but here's
the comments I wrote in the margin.
---- "No. No. No. You cheated Eliezer. You cheated ! You can't assign a probability of zero ! * Not fair!! You said it did happen. Your being dishonest with the data to say its not going to happen." ---- Most of what I know of Bayesian reasoning I know as a result of reading Eliezer's two essays on it. So perhaps if my understanding of Bayesian reasoning or inference is wrong I can escape by blaming Eliezer for it :-) I suspect, on the basis of those two essays that I am a Bayesian although I didn't know I was and so I haven't been calling myself one. The merit I see in the Bayesian approach is that it manages uncertainties more carefully and consistently then most people do intuitively. [And boy does the world need that]. So, it's 2005. I'm a Bayesian. And as long as I'm wearing metaphorical teeshirts I'm also a Bright. Regards, Brett Paatsch * Eliezer's assigning a probability of zero to observed facts however unlikely those facts might have been a priori is the reason for my heading this post Bad Bayesian - no buscuit. PS: Happy new year.
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