Will Cryonics Work? Examining the Probabilities

Cryonics, May 1989

by Steven B. Harris, M.D.

With an Appendix by R. Michael Perry, Ph.D.: Further Thoughts on the Probability That Cryonics Will Succeed. See also Responsibillity, Probability, and Durability by Thomas Donaldson.


The idea of cryonics has been branded “unscientific” in the past by a number of scientists who are privately religious people, and who would no doubt become highly irate if one were to attempt to smear (say) Christianity with the same label. There is considerable irony in this.

The problem is simple prejudice. There is nothing particularly epistemologically heinous about cryonics. Most scientists recognize that there are many non-testable aspects of human belief (religious and otherwise) which, precisely because they are untestable, are outside the purview of science. These ideas include much of what constitutes religion, philosophy, ethics, history, and art, as well as much of what goes into ordinary planning for the future. A person who had never entertained an idea that was not immediately testable (i.e., scientific) would be in a sad way indeed.

There is, of course, a very great difference between ideas that are not scientific (i.e., non-scientific), and ideas that are un-scientific. Un- scientific beliefs are those which can be tested, which have been tested, and which have failed the test. The idea that laetrile cures cancer, for instance, is unscientific. Many specific claims of religious faith healers have been found to be unscientific. In general, religious claims may be scientific, unscientific, or nonscientific, depending upon whether or not they are subject to scientific testing, and what the results of the tests are.

Many good scientists not only hold nonscientific religious beliefs, but also other nonscientific beliefs as well. Examples of nonreligious nonscientific claims (as noted already) are all claims which involve aspects of the far future. The idea that the stock market will crash in the year 2010 is a nonscientific one, for it is not testable at the present time. It might even be true — it is just that science cannot say either way. Another example of a nonscientific claim is the idea that men will one day colonize the planet Mars. Scientists and other rational people are free to accept or reject such claims as a matter of taste.

What, then, shall we say about cryonics? Because it involves a guess about the state of science in the far future, the idea of cryonics is very similar to the idea that men will one day colonize Mars. However, because cryonics involves claims which strike deep at certain mental defenses against the idea of death harbored by many, cryonics is an idea usually rejected with an amazing amount of “scientific” rationalization by scientists who in truth have no better reason to ridicule it than the fact that they find the idea personally repugnant.

This causes curious results. It is hard to imagine a late 20th century U.S. scientist being subjected to prejudice because he (or she) believes that star travel will one day be a reality, or because he believes that Jesus was the son of God, or because he invested heavily in soybean futures — yet these are all nontestable and nonscientific beliefs. Prejudice against a scientist who has decided to gamble upon the idea of cryonics, however, is a real possibility here and now — especially in some scientific fields like medicine and cryobiology. The reasons for this are complicated and have been discussed before in these pages. They are very similar to religious and cultural prejudice, and involve cultural psychological fears associated with the idea of nonreligious resurrection, and (especially among women) certain fundamental fears of isolation from the community which the idea of cryonics may imply.

The bottom line, though, is that cryonics is not a fully scientific idea, even though a certain portion of its claims are testable and have indeed been found to be consistent with what is known of science in medicine, biology, physics, and other disciplines which relate to the subject. Cryonics is not unscientific, but neither is it proven. Thus, when we speak about the workability of cryonics, we are forced to speak in terms of guesses and probabilities in much the same way as when we speak of damage which may be caused by future earthquakes along the San Andreas fault.

Because cryonics involves thinking about the future, any logical way of thinking about cryonics must be in terms of probabilities. Such a probabilistic model might help to identify exactly where the difficulties lie in the potential workability of cryonics, and might therefore be useful as a way to facilitate discussion of these problems.

This essay is to formally propose that we begin this process. In order to construct a probabilistic model of the workability of cryonics, it seems fitting that we take as starting point similar speculative work in other areas of science. What follows is a preliminary attempt to do this.

The Sagan-Drake Equation

As an example and a paradigm, let us begin with a purely speculative area of science relating to a belief that is nonscientific. Namely, the problem of whether there are other intelligent beings in our galaxy which we might potentially detect using a radio telescope. What are the probabilities? In the 1970’s, astronomers Carl Sagan and Frank Drake first expressed this problem as a string of independent probabilities which, when multiplied together, gave a final probability of detecting such an extraterrestrial civilization. We will not reproduce and explain the entire Sagan-Drake equation here, but we will note that it begins with the number of stars in the galaxy, and is a simple product of this number multiplied by probabilities such as; 1) the probability that a star has Earth-like planets, 2) the probability that life evolves on Earthlike planets, 3) the probability that life evolves intelligence, 4) the probability that intelligence develops radio, 5) the fraction of time an intelligent civilization generates radio broadcasts before it goes on to other communications or destroys itself, etc.

The idea that intelligence may reside upon other worlds is a nonscientific idea because it is not falsifiable at present or for the immediate future. Nevertheless, even given that limitation, the idea is still amenable to a certain amount of rational dissection. The probability number which the Sagan-Drake equation gives can be encouraging or discouraging depending upon what numbers one chooses for the various probability parameters. The equation, although providing no firm answers, does help to identify at which points the greatest uncertainties lie. It even demonstrates that the probability of detection of ETs is not too bad, even if one is conservative in many estimates of these parameters. Sagan and Drake have successfully used their equation to lobby for the building of radio telescope listening devices in the Search for Extraterrestrial Intelligence (SETI).

