To keep the information all in one place, I’ll reply here.
Cryogenic preservation exists in the proof of tardigrades—also called waterbears—which can reanimate from temperatures as low as 0.15 K, and have sufficient neurophysiological complexity to enable analysis of neuronal structural damage.
We don’t know if the identity of a given waterbear pre-cyrobiosis is preserved post-reanimation. For that we’d need a more complex organism. However, the waterbear is idiosyncratic in its capacity for preservation; while it proves the possibility for cyrogenic preservation exists, we ourselves do not have the traits of the waterbear that facilitate its capacity for preservation.
In the human brain, there are billions of synapses—to what neurones other neurones connect, we call the connectome: this informs who you are. According to our current theoretical and practical understanding of how memories work, if synapses degrade even the slightest amount your connectome will change dramatically, and will thus represent a different person—perhaps even a lesser human (fewer memories, etcetera).
Now, let’s assume uploading becomes commonplace and you mainly care about preserving your genetic self rather than your developed self (you without most of your memories and different thought processes vs. the person you’ve endeavoured to become), so any synaptic degradation of subsistence brain areas becomes irrelevant. What will the computer upload? Into what kind of person will your synapses reorganise? Even assuming they will reorganise might ask too much of the hypothetical.
Ask yourself who—or what—you would like to cyropreserve; the more particular your answer, the more science needed to accommodate the possibility.
We don’t know if the identity of a given waterbear pre-cyrobiosis is preserved post-reanimation. For that we’d need a more complex organism.
How would you design that experiment? I would think all you’d need is a better understanding of what identity is. But maybe we mean different things by identity.
We’d need to have a means of differentiating the subject waterbear’s behaviour from other waterbears; while not exhaustive, classically conditioning a modified reflexive reaction to stimuli (desensitisation, sensitisation) or inducing LTP or LTD on a synapse, then testing whether the adaptations were retained post-reanimation, would be a starting point.
The problem comes when you try to extrapolate success in the above experiment to mean potential for more complex organisms to survive the same procedure given x. Ideally you would image all of the subjects synapses pre-freeze or pre-cryobiosis (depending on what x turns out to be), then image them again post-reanimation, and have a program search for discrepancies. Unfortunately, the closest we are to whole-brain imaging is neuronal fluorescence imaging, which doesn’t light up every synapse. Perhaps it might if we use transcranial DC or magnetic stimulation to activate every cell in the brain; doing so may explode a bunch of cells, too. I’ve just about bent over the conjecture tree by this point.
Does the waterbear experience verification and then wake up again after being thawed, or does subjective experience terminate with vitrification—subjective experience of death / oblivion—and a new waterbear with identical memories begin living?
We need to stop and (biologically) define life and death for a moment. A human can be cryogenically frozen before or after their brain shuts down; in either case, their metabolism will cease all function. This is typically a criterion of death. However if, when reanimated, the human carries on as they would from a wee kip, does this mean they have begun a new life? resumed their old life after a sojourn to the Underworld?
You see the quandary our scenario puts to this definition of life, for the waterbear does the exact above. They will suspend their metabolism, which can be considered death, reanimate when harsh environmental conditions subside, and go about their waterbearing ways. Again, do the waterbears live a subset of multiple lives within the set of one life? Quite confusing to think about, yes?
Now let’s redefine life.
A waterbear ceases all metabolic activity, resumes it, then lumbers away. In sleep, one’s state pre- and post-sleep will differ; one wakes up with changed neuronal connections, yet considers themselves the same person—or not, but let’s presume they do. Take, then, the scenario in which one’s state pre- and post-sleep does not differ; indeed, neurophysiologically speaking, it appears they’ve merely paused then recommenced their brain’s processes, just as the time 1:31:00 follows 1:30:59.
This suggests that biological life depends not on metabolic function, but on the presence of an organised system of (metabolic) processes. If the system maintains a pristine state, then it matters not how much time has passed since it last operated; the life of the system’s organism will end only when when that system becomes so corrupted as to lose the capacity for function. Sufficient corruption might amount to one specalated synapse; it might amount to a missing ganglion. Thus cyrogenics’ knottiness.
