My comments in this sub-thread brought out more challenges and queries than I expected. I thought that by now everyone would expect me to periodically say a few things out of line regarding identity, consciousness, and so on, and that only the people I was addressing might respond. I want to reply in a way which provides some context for the answers I'm going to give, but which covers old territory as little as possible. So I would first direct interested parties to my articles here, for the big picture according to me. Those articles are flawed in various ways, but much of what I have to say is there.
Just to review some basics: The problems of consciousness and personal identity are even more severe than is generally acknowledged here. Understanding consciousness, for example, is not just a matter of identifying which part of the brain is the conscious part. From the perspective of physics, any such identification looks like property dualism. Here I want to mention a view due to JanetK, which I never answered, according to which the missing ingredient is "biology": the reason that consciousness looks like a problem from a physical perspective is because one has failed to take into account various biological facts. My reply is that certainly consciousness will not be understood without those facts, but nonetheless, they do nothing to resolve the sort of problems described in my article on consciousness, because they can still be ontologically reduced to elaborate combinations of the same physical basics. Some far more radical ontological novelty will be required if we are going to assemble stuff like "color", "meaning", or "the flow of time" out of what physics gives us.
What we have, in our theories of consciousness, is property dualism that wants to be a monism. We say, here is the physical thing - a brain, or maybe a computer or an upload if we are being futuristic - and that is where the mind-stuff resides, or it is the mind-stuff. But for now, the two sides of the alleged identity are qualitatively distinct. That is why it is really a dualism, but a "property dualism" rather than a "substance dualism". The mind is (some part of) the brain, but the mindlike properties of the mind simply cannot be identified with the physical properties of the brain.
The instinct of people trained in modern science is to collapse the dualism onto the physical side of the equation, because they have been educated to think of reality in those terms. But color, meaning and time are real, so if they are not really present on the physical side of the identity, then a truly monistic solution has to go the other way. The problem now is that it sounds as if we are rejecting the reality of matter. This is why I talked about monads: it is a concept of what is physically elementary which can nonetheless be expanded into something which is actually mindlike in its "interior". It requires a considerable rethink of how the basic degrees of freedom in physics are grouped into things; and it also requires that what we would now call quantum effects are somewhere functionally relevant to conscious cognition, or else this ontological regrouping would make no difference at the level where the problem of consciousness resides. So yes, there are several big inferential leaps there, and a prediction (that there is a quantum neurobiology) for which there is as yet no support. All I can say is that I didn't make those leaps lightly, and that all simpler alternatives appear to be fatally compromised in some way.
One consequence of all this is that I can be a realist about the existence of a conscious self in ways which must sound very retrograde to everyone here who has embraced the brave new ideas of copying, patternist theories of identity, the unreality of time on the physical level, and so on. To my way of thinking, I am a "monad", some subsystem of the brain with many degrees of freedom, which is a genuine ontological unity, and whose state can be directly identified with (and not just associated with) my state in the world as I perceive it subjectively. This is an entity which persists in time, and which interacts with its environment (presumably, simpler monads making up the neighboring subsystems of the brain). If one grants for a moment the possibility of thinking about reality in these terms, clearly it makes these riddles about personal identity a lot simpler. There is a very clear sense in which I am not my copies. At best, they are other monads who start out in the same state. There is no conscious sorites paradox. Whenever you have consciousness, it is because you have a monad big enough to be conscious - it's that simple.
So having set the stage - and apologies to anyone tired of my screeds on these subjects - now we can turn to cryonics. I said to Roko
I would be rather surprised if the "neurophysical correlate of selfhood" survives the freezing transition.
to which he responded
The neurophysical correlate of selfhood can survive a temperature drop to 0 but it can't survive a phase change?
I posit that, in terms of current physics, the locus of consciousness is some mesoscopic quantum-coherent subsystem of the brain, whose coherence persists even during unconsciousness (which is just a change of its state) but which would not last through the cryonic freezing of the brain. If this persistent biological quantum coherence exists, it will exist because of, and not in spite of, metabolic activity. When that ceases, something must happen to the "monad" (which is just another name for something like "big irreducible tensor factor in the brain's wavefunction") - it comes apart into simpler monads, it sheds degrees of freedom until it becomes just another couple of correlated electrons, I don't have a fixed idea about it. But this is what death is, in the monadic "theory". If the frozen brain is restored to life, and a new conscious condensate (or whatever) forms, that will be a new "big tensor factor", a new "monad", and a new self. That is the idea.
You could accept my proposed metaphysics for the sake of argument and still say, but can't you identify with the successor monad? It will have your memories, and so forth. In other words, this ontology of monadic minds should still allow for something like a copy. I don't really have a fixed opinion about this, largely because how the conscious monad accesses and experiences its memories and identity remains completely untheorized by me. The existence of a monad as a persistent "substance" suggests the possibility that memories in a monad might be somehow internal to it, rather than externally supplied data which pops into its field of consciousness when appropriate. This in turn suggests that a lot of what is written, in futurist speculation about digital minds, transferrable memories, and so forth, would not apply. You might be able to transfer unconscious dispositions but not a certain type of authentic conscious memory; it might be that the only way in which the latter could be induced in a monad would be for it, that particular monad, to "personally" undergo the experience in question. Or, it might really be the case that all forms of memory, knowledge, perception and so forth are externally based and externally induced, so that my recollection of what happened this morning is not ontologically any different from the same "recollection" occurring in a newly created copy which never actually had the experience.