The Warren Equation

Now we ask: might not something analogous to the Sagan-Drake equation be useful in addressing the equally speculative question of whether cryonics will work? The answer turns out to be yes. Such an equation has recently been proposed by Alcor associate member Dale Warren, Ph.D., a Caltech-educated chemical engineer now living in Illinois. Warren’s recently proposed simple equation for the workability of cryonics, with a few modifications, looks like this:

P(t) = (Pa)(Pb)(Pc)(Pd)(Pe)(Pf)(Pg)(Ph)(Pi)(Pj)(Pk)(Pl)(Pm)

P(t) is the chance that cryonics will “work” (i.e., be successful) for any given cryonaut frozen at time t. I have arbitrarily defined success as obtaining if, at any time in the future, there will exist an ageless entity who has access to at least 50% of the memories of the cryonaut, and who feels him/herself, at least initially, to have the same identity (i.e., to be substantially the same person) as the cryonaut. I have picked the value of 50% also somewhat arbitrarily as the number above which I myself will be personally satisfied with the process.

The remainder of the variables are probabilistic ones which have to do with the assumptions and events upon which the workability of cryonics depends. As the Warren equation identifies these factors, they are as follows:

  • Pa is the probability that the materialistic view of life is correct, and some vital essence or soul does not leave the body after metabolism stops, thus making it impossible to ever revive a frozen person. In other words, Pa is the probability that personal identity is a purely physically-defined quantity.
  • Pb is the probability that personal identity resides in the mechanical structure of the brain, rather than a brain electrical activity pattern which would of necessity disappear during suspension, if not long before. Thus, Pb is the probability that personal identity is a purely mechanically-defined quantity.
  • Pc is the probability of suffering clinical death in such a fashion as to have the physical control of one’s brain be passed to cryonicists before one’s mechanical identity patterns have been degraded to the point that a significant fraction of one’s memories are gone. (Obviously Pc is zero if you don’t get that paperwork in, folks). “Gone” here implies information being degraded below the level of quantum noise, where it is theoretically irrecoverable even with the ultimate “neural archaeology” robots.
  • Pd is the probability that the cryonic suspension process does not destroy so much mechanical information in the brain as to take one down below the 50% memory line. Note that this variable is not entirely independent of Pc, since the longer one goes before suspension, the better the suspension needs to be.
  • Pe is the probability that your brain will make it to future revival time t(r) without a mechanical accident thawing you into unfixable neural sludge.
  • Pf is the probability that your cryonics organization will make it to revival time t(r) without suffering an internal collapse due to greed, bureaucratic incompetence, or ideological perversion.
  • Pg is the probability that your society will make it to time t(r) intact without major social upheavals (economic collapse, nuclear war) which would force cryonics organizations out of existence even though the Earth and (ultimately society) would survive.
  • Ph is the probability that cryogenic storage of bodies or brains will stay continuously legal until time t(r).
  • Pi is the probability that full scale development of nanotechnology, complete with nanocomputers, replicators, and assemblers, is possible within the context of physical law.
  • Pj is the probability that, if nanotechnology can be done, mankind will do it.
  • Pk is the probability that mankind, your society, and your cryonics organization will survive the development of nanotechnology.
  • Pl is the probability that the cryonic revival process will ever be inexpensive enough to be paid for by your cryonics organization or somebody else.
  • Pm is the probability that society will permit the revival of cryonauts, once possessed of the ability to do so.

Values of Parameters

What are the values of each of these parameters? Each represents a probability and a guess, and the value of each can only be assigned on the basis of individual estimates and outright guesses.

In what follows, I am going to risk charges of egoism in order to give some of my personal prejudices. I am, in fact, going to go so far as to inflict upon the reader two probabilities for each variable — one which I personally believe when I am a bit optimistic, and another which I believe when I am a bit pessimistic. (There is no use giving the values for my most pessimistic moments, for during those times I believe that several of the above parameters are zero, and life is best served by sitting in front of the television and drinking beer). Nevertheless, I include these values to give some sense of reference for the reader to compare his or her own reactions against, and I invite personal estimations of these parameters by others in future editions of Cryonics. It might even be interesting at some time in the future to conduct a poll to see what this equation gives when the average responses of all suspension members are put in. Although this approach might not provide any better guess about the future, at least it might show us what we collectively most fear.

My Own Guesses

To begin with, I personally believe that the mechanistic view of life is the correct one, for to me as a physician the idea that the brain is the seat of memory and intelligence best explains the results of numerous neurological syndromes. Many people entertain the popular idea that the brain, which is clearly a computer, nevertheless only functions as a sort of “smart terminal” — a complicated transducer which allows an immaterial “soul” to jerk the muscles. Under this dualistic scenario, each human being is to be seen as what philosophers used to call a “ghost in a machine.” I view this as unlikely.

I have many reasons for this view. For one thing, if a “ghost in a machine” person is to survive death as an individual, his or her “ghost” must have a way of storing memories when the machine is cremated. Yet evidence for an “extracerebral” store of memories is hardly what we see experimentally. In split-brain experiments, for instance, where the connections of the two brain hemispheres have been cut, the two halves of the brain store memories independently of each other’s knowledge, and make decisions independently of each other’s knowledge. This would be impossible if they still shared a metaphysical connection (unless the “soul” can be cut into two parts, too!). Again, in the terminal portions of Alzheimer’s disease (a degenerative brain disease), a patient may progress to the point of no longer recognizing his or her children, or remembering that he or she even has children, yet may still be able to carry on conversations. If personal identity is stored in a “soul,” who then are we talking with in these cases of dementia, if the soul always remembers? The brain cannot be simply a communications device, for there is no way that a communications device may fail in such a way as to allow conversation but make it appear that the person on the other end has lost his memory. Thus, to me it seems very likely that the brain is exactly what it looks like — a computer — and I will thus set Pa, the probability that philosophical materialism is correct, at 0.99 to 0.95.

