For evolution we have enough data that evolution comes out as the most likely theory given the data. Without freezing and thawing a brain, how do we get sufficient evidence that we're storing everything necessary, such that "it's all still there" becomes the most likely theory?
A good starting point would be electron micrographs of the tissue. Another would be cellular viability assays based on cellular ion pumping action.
We can also rule out competing hypotheses of memory formation which would negate the premise by examining what happens to the memories of humans subjected to hypothermia. Even better, there are some tests on the connectome hypothesis we can plausibly run in the near future (IIRC this involves teaching music to some neurons, then scanning them and recreating the song in the computer).
Then there is the measurement of electrical activity in tissue samples. Organized whole-brain electrical activity should be adequate proof of biological (far more conservative than the standard of information-theoretic) survival. I expect this to be achieved in 20 years or so, given adequate funding and attention. I would expect perfect brain preservation to be a bit further on, probably closer to 50-year.
Most complex scientific procedures need a lot of testing to get right. We can't test here. We might be lucky, but I do think we have only a ~20% chance of being lucky enough.
I agree that the process needs a lot of testing to get right. However the testing can take the form of tissue viability assays, it does not need to take the form of a whole body. That is far more ambitious than a whole brain and thus harder to perfect. Different organs have different optimal cooling rates and perfusion rates. We should only expect that particular test to be possible either when we are at the point of printing bodies and transplanting brains into them on demand, or when we have long since solved the problem of individual organ (including brain) preservation.
Another thing we have going for us is that technology of the future can almost certainly repair the brain to some degree. Even if we are limited to bio-analogous nanotech, such as genetically engineered microbes (and I don't think this is the case where cryopreserved brains are concerned), we can still expect fairly extensive repair work to be possible.
Each of those steps needs to go right for cryonics to work. I've already moved my probabilities of success towards .5 to reflect uncertainty, but when you multiply them all together you still get a very small number.
They don't all have to go right in the most dramatic 100% manner. For example, you probably do not need the brain to be able to remember more than 90% of the past self to be a valid form of survival, and you might not need more than 10%. To some degree this is a subjective values question. A clone-like individual with vague memories of your childhood may be worth spending a lot of money on, or it may not be... But it's extremely low probability that you won't preserve enough information for at least that kind of reanimation, whereas the likelihood that you won't have any perceptible memory loss at all is also pretty low (for a cryopreservation performed today).
I'm not sure what you're saying here. How would we know whether the current cryonics process were storing everything? The brain is very fragile, with lots of tiny connections, and it seems we could easily be disrupting them.
The brain is warm, wet, and protein-based, and has to put up with a lot of chaos on a day to day basis. It is composed of wetware, not hardware. Thus it is reasonable to expect the data to be stored fairly redundantly and with the most important and oldest information in the toughest/thickest connections.
Many of the smaller connections are likely to be lost in a suboptimal preservation, as happens I believe with some forms of dementia. However this is one of the things we can get empirical feedback on by scanning dendrite preservation in small animals as we cryopreserve and thaw them.
Sure. I put the impossibility of extraction given that we preserved everything at 5%.
Sure, but it makes a big difference whether everything is preserved by say preserving viability in all the cells (a theoretical ideal currently achievable only in slices), versus say fixation, which locks the information in place but completely eliminates viability. All other things equal, a zero-viability mechanism has less probability of being survivable than a viability-preserving mechanism.
I put us killing ourselves off at 10% and society falling apart (if we don't kill ourselves first) at 40%. Together this gives a 46% chance of one of them happening. Do you think these odds are too pessimistic?
Yes I think they are, given how long we have avoided either of these fates so far. Although I'd be cautious about downplaying them since the act of downplaying them could lead to them happening due to lack of caution. Literacy, science, and so forth have a very strong rachet effect on progress. I'd give the conjunction of the two (downfall of civilization and killing ourselves off) a 10% maybe, supposing relative tech stagnation over the next 200 years consistent with no reanimation. Less if tech doesn't stagnate, since that is more correlated with literacy.
Another point worth raising at this point is that cryonicists have added incentive to look at extinction and civilization-wrecking events using near-mode reasoning. This could be a positive externality worth taking into consideration.
Reviving someone means very powerful computers and lots of storage. We might figure out how to do this for some people, but still have it be too expensive for everyone. I do think this is unlikely, though: I put down 10% as the chances that it would be simply too expensive.
The storage space needed (ongoing) should be no more than that of the brain itself, though I can see some being required temporarily for heavy extrapolations if we need to infer lots of details from badly preserved tissue. This should be correlated with worst case viable preservation (low to no cellular viability, lots of simulation and educated guesswork involved in the reanimation process).