Again, I apologize somewhat for going on at such length with these speculations. But I do think that the philosophies of both mind and matter which are the consensus here - I'm thinking of a sort of blithe computationalism with respect to consciousness, and the splitting multiverse of MWI as a theory of physics - are very likely to be partly or even completely false, and this has to have implications for topics like cryonics, AI, various exotic ethical doctrines based on a future-centric utilitarianism, and so on.
Not only does this quantum brain idea violate known experimental and theoretical facts about the brain, it also violates what we know about evolution. Why would evolution design a system that maintains coherence during sleep and unconsciousness, if this has no effect on inclusive genetic fitness?
(Mitchell Porter thinks that his "copy" would behave essentially identically to what he would have done had he not "lost his selfhood", so in terms of reproductive fitness, there's no difference)
Followup to: Cryonics wants to be big
We've all wondered about the wisdom of paying money to be cryopreserved, when the current social attitude to cryopreservation is relatively hostile (though improving, it seems). In particular, the probability that either or both of Alcor and CI go bankrupt in the next 100 years is nontrivial (perhaps 50% for "either"?). If this happened, cryopreserved patients may be left to die at room temperature. There is also the possibility that the organizations are closed down by hostile legal action.A
The ideal solution to this problem is a way of keeping bodies cold (colder than -170C, probably) in a grave. Our society already has strong inhibitions against disturbing the dead, which means that a cryonic grave that required no human intervention would be much less vulnerable. Furthermore, such graves could be put in unmarked locations in northern Canada, Scandinavia, Siberia and even Antarctica, where it is highly unlikely people will go, thereby providing further protection.
In the comments to "Cryonics wants to be big", it was suggested that a large enough volume of liquid nitrogen would simply take > 100 years to boil off. Therefore, a cryogenic grave of sufficient size would just be a big tank of LN2 (or some other cryogen) with massive amonuts of insulation.
So, I'll present what I think is the best possible engineering case, and invite LW commenters to correct my mistakes and add suggestions and improvements of their own.
If you have a spherical tank of radius r with insulation of thermal conductivity k and thickness r (so a total radius for insulation and tank of 2r) and a temperature difference of ΔT, the power getting from the outside to the inside is approximately
25 × k × r × ΔT
If the insulation is made much thicker, we get into sharply diminishing returns (asymptotically, we can achieve only another factor of 2). The volume of cryogen that can be stored is approximately 4.2 × r3, and the total amount of heat required to evaporate and heat all of that cryogen is
4.2 × r3 × (volumetric heat of vaporization + gas enthalpy)
The quantity is brackets for Nitrogen and a ΔT of 220 °C is approximately 346,000,000 J m-3. Dividing energy by power gives a boiloff time of
1/12,000 × r2 × k-1 centuries
Setting this equal to 1 century, we get:
r2/k = 12,000.
Now the question is, can we satisfy this constraint without an exorbitant price tag? Can we do better and get 2 or 3 centuries?
"Cryogel" insulation with a k-value of 0.012 is commercially available Meaning that r would have to be at least 12 meters. A full 12-meter radius tank would weigh 6000 tons (!) meaning that some fairly serious mechanical engineering would be needed to support it. I'd like to hear what people think this would cost, and how the cost scales with r.
The best feasible k seems to be fine granules or powder in a vacuum. When the mean free path of a gas increases significantly beyond the characteristic dimension of the space that encloses it, the thermal conductivity drops linearly with pressure. This company quotes 0.0007 W/m-K, though this is at high vacuum. Fine granules of aerogel would probably outperform this in terms of the vacuum required to get down to < 0.001 W/m-K.
Supposing that it is feasible to maintain a good enough vacuum to get to 0.0007 W/m-K, perhaps with aerogel or some other material. Then r is a mere 2.9 meters, and we're looking at a structure that's the size of a large room rather than the size of tower block, and a cryogen weight of a mere 80 tons. Or you could double the radius and have a system that would survive for 400 years, with a size and weight that was still not in the "silly" range.
The option that works without the need for a vacuum is inviting because there's one less thing to go wrong, but I am no expert on how hard it would be to make a system hold a rough vacuum for 100 years, so it is not clear how useful that is.
As a final comment, I disagree that storing all patients in one system is a good idea. Too many eggs in one basket is never good when you're trying to maximize the probability that each patient will survive. That's why I'm keen on finding a system that would be small enough that it would be economical to build one for a few dozen patients, say (cost < 30 million).
So, I invite Less Wrong to comment: is this feasible, and if so how much would it cost, and can you improve on my ideas?
In particular, any commenters with experience in cryogenic engineering would delight me with either refinement or critique of my cryogenic ideas, and delight me even more with cost estimates of these systems. Its also fairly critical to know whether you can hold a 99% vacuum for a century or two.
A: In addition to this, many scenarios where cryonics is useful to the average LW reader are scenarios where technological progress is slow but "eventually" gets to the required level of technology to reanimate you, because if progress is fast you simply won't have time to get old and die before we hit longevity escape velocity. Slow progress in turn correlates with the world experiencing a significant "dip" in the next 50 or so years, such as a very severe recession or a disaster of some kind. These are precisely the scenarios where a combination of economic hardship and hostile public opinion might kill cryonics organizations.