The probability that identity resides in the mechanical structure of the brain, rather than in a brain electrical pattern, I also believe to be high. Evidence for purely physical storage of identity in the brain comes from cases of both humans and laboratory animals who have survived complete stoppage of measurable brain electrical activity due to cold or drugs, and have subsequently recovered with no loss of long-term memory or personality. Further evidence for this point comes from the fact that many people have received heavy currents of electricity through their brains, strong enough to completely override the brain’s delicate internal electrical activity, and nevertheless have recovered with personality and memory (except recent memory) intact.

Thus, it seems that only the expression of personality is electrical. To use a modern analogy: if the brain is like a computer, then the continuously running computer program we call “the mind” is apparently capable of being “booted up” after a nearly complete stoppage of brain activity. But the true identity of the person lies in the computer hardware (the physical brain) that newly generates the “mind” (from a hardwired, though rewritable, program) whenever the physiologic conditions necessary for consciousness are achieved. Thus, I will set Pb (the probability that mind and memory are defined by purely mechanical structures), at 0.99 to 0.95.

The probability that one’s brain will be degraded significantly before control of it passes to a cryonics organization, is very difficult to judge. For one thing, we have no idea of how much degradation is critical, for we have no absolute data on where memory is stored. Let us then take a conservative guess. If memory is stored in changes in synapse proteins, as seems most likely from current knowledge, then it appears grossly from electron microscopy studies that synapses stay intact for at least two hours after the beginning of ischemia.

If we take the two hour warm ischemic time for a standard (and the actual time may well be longer), and ask ourselves what fraction of cryonicists may we expect to suffer at least two hours of warm ischemia before being turned over to Alcor, then the fraction may be expected to be small. In fact those suffering major (> 2 hours) ischemic injury will probably be limited to persons who are allowed to suffer “brain death” on respirators, those who die suddenly without warning far from home or alone, and/or those who are deliberately autopsied at room temperature by spiteful medical examiners. A review of the circumstances surrounding the deaths of all cryonics patients ever frozen reveals many people who have suffered at least this much damage, and the numbers we’ve seen in the past are subject to only so much improvement at present. At best, then, I will set Pc (probability that Alcor will get you before two hours of warm ischemia does) = 0.95, and at worst 0.75. Historically, it is encouraging to note that about 68% of all cryonics patients since 1967 that we have information about have had less than two hours of warm ischemia (and 100% since 1981). Hopefully we will continue to do this well.

The question of how much damage the perfusion and freezing process now does is, if anything, more difficult to answer. As previously noted, studies of brains show that long periods of ischemia (two hours and more) by itself causes surprisingly little structural damage to neurons, while the damage done during blood reperfusion is massive and almost explosive. In reperfusion, neuronal membranes are holed and ripped away. Organelles are destroyed. Sad to say, reperfusion damage does indeed seem like the kind of damage that one might expect to destroy memory.

The solution might seem to be to freeze brains slowly after clinical death without attempting to perfuse at all, but unfortunately electron microscope studies of such brains show massive structural damage as well. Thus, cryonics is between a rock and a hard place until more studies are done. We know that early cryoprotectant perfusion of animals (within a few minutes after death) yields good preservation of structure. Hopefully, we will be able to develop cryoprotectant perfusion protocols which allow extension of this time interval. As to whether the present protocol works, especially with longer periods of warm ischemia (30 minutes or more), we can only guess. Thus, my probability figures are wide here, with Pd (probability that memory is preserved by present perfusion techniques after the present day average ischemic coma time) = 0.90 to 0.50.

The question of whether brains can be preserved into the future without mechanical breakdown of the freezer seems to be pretty well answered. The answer is yes, if we keep doing what we do now. All cryonics patients are presently cared for indoors in large dewars under constant surveillance, and in the history of cryonics there has yet to be a body loss or significant warmup due to mechanical failure under these conditions. Because of the long time interval between failure of dewar vacuum and ultimate warming, this seems likely to remain the case. The longest preserved cryonaut (who happens to be maintained under the above conditions) has, as of this writing, been frozen for more than 22 years. This may very well be a significant fraction of what will be the necessary time. Thus I put Pe (no significant warming due to mechanical failure) = 0.99 to 0.95. As things are presently done, any thawing in cryonics vaults in the best-run organizations will not be by accident.

The question of whether cryonics organizations will make it into the future without collapsing due to internal problems, however, is more problematic. Certainly catastrophe can happen, as witness the debacle of Cryonic Interment, Inc. of California, which collapsed in the mid-70’s due to poor management, with the loss of at least a dozen suspendees. No matter how well run an organization, it is impossible to guarantee that it will always be so; anyone who doubts should consider what happened to NASA in the short 15 years after 1970. If cryonics is ever to work, it follows that it must become popular for a significant amount of time beforehand, since surely the utility of the technological advances which precede the first revival will be glaringly obvious for many years preceding the event. Thus, it may well be that in the inevitable “popular period” of cryonics to come, old and respectable cryonics organizations will suddenly find themselves competing on a dog-eat-dog open market with well- capitalized newcomers, in somewhat the fashion that mom and pop microcomputer makers found themselves in 1979 suddenly faced with the IBM PC. How well old cryonics organizations do at this new game will depend on many factors. However, it is not a comforting thought that the lives of people in storage at that time may well depend on the answer.

Another worry here is the possibility of corruption in cryonics organizations. Suspension funds represent a large amount of money, and a cryonics organization with only a hundred whole body suspendees will be look- ing at liquid assets in excess of 10 million dollars. The relevant question here is what sort of people may be drawn to leadership in cryonics in the future solely out of profit motive. With suspension fund interest paying fat salaries to company directors, might it not be easier one day in the future to simply put off reanimation of anyone (or just most people) in an organization indefinitely while the revival problem is studied further? I will set Pf (probability that there is no significant internal cryonics organization rot) = 0.60 to 0.20.

