In June 2012, Robin Hanson wrote a post promoting plastination as a superior to cryopreservation as an approach to preserving people for later uploading. His post included a paragraph which said:
We don’t actually know that frozen brains preserve enough brain info. Until recently, ice formation in the freezing process ripped out huge brain chunks everywhere and shoved them to distant locations. Recent use of a special anti-freeze has reduced that, but we don’t actually know if the anti-freeze gets to enough places. Or even if enough info is saved where it does go.
This left me with the impression that the chances of the average cryopreserved person today of being later revived aren't great, even when you conditionalize on no existential catastrophe. More recently, I did a systematic read-through of the sequences for the first time (about a month 1/2 ago), and Eliezer's post You Only Live Twice convinced me to finally sign up for cryonics for three reasons:
- It's cheaper than I realized
- Eliezer recommended Rudi Hoffman to help with the paperwork
- Eliezer's hard drive analogy convinced me the chances of revival (at least conditionalizing on no existential catastrophe) are good
Note: Signing of this letter does not imply endorsement of any particular cryonics organization or its practices. Opinions on how much cerebral ischemic injury (delay after clinical death) and preservation injury may be reversible in the future vary widely among signatories.
I don't find that terribly encouraging. So now I'm back to being pessimistic about current cryopreservation techniques (though I'm still signing up for cryonics because the cost is low enough even given my current estimate of my chances). But I'd very much be curious to know if anyone knows what, say, Nick Bostrom or Anders Sandberg think about the issue. Anyone?
Edit: I'm aware of estimates given by LessWrong folks in the census of the chances of revival, but I don't know how much of that is people taking things like existential risk into account. There are lots of different ways you could arrive at a ~10% chance of revival overall:
- (50% chance of no existential catastrophe) * (30% chance current cryopreservation techniques are adequate) * (70% chance my fellow humans will come through for me beyond avoiding existential catastrophe) = 10.5%
is one way. But:
- (15% chance no existential catastrophe) * (99% chance current cryopreservation techniques are adequate) * (70% chance my fellow humans will come through for me beyond avoiding existential catastrophe) = ~10.4%
is a very similar conclusion from very different premises. Gwern has more on this sort of reasoning in Plastination versus cryonics, but I don't know who most of the people he links to are so I'm not sure whether to trust them. He does link to a breakdown of probabilities by Robin, but I don't fully understand the way Robin is breaking the issue down.
The basic idea of getting cryonics is that it offers a chance of massively extended lifespan, because there is a chance that it preserves one's identity. That's the first-run approximation, with additional considerations arising from making this reasoning a bit more rigorous, e.g. that cryonics is competitive against other interventions, that the chance is not metaphysically tiny, etc.
One thing we might make more rigorous is what we mean by 'preservation'. Well, preservation refers to reliably being able to retrieve the person from the hopefully-preserved state, which requires that the hopefully-preserved state cannot have arisen from many non-matching states undergoing the process.
The process that squares positive numbers preserves perfectly (is an injection), because you can always in theory tell me the original number if I give you its square. The process that squares real numbers preserves imperfectly but respectably since, for any positive output, that output could have come from two numbers (e.g. 1^2=1=(-1)^2). Moreover, if we only cared about the magnitude (modulus, i.e. ignoring the sign) of the input, even squaring over real numbers would perfectly preserve what we cared about.
Similarly, there is a chance that the hopefully-preserved states generated by cryonics do/will be generated only by the original identity, or possibly some acceptably close identities. That we do not currently know if it is possible to retrieve acceptably close identities from hopefully-preserved states—or even if we did, how one would do so—does not necessarily make the probability that it is possible to do so in principle low enough that cryonics can be laughed off.
A monkey might be bamboozled by the sequence of square numbers written in Arabic numerals, but that would not prove that the rule could not be deduced in principle, or that information had been lost for human purposes. Similarly we might currently be unable to reverse vitrification or look under a microscope and retrieve the identity, but it is unfair to demand this level of proof, and it is annoying and frustrating in the same way as logical rudeness (even if technically it is not logically rude) when every few months another person smugly spouts this type of argument as a 'refutation' of cryonics and writes cryonicists off, and then gets upvoted handsomely. (Hence Eliezer losing patience and outright declaring that people who don't seem to (effectively) understand this point about mappings don't have a clue.)
Formalisations of these concepts arise in more obviously mathematical contexts like the study of functions and information theory, but it feels like neither of those should be necessary background for a smart person to understand the basic idea. But in all honesty, I think the inferential gap for someone who has not explicitly considered at least the idea of injections before is big enough that often people apply the absurdity heuristic or become scared to do something unconventional before the time it takes to cross that inferential gap.
I think there's a good chance that there are neurodegenerative conditions that are currently irreversible but which many more would think worth working on than cryonics, simply because they associate cryonics with 'computer nerd failure mode' or apply the absurdity heuristic or because attacking neurodegenrative conditions is Endorsed by Experts whereas cryonics is not or because RationalWiki will laugh at them. Possible partial explanation: social anxiety that mockery will ensure for trying something not explicitly endorsed by an Expert consensus (which is a realistic fear, given how many people basically laugh at cryonicists or superficially write it off as 'bullshit'). And yes, in this mad world, social anxiety really might be the decisive factor for actual humans in whether to pursue an intervention that could possibly grant them orders of magnitude more lifespan.