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There is a broader, perhaps slightly less biased, article on Wikipedia about Cryonics
When you freeze a steak and bring it back to edible, I'll believe it.
—Mike Godwin[1]
That is not dead which can eternal lie.
And with strange aeons even death may die.
Promotional photo of Alcor technicians playing with dead bodies. Here lies Maximum Transhuman - not dead, only a broken braincell mush with billions of dendrites shattered by freezing.

Cryonics is the practice of freezing clinically dead people in liquid nitrogen with the aim of future reanimation by as-yet-unknown advanced medical technology. They quick-freeze the body (or, for less money, the head alone) and preserve it for as long as possible, possibly centuries. Presently nonexistent sufficiently advanced nanotechnology is the favored prospect for implementing "and then a miracle occurs," which is all steps past the initial freezing. Several companies exist which offer to perform this service for a fee, usually organized as non-profits.

Scientists will admit that some sort of cryogenic preservation and revival does not provably defy physics. Probably. But they stress that, in practical terms, freezing and reviving dead humans is so far off as to hardly be worth taking seriously and the present cryonics industry is based on speculation at best and quackery and pseudoscience at worst. However, cryonicists will accept considerable amounts of your money right now for a business based only on vague science-fiction-level speculations, with no scientific evidence whatsoever that any of their present actions will help achieve their declared aims.

In the US, cryonics is legally considered an extremely elaborate form of burial, and cannot be performed on someone who has not been declared medically dead.

Cryonics should not be confused with cryobiology (the study of living things and tissues thereof at low temperatures) or cryogenics (subjecting things to cold temperatures in general).


Robert Ettinger, a physics and maths teacher, published The Prospect of Immortality in 1964. He then founded the Cryonics Institute and the related Immortalist Society. Ettinger was inspired by "The Jameson Satellite" by Neil R. Jones (Amazing Stories, July 1931).[2] Lots of science fiction fans and early transhumanists then seized upon the notion with tremendous enthusiasm.

Corpses were being frozen in liquid nitrogen by the early 1960s, though only for cosmetic preservation. The first person to be frozen with the aim of revival was James Bedford, frozen in early 1967.

The current state of cryonics

Cryonics for dead humans is still a process of freeze and hope for a miracle to be developed. There is no revival method proposed beyond "one day we will be able to do anything!" and there is no evidence that current methods are even a revivable method of preservation.

As the Society for Cryobiology put it :

The Society does, however, take the position that cadaver freezing is not science. The knowledge necessary for the revival of whole mammals following freezing and for bringing the dead to life does not currently exist and can come only from conscientious and patient research in cryobiology, biology, chemistry, and medicine.

(Note that Smith et al. 1957 did manage to drop mice into LN2 and revive them.[3])

As normal freezing damages cells with expanding ice crystals, the body is frozen rapidly in a bath of liquid nitrogen, which is around -196°C. The body is also given large doses of anti-clotting drugs, as well as being infused with cryoprotectant chemicals that cause the water within the body to freeze in a glassy form (vitrification), so as to avoid it crystallizing and puncturing cells. Note that the cryopreservatives are themselves toxic.

Cryonics enthusiasts will allow that you're 100% dead dead when you reach "information-theoretic death," where the information in your mind is beyond recovery. Neural net information (your mind) appears to be preserved in strengths of neuron connections in dendrites. (Rather than electrical activity - coma patients and sufferers of severe hypothermia frequently come back from near-zero brain activity with memory, intelligence and personality intact.)

Scientific evidence for efficacy

There is no scientific evidence whatsoever that any of what cryonicists currently do will in fact make revival any easier or even that it does preserve the neural information — they just think it sounds like a plausible hypothesis that it will.

There is no evidence that it will be any better at allowing a future resurrection of the long dead than the preservation technology the ancient Egyptians used on their pharaohs. The ancient Egyptians could just have easily said "in 6000 years we'll be able to do anything!" But even the Singularity won't be enough to get the pharaohs back.

Ben Best, CEO of the Cryonics Institute, supplies in Scientific Justification of Cryonics Practice a list of cryobiology findings that suggest that cryonicists might not be completely wrong, with considerable "then a miracle occurs" mixed in, which is not quite what the title promises.[4] His assertions as to what cited papers say also vary considerably from what the cited papers' abstracts assert.

Alcor Corporation calls cryonics "a scientific approach to extending human life" and compares it to heart surgery.[5] This is a gross misrepresentation of the state of both the science and technology and verges on both pseudoscience and quackery.