If a cryonics organization fails to decay from within, there is always the poss- ibility that it will be blasted from without by circumstances beyond its control. By “circumstances” here we speak not just of SWAT teams sent by the local paranoid author- ities, but also of more general social up- heavals that might make cryonics untenable in the face of trying to stay alive the convent- ional way. A nuclear war, for instance. Or even an economic collapse of the magnitude of the Great Depression of 1929. Cryonics is made possible presently by the fact that liquid nitrogen is the third cheapest commercially-sold fluid on the planet (behind water and petroleum), but this happy state of affairs is the result of some pretty delicate industrial networks that might go belly up in a depressed economy or a national disaster. Thus, although the future might be infinitely rosy, cryonicists will still be out of luck if the road to how mankind arrives there is sufficiently rocky. The optimistic side to all of this is that mankind seems to be growing richer and richer yearly. Computer-robot manufacturing is already having a significant stabilizing effect on economies, and seems likely to have far more in the future. Pg (no rollercoaster economic disasters) = 0.90 to 0.70.

Aside from general collapses of the economy, there are social forces inimical to cryonics in particular to worry about. Once cryonics begins to become popular, it will come to the attention of the conservative medical establishment. That medical establishment will rightly perceive the insult implied by the fact that cryonicists see something of infinite value in what conventional medicine throws away, and disputes over perceived insults are always far more deadly than simple disputes over scientific fact. Adding to the problems which cryonics will certainly have with the A.M.A. are those which it may face from the ever-present problem of social maldistribution of resources, and the jealousy which attends that state. Cryonicists have long understood the lesson of Norman Spinrad’s novel Bug Jack Barron; we will know that cryonics has succeeded socially when economically disadvantaged minority groups begin to complain that they do not have access to it. Ironically, however, it is at just this point that cryonics faces one of its greatest dangers. As the recent history of medicine has demonstrated, democratic societies tend to suppress that which everyone cannot have. I set Ph (cryonics will not be outlawed altogether at some point in the U.S.) = 0.90 to 0.70.

For cryonics to succeed, it appears necessary that devices be developed which can repair aging and freezing damage to cells from the inside out. Fortunately this (nanotechnology) seems technically possible. Self-replicating machines are possible in this universe, because we have the example of living organisms. There are no quantum problems with manipulation of atoms one at a time — for in fact we do it with tunneling microscopes now. Also there appears no limit to how small Babbage computing engines can get until one finally runs up against molecular constraints, although this is a much less sure conclusion since there is no example from nature or engineering. Thus, I give Pi (nanotechnology is possible) = 0.98 to 0.90, only because there may be applicable laws of physics we haven’t discovered (or if you prefer: formulated) yet. With a large amount of faith in the ability of man to fathom the universe on (at least) the atomic level, and a large amount of confidence in mankind’s ego when it comes to doing anything that he finds it possible to do, I will set Pj (mankind can and will pursue nanotechnology until it works) = 0.99 to 0.95.

If nanotechnology is possible, it seems very probable that man will develop it eventually, for the rewards are simply too great. The big question, however, is whether mankind will survive it. Self replicating assemblers make fearsome weapons. One can think of nanotechnological weapons possibilities as subtle as bullets which make the targets into psychic slaves, or as gross as Drexler’s vision of “grey goo” — a morass of assemblers which feeds on life and thereby turns the entire biosphere of a planet into dirty tapioca pudding.

These are scary scenarios to contemplate, and our minds are not at all put at ease by looking at the universe to see how everybody else out there is doing with their own nanotech research programs — for it all looks horribly quiet out there. In fact, it looks sort of dead. If alien civilizations develop self-replicating assemblers, according to current theory this should give them the power to manipulate the resources of entire solar systems. Such civilizations seem both likely to spread, and unlikely to waste all the free energy of high temperature sunlight that we see coming from other stars and galaxies. Yet such waste is what we do see. To borrow an analogy from Carl Sagan’s last novel, the universe as we look at it does not look at all cultivated — it looks wild. Thus the question that Enrico Fermi asked famously in regard to UFOs half a century ago: “Where is everybody?”

There are unsettling possibilities. In the late nineteen-forties, a number of science fiction stories explored the possibility that other civil- izations had arisen in the universe, only to destroy themselves with atomic energy (probably the first author to use this theme was Heinlein). Now, nanotechnology presents an alternative sort of scenario. If the rise of intelligence is common in the uni- verse, then our simple observation that most stars out there are not surrounded by Dyson spheres [artifacts made by taking apart large planets and forming a sphere made out of their materials to surround a star] or similar infrared-radiating artifacts, suggests something about nanotechnology. To wit: it is either impossible, or it is horribly dangerous. Neither of these possibilities is good news for cryonicists, which is possibly why certain nanotech-oriented futurists have lately taken to suggesting (with a peculiar fervor) that intelligent life on Earth is an anomaly in the universe. In short, according to this view the reason we don’t see the galactic aliens is that there never were any, and so everything is okay after all. Thus, it is amusing to find the entire Sagan-Drake equation itself entering in at one point as one of the factors which bears upon the workability of cryonics. We never claimed this would be an easy calculation!

