This is a valid point, but it is slightly OT to discuss precise probability for cryonics. I think that one reason people might not be trying to reach a consensus about the actual probability of success is because it may simply require so much background knowledge that one might need to be an expert to reasonably evaluate the subject. (Incidentally, I’m not aware of any sequence discussing what the proper thing to do is when one has to depend heavily on experts. We need more discussion of that.) The fact that there are genuine subject matter experts like de Magalhaes who have thought about this issue a lot and come to the conclusion that it is extremely unlikely while others who have thought about consider it likely makes it very hard to estimate. (Consider for example if someone asks me if string theory is correct. The most I’m going to be able to do is to shrug my shoulders. And I’m a mathematician. Some issues are just really much too complicated for non-experts to work out a reliable likelyhood estimate based on their own data.)
It might however be useful to start a subthread discussing pro and anti arguments.
To keep the question narrow, I suggest that we simply focus on the technical feasibility question, not on the probability that a society would decide to revive people.
I’ll start by listing a few:
For:
1) Non-brain animal organs have been successfully vitrified and revived. See e.g. here
2) Humans have been revived from low-oxygen, very cold circumstances with no apparent loss of memory. This has been duplicated in dogs and other small mammals in controlled conditions for upwards of two hours. (However the temperatures reduced are still above freezing).
Against:
1) Vitrification denatures and damages proteins. This may permanently damage neurons in a way that makes their information content not recoverable. If glial cells have a non-trivial role in thought then this issue becomes even more severe. There’s a fair bit of circumstantial evidence for glial cells having some role in cognition, including the fact that they often behave abnormally in severe mental illness. See for example this paper discussing glial cells and schizophrenia. We also know that in some limited circumstances glial cells can release neurotransmitters.
2) Even today’s vitrification procedures do not necessarily penetrate every brain cell, so there may be severe ice-crystal formation in a lot of neurons.
3) Acoustic fracturing is still a major issue. Since acoustic fracturing occurs even when one is just preserving the head, there’s likely severe macroscopic brain damage occurring. This also likely can cause permanent damage to memory and other basic functions in a non-recoverable way. Moreover, acoustic fracturing is only the fracturing from cooling that is so bad that we hear it. There’s likely a lot of much smaller fracturing going on. (No one seems to have put a sensitive microphone right near a body or a neuro when cooling. The results could be disconcerting).
This is a valid point, but it is slightly OT to discuss precise probability for cryonics. I think that one reason people might not be trying to reach a consensus about the actual probability of success is because it may simply require so much background knowledge that one might need to be an expert to reasonably evaluate the subject. (Incidentally, I’m not aware of any sequence discussing what the proper thing to do is when one has to depend heavily on experts. We need more discussion of that.) The fact that there are genuine subject matter experts like de Magalhaes who have thought about this issue a lot and come to the conclusion that it is extremely unlikely while others who have thought about consider it likely makes it very hard to estimate. (Consider for example if someone asks me if string theory is correct. The most I’m going to be able to do is to shrug my shoulders. And I’m a mathematician. Some issues are just really much too complicated for non-experts to work out a reliable likelyhood estimate based on their own data.)
It might however be useful to start a subthread discussing pro and anti arguments. To keep the question narrow, I suggest that we simply focus on the technical feasibility question, not on the probability that a society would decide to revive people.
I’ll start by listing a few:
For:
1) Non-brain animal organs have been successfully vitrified and revived. See e.g. here
2) Humans have been revived from low-oxygen, very cold circumstances with no apparent loss of memory. This has been duplicated in dogs and other small mammals in controlled conditions for upwards of two hours. (However the temperatures reduced are still above freezing).
Against:
1) Vitrification denatures and damages proteins. This may permanently damage neurons in a way that makes their information content not recoverable. If glial cells have a non-trivial role in thought then this issue becomes even more severe. There’s a fair bit of circumstantial evidence for glial cells having some role in cognition, including the fact that they often behave abnormally in severe mental illness. See for example this paper discussing glial cells and schizophrenia. We also know that in some limited circumstances glial cells can release neurotransmitters.
2) Even today’s vitrification procedures do not necessarily penetrate every brain cell, so there may be severe ice-crystal formation in a lot of neurons.
3) Acoustic fracturing is still a major issue. Since acoustic fracturing occurs even when one is just preserving the head, there’s likely severe macroscopic brain damage occurring. This also likely can cause permanent damage to memory and other basic functions in a non-recoverable way. Moreover, acoustic fracturing is only the fracturing from cooling that is so bad that we hear it. There’s likely a lot of much smaller fracturing going on. (No one seems to have put a sensitive microphone right near a body or a neuro when cooling. The results could be disconcerting).
Yeah, this is a good list.
Note Eliezer’s argument that partial damage is not necessarily a problem.
Also note my post: Rationality, Cryonics and Pascal’s Wager.