Technical problems

These would all need to be solved to bring a frozen head back to life. Cryonicists do acknowledge many of these problems.[6]

  • Freezing frozen organs recoverably. (We already do this routinely with embryos.)
  • Cloning most of a body from recoverable DNA. (We're closer to this one than any of the others below.)
  • Nanobots. Present nanotechnology has no idea how to get there from here. Computer-controlled nanoscopic miracle workers are pure cheesy sci-fi. Nanobots won't resemble the popular image of macroscopic industrial robots a millionth of the size with their own built-in supercomputers - they'll be carefully designed chemicals, much like cells or enzymes (the real-life examples of nanobots). Things are different at nanoscale.
    • "Nanobots!" is not the magic answer to everything any more than "really small tweezers!" is. Fixing the damage would have to be physically possible - which it may not be - and humans would still need to know how to actually fix whatever it was in order to program the nanobots.
  • Fixing the freezing damage to the original frozen brain. The dendrites (10,000 connections for each of the 100 billion neurons - that's 1015 dendrites to check) are cracked badly by the freezing process - "acoustic fracturing events," like when you drop an ice cube into a drink. What is the process for fixing a frozen brain that's cracked into several, or hundreds of, pieces, with dendrites shattered at a microscopic level? This is a problem even with vitrification.
    • The damage may not be mappable, let alone repairable. Damaging energies are required to scan at 5 nm resolutions, where things start going quantum.[7]
  • Reattaching a severed head or transplanting the brain.
    • Alternately: reading the patterns from the original brain and writing those to the cloned brain (uploading and downloading minds). Cryonicists speak of mind-uploading as if it's a mere technical detail that's just around the corner, rather than something we don't even know can meaningfully be discussed.
  • The cryopreservatives, that prevent ice crystal damage, are themselves toxic and would need to be removed from the tissues. (This is really a pretty minor problem compared to everything else listed herein.)
  • Preserve cells at ~100% viability. "~99% ain't gonna cut it. We're barely there even in ideal situations like loose cells in rich media loaded with antifreeze compounds."[8] As those who work with stroke victims know, large chunks of personality and memory can go out the window. They are generally considered to be the same person afterward (occupying the same body and all that), but cryonics needs to preserve pretty much the entire person if it is to live up to its promise.
  • Cure the disease or other condition that originally killed the subject.
  • Once you've fixed the body cells and the brain paths, you have a recovered corpse. Your next task is to resurrect the dead.

Specific scenarios that would keep today's cryonics from working

  • Insufficient information being preserved by today's cryonics. (This is the null hypothesis that cryonics advocates have no evidence against.)
  • Nanobots, uploading or other "reanimation" technologies never being invented or turning out not to be possible.
  • Reanimation technologies taking so long to develop that other unpredictable factors (social upheaval, global warming, etc.) prevent them from being carried out, even if current techniques preserve sufficiently well and recovery doesn't defy physics.

Organisational problems

The existing two cryonics facilities are small and financially shaky.[9] In 1979, the Chatsworth facility ran out of money and the frozen bodies thawed.

Of the early frozen corpses, only James Bedford remains, due to tremendous effort on the part of his surviving relatives. Though they didn't do anything to alleviate ice crystals, so he'll pretty much be irrecoverable broken cell mush by now.

In popular culture

Cryonics in various forms has become something of a fictional trope[10], either as a serious plot device (the Alien tetralogy), a source of humor (Futurama, Sleeper), or sheer boneheaded incomprehensibility (Vanilla Sky). Its usual job is one-way time travel, the cryonics itself being handwaved (as you are allowed to do in science fiction, though not in reality) as a pretext for one of various Rip Van Winkle scenarios.

As a fictional concept, "cryogenics" generally refers to a not-yet-invented form of suspended animation rather than present-day cryonics, in that the worst technical issue to be resolved (if at all) in the far future is portrayed as aging, or whatever killed you.

Timothy Leary was famously interested in the "one in a thousand" chance of revival and signed up with Alcor soon after it opened.[11] Eventually, though, the cryonicists themselves creeped him out so much[12] he opted for cremation.[13]

Walt Disney, who is often thought to have had his head or body frozen, died in December 1966, a few weeks before the first cryonicist freezing in early 1967. He also failed to get the Supreme Court to extend his life so that his copyrights would never, ever run out.

Mainstream scientific opinion of cryonics

Cryonics is not considered a part of cryobiology, and cryobiologists consider cryonicists nuisances. The Society for Cryobiology banned cryonicists from membership in 1982, specifically those "misrepresenting the science of cryobiology, including any practice or application of freezing deceased persons in anticipation of their reanimation."[14] As they put it in an official statement:

"The act of freezing a dead body and storing it indefinitely on the chance that some future generation may restore it to life is an act of faith, not science."

The Society's planned statement was actually considerably toned down (it originally called cryonics a "fraud") after threats of litigation from Mike Darwin of Alcor.[15]

It can be difficult to find scientific critics willing to bother detailing why they think what the cryonics industry does is silly.[16] Mostly they consider that cryonicists are failing to acknowledge the hard, grinding work to advance the several sciences and technologies that are prerequisites for their goals.[8] Castles in the air are a completely acceptable, indeed standard, part of turning science fiction into practical technology, but you do have to go through the brick-by-brick slog of building the foundations underneath. Or, indeed, inventing the bricks.

Mainstream medical opinion of cryonics

National Council Against Health Fraud president William T. Jarvis said: "Cryonics might be a suitable subject for scientific research, but marketing an unproven method to the public is quackery."[17] Mostly, doctors ignore cryonics and consider it a nice but expensive long shot.

Cryonics advocacy


Demographically, cryonics advocates tend to intersect strongly with transhumanists — almost all well-educated, mostly male, mostly atheist or agnostic but with some religious, and disproportionately involved in mathematics, computers, or physics.[18] Belief in cryonics is pretty much required on LessWrong to be accepted as "rational."[19]

Hardly any celebrities have signed up to be brought back to life in the far future.[20] Which may be a net win.

Discussion tropes

In argument, cryonics advocates tend to freely confuse technologies we have any idea of how to get to with science-fiction-level speculation that is only somewhat plausible, and speak of "first, achieve the singularity" as if it were a minor detail that will just happen, rather than a huge amount of work by a huge number of people solving the many, many prerequisite tiny details.

The proposals and speculations are so vague as to be pretty much unfalsifiable. Solid objection to a speculation is met with another speculation that may (but does not necessarily, or sometimes even probably) escape the problem. You will find many attempts to reverse the burden of proof and demand that you prove a given speculation isn't possible.

Cryonicists also tend to assert unsupported high probabilities for as-yet nonexistent technologies[21][22]. Figures are derived on the basis of no evidence at all, concerning the behaviour of systems we've built nothing like and therefore have no empirical understanding of. (Saying "Bayesian!" is apparently sufficient support with no further working being shown under any circumstances.)

Take care to distinguish the queries "is some sort of cryogenic suspension and revival not theoretically impossible with as yet unrealised future technologies?" from "is there any evidence that what the cryonics industry is doing right now does any good at all?" Cryonics advocates tend to hear the second question and answer with the first. Nailing them down on precisely what their falsifiable claim is at that point is just about fucking impossible.

When you ask about a particularly tricky part and the answer is "but, nanobots!" take a drink.

Not deliberate fraud (mostly)

Cryonicists are almost entirely scarily sincere, exceedingly smart and capable people and really believe that freezing your freshly-dead body is the best current hope of evading permanent death (maybe it is) and that the $50–120,000 this costs is an excellent investment in the far future (a little less certain). There is little deliberate fraud going on.

  • The Chatsworth facility, run by Robert Nelson, ran out of money and the frozen bodies thawed.[23][24] The cryonics movement as a whole was outraged and facility operators are much more careful these days.
  • In widely-reported allegations by their ex-COO, Alcor have been incredibly careless with the frozen heads in their care.[25] Alcor denies all allegations, tried to get his book blocked from publication[26] and has threatened further legal action. Considering that cryonics people are by and large absolute fanatics, the allegations are, on the surface, about as plausible as a Palestinian/Israeli peace conference held in BaconWorld theme park.

Pascal's wager

Cryonics enthusiasts are fond of applying a variant of Pascal's wager to cryonics[27] and saying that being a Pascal's Wager variant doesn't make their argument fallacious.[22][28][29] Ralph Merkle gives us Merkle's Matrix:

 It works  It doesn't work
Sign up Live Die, lose life insurance
Do nothing Die Die

The questionable aspect here is omitting the bit where "sign up" means you pay $120,000 of present-life money for the chance at an afterlife, the details of which completely lack scientific backing for the obvious hard bits.

Cooling processes known to work

The basic notion of freezing and reviving an animal, e.g. a human, is far from completely implausible.


  • Cryogenics has proven usably effective for single human cells — it is widely used in in vitro fertilization to store fertilized zygotes for later implantation.
  • There are many reported cases of humans (adult and child) who have had a severely lowered core temperature and been brought back to full health once warmed. (Of course, there are quite a lot more reported cases where they just died. And there are, of course, no cases of a human being frozen solid and surviving the process.)
  • Therapeutic hypothermia (down to 32°C, from the normal 37°C) is routinely practiced in hospitals as a method of reversing ischemia damage.


  • Small mammals freeze and revive surprisingly well. Smith et al. (1957)[3] is a sterling piece of mad science, with remarkable success for half a century ago. Mice simply dropped in beakers of LN2 revive fairly reliably with careful warming, artificial respiration and electrical shocks, because they are so small they flash freeze. However, the females are infertile because large oocyte cells are particularly sensitive to ice crystals, and they suffer slightly diminished remaining lifespans for various related reasons. Bushbabies were revived but died within 24 hours.
  • Experiments have been done involving suspended animation at temperatures higher than freezing, in which the life processes of a mammal subject [30] are reduced to almost nothing for a short period then brought back. Pigs can be taken down to 10°C and revived.[31]
  • Some frogs have been frozen and revived quite reliably, and actually appear to have evolved to survive partial freezing.[32] Cold-blooded animals in general are rather better at dealing with cold than mammals or birds.
  • Flies and insects freeze and revive pretty well.[33] Freezing and reviving houseflies is reliable enough to make a nice magic trick.[34]
  • A bacterium was revived after 120,000 years in a Greenland ice sheet.[35]


  • Viable eggs are recoverable from frozen mouse ovaries.[36] This is, of course, not the same as recovering a working organ. Ovaries are not as complex as kidneys or hearts. This paper states that complete mouse ovaries were cryopreserved at liquid nitrogen temperature and rewarmed to produce live pup birth rates compararable to that seen with fresh ovaries.[36]
  • A rabbit kidney (cryobiologists like rabbit kidneys, and experiment on them a lot) was frozen to -135°C and retransplanted, and supported life.[37] Best[4] claims it "functioned well enough as the sole kidney to keep the rabbit alive indefinitely," but the original paper does not go that far. The 2009 paper does show that the vitrified rabbit kidney when rewarmed was able to function as the sole functioning kidney — but only for a few days, not "indefinitely". Best has since admitted that this was an erroneous interpretation on his part, but maintains that the study nonetheless has significance in demonstrating continued functionality in complex organs.[38]
  • Best claims that cryobiologists have taken out a rat hippocampus, frozen it, inspected it and declared that it would possibly be viable (presumably, working when replaced).[4] This would be very promising, except that the abstract of the cited paper does not claim any such success and only claims that the slice looked good.[39] (Note: The authors of the paper are cryonicists as well as cryobiologists, but appear to understand what brick-by-brick science and technology entails.)