K. Eric Drexler in his marvelously lucid book Engines of Creation argues that there may be ways to minimize the danger of the development of nanotechnology. But most of the methods Drexler discusses only guard against accidental problems. Weapons are another matter. One hopes for the safety of mankind as a whole that humans have situated themselves in multiple space colonies before nanotechnology becomes commonly used. Though this sort of thing is not likely to help today’s cryonicists (who by then will probably be pretty much immobilized in storage on Earth), it would perhaps be best for our species not to have all of our eggs in one basket. In any case, I will set Pk (we will not destroy the Earth and the suspendees with nanotechnology) at 0.50 to 0.20. [Footnote: It probably will be difficult trying to escape an assembler plague once started, though. The nasty little devices replicate anywhere there is sunlight and rock, and (if malevolently designed) launch themselves outward randomly as seeds at high speed. Calculation shows that a plague-ridden star system might conceivably “spoor” with enough assembler seeds to nail anything bigger than a baseball for light years around. So, Dr. Fermi, that’s where everybody is out there — they’re all huddled in spaceships, headed outward from their native systems at maximum thrust, biting their tentacles in anxiety and looking back over whatever serves them as shoulders. And although we know there are not (or were not) a lot of Dyson spheres around the older stars at the core of our galaxy, we cannot hope to see the “mini-berserker” assembler plagues which even now might be spreading outward like some sort of dry rot toward peripheral stars like ours. . . . ]

If nanotechnology ever proves out, it is likely that the expense of routine robot-controlled tasks will drop to nearly zero. Energy and raw materials are plentiful in space, and self-replicating technology is nothing if not cheap. Thus, the only thing likely to have much value in a post-nanotech world is information. Archaeological and historical information about the past is likely to be particularly prized, since it will be in limited (and because of entropy, always decreasing) supply. As such, the lifetime memories of every 20th century brain (no matter from what walk of life) represent a sort of videocamera recording of a unique slice of 20th century life — a way of life which by the era of nanotech will be completely gone. Cryonicists should be historically valuable, then — well worth reviving from a completely economic standpoint. I set Pl (that economics will be favorable) = 0.95 to 0.85.

The question of whether society will choose to defer revival of cryonicists at all because of other considerations, is the final question. Besides historical considerations there will certainly be humanitarian reasons to revive cryonicists as well. The problem, though, is that there may also be humanitarian reasons against it. There will certainly be a population explosion by the time revival becomes possible. Although it seems probable that nanotechnology will help turn the materials of the solar system into space colonies and starships, it also seems true that humans are self-replicating machines, too, and may be able to keep up with anything the assemblers can do, if physical law puts limitations to interstellar growth. In particular, the speed of light itself may end up posing enough of a barrier on the expansion of mankind that immortal humans may well be forced to partially curtail their reproduction indefinitely for lack of energy and material resources. If that happens, it is not at all clear that cryonauts will be welcome, if new babies are not. At the very least, we may expect to either wake up on space colonies, or with one-way tickets already in our uncalloused hands. Or some of us may find ourselves waking to full consciousness and memory gradually over 20 years time, as our cloned bodies with hardwired (but not immediately accessible) memories are allowed to be raised from infancy by sterilized humans who need some outlet for the parental instinct. That should give us a great cultural head start if we can stand the Freudian stresses. Pm that they’ll decide to revive us, via adoption agency or not: 0.80 to 0.50.

The Final Odds

At the end, then, what is the combined probability of success? If all my best case figures are used, P(now) from the Warren Equation is 0.15, or a bit better than one chance in seven. This is my most optimistic scenario. The pessimistic scenario puts P at 0.0023, or less than one chance in 400.

The idea that (in my personal estimation) cryonics has all told at best only a 15% chance of working, may be a bit shocking. But answers of this sort fall naturally out of chained probability equations. Like it or not, the Warren equation simply forces one to remember that the success of cryonics depends on the correctness of at least four separate physical hypotheses, the fortunate consummation of at least eight modern social trends, and some luck in the circumstances surrounding one’s demise. That’s a lot of hurdles. Even if the probability for each of these 13 factors is a flat 95%, the total probability of success would still only be 51% — barely better than flipping a coin.

Not to feel bad. Results of this sort are often not obvious at the beginning, and perceptual failures in assessing the overall probability of complex events are common. In looking at enterprises which depend on a number of things happening, people in a normal state of mental health tend to be overly optimistic. We trust Rube Goldberg schemes more than we should, because we focus on the probability of events in any cause-and-effect chain one at a time, and therefore miss evaluating the big picture. That is why we humans continue to lose money at crap tables; it is a weakness of our species.

Can These Odds Be Bettered?

That said, there are still a few soothing observations to be made about the figures given above. The first thing I note personally is that these figures, although probabilities of significant happenings, are still not entirely independent of my own effort. I can, for instance, significantly increase the probability of preservation of my own memories if I take steps to avoid autopsy (such as eating a low saturated fat diet and driving a large car), and if I spend some time carefully preparing both my estate and my family for the event of my suspension.

Furthermore, it is well to remember that these figures represent my estimation of my chances of making it if I’m frozen tomorrow, not in the future. Nearly all of the probability figures discussed will doubtless be higher if I take advantage of all future life extension technology and am instead frozen in 75 years. Why? For one thing, I suspect that 75 years is a significant fraction of the required time to the development of nanotechnology, and I suspect that I will do better weathering social problems in the interim if I can do it on my own two feet, rather than helpless in a dewar. And of course there are other benefits of time: suspension and medical technology is sure to improve in coming years, and every cryonicist may lend a significant hand in that (successful brain vitrification, for example, is a research project which should not require a tremendous amount of money). And there are other future developments which should increase the chances of a “good freeze.” Euthanasia may become legal for terminal patients, and so on.

Seventy-five years is also time enough that I may be able to have a significant impact on certain social factors which affect the ultimate success of my suspension. The long-term success chances of cryonics organizations in particular are susceptible to the efforts of single individuals, but that is not the only way to change the probabilities. The power of an individual is not necessarily limited to small spheres, for it is nothing but ideas which shape civilizations, and most ideas begin as the products of single minds. Might cryonics be outlawed in the future, we ask? It is then up to us to begin the necessary lobbying efforts now.

Is It Worth Doing?