If we get to the point of perfectly or near-perfectly preserved brains, it should be cheap in principle to implant them into printed bodies (possibly with artificial limbs, hearts, etc.) The reason to think simulation is the viable candidate is mainly an extrapolation of Moore's Law which indicates this kind of storage space should be extremely cheap before we hit physical limits, and the fact that you'd need some hefty nano-equipment to scan on that level of detail anyway.
I was thinking more about the cooling we do for heart surgery.
This is hypothermic medicine, which is both important for cryonics and important to distinguish from cryonics (which is more a subset of cryobiology). The temperature levels involved are much closer to room temperature, not cryogenic. There is an interesting parallel to cryonics in that a patient might be cooled to hypothermic temperatures (similar to a hibernating animal), and if they could be stabilized there they would age more slowly, cancers would progress more slowly, etc.
You've convinced me that there's actually a lot we can do to test how well current cryonics processes work that doesn't require round trips on human brains.
If we do these tests and adjust the cryonics procedures in response to what we learn, my estimate for the chances that we're not preserving what we need to will probably go down a lot.
They don't all have to go right in the most dramatic 100% manner
Most of the steps I'm on the negative side for are pretty much binary: either they succeed and you proceed to the next step or they fail and you're done. ...
Most people, given the option to halt aging and continue in good heath for centuries, would. Anti-aging research is popular, but medicine is only minimally increasing lifespan for healthy adults. You, I, and everyone we know have bodies that are incredibly unlikely to make it past 120. They're just not built to last.
But what are you, really? Your personality, your memories, they don't leave you when you lose a leg. Lose most parts of your body and you're still you. Lose your brain and that's it. [1] You are a pattern, instantiated in the neurons of your brain. That pattern is sustained by your body, growing and changing as you learn and experience the world. Your body supports you for years, but it deteriorates and eventually isn't up to the task any more. Is that 'game over'?
Perhaps we could scan people's brains at extremely high detail so we could run them in some sort of human emulator. This requires a thorough understanding of the brain, huge amounts of storage, unbelievably fast computers, and very detailed scanning. If it's even possible, it may be several hundred years away.
Our bodies aren't going to last that long, but what if we could figure out how to preserve our brains so that the information didn't decay? Then, if the future turned out to be one in which we had advanced brain emulation and scanning technology, we could be revived. I don't know if people in the future would want to spend the time or money to revive us, but in a future with technology this advanced, reviving a preserved brain as a computer simulation could be really cheap.
The most advanced technology for long-term tissue preservation today [2] is cryonics: freezing with vitrification. You add something to the blood that keeps ice crystals from forming and then freeze it. This is pretty much the same thing frogs do, hibernating frozen through the winter. The biggest organs that have been successfully brought back to working order after vitrification are rabbit kidneys, and the brain is a lot bigger and much more complex. While there are people applying this technique to human brains after death, it's very much a one way street; we can't revive them with current technology.
How much should it worry us that we can't reverse this freezing process? If we're already talking about revival via high-detail scanning and emulation, which is only practical after hundreds of years of technological development, does it matter that we can't currently reverse it? The real question in determining whether vitrification is sufficient is whether we're preserving all the information in your brain. If something critical is missing, or if something about our current freezing process loses information, the brains we think are properly preserved might be damaged or deteriorated beyond repair. Without a round trip test where we freeze and then revive a brain, we don't know whether what we're doing will work.
Another issue is that once you've frozen the brain you need to keep it cold for a few centuries at least. Liquid nitrogen is pretty cheap, but providing it constantly over such a long time is hard. Organizations fall apart: very few stay in business for even 100 years, and those that do often have departed from their original missions. Current cryonics organizations seem no different from others, with financial difficulties and imperfect management, so I don't think 200+ years of full functioning is very likely.
Even if nothing goes wrong with the organization itself, will our society last that long? Nuclear war, 'ordinary' war, bioterrorism, global warming, plagues, and future technologies all pose major risks. Even if these don't kill everyone, they might disrupt the cryonics organizations or stop technological development such that revival technology is never developed.
Taking all these potential problems and risks into account, it's unlikely that you can get around death by signing up for cryonics. In attempts to calculate overall odds for success from estimated chances of each step I've seen various numbers: 1:3, 1:4, 1:7, 1:15 and 1:400. I'm even more pessimistic: I calculated 1:600 when I first posted to lesswrong and have since revised down to 1:1000. To some people the probability doesn't matter, but because it's expensive and there are plenty of other things one can do with money, I don't think it's obviously the sensible thing to do.
(I also posted this on my blog.)
[1] Well, lose your heart and you're gone too. Except that we can make mechanical hearts and you stay the same person on receiving one. Not so much with a mechanical brain.
[2] Plastination is also an option, but it's not yet to a point where we can do it on even a mouse brain.