As to whether they experience verification, you’ll have to query a waterbear yourself. More seriously, for any questions on waterbear experience I refer you to a waterbear, or a waterbear philosopher. As to whether and to what degree they experience sensation when undergoing cryptobiosis, we can test to find out, but any results will be interpreted through layers of extrapolation: “Ganglion A was observed inhibiting Ganglion B via neurotransmitter D binding postsynaptic alpha receptors upon tickling the watebear’s belly; based on the conclusions of Researchers et. al., this suggests the waterbear experienced either mildly positive or extremely negative sensation.”
Going under anesthesia is a similar discontinuity in subjective experience, along with sleep, situations where people are technically dead for a few moments and then brought back to life, coma patients, and so on.
I don’t personally regard any of these as the death of one person followed by the resurrection of a new person with identical memories, so I also reject the sort of reasoning that says cryogenic resurrection, mind uploading, and Star Trek-style transportation is death.
Eliezer has a post here about similar concerns. It’s perhaps of interest to note that the PhilPapers survey revealed a fairly even split on the teletransporter problem among philosophers, with the breakdown being 36.2%/32.7%/31.1% as survive/other/die respectively.
Yes, that post still reflects my views. I should point out again that sleep and many forms of anesthesia don’t stop operation of the brain, they just halt the creation of new memories so people don’t remember. That’s why, for example, some surgery patients end up with PTSD from waking up on the table, even if they don’t remember.
Other cases like temporary (clinical) death and revival also aren’t useful comparisons. Even if the body is dying, the heart and breathing stops, etc., there are still neural computations going on from which identity is derived. The irrecoverable disassociation of the particle interactions underlying consciousness probably takes a while—hours or more, unless there is violent physical damage to the brain. Eventually the brain state fully reverts to random interactions and identity is destroyed, but clinical revival becomes impossible well before then.
Cryonics is more of a weird edge case … we don’t know enough now to say with any certainty whether cryonics patients have crossed that red line or not with respect to destruction of identity.
To keep the information all in one place, I’ll reply here.
Cryogenic preservation exists in the proof of tardigrades—also called waterbears—which can reanimate from temperatures as low as 0.15 K, and have sufficient neurophysiological complexity to enable analysis of neuronal structural damage.
We don’t know if the identity of a given waterbear pre-cyrobiosis is preserved post-reanimation. For that we’d need a more complex organism. However, the waterbear is idiosyncratic in its capacity for preservation; while it proves the possibility for cyrogenic preservation exists, we ourselves do not have the traits of the waterbear that facilitate its capacity for preservation.
In the human brain, there are billions of synapses—to what neurones other neurones connect, we call the connectome: this informs who you are. According to our current theoretical and practical understanding of how memories work, if synapses degrade even the slightest amount your connectome will change dramatically, and will thus represent a different person—perhaps even a lesser human (fewer memories, etcetera).
Now, let’s assume uploading becomes commonplace and you mainly care about preserving your genetic self rather than your developed self (you without most of your memories and different thought processes vs. the person you’ve endeavoured to become), so any synaptic degradation of subsistence brain areas becomes irrelevant. What will the computer upload? Into what kind of person will your synapses reorganise? Even assuming they will reorganise might ask too much of the hypothetical.
Ask yourself who—or what—you would like to cyropreserve; the more particular your answer, the more science needed to accommodate the possibility.
How would you design that experiment? I would think all you’d need is a better understanding of what identity is. But maybe we mean different things by identity.
We’d need to have a means of differentiating the subject waterbear’s behaviour from other waterbears; while not exhaustive, classically conditioning a modified reflexive reaction to stimuli (desensitisation, sensitisation) or inducing LTP or LTD on a synapse, then testing whether the adaptations were retained post-reanimation, would be a starting point.
The problem comes when you try to extrapolate success in the above experiment to mean potential for more complex organisms to survive the same procedure given x. Ideally you would image all of the subjects synapses pre-freeze or pre-cryobiosis (depending on what x turns out to be), then image them again post-reanimation, and have a program search for discrepancies. Unfortunately, the closest we are to whole-brain imaging is neuronal fluorescence imaging, which doesn’t light up every synapse. Perhaps it might if we use transcranial DC or magnetic stimulation to activate every cell in the brain; doing so may explode a bunch of cells, too. I’ve just about bent over the conjecture tree by this point.
