What is striking about cryonics is that those who have taken serious efforts to understand the arguments in favor of its technical feasibility generally endorse the idea. Those who have not made cryonics arrangements usually give non-technical arguments (anxiety about the future, loss of family and friends, etc), lack funding or life insurance, or are (self-identified) procrastinators. In contrast, those who reject cryonics are almost invariably uninformed. They do not understand what happens to cells when they freeze, they are not aware of vitrification (solidification without ice formation), they think that brain cells “disappear” five minutes after cardiac arrest, they demand proof of suspended animation as a condition for endorsing cryonics, etc.
This does not mean that no serious arguments could be presented. I can see two major technical arguments that could be made against cryonics:
1. Memory and identity are encoded in such a fragile and delicate manner that cerebral ischemia, ice formation or cryoprotectant toxicity irreversibly destroy it. Considering our limited understanding of the nature of consciousness, and the biochemical and molecular basis of memory, this cannot be ruled out. Cryonics advocates can respond to such a challenge by producing an argument that pairs our current understanding of the neuroanatomical basis of identity and memory to a cryobiological argument in order to argue that existing cryonics procedures are expected to preserve it. An excellent, knowledgeable, response of this kind is offered in Mike Darwin’s Does Personal Identity Survive Cryopreservation? Cryonics skeptics in turn could produce evidence that existing cryonics procedures fall short of this goal.
2. The cell repair technologies that are required for cryonics are not technically feasible. This argument should be presented with care and rigor because the general argument that cell repair technologies as such are not possible contradicts existing biology. A distinct difference from the first argument is that it is harder, if not impossible, to use existing empirical evidence to settle this issue. After all, making cryonics arrangements is a form of decision making under uncertainty and such decisions are not straightforwardly “correct” or “incorrect,” “right” or “wrong.” What can be done is to provide a detailed scientific exposition of the nature and scope of the the kind of repairs that are necessary for meaningful resuscitation and to argue that both biological and mechanical cell repair technologies are not conceivable – or are conceivable.
One thing that becomes immediately clear from this exercise is that there is no single answer to the question of whether cryonics can work because the answer to this question depends on the conditions and technologies that prevail during the cryopreservation of a patient. This introduces a set of more subtle distinctions concerning the question of what kind of cryonics should be assessed. It also produces an argument in favor of continuous improvement of cryonics technologies, and standby and stabilization services.
This short examination of technical arguments that could be made against cryonics gives advocates of the practice two talking points in discussion with skeptics or hostile critics:
(a) If a critic flat-out denies that cryonics is technically feasible, it is not unreasonable to ask him/her to be specific about what (s)he means by cryonics. This simple question often will reveal a poor understanding of existing cryonics technologies and procedures.
(b) A decision made on the basis of incomplete knowledge cannot be “right” or “wrong” and should be respected as one’s best efforts to deal with uncertainty.