It is sometimes noted that however small is the probability of cryonics working, the chance of coming back without it must be smaller still — perhaps (religious considerations and bizarre quantum theories aside) zero. Thus, it is sometimes argued that for atheists (or even agnostics) cryonics may represent a rational gamble, no matter what the odds. Actually, to my mind, this is only true if there are no losses associated with taking the cryonics option, and of course in a way there are. Cryonics is expensive and time-consuming — which is to say that gambling on it costs a bit of your life. Thus, cryonics in worst case is a sort of “life lottery” in which the payoff is gigantic, but the odds are so bad that one is not sure whether even a small investment is intelligent.

The numbers I have generated above suggest, however, that (at least in my personal estimation) the “life lottery” scenario is a bad description for cryonics. Even if the lower figure of a 0.23% chance of cryonics working is more realistic, and we conservatively estimate that a revived cryonicist may look forward to a lifespan of 1,000 years, then a cryonicist looking at a 75 year “normal” lifespan before suspension may still rationally spend 1,000/75 X 0.23% = 3% of his or her time on cryonics. (The only assumption made here is that the goal is to maximize years of life). This isn’t very much time — about half an hour of every waking day. People as a rule spend that much of their time doing sillier and less significant things than cryonics. Consider stamp collecting.

Lifework — Conclusion

Of course, in this vein there is also a sense in which time spent in the service of cryonics is not lost, no matter what. In living life, most people as a simple point of pride feel the need to leave the world a better place than they found it. Thus, some sort of “lifework” is necessary to most people for long term life satisfaction, and the only necessary ingredient to define a “lifework” is a sense that one is doing something to organize or improve things — in other words, something against entropy. There is even evidence that a sense of having accomplished a significant lifework is necessary to a psychologically healthy old age. Thus, despite my earlier comment about beer and television, a “lifework” is necessary even to people who do not believe that they will survive their own deaths — in fact it is probably more important to such people.

Here is where cryonics shines, even if the odds of it working for a person personally are lower than one would like. Death is the ultimate expression of entropy for human beings, and the ultimate outrage in human life. The fight against Death, then, makes a first-class lifework — and those who choose it may count themselves lucky no matter how things turn out at the freezers.

I personally, then, have decided that cryonics is worth the gamble. I could spend the time collecting stamps, yes, but I doubt if I am going to find a stamp as interesting as an endeavor that may be one of the greatest adventures that human beings have ever undertaken.

After all, who knows? If we — the first and second generation of cryonicists — succeed in our efforts, some of us may well end up on stamps ourselves one day. And if that happens, consider: we’ll be the only people on U.S. stamps to ever be able to take pride in being there.

Further Thoughts On The Probability That Cryonics Will Succeed

by Mike Perry

[Mike Perry has a Ph.D. in computer science, specializing in mathematical methods.]

Steve Harris has written a groundbreaking article on the probability that cryonics will work. The bottom line is that cryonics is worth pursuing, given the prospects that appear to exist both for success and failure; something in which I concur wholeheartedly. I confess I don’t like Steve’s conclusion that cryonics has at best only a 15% chance of working, but that in no way detracts from the thought and effort that went into the article, nor does it prove this conclusion inaccurate. However, in looking over the various probabilities and their rationales, I spot features I consider questionable, which when altered to fit my perspective on this issue, also lead to different (and more optimistic) conclusions. The major difficulty, as I see it, is that a good many of the social variables that could kill cryonics, and which are treated as independent, are not really independent at all.

Calculating the probability of an event that depends on numerous conditions holding becomes easy if the conditions are independent; the probabilities of the conditions holding are simply multiplied. On the basis of independence, for example, we conclude that the probability of obtaining “heads” on two consecutive coin tosses is 0.25 (0.5 times 0.5). Thus, if we do a great many (say 1,000,000) experiments where we toss a coin twice, in about half of these experiments, or 500,000, the first coin toss will be a head, and for about half of these in turn, or 250,000, the second toss will also be a head. This reasoning is valid because the outcome of the first toss does not influence the outcome of the second toss (and vice versa). Multiplying many probabilities this way, each of which is significantly less than 1, can produce a very small overall result. For instance the probability of ten consecutive heads in a coin toss experiment is (0.5)10 or about 0.001. Thus an outcome that depends on all of a set of mutually independent conditions holding may have a very low probability, even though the likelihood of each condition individually is moderate or high.

Steve has enumerated thirteen conditions, designated a through m, that “must hold” for cryonic resuscitation to occur. (I have some relatively minor disagreement that all of these would be required, but more about that later.) For each condition, call it x, there is an associated probability Px , that condition x will hold. More precisely, Steve gives two estimates of each probability, a high and a low. (These probabilities must be based on gut feelings at this stage.) Since all the conditions are treated as independent, the probabilities must be multiplied together to estimate the probability that cryonics will work. Mult- iplying the high probabilities gives a high estimate while multiplying the low probabilities gives a low estimate. (The definition that Steve gives of what it would mean for cryonics to “work,” namely that at least “50% of your memory” must survive in an ageless being that thinks he, she or it, is you, is not without its difficulties, but at least makes a useful start- ing criterion. It is a lenient approach that allows for some, but not an arbitrary, loss of fidelity in the resuscitation/reconstruct- ion, and relieves the need to worry about a precise definition at this stage.) The assumption of independence makes the calculation of overall probability easy but makes the result discouragingly low (15% as an upper limit).

Seven of the thirteen conditions are not related to the technical feasibility of cryonics, or the requirement that cryonic suspension be performed under reasonable conditions, but instead are what I would lump under “the social problem,” which I call condition n. I don’t believe these seven conditions can be treated as independent, for reasons to be discussed. Steve’s 13 conditions, with his probabilities and my revisions, including category 14 (n) relating to the social problem, are summarized in the table below.

