I was under the impression that hypothermia is not the same as cryonic freezing, and that even when a person is undergoing hypothermia, he still has brain activity. I am reasonably sure that the person is at least undergoing metabolic activity, because otherwise, in the absence of cryoprotectants, his cells would freeze and burst. I could be wrong about this, though.
Yes there is some metabolic activity in hypothermia patients. However, metabolic activity isn't the reason for no ice crystal formation in hypothermia patients. The relatively high temperature (vs. cryogenic temperatures) is responsible for both phenomena. However, because it is much lower than ordinary body temperatures, hypothermia slows metabolism down and reduces (and halts) electrical activity in the brain.
As far as tissue damage is concerned, AFAIK our current technology is not advanced enough to even preserve human hearts, livers, and other organs (for the purposes of transplanting them into other patients). That is, we can freeze an organ, and we can thaw it, but in the process it is damaged beyound repair -- and we're talking about relatively simple organs here, not brains.
This is correct. However, vitrification has been used to vitrify and revive a rabbit kidney. The brain has a higher degree of vascularization than other organs, which is positive for cryonics purposes. However, nobody is suggesting that the brain can be perfectly preserved as a functioning organ at present. Its size and the conditions under which cryonics is practiced make this unlikely, although it is a reasonable goal for researchers to work towards (and is much easier than full body).
Mechanical damage to cells due to thermal contraction (during freezing) and expansion (during thawing)
Cracking due to temperature differentials is macroscopic in vitrification, thus doesn't apply to "cells" so much as to tissues. It is also preventable, by stopping cooling at the glass transition temperature rather than continuing down to LN2 temperature.
Formation of ice crystals (mitigated but not entirely eliminated by cryoprotectants)
Entirely eliminated in parts of the tissue that are well-perfused. In ideal cases, my understanding is that the entire brain can be vitrified. The cost of this is the toxicity of the required concentrations of cryoprotectants.
Ischemic cascade (I didn't actually know the name of this process, thanks for pointing it out)
Largely prevented (under ideal conditions) with prompt cooling.
Slow diffusion and chemical reaction over long periods of time (which is why even simpler tissues such as plant seeds have a limited "shelf life" when frozen)
My understanding is that this is not a problem when you get to the glass transition temperature (-135C).
You say that this damage is not a "deal-killer", but if this were the case, we could at least cryopreserve individual organs today (not to mention whole mammals). Cryonics advocates usually agree with me here, but postulate some form of future technology which will be able to repair this damage.
I don't know why your interpretation of the phrase "deal-killer" would exclude the possibility of repairs using future technology. That's explicitly part of the deal when discussing cryonics.
I'm not sure what kind of technology could do that, though. Molecular nanotechnology is the most popular candidate, but I am not convinced that it could, in fact, exist (which is one of the reasons I'm not too enthusiastic about the Singularity, as well).
Classic MNT is the most extreme candidate, and is easy to visualize as something likely to work if it does come to exist. However, there is a spectrum of possible candidates for implementing the repairs, ranging from bioengineered microbes to synthetic proteins, or other constructs ("soft machines") that mimic life's mechanisms.
Note that the most compelling arguments against MNT are because it would be too fragile to work in warm, wet conditions. Cryonics puts the body in non-warm, non-wet conditions, which could be considered ideal for forms of nanotech (and/or a spectrum of microtech featuring nanoscale components) that are not suitable for higher temperatures.
There's also no reason (of which I am aware) that you could not convert the cryopreserved body into very small micro-scale blocks or slices, fix them individually using advanced lithographic techniques applied to the exposed surface area, then reassemble them. This sort of thing could require extreme amounts of resources to pull off, which (at least given a non-MNT universe) indicates that a large amount of money should be set aside to generate interest for reanimation.
I haven't yet mentioned uploading, because it's worth addressing the least convenient possible universe the skeptic can imagine first. But this is another possible track which could proceed in the absence of MNT, so if you accept that an upload is a valid continuation of self (which plenty of lesswrongers will be happy to defend), this would also need to be eliminated for cryonics to be rendered implausible.
What do you mean by "immediate results" ? Cryonics is kind of the opposite of "immediate", by definition.
I was referring to the outcomes of cryobiology experiments. You can experiment with new cryoprotectants and get meaningful results right away. Virtually all of the damage (toxicity) is done on the way to and from the reduced temperature, with virtually none occurring during the long-term storage.
With anti-aging interventions by contrast, you cannot tell whether something is helping until the experimental animal reaches old age. Also, the more effective the anti-aging treatment is, the longer it takes to test. The shorter-lived the animal is the less humanlike its genome, and thus the less likely the treatment will successfully translate to humans. Thus we might take hundreds or thousands of years to reach actuarial escape velocity or comprehensively cure aging.
Yes there is some metabolic activity in hypothermia patients. However, metabolic activity isn't the reason for no ice crystal formation in hypothermia patients.
Sorry, my reply came out differently from what it sounded like in my head. What I meant to say was something like, "hypothermia patients still undergo noticeable metabolic activity, as opposed to cryonic patients, because the temperatures involved are much higher (among other reasons)". So, you and I mostly agree here; still, what I tried to say is that hypothermia and cryopreservation ...
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: