Eliezer wrote "This isn't the whole story..., but it will do for a start", and in the referenced post: "This I will not describe, for it would be a long tale and complicated. I ... knew not the teachings of Tversky and Kahneman."
I've seen tantalizing hints of this "long tale," but I'd love to see the whole story, even in summary. If nothing else, it would be quite in place in a blog on Overcoming Bias.
This reminds me of a post that i think you wrote quite a while ago, in which i think you stated that the belief that 'molecular nanotech is possible'(along with other similar beliefs) was not a scientific belief, but that it was a rational one. I wasn't entirely sure that your statement was valid then, but now, after several hundred posts of information dumping, your reasoning makes a great deal more sense.
I think some of the confusion of the 'choice between science and bayes' occurs because science as a process does incorporate a number of bayesean methods, but the theory of science has not yet managed to incorporate them.
Just a minor question about cryonics: To what extent does it preserve the synaptic weights? ie, I'm kinda looking toward saving up to sign up, but I want to understand this bit first. It seems obviously likely that it preserves the information assotiated with the neural structure, but what of the information encoded in the weights?
How quickly do those decay after (regularly accepted) death? ie, by the time the suspension process begins, are they still there? How much of that is lost in the suspension process?
A good way I've found to explain this to lay people is that Science is a very high quality way of finding out what is almost certainly wrong. If Science says something is wrong and here is why, then it most probably is correct (relative to other methods of finding truth that is). Science is much worse at figuring out what is right because it's method of determining what is right is "Of all the possible hypotheses, we'll eliminate the wrong ones and choose the most probably of what exists". As a result, scientific knowledge is often over turned an...
Good point, Robin, in my opinion. Eliezer, lots of good ideas in this post, well-articulated, but I think there's sleight of hand in your distinguishing empirical science from bayesian rationality. You're not being transparent that our confidence in bayesian rationality stems from empirical verification. Beyond that, it's decision-making/resource allocation in the context of scarcity. We have a scarcity of time and human capital, and we need to decide how to allocate our efforts in the context of that scarcity. That doesn't take us away from empiricism, it...
And the ability of science to permit long-shot hypotheses is not a bug, it's a feature. If you want to fully explore a hypothesis space, you have to be willing to be wrong most of the time.
Even when Bayesian reasoning is applied correctly, it is obviously limited to the available data. When it determines how we seek more data, we become stuck in a feedback loop and trapped in local minimization ruts.
How much of Eliezer's behavior is because he's truly convinced himself he's found something better than the scientific method, and how much because his cherished beliefs are not supported by the scientific mainstream and so he must find a way to minimize its perceived importance?
The best argument against Cryonics as far as I'm concerned is economic: It's a self-negating prophecy. Once the technology exists to revive frozen people (I don't have any problem believing this will happen some day) there will be no market for cryonics - in this future, why bother signing up for cryonics when you can get revived at "death" or otherwise forestall it - and therefore no income for cryonic companies. Who is going to maintain the freezers or revive you? Chances are everyone who cares about you is either dead or in a similar predicament.
If you accept that there is no "soul" and your entire consciousness exists only in the physical arrangement of your brain (I more or less believe this), then it would be the height of egotism to require someone to actively preserve your particular brain pattern for an unknown number of years until your body can be reactivated. Simply because better ones are sure to come along in the meantime.
I mean, think about your 70-year-old uncle with his outdated ways of thinking and generally eccentric behavior -- now think of a freezer full of 700-year-old...
Finally this sequence of posts is beginning to build to its hysterical climax. It might be difficult to convince us that doomsday probability calculations are more than swag-based-Bayesianism, but the effort will probably be entertaining. I know I love getting lost in trying to calculate "almost infinity" times "almost zero".
As a substantive point from this sequence, at least now scientists know that they should choose reasonable theories to test in preference to ridiculous ones; I'm sure that will be a very helpful insight.
Who is going to maintain the freezers or revive you?
How much do 4 Gb cost now? It's free for anyone on Gmail. Would you believe that 4 Gb of storage would be free in 2008 if you heard it suggested in 1955, when computers with 10 Kb of memory cost $500,000? Likewise if revival procedure is sufficiently automated, it can become essentially free. It will probably take an AI to "manually" fix some of the damage though.
The problem, ME, is that the people interested in cryonic preservation all think they're fantastic individuals that people in the future will be keenly interested in reviving.
No '70-year-old eccentric uncle' believes that they're not inherently special, or that they either are or will be obsolete by the time revivification technology exists.
When [Bayesian reasoning] determines how we seek more data, we become stuck in a feedback loop and trapped in local minimization ruts.
I believe this is incorrect. Bayesian reasoning says (roughly) collect the data that will help nail down your current most uncertain predictions. It's tricky to encode into Bayesian algorithms the model,
"An underspecified generalization of our current model which is constrained to give the same answers as our current model in presently available experiments but could give different answers in new experimental regimes....
I love this post. Even though "Science" is an oversimplification of real science, the specific statements attacked aren't strawmen.
For cryonics patients to eventually be revived, the future just has to be very rich (like Vladimir says) and contain a few altruists. Sounds like a good bet. Calling trying not to die "the height of egotism" (because you ought to die to be replaced by "better... brain patterns"?) is ridiculous.
You have strange ideas about what science is. That's not surprising since philosophy and popular science have strange ideas about what science is. Science does not involve plucking theories out of thin air and subjecting them to tests. Hypotheses themselves are borne of experiments and the application of prior theory. The part of science you've chosen to eschew, the part where you obtain a formal education and spend many years integrating yourself into the professional community, happens to be the part where you learn to construct hypotheses. The fact that...
Nick: Not any more ridiculous than throwing out an old computer or an old car or whatever else. If we dispense with the concept of a soul, then there is really no such thing as death, but just states of activity and inactivity for a particular brain. So if you accept that you are going to be inactive for probably decades, then what makes you think you're going to be worth reactivating?
...none of them involve or have any use for "logic" or "reason" or Bayesian probability theory; none of these things are taught, used or applied by scientists...
Logic and reason are not taught, used, or applied by scientists -- what!? I'm not sure what the scare-quotes around "logic" and "reason" are supposed to convey, but on its face, this statement is jaw-dropping.
As a working scientist, I can tell you I have fruitfully applied Bayesian probability theory, and that it has informed my entire approach to research....
While we are (sort of) on the topic of cryonics, who here is signed up for it? For those that are, what organization are you with, and are you going with the full-body plan, or just the brain? I'm considering Alcor's neuropreservation process.
But science is so much MORE than that, Cyan. It has incorporated forms of reasoning that are far more subtle and powerful than Bayesian reasoning - which is why poke is mostly wrong, but not completely wrong.
The emphasis and reliance on Bayesian thought is a regression, not progress.
It has incorporated forms of reasoning that are far more subtle and powerful than Bayesian reasoning
Name one that doesn't reduce to Bayes.
...forms of reasoning that are far more subtle and powerful than Bayesian reasoning...
I am always interested in expanding my repertoire. Please give examples with links if possible.
"Finally this sequence of posts is beginning to build to its hysterical climax. It might be difficult to convince us that doomsday probability calculations are more than swag-based-Bayesianism, but the effort will probably be entertaining."
Hmm. I've seen little to indicate that this is going to end up being a discussion of the Doomsday Argument. Still, it would be interesting to see Eliezer's own view. Everyone seems to have their own opinion as to why its unsound (and I agree that it's unsound, for my own reasons...)
The last paragraph though is ...
For cryonics patients to eventually be revived, the future just has to be very rich (like Vladimir says) and contain a few altruists. Sounds like a good bet
Seeing as the theme of this blog is overcoming bias, one ought to be conscious of an overly hopeful bias. It may well be a deficiency of my own imagination but I can't see the notion of reviving old geezers having much of an appeal for future altruists but that doesn't even matter: It's likely that technology will be sufficiently advanced at some stage to postpone ageing and death and it's probable th...
Name one that doesn't reduce to Bayes.
Not all rectangles are squares, Mr. Tarleton.
If scientific reasoning is merely Bayesian, why does Eliezer tell us to abandon science in order to stick with Bayes? It seems to me that it is easy to represent strict standards of evidence within looser ones, but not vice versa. The frequency of 'Bayesian reasoners' mistaking data for evidence on this site should serve as example enough.
"If scientific reasoning is merely Bayesian,"
Scientific reasoning is an imperfect approximation of Bayesian reasoning. Using your geometric analogy, science is the process of sketching a circle, while Bayesian reasoning is a compass.
"It seems to me that it is easy to represent strict standards of evidence within looser ones, but not vice versa."
If you already understand the strict standard, it's usually easy to understand the looser standard, but not vice-versa. Physicists would have a much easier time writing literature papers than lit...
On cryonics: it's easy to come up with poorly supported future scenarios -- either pro or con. We've heard from the cons, so here's a pro: at the point where it looks plausible to the general public that frozen dead people might be revived, pulling the plug on the freezers may appear to become morally equivalent to pulling the plug on patients with intact brains who are comatose but not medically dead. It may no longer a purely financial question in the eye of the public, especially if some enterprising journalist decides to focus on the issue.
This sort of prognostication is a mug's game.
Using your geometric analogy, science is the process of sketching a circle, while Bayesian reasoning is a compass.
To continue the metaphor: science is the system of reasoning we use to recognize that the compass will make approximate circles, figure out how to build compasses, and recommend that people use them when they want to draw a circle.
As a system, Bayesian reasoning it is sufficiently broad and flexible that it can be used to represent more sophisicated forms of reasoning, in the same way that everyday language can represent formal logic. But a...
it's probable that this will happen before the technology exists to revive "dead" people cutting at a stroke the financial viability of cryonics companies and the income stream which keeps their freezers from defrosting.
They have investments.
Cyan, I should perhaps have noted that probabilistic techniques are used in data analysis and the statistical sciences, but I thought it was obvious I was talking about the foundations of the scientific method rather than specific applications of mathematical techniques. Scientists use algebra and calculus and complex numbers and all manner of things and none of them are therefore the foundation of the scientific method (or its "hidden structure" as Eliezer likes to say).
And, no, logic and reason are explicitly not taught, used or applied by scie...
Nick, if a roll a spherical Bayes down an inclined Bayes will it give me a good approximation of acceleration due to gravity near the Earth's surface?
We've heard from the cons, so here's a pro: at the point where it looks plausible to the general public that frozen dead people might be revived, pulling the plug on the freezers may appear to become morally equivalent to pulling the plug on patients with intact brains who are comatose but not medically dead. It may no longer a purely financial question in the eye of the public, especially if some enterprising journalist decides to focus on the issue.
Talk about wishful thinking! Do people, other than family and friends, even care about pulling the plug o...
Also - I'm assuming that postponing ageing for living people is easier than reviving dead people and is likely to arrive sooner. Not that I'm in anyway conversant with Bayesianism but I'm figuring it supports this assumption - technology to extend lifespan is, as far as I can see, a necessary component of reviving dead people. So the probability of the former is necessarily higher than the probability of the latter. There is no scenario in which reviving dead people arrives first and only a tiny probability that both technologies arrive simultaneously. Thi...
poke, I take "logic" and "reason" to mean making inferences by syllogism. I really have no idea what your usage of the terms denote, so I can't speak to it. I guess we were talking past each other. But I'm not so sure it's wise to draw a sharp distinction between "the foundations of the scientific method" and what at least some scientists spend a good deal of time actually doing, i.e., specific applications of mathematical techniques.
Frank McGahon, you're missing my point. Hint: reread my first sentence and my last sentence.
The critics of cryonics here for the most part seem to miss the attraction of cryonics, at least for people like me. I don't think the future will find me a fantastic individual worthy of reviving. I don't think there will be a market or even a will to revive me in the future. I don't even have much expectation that current cryonics is sufficient to save me from information theoretic death. I just think it's a better strategy than alternatives such as burial or cremation in maximizing my persistence odds. Maybe not a much better strategy. But still, it seems to me to be a better strategy. And my reasons for wanting to maximize my persistence odds are selfish and solipstic. That's it.
Cyan, oh, I get your point, I just think it's wrong to frame it as "on the one hand, on the other hand" as if the pro and con scenarios are equally likely and it's a toss-up between the two. The reason to point out that the very technology which is necessary for Cryonics to succeed is likely to make it obsolete and consequently unlikely to fulfil its promise is to illustrate a fatal flaw in the concept not to merely paint one pessimistic scenario. There are plenty of alternative pessimistic scenarios but none of which (individually that is) is a ...
"I say again: name one concrete scientific process that does something Bayes can't."
Bayes does not explain the development of new concepts and conceptual schemes, and yet this is one important thing that the best scientists are able to do. I'm thinking of scientific revolutions in physics and biology especially, but there are many other examples (e.g. theoretical computer science, statistics, game theory, information theory, and--going back further--the notion of a mathematical proof). AFAIK, we don't have a good understand of conceptual developm...
But if you followed the physics and anti-Zombie sequences, it should now seem a lot more plausible, that whatever preserves the pattern of synapses, preserves as much of "you" as is preserved from one night's sleep to morning's waking.
Part of the problem here, though, is we don't even have proof-of-concept. We know the freezing process damages the brain, or else we'd already be able to revive people, no problem. Being complicated, the brain tends to get complicated in damaged ways. In spite of our best efforts to provide effective treatments f...
'Ever' is a terribly long time, Hallq. All sorts of things might be possible with enough time; I think the real question is whether we'll see such a development in our lifetimes.
This isn't a matter of taking on faith where an ambulance is going. We know hospitals exists, and that all sorts of injuries can be treated; we know that there are ambulance services which take people to hospitals.
We do not know that cryonic techniques are capable of preserving a person, most especially after their death, or that they are likely to be maintained for a long durati...
Frank, you might want to read my blog to get a better sense of where I stand on this. I aspire to the position of contradicting your central presumption about me: that I would use my full resources in this life towards maximizing my persistence odds. The truth is, I think any other position is absurd, or a triumph of genes/species over me as a subjective conscious entity. The analogy I'm working with is not buying a lottery ticket for a chance at a big lifechanging payoff, it's more disaster movie survivalism. Current hedonism in the context of future none...
HA, I'll certainly go and read your blog but just to comment on your point:
I aspire to the position of contradicting your central presumption about me: that I would use my full resources in this life towards maximizing my persistence odds. The truth is, I think any other position is absurd, or a triumph of genes/species over me as a subjective conscious entity.
Your characterisation of the case against denial in this life with the promise of an eternal after-life (now that sounds familiar...) as if it were about the interests of the genes/species set ag...
HA: "Trying cryonics requires a leap of faith straight into the unknown for a benefit with an unestimable likelihood."
It's what probability is for, isn't it? If you don't know and don't have good prior hints, you just choose prior at random, merely making sure that mutually exclusive outcomes sum up to 1, and then adjust with what little evidence you've got. In reality, you usually do have some prior predispositions though. You don't raise your hands in awe and exclaim that this probability is too shaky to be estimated and even thought about, bec...
do you try and build your own missile to divert it off course or do you try and enjoy the time you have left.
How about if you're told that if your missile succeeds, you can live forever in a computer? Cryonics isn't a life extension strategy, it's an immortality gambit. Otherwise no-one would bother. By the time we can defrost brains, we'll be able to scan and emulate them.
This thread has been long since jacked. Bob Unwin, great link. Science and Bayes - both great, both useful. Can't we all just get along?
Late in the game and perhaps missing the point, but in order to try and understand for myself...
Your objection was that you:
(1) followed the 'method' or 'ideal' as (2) well as possible and (3) ended up with a hypothesis that was factually incorrect (4) risked of 'wasting' a very long time researching something that ended up being wrong and (5) that the 'method' or 'ideal' does not help one to avoid this properly (6) all of which combined make the method/ideal problematic as it is likely to statistically to also result in a high number of 'wasted years rese...
Cryonics isn't a life extension strategy, it's an immortality gambit.
You have this the wrong way around. Cryonics can only succeed in the event of practical immortality being achieved which requires that radical life extension is achieved. It's a necessary (but importantly not sufficient) condition of revival that the technology exist to radically extend lifespans in which case there will be nobody signing up for cryonics and no market to develop the technology to defrost and revive.
"in which case there will be nobody signing up for cryonics and no market to develop the technology to defrost and revive." ...except for all that has already died while being signed up. Their wills and possibly foundations they set up would provide large enough a market if only a sufficient amount of rich people do sign up.
Another point: if we just achieved the defrosting techniques and had a bunch of cryonically suspended individuals from say the 19th century, we would be ankle deep in the saliva from all psycologists, historians etc. that woul...
..except for all that has already died while being signed up.
It's not like they're going to be in a position to lobby for it. And there's a world of a difference between a paying customer or potential customer and a will or foundation. The wishes of the dead are frequently flouted when convenient today - look at what happened to Nabakov's manuscript.
In any case, in the event that radical life extension is already here, there's just no need to solve the problem of defrosting frozen brains for paying customers so I'd expect that to be, at least, put on the...
I think it is quite possible for rich individuals to create structures surviving themselves such that it would be very hard to distinguish them for institutes/foundations/whatever that has a living person at the bottom. I'm not very familiar with the subject, but I would guess that there exists accounts on the Cayman Islands and similar states whose owners have died but the owners is too well hidden for anyone to find out.
Concerning the academic interest, I think that coming generations will, like us, find the preceding documentation terribly lacking. &quo...
Sorry to be late to the partyâ but has nobody yet mentioned the effect that MWI has on assessing cryonics from a personal standpoint; i.e. that your subjective probability of being revived should very nearly be your probability estimate that revival will happen in some universe? If 9/10 of future worlds destroy all cryogenic chambers, and 9/10 of the ones left don't bother to revive you, then it doesn't matter to you: you'll still wake up and find yourself in the hundredth world. Such factors only matter if you think your revival would be a significant...
You describe only a part of science. In addition to testing hypotheses, scientists spend an lot amount of time developing hypotheses. In fact, they probably spend more time developing hypotheses than testing them. They tinker around in a lab trying various things, and they search for better mental models so that their thinking becomes more effective. A major class of breakthrough for a scientist is to make a realization of the form, "A looks an awful lot like B".
If you don't want to waste ten years, spend some time on hypothesis development. That's not outside of science, but a core part of it.
Erik, in the event that RLE is already here - there will be no future stream of "paying customers" as they will surely avail themselves of RLE, that's what I meant. Therefore this market, at least, won't be driving innovation in the "how to revive a frozen brain" problem.
Fair point about how our own recording of information might look to future generations, however the many Methuselahs issue remains. It may be that my imagination is lacking or it may be that cryonics advocates are biased to overweight any indicators that cryonics might ...
Bad analogy, actually. If I have an incurable terminal illness today and fall asleep, I'll still have an incurable terminal illness in most of the worlds in which I wake upâ so I should assign a very low subjective probability to finding myself cured tomorrow. (Or, more precisely, the vast majority of the configurations that contain someone with all my memories up to that point will be ones in which I'm waking up the next day with the illness.)
I'm not quite sure how it might play out subjectively at the very end of life sans cryonics; this is where the...
Ok, then say you are definitely going to die of that illness tonight - that is, you won't wake up in the morning. It's preposterous to suggest that any consolation would be provided by the notion that in some parallel universe a cure is invented and implemented overnight and "you" will wake up cured in that universe.
It's preposterous to suggest that any consolation would be provided by the notion that in some parallel universe a cure is invented and implemented overnight and "you" will wake up cured in that universe.
But I'm already in that universe. "I" am the set of all processes having my experience.
Frank, I think you have an idea that many-worlds means a bunch of parallel universes, each with a single past and future, like parallel train tracks. That is most emphatically not what the interpretation means. Rather*, all of the universes with my current state in their history are actual futures that the current me will experience (weighted by the Born probabilities).
If there's an event which I might or might not witness (but which won't interfere with my existence), then that's really saying that there are versions of me that witness it and versions o...
Why will they unfreeze us?
Well, if they're pretty rich, which is likely, given that they're technologically advanced enough to do so, they may well still have history and sociology departments and universities, with ambitious grad students, and Professors with grant money to spend. Welcome to being an adjunct lecturer (or would that be lab rat) for History 201(An Introduction to the Crazy Years).
"Call me when cryonicists actually revive someone," they say; which, as Mike Li observes, is like saying "I refuse to get into this ambulance; call me when it's actually at the hospital".
There was a time when expecting mothers did the rational thing by not going to the maternity ward. http://www.ehso.com/ehshome/washing_hands.htm#History
Resources to be devoted to cryonics and a future lifespan could also be devoted to the lifespan you are fairly sure you have right now. The situation would be more like getting into an ambulance, whe...
After a few years in grad school, I think the principles of science are different from what you've picked up from your own sources.
In particular, this stands out to me as incorrect:
(1) I had carefully followed everything I'd been told was Traditionally Rational, in the course of going astray. For example, I'd been careful to only believe in stupid theories that made novel experimental predictions, e.g., that neuronal microtubules would be found to support coherent quantum states.
My training in writing grant applications contradicts this depiction of s...
Concerning cryonics, you seem to be operating under the assumption that future scientists would actually want to revive anyone, which is not exactly rational. Yeah, conquering Death and all that, but humans aren't that well-trainable, so would you really expect that they'd find us being able to adapt to the world which has advanced beyond belief?
My working theory since ~1st grade, is that math is consistent and therefore worth learning. But of course, Goedel says I can't prove it. I derive some Bayesian comfort though, as I see more and more mathematical propositions added to the pile of propositions proven true, and as they obligingly keep on not contradicting each other.
This is... really not how scientific practice works, though.
This is how some, older, philosophers of science thought science ought to work. Namely Karl Popper. Who had some points, for sure, but notably, was not a scientist himself, so he was speculating about a practice he was not a part of - and had to discover that, having described to scientists the laws that ought to govern how they ought to act, found that they in fact did not, nor agreed that they would get better results that way. Philosophy of science really took off as an entire discipline here, and a lot of it pointed out huge aspects that Popper had overlooked, or outright contradictions between his ideas and actual scientific practice - in part, because his clean idea of falsification does not translate well to the testing of complex theories.
Instead of speculating about how science might work, and then saying it is bad, let's look at how it actually does, to see if your criticism applies. Say you applied for a grant to develop this theory of yours. Or submitted a talk on it at a scientific conference. Or drafted it as a project todo for an academic position. This is usually when the scientific community determines if ...
Once upon a time, a younger Eliezer had a stupid theory. Let's say that Eliezer18's stupid theory was that consciousness was caused by closed timelike curves hiding in quantum gravity. This isn't the whole story, not even close, but it will do for a start.
And there came a point where I looked back, and realized:
From Science's perspective, that is how things are supposed to work—happy fun for everyone. You admitted your error! Good for you! Isn't that what Science is all about?
But what if I didn't want to waste ten years?
Well... Science didn't have much to say about that. How could Science say which theory was right, in advance of the experimental test? Science doesn't care where your theory comes from—it just says, "Go test it."
This is the great strength of Science, and also its great weakness.
Gray Area asked:
Because questions that are easily immediately tested are hard for Science to get wrong.
I mean, sure, when there's already definite unmistakable experimental evidence available, go with it. Why on Earth wouldn't you?
But sometimes a question will have very large, very definite experimental consequences in your future—but you can't easily test it experimentally right now—and yet there is a strong rational argument.
Macroscopic quantum superpositions are readily testable: It would just take nanotechnologic precision, very low temperatures, and a nice clear area of interstellar space. Oh, sure, you can't do it right now, because it's too expensive or impossible for today's technology or something like that—but in theory, sure! Why, maybe someday they'll run whole civilizations on macroscopically superposed quantum computers, way out in a well-swept volume of a Great Void. (Asking what quantum non-realism says about the status of any observers inside these computers, helps to reveal the underspecification of quantum non-realism.)
This doesn't seem immediately pragmatically relevant to your life, I'm guessing, but it establishes the pattern: Not everything with future consequences is cheap to test now.
Evolutionary psychology is another example of a case where rationality has to take over from science. While theories of evolutionary psychology form a connected whole, only some of those theories are readily testable experimentally. But you still need the other parts of the theory, because they form a connected web that helps you to form the hypotheses that are actually testable—and then the helper hypotheses are supported in a Bayesian sense, but not supported experimentally. Science would render a verdict of "not proven" on individual parts of a connected theoretical mesh that is experimentally productive as a whole. We'd need a new kind of verdict for that, something like "indirectly supported".
