I will quickly remark that some aspects of this comment seem to betray a non-info-theoretic point of view. From the perspective of someone like me, the key question for cryonics are "Do two functionally different start states (two different people) map onto theoretically indistinguishable molecular end states?" You are not an expert on the future possibilities of molecular nanotechnology and will not be asked to testify as such, but of course we all accept that arbitrarily great physical power cannot reconstruct a canister of ash because the cremation process maps many different possible starting people to widely overlapping possible canisters of ash. It is this question of many-to-one mapping alone on which we are interested in your expertise, and I would ask you to please presume for the sake of discussion that the end states of interest will be distinguished to molecular granularity (albeit obviously not to a finer position than thermal noise, let alone quantum uncertainty).

That said, I think we will all be interested if you can expand on

many aspects of synaptic strength and connectivity are irretrievably lost as soon as the synaptic membrane gets distorted

and whether you mean this in the customary sense of "it won't boot back up when you switch it on" or in the info-theoretic sense of "this process will map functionally different synapses to exactly similar molecular states, or a spread of such states, up to thermal noise". You are not being asked to overcome a burden of infinite proof either - heuristic argument is fine, we're not asking for particular proofs you can't possibly provide - we just want to make sure that what is being argued is the precise question we are interested in, that of many-to-one mappings onto molecular end states up to thermal noise.

EDIT: Oops, didn't realize this was an old comment.

No doubt you can identify particular local info that is causally effective in changing local states, and that is lost or destroyed in cryonics. The key question is the redundancy of this info with other info elsewhere. If there is lots of redundancy, then we only need one place where it is held to be preserved. Your comments here have not spoken to this key issue.

You'll need to read Molecular Repair of the Brain. Note that it discusses a variety of repair methods, including methods which carry out repairs at sufficiently low temperatures (between 4K and 77K) that there is no risk that "molecular drift" would undo previous work. By making incredibly conservative assumptions about the speed of operations, it is possible to stretch out the time required to repair a system the size of the human brain to three years, but really this time was chosen for psychological reasons. Repairing a person "too quickly" seems to annoy people.

You might also want to read Convergent Assembly. As this is a technical paper which makes no mention of controversial topics, it provides more realistic estimates of manufacturing times. Total manufacturing time for rigid objects such as a human brain at (say) 20K are likely to be 100 to 1000 seconds. This does not include the time required to analyze your cryopreserved brain and determine the healthy state, which is likely to be significantly longer. Note that some alterations to the healthy state (the blueprints) will be required prior to manufacture, including various modifications to facilitate manufacture, the inclusion of heating elements for rewarming, and various control systems to monitor and modulate the rewarming and metabolic start-up processes as well as the resumption of consciousness.

After you've had time to digest the paper, I'd be interested in your comments. As Ciphergoth has said, there are no (repeat no) credible arguments against the feasibility of cryonics in the extant literature. If you have any, it would be most interesting.

As a neuroscientist, you might also be amused by Large Scale Analysis of Neural Structures.

For recent work on vitrification, I refer you to Greg Fahy at 21st Century Medicine.

I'm reading your comment and am now thinking of this as startlingly optimistic, particularly this bit, which appears just wrong per your comment. Except I realise I don't understand the area enough to rewrite that bit. Gah. Are the Wikipedia articles on what you're talking about here any good for getting up to speed?

If you have a technical argument against cryonics, please write it up as an actual blog post, ideally under your real name so you can flash your credentials. It will be the most substantial essay arguing for such a point ever written: see my blog. I'm pretty convinced that if there was really a strong argument of the sort you're trying to make, someone would already have done this, so I take it as strong evidence that they haven't.

The point you're making seems to be that performing the repair is impossible in practice. Apart from that difficulty, do you think enough information is preserved in the location of all atoms in a cryopreserved brain, so that given detailed knowledge of how brains work in general this information would in theory be sufficient to reconstruct the initial person (even if this information is impractical to actually extract or process)? One possibility for avoiding the reconstruction of brains out of atoms is to instead reconstruct a Whole Brain Emulation of the original person. Do you think developing the technology of WBE is similarly impossible, or that there are analogous difficulties with use of WBE for this purpose?

Do you think uploading C. elegans is impossible?

Fascinating. I've been waiting for a while for a well-educated neuroscientist to come here, as I think there are a lot of interesting questions that hinge on issues in neuroscience that are at least hard for me to answer (my only exposure to it is a semester-long class in undergrad). In particular, I'd be interested to know what level of resolution you think would be necessary to simulate a brain to actually get reasonable whole-brain emulations (for instance, is neuronal population level enough? Or do we need to look at individual neurons? Or even further, to look at local ion channel density on the membrane?)

Can you elaborate on the damage that is occurring, even with cryoprotectants?

Why/how would low temps in a cryoprotectant denature proteins?

If you have time I would really like to see the detailed posts, perhaps even in a new thread. I am also a bioengineer/biophysicist but I have little knowledge of neuroscience.

I agree with you that the enormous cost is probably not worth it, when you start thinking what else could be accomplished with the money in the context of it's low probability of success.

However, those technologies that increase human lifespan are really something entirely different than cryonics, not a replacement for it.

Even if we increase lifespan significantly, as long as we still have a lifespan cryonics would allow us to remain frozen until even more life extension technologies come about. It's also a potentially viable method for keeping people alive for long distance space travel at sub-relativistic speeds.

I'd look forward to seeing a more detailed post (or even a journal article) from you going into the biochemistry specifics of the problems with cryonics you mention in this post, and your other posts in this thread. I am particularly curious why rehydration would denature proteins which are naturally stable in water? And what sort of membrane distortions would occur that aren't reversible?