See also

External links


  1. Bar conversation with a RationalWikian.
  2. Cryonics Robert T. Carroll, Skeptic's Dictionary
  3. 3.0 3.1 Smith, A.U. (1957) "Problems in the Resuscitation of Mammals from Body Temperatures Below 0°C" Proceedings of the Royal Society of London. Series B, Biological Sciences, 147(929):533-544 (14 pages.) Excerpt: "Two of the galagos [bushbabies] regurgitated and inhaled bicarbonate from the stomach during administration of artificial respiration. The other two galagos which had been treated with bicarbonate and then frozen for 45 minutes seemed to make an excellent recovery after thawing. One of them regained an appetite as well as normal posture and behaviour. Within 24 hours they both died. At post mortem the stomach was normal, but in one animal the duodenum and jejunum contained bloodstained fluid. In both instances there was oedema of the lungs and froth in the trachea. This may have been a terminal event. Survival may have been limited by some other physico-chemical or physiological derangement which, if diagnosed, might well have been susceptible to treatment. It was therefore decided to postpone further experiments on freezing the larger mammals until the effects on other organs of freezing in vivo and in vitro were better understood." (p. 538)
  4. 4.0 4.1 4.2 Abstract: Benjamin P. Best. Scientific Justification of Cryonics Practice. Rejuvenation Research. April 2008, 11(2): 493-503. doi:10.1089/rej.2008.0661. Full text (PDF)
  5. Christianity and Cryonics: Questions and Answers (Alcor)
  6. Cryonics, Cryptography, and Maximum Likelihood Estimation (Ralph Merkle, Xerox PARC, Proceedings of the First Extropy Institute Conference, 1994)
  7. David Matthewman on the Whole Brain Emulation roadmap (Paul Crowley, blog post, 20 Feb 2010)
  8. 8.0 8.1 Corpsicles in the New Yorker (Ouroboros, 5 Feb 2010)
  9. Re: CryoNet #31623 (Ron Havelock, CryoNet mailing list, 20 Apr 2009)
  10. Human Popsicle (TV Tropes)
  11. Dr. Leary Joins Up (Cryonics, Volume 9(9), September, 1988, Issue #98)
  12. Re: Timothy Leary Renounces Cryonics (David Cosenza, CryoNet mailing list, 07 May 1996)
  13. Timothy Leary Renounces Cryonics (Charles Platt, CryoNet mailing list, 06 May 1996)
  14. "Upon a two-thirds vote of the Governors in office, the Board of Governors may refuse membership to applicants, or suspend or expel members (including both individual and institutional members), whose conduct is deemed detrimental to the Society, including applicants or members engaged in or who promote any practice or application which the Board of Governors deems incompatible with the ethical and scientific standards of the Society or as misrepresenting the science of cryobiology, including any practice or application of freezing deceased persons in anticipation of their reanimation. [Sec. 2.04 of the bylaws of the Society for Cryobiology]". Note that the quote is on the site of cryonics company Alcor.
  15. Society for Cryobiology statements on cryonics (Paul Crowley, blog post, 12 Feb 2010)
  16. An open letter to scientific critics of cryonics (Paul Crowley, blog post, 14 February 2010)
  17. Quackwatch
  18. Quigley, Christine (1998). Modern Mummies: The Preservation of the Human Body in the Twentieth Century. McFarland. p. 143. ISBN 0786404922. According to Wikipedia.
  19. "I'm going to come out and say it: If you don't sign up your kids for cryonics then you are a lousy parent." (Eliezer Yudkowsky, Normal Cryonics, 19 Jan 2010)
  20. Category:Cryonically preserved people on Wikipedia. What, you don't trust Wikipedia?
  21. Debates about Cryonics with Skeptics ( When told that the revival rate is 0% (as far as we know), and that it is therefore too soon to be charging for it, Mr Best repeatedly tells skeptics "You are treating cryonics as if it were sex with minors." He then puts this on his web page as if accusing opponents of reductio as Hitlerum makes him look good.
  22. 22.0 22.1 Rationality, Cryonics and Pascal's Wager (Roko,, 08 April 2009)
  23. Suspension Failures: Lessons from the Early Years (R. Michael Perry, Cryonics, February 1992)
  24. Mistakes Were Made. An extraordinary episode of radio documentary series This American Life tells the funny, bizarre, and tragic story of a cryonics facility owner and client family for whom things didn't go quite as planned with the frozen body thing. It's an excellent cautionary primer to the complexities of actually running such a business.
  25. Ted Williams' frozen head for batting practice at cryogenics lab: book (Nathaniel Vinton, New York Daily News, 2nd October 2009).
  26. Alcor Sues to Block Book Expose of Ted Williams Cryonics (Ethics Soup, 06 October 2009)
  27. Pascal's Wager and cryonics (
  28. The Pascal's Wager Fallacy Fallacy (
  29. Pascal’s Wager taken out of deep freeze (Michael Cook, BioEdge, 24 Oct 2009
  30. Most notably Miles the Beagle, suspended for an hour in 1987. (dead link - anyone got a good ref?)
  31. Stuck Pig (Bijal P. Trivedi, Wired 14.07)
  32. Ask the expert: Jon Costanzo (NovaScience Now, PBS, April 2005)
  33. Frozen Flies Safeguard Research, Screwworm Eradication Efforts (ScienceBlog, 04 Feb 2005)
  34. Reviving a Dead Fly Magic Trick
  35. Resurrection bug' revived after 120,000 years (Andy Coghlan, New Scientist, 15 June 2009)
  36. 36.0 36.1 Hasegawa A, Mochida N, Ogasawara T, Koyama K. Pup birth from mouse oocytes in preantral follicles derived from vitrified and warmed ovaries followed by in vitro growth, in vitro maturation, and in vitro fertilization. Fertil Steril. 2006 Oct;86 Suppl 4:1182-92.
  37. Fahy GM, Wowk B, Wu J, Phan J, Rasch C, Chang A, Zendejas E. Cryopreservation of organs by vitrification: perspectives and recent advances. Cryobiology. 2004 Apr;48(2):157-78.
  38. Fahy GM, Wowk B, Pagotan R, Chang A, Phan J, Thomson B, Phan L Physical and biological aspects of renal vitrification Organogenesis. 2009 Jul;5(3):167-75.
  39. Pichugin Y, Fahy GM, Morin R Cryopreservation of rat hippocampal slices by vitrification Cryobiology. 2006 Apr;52(2):228-40.