Or what about cryonics?
Cryonics is an archetypal example of an extremely important issue (150,000 people die per day) that will have huge consequences in the foreseeable future, but doesn't offer definite unmistakable experimental evidence that we can get right now.
So do you say, "I don't believe in cryonics because it hasn't been experimentally proven, and you shouldn't believe in things that haven't been experimentally proven?"
Well, from a Bayesian perspective, that's incorrect. Absence of evidence is evidence of absence only to the degree that we could reasonably expect the evidence to appear. If someone is trumpeting that snake oil cures cancer, you can reasonably expect that, if the snake oil was actually curing cancer, some scientist would be performing a controlled study to verify it—that, at the least, doctors would be reporting case studies of amazing recoveries—and so the absence of this evidence is strong evidence of absence. But "gaps in the fossil record" are not strong evidence against evolution; fossils form only rarely, and even if an intermediate species did in fact exist, you cannot expect with high probability that Nature will obligingly fossilize it and that the fossil will be discovered.
Reviving a cryonically frozen mammal is just not something you'd expect to be able to do with modern technology, even if future nanotechnologies could in fact perform a successful revival. That's how I see Bayes seeing it.
Oh, and as for the actual arguments for cryonics—I'm not going to go into those at the moment. But if you followed the physics and anti-Zombie sequences, it should now seem a lot more plausible, that whatever preserves the pattern of synapses, preserves as much of "you" as is preserved from one night's sleep to morning's waking.
Now, to be fair, someone who says, "I don't believe in cryonics because it hasn't been proven experimentally" is misapplying the rules of Science; this is not a case where science actually gives the wrong answer. In the absence of a definite experimental test, the verdict of science here is "Not proven". Anyone who interprets that as a rejection is taking an extra step outside of science, not a misstep within science.
John McCarthy's Wikiquotes page has him saying, "Your statements amount to saying that if AI is possible, it should be easy. Why is that?" The Wikiquotes page doesn't say what McCarthy was responding to, but I could venture a guess.
The general mistake probably arises because there are cases where the absence of scientific proof is strong evidence—because an experiment would be readily performable, and so failure to perform it is itself suspicious. (Though not as suspicious as I used to think—with all the strangely varied anecdotal evidence coming in from respected sources, why the hell isn't anyone testing Seth Roberts's theory of appetite suppression?)
Another confusion factor may be that if you test Pharmaceutical X on 1000 subjects and find that 56% of the control group and 57% of the experimental group recover, some people will call that a verdict of "Not proven". I would call it an experimental verdict of "Pharmaceutical X doesn't work well, if at all". Just because this verdict is theoretically retractable in the face of new evidence, doesn't make it ambiguous.
In any case, right now you've got people dismissing cryonics out of hand as "not scientific", like it was some kind of pharmaceutical you could easily administer to 1000 patients and see what happened. "Call me when cryonicists actually revive someone," they say; which, as Mike Li observes, is like saying "I refuse to get into this ambulance; call me when it's actually at the hospital". Maybe Martin Gardner warned them against believing in strange things without experimental evidence. So they wait for the definite unmistakable verdict of Science, while their family and friends and 150,000 people per day are dying right now, and might or might not be savable—
—a calculated bet you could only make rationally.
The drive of Science is to obtain a mountain of evidence so huge that not even fallible human scientists can misread it. But even that sometimes goes wrong, when people become confused about which theory predicts what, or bake extremely-hard-to-test components into an early version of their theory. And sometimes you just can't get clear experimental evidence at all.
Either way, you have to try to do the thing that Science doesn't trust anyone to do—think rationally, and figure out the answer before you get clubbed over the head with it.
(Oh, and sometimes a disconfirming experimental result looks like: "Your entire species has just been wiped out! You are now scientifically required to relinquish your theory. If you publicly recant, good for you! Remember, it takes a strong mind to give up strongly held beliefs. Feel free to try another hypothesis next time!")