Does the waterbear experience verification and then wake up again after being thawed, or does subjective experience terminate with vitrification—subjective experience of death / oblivion—and a new waterbear with identical memories begin living?
We need to stop and (biologically) define life and death for a moment. A human can be cryogenically frozen before or after their brain shuts down; in either case, their metabolism will cease all function. This is typically a criterion of death. However if, when reanimated, the human carries on as they would from a wee kip, does this mean they have begun a new life? resumed their old life after a sojourn to the Underworld?
You see the quandary our scenario puts to this definition of life, for the waterbear does the exact above. They will suspend their metabolism, which can be considered death, reanimate when harsh environmental conditions subside, and go about their waterbearing ways. Again, do the waterbears live a subset of multiple lives within the set of one life? Quite confusing to think about, yes?
Now let’s redefine life.
A waterbear ceases all metabolic activity, resumes it, then lumbers away. In sleep, one’s state pre- and post-sleep will differ; one wakes up with changed neuronal connections, yet considers themselves the same person—or not, but let’s presume they do. Take, then, the scenario in which one’s state pre- and post-sleep does not differ; indeed, neurophysiologically speaking, it appears they’ve merely paused then recommenced their brain’s processes, just as the time 1:31:00 follows 1:30:59.
This suggests that biological life depends not on metabolic function, but on the presence of an organised system of (metabolic) processes. If the system maintains a pristine state, then it matters not how much time has passed since it last operated; the life of the system’s organism will end only when when that system becomes so corrupted as to lose the capacity for function. Sufficient corruption might amount to one specalated synapse; it might amount to a missing ganglion. Thus cyrogenics’ knottiness.
As to whether they experience verification, you’ll have to query a waterbear yourself. More seriously, for any questions on waterbear experience I refer you to a waterbear, or a waterbear philosopher. As to whether and to what degree they experience sensation when undergoing cryptobiosis, we can test to find out, but any results will be interpreted through layers of extrapolation: “Ganglion A was observed inhibiting Ganglion B via neurotransmitter D binding postsynaptic alpha receptors upon tickling the watebear’s belly; based on the conclusions of Researchers et. al., this suggests the waterbear experienced either mildly positive or extremely negative sensation.”
I think the question was a practical one and “verification” should have been “vitrification.”
I considered that, but the words seemed too different to result from a typo; I’m interested to learn the fact of the matter.
I’ve edited the grandparent to accommodate your interpretation.
Going under anesthesia is a similar discontinuity in subjective experience, along with sleep, situations where people are technically dead for a few moments and then brought back to life, coma patients, and so on.
I don’t personally regard any of these as the death of one person followed by the resurrection of a new person with identical memories, so I also reject the sort of reasoning that says cryogenic resurrection, mind uploading, and Star Trek-style transportation is death.
Eliezer has a post here about similar concerns. It’s perhaps of interest to note that the PhilPapers survey revealed a fairly even split on the teletransporter problem among philosophers, with the breakdown being 36.2%/32.7%/31.1% as survive/other/die respectively.
ETA: Ah, nevermind, I see you’ve already considered this.
Yes, that post still reflects my views. I should point out again that sleep and many forms of anesthesia don’t stop operation of the brain, they just halt the creation of new memories so people don’t remember. That’s why, for example, some surgery patients end up with PTSD from waking up on the table, even if they don’t remember.
Other cases like temporary (clinical) death and revival also aren’t useful comparisons. Even if the body is dying, the heart and breathing stops, etc., there are still neural computations going on from which identity is derived. The irrecoverable disassociation of the particle interactions underlying consciousness probably takes a while—hours or more, unless there is violent physical damage to the brain. Eventually the brain state fully reverts to random interactions and identity is destroyed, but clinical revival becomes impossible well before then.
Cryonics is more of a weird edge case … we don’t know enough now to say with any certainty whether cryonics patients have crossed that red line or not with respect to destruction of identity.