   Condition                                       Probabilities
                                               Harris         Perry
                                               Lo   Hi       Lo   Hi
a. Materialism is correct                    0.95 0.99       1     1
b. Identity encoded in structure             0.95 0.99       1     1
c. Favorable conditions for suspension       0.75 0.95     0.75 0.95
d. Suspension preserves enough information   0.50 0.90     0.50 0.95
e. Mishap-free storage                       0.95 0.99     0.90 0.99
f. Cryonics organization survives            0.20 0.60       n     n
g. Sufficient social stability               0.70 0.90       n     n
h. Cryonics is continuously legal            0.70 0.90       n     n
i. Nanotechnology is physically possible     0.90 0.98       1     1
j. Nanotechnology is perfected               0.95 0.99       n     n
k. Nanotechnology is non-catastrophic        0.20 0.50       n     n
l. Cryonic revival is "cheap enough"         0.85 0.95       n     n
m. Cryonic revival is permitted              0.50 0.80       n     n
n. The social problem is non-catastrophic    0.008 0.18    0.39 0.86
o. Technologically, will it work?            0.29 0.81     0.34 0.89
p. Overall, will it work?                    0.002 0.15    0.13 0.77

The probabilities for “technologically, will it work?” (condition o) are obtained by multiplying the probabilities for the conditions not relating to the social problem, that is, conditions a through e and i. It will be noted that the differences I have with Steve in this area are relatively minor and our overall estimates do not differ greatly, even though they are obtained by multiplying six quantities, which itself will tend to magnify the differences. (In fact I tended to use his values unless I could come up with a specific reason for something different.)

To consider the differences briefly, I am more certain on some things such as materialism. (Since I resist claiming I am absolutely certain, you should read a “1” as “(1 – n), where n is small enough not to worry about.”) I am “certain” (at least 0.999) that “nanotechnology will prove physically possible.” In our case, success would require recovery of a certain amount of information from the molecular structure of a piece of solid matter (i.e., frozen human tissue). Probably not nearly all the information that ought to be locked in those molecules would be needed, but I consider it likely that the full atomic-scale structure of any given piece of matter could be elucidated, making a small allowance for errors, if you wanted to take long enough. (Similar information recovery is being done right now, on a small scale, with tunnelling microscopes.) This, of course, means only “possible in principle,” not that we will carry it out. I am a little higher on the upper limit for “suspension preserves enough information” (neural archaeology may allow some stunning inferences, if we work at it) and a little lower on the minimum for “mishap-free storage” (this may have to be under adverse conditions, e.g. by an underground organization, which however, would also be expected to be very careful).

That said, let’s now consider the major differences I have with Steve, which are tabulated under condition n, “the social problem is non-catastrophic.” For Steve the probability estimates are obtained by multiplying the probabilities for the six conditions that relate to the social problem (and which are consequently excluded from the technological problem considered above), namely: fgh, jk, and m. Steve’s probabilities for the six conditions are not high, and the corresponding probabilities for condition n are quite low. My estimates are considerably higher and are obtained by a process to be described. Multiplying the probabilities for conditions n and o gives the estimates for “Overall, will it work?” condition p, which are correspondingly higher in my case.

One reason it may seem plausible to treat the six social conditions as independent is an underlying assumption that cryonics itself is not considered likely to have a serious impact on how people think and feel, in general. If, on the contrary, we could assume that the population after 50 years would be largely made up of cryonicists, the outlook would change substantially. For example, we could then assume that it would not be considered “too expensive” to revive cryonics patients, a particularly repugnant idea, in my estimation. It would be highly likely that cryonic revivals of 20th century suspendees would be carried out, assuming it was technologically possible, and that cryonics would be continuously legal. A large population of anti-death individuals would also, I believe, substantially diminish other risks, such as nuclear catastrophe, nanotech running amok, or even failure of a cryonics organization. (In the latter case there would be more organizations with more competition and greater demands for accountability.) Once a substantial population became converted to an immortalist outlook, I think there would be tremendous pressures to suppress opposition, which in short would include every tendency to wind up sacrificing human life. So overall, the social outlook would be far brighter if we could only convert a major portion of the population to cryonics. If that didn’t succeed, the outlook would still be encouraging if a substantial, hardcore following for cryonics existed. Ten thousand dedicated people could substantially reduce the risks of hostile legislation or patients being thawed (whether the latter was caused by outside pressures or by difficulties within a particular organization). If necessary, ten thousand might successfully support an underground operation for a number of years, so that cryonics would not have to be continuously legal to succeed. (By analogy note that the Fugitive Slave Law did not stop the Underground Railroad. Some may object that “you didn’t have the potential for social and economic control (through electronic data bases) in the 1850’s you are likely to have in the future, either,” to which I would reply, “maybe so, but our hardcore cryonicists may have new options too, such as private spaceflight.”)

Is there any reasonable ground for thinking the social outlook might improve according to one or the other of the above scenarios? I believe there is. The most significant event in this process, I think, would be the development of reversible suspended animation of brains. This now seems possible through vitrification. If successful, it would demonstrate, once and for all, that a human life can be held in suspension indefinitely. Once that point became incontestable, it could be used with devastating force against those who would oppose cryonics or the goal it aims for, the elimination of biological death. Burial and cremation, to survive as choices, would have to be treated as acceptable forms of euthanasia. The arguments for why such human sacrifice would be better than cryonic preservation could be attacked from many directions.

Even cryonics patients frozen before the advent of vitrification would benefit. If some patients could not be thawed without committing murder, it would become untenable to thaw any patients without first ascertaining, beyond a reasonable doubt, that there was no chance of ever bringing them back. Cryonicists could easily enforce their own standards in deciding whether there was “reasonable doubt.”

