This is a valid point, but it is slightly OT to discuss precise probability for cryonics. I think that one reason people might not be trying to reach a consensus about the actual probability of success is because it may simply require so much background knowledge that one might need to be an expert to reasonably evaluate the subject. (Incidentally, I'm not aware of any sequence discussing what the proper thing to do is when one has to depend heavily on experts. We need more discussion of that.) The fact that there are genuine subject matter experts like de Magalhaes who have thought about this issue a lot and come to the conclusion that it is extremely unlikely while others who have thought about consider it likely makes it very hard to estimate. (Consider for example if someone asks me if string theory is correct. The most I'm going to be able to do is to shrug my shoulders. And I'm a mathematician. Some issues are just really much too complicated for non-experts to work out a reliable likelyhood estimate based on their own data.)
It might however be useful to start a subthread discussing pro and anti arguments. To keep the question narrow, I suggest that we simply focus on the technical feasibility question, not on the probability that a society would decide to revive people.
I'll start by listing a few:
For:
1) Non-brain animal organs have been successfully vitrified and revived. See e.g. here
2) Humans have been revived from low-oxygen, very cold circumstances with no apparent loss of memory. This has been duplicated in dogs and other small mammals in controlled conditions for upwards of two hours. (However the temperatures reduced are still above freezing).
Against:
1) Vitrification denatures and damages proteins. This may permanently damage neurons in a way that makes their information content not recoverable. If glial cells have a non-trivial role in thought then this issue becomes even more severe. There's a fair bit of circumstantial evidence for glial cells having some role in cognition, including the fact that they often behave abnormally in severe mental illness. See for example this paper discussing glial cells and schizophrenia. We also know that in some limited circumstances glial cells can release neurotransmitters.
2) Even today's vitrification procedures do not necessarily penetrate every brain cell, so there may be severe ice-crystal formation in a lot of neurons.
3) Acoustic fracturing is still a major issue. Since acoustic fracturing occurs even when one is just preserving the head, there's likely severe macroscopic brain damage occurring. This also likely can cause permanent damage to memory and other basic functions in a non-recoverable way. Moreover, acoustic fracturing is only the fracturing from cooling that is so bad that we hear it. There's likely a lot of much smaller fracturing going on. (No one seems to have put a sensitive microphone right near a body or a neuro when cooling. The results could be disconcerting).
Yeah, this is a good list.
Note Eliezer's argument that partial damage is not necessarily a problem.
Also note my post: Rationality, Cryonics and Pascal's Wager.
Written with much help from Nick Tarleton and Kaj Sotala, in response to various themes here, here, and throughout Less Wrong; but a casual mention here1 inspired me to finally write this post. (Note: The first, second, and third footnotes of this post are abnormally important.)
It seems to have become a trend on Less Wrong for people to include belief in the rationality of signing up for cryonics as an obviously correct position2 to take, much the same as thinking the theories of continental drift or anthropogenic global warming are almost certainly correct. I find this mildly disturbing on two counts. First, it really isn't all that obvious that signing up for cryonics is the best use of one's time and money. And second, regardless of whether cryonics turns out to have been the best choice all along, ostracizing those who do not find signing up for cryonics obvious is not at all helpful for people struggling to become more rational. Below I try to provide some decent arguments against signing up for cryonics — not with the aim of showing that signing up for cryonics is wrong, but simply to show that it is not obviously correct, and why it shouldn't be treated as such. (Please note that I am not arguing against the feasibility of cryopreservation!)
Signing up for cryonics is not obviously correct, and especially cannot obviously be expected to have been correct upon due reflection (even if it was the best decision given the uncertainty at the time):
Calling non-cryonauts irrational is not productive nor conducive to fostering a good epistemic atmosphere:
Debate over cryonics is only one of many opportunities for politics-like thinking to taint the epistemic waters of a rationalist community; it is a topic where it is easy to say 'we are right and you are wrong' where 'we' and 'you' are much too poorly defined to be used without disclaimers. If 'you' really means 'you people who don't understand reductionist thinking', or 'you people who haven't considered the impact of existential risk', then it is important to say so. If such an epistemic norm is not established I fear that the quality of discourse at Less Wrong will suffer for the lack of it.
One easily falls to the trap of thinking that disagreements with other people happen because the others are irrational in simple, obviously flawed ways. It's harder to avoid the fundamental attribution error and the typical mind fallacy, and admit that the others may have a non-insane reason for their disagreement.
1 I don't disagree with Roko's real point, that the prevailing attitude towards cryonics is decisive evidence that people are crazy and the world is mad. Given uncertainty about whether one's real values would endorse signing up for cryonics, it's not plausible that the staggering potential benefit would fail to recommend extremely careful reasoning about the subject, and investment of plenty of resources if such reasoning didn't come up with a confident no. Even if the decision not to sign up for cryonics were obviously correct upon even a moderate level of reflection, it would still constitute a serious failure of instrumental rationality to make that decision non-reflectively and independently of its correctness, as almost everyone does. I think that usually when someone brings up the obvious correctness of cryonics, they mostly just mean to make this observation, which is no less sound even if cryonics isn't obviously correct.
2 To those who would immediately respond that signing up for cryonics is obviously correct, either for you or for people generally, it seems you could mean two very different things: Do you believe that signing up for cryonics is the best course of action given your level of uncertainty? or, Do you believe that signing up for cryonics can obviously be expected to have been correct upon due reflection? (That is, would you expect a logically omniscient agent to sign up for cryonics in roughly your situation given your utility function?) One is a statement about your decision algorithm, another is a statement about your meta-level uncertainty. I am primarily (though not entirely) arguing against the epistemic correctness of making a strong statement such as the latter.
3 By raising this point as an objection to strong certainty in cryonics specifically, I am essentially bludgeoning a fly with a sledgehammer. With much generalization and effort this post could also have been written as 'Abnormal Everything'. Structural uncertainty is a potent force and the various effects it has on whether or not 'it all adds up to normality' would not fit in the margin of this post. However, Nick Tarleton and I have expressed interest in writing a pseudo-sequence on the subject. We're just not sure about how to format it, and it might or might not come to fruition. If so, this would be the first post in the 'sequence'.
4 Disclaimer and alert to potential bias: I'm an intern (not any sort of Fellow) at the Singularity Institute for (or 'against' or 'ambivalent about' if that is what, upon due reflection, is seen as the best stance) Artificial Intelligence.