It is possible that a catastrophic social upheaval would follow if society could no longer deny that the conquest of death was possible. We, as cryonicists, need to be prepared for the day when others will need a new set of values for a future different from what they were conditioned for. Such values would recognize that it is the destiny of the human race to throw off the yoke of mortality, and that the preservation and protection of a human life must take precedence over other endeavors that would interfere with or prevent it. What we must seek then is a philosophical transformation, to alter the ages-old deathist orientation to an outlook that recognizes that current limitations on lifespan are cruel and unnecessary, and that a more open-ended existence will be a more rewarding one.

So, we have identified three possible developments that would appear to greatly improve the odds that the social problem will not become catastrophic: (1) vitrification, (2) a sizable group of hard-core cryonicists and (3) a philosophical transformation of society. Although none of these has occurred yet, I think the outlook is reasonably good that all will happen. First, progress continues in vitrification, with success apparently a few years away. (It is worth mentioning that most of the progress to date has been with non-neural organs such as kidneys. The adaptation of vitrification to the brain is expected to be reasonably straightforward, though much of the work may have to be done by cryonicists since mainstream cryobiologists are not interested in this “useless” organ!) Second, there is a hardcore group of cryonicists. It can’t be called “sizable” yet (numbering in the thousands or more), but as I think Alcorians have proved in their battles with officialdom over the past year or so, it does exist and it is not an “easy target” for those who might oppose it. Finally, though nothing approaching a large-scale philosophical transformation has occurred, cryonics is gaining publicity and efforts are underway to formulate a cogent and satisfying philosophy that incorporates the idea of eliminating death through nonsupernatural means.

How might these three developments affect the seriousness of the social problem for cryonics? Clearly this is a complex question. I don’t feel it can be easily reduced to a matter of multiplying independent probabilities, but instead a more elaborate approach is needed. To make a beginning I will assume the following rationale. The key event, I think, is the development of vitrification, which I think will likely initiate a chain of events leading to substantial growth of a cryonics community and possibly a mass conversion of society to cryonics through a philosophical transformation. For cryonics to work, a cryonics organization must first survive until vitrification is perfected. I will invoke gut feelings to estimate (1) a reasonable period of time for vitrification to be developed, (2) the probability that a cryonics patient at Alcor will stay in suspension during this period, (3) the probability that vitrification will in fact be developed by the end of the selected period, (4) the probability that the social problem will not later become catastrophic, if vitrification is developed, and (5) the probability of no social catastrophe, if vitrification is not developed.

To start with, I will set the time interval at twenty years. That is a short enough time (one patient having now been in suspension longer) that I feel reasonably confident about making a gut-level prediction about the probability of a patient staying in suspension. I will set this probability, call it Ps, at 0.75 to 0.95. Strictly speaking, this is the probability that a patient is not thawed for “social” as opposed to technological reasons. In other words, a suspension failure would be equivalent to “the social problem having become catastrophic” over the twenty-year period, rather than cryonics being found to be scientifically untenable. (The latter possibility is already provided for in the technological probabilities.)

On the other hand, twenty years ought to be long enough to develop vitrification, if indeed it is “just around the corner.” If we haven’t perfected it by then, it might be a much harder problem than it looks to us now, and thus not likely to be solved for several more decades (if then). I think that there is a good chance that vitrification will prove relatively easy, in view of the partial successes to date, so I set the probability Pv of doing it in twenty years or less at 0.60 to 0.90. If vitrification succeeds I set the probability of a favorable social outcome, call it Py, at 0.85 to 0.95, i.e. high, though with some allowance that things could still go wrong. If vitrification is not developed, I am more uncertain about what probability range should be assigned, except that it should definitely be lower. I will set the probability, call it Pz, in the broad range of 0.01 to 0.50. We are now ready to calculate the probability Pn of a favorable social outcome, condition n. It is the probability of a patient staying in suspension for twenty years times the probability of a favorable social outcome from then on. That in turn is the probability that vitrification has been developed in twenty years times the probability of a favorable social outcome if vitrification is developed, plus the probability that vitrification has not been developed times the probability of a favorable social outcome if vitrification is not developed. In symbols,

Pn = Ps(PvPy + (1-Pv)Pz)

It will be seen that Pn is maximized when the four quantities Ps, Pv, Py and Pz are maximized, given their respective ranges, and minimized when these quantities are minimized. Given the assumed ranges of the four quantities, the range in Pn works out to 0.39 to 0.86, which is similar to my estimates for the technological problem, and of course, much higher than Steve’s estimates in which the social problem is partitioned into independent subproblems. Overall, the probability that cryonics will work, according to my rationale, is 13-77%. I think I would sum it up, for a prospective newcomer, by saying: “In my estimation, cryonics will probably work on purely technological grounds, though there are uncertainties. When social factors are taken into consideration the outcome is less certain, maybe in the 50-50 range, but it still leaves reasonable ground for hope.” I would not say, “Cryonics probably will not work,” which I believe is the inevitable conclusion if the most optimistic estimate of it working is well under 50%. On the other hand my scenario puts a lot of the burden for seeing that the social problem is successfully resolved on the shoulders of us cryonicists, and there aren’t many of us yet, though our number and resources are growing.

There is another argument Steve mentions against the high probability of cryonics, considered as a subset of biological immortality; namely, that we ought to see evidence of extraterrestrial civilizations elsewhere in the universe who made it to immortality. Instead, we see no signs of life. This can be explained by assuming that the putative extraterrestrials are (1) self-annihilating, (2) very rare, or (3) just unobtrusive. Whatever goes for the extraterrestrials is likely, on statistical odds, to apply to us too. Either we will destroy ourselves (the social problem will prove catastrophic after all), or we are an anomaly, with no cosmic near neighbors, or we will find no particular motive to massively advertise our presence, however far we advance. Several of these alternatives may be true, or none may be true (as, for instance, if we were created by some giant intelligence, as parts of a giant computer program). This is a mystery we are not yet in a position to resolve. Let us pursue our quest for immortality in the meantime, and hope for the best.