As part of the story I am writing, an individual has been frozen with relatively crude cryogenic technology, then preserved as well as possible. Given the constraints of biology, what would waking them up entail in terms of real/current (or hypothetical/future) technology in order to be successful?

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    $\begingroup$ Without wishing to seem unhelpful, I'd like to point out that we don't really know how you'd usefully freeze someone so that they could be reanimated in future, let alone how you might thaw someone safely. Probably won't know for years or decades. That means you get to handwave the tech level yourself; pick whatever fits your scenario. $\endgroup$ May 8, 2019 at 10:47
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    $\begingroup$ Welcome to worldbuilding. Considering how many people have paid good money to be cryogenically frozen without knowing a way to be thawed back to life, if I had an answer to this I would patent it and start living out of the royalties. I would not post it here for free. $\endgroup$
    – L.Dutch
    May 8, 2019 at 10:47
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    $\begingroup$ Note that the water in cells can be frozen in a way that avoids the formation of ice crystals. This method of preservation is called vitrification. $\endgroup$
    – kfx
    May 8, 2019 at 16:42
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    $\begingroup$ @StarfishPrime I originally misunderstood this too, but it seems OP is asking about reviving someone who was poorly frozen (e.g., the kind you can actually get today) rather than reviving someone using a more sophisticated form of freezing. OP, can you clarify please? $\endgroup$ May 8, 2019 at 17:06
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    $\begingroup$ @CaptainMan yes, this is the case. It is someone who was frozen poorly, but kept preserved as well as possible until the reanimation was performed. $\endgroup$ May 9, 2019 at 6:58

5 Answers 5


Well, we can't do it now so the only answer we have is 'more than we have now'.

Alright, this isn't strictly true, insofar as we can cryogenically freeze embryos and the like, and we can then thaw them and bring them to term so depending on your definition of 'someone', arguably the minimum technology someone needs is the ability to create and maintain liquid nitrogen. For full fledged human beings however, the problem is a little more complex.

When you get down to it, the problem is that around 70% of the human body is water. That may not sound like so much of a big deal - we freeze water all the time, right? Well true, but it's the stuff around the water that presents the problem here.

Ever wonder about the Titanic? Why it was possible for it to hit an iceberg in the first place? I mean, water is a liquid and most liquids are less dense than the solid made of the same material right? But icebergs float. So do those little cubes we put in our Scotch drinks other than Scotch. That's because water expands when frozen, unlike most other molecules and compounds. Suffice it to say that freezing a complex human body actually causes massive damage to the cells because the frozen water actually damages the rest of the chemical compounds in the cell. (This is a simplification, but functionally correct.)

So; either we find a way to freeze water in a way that doesn't cause it to expand while the compounds around it increase their density, or we replace the water with another compound that doesn't react in that manner.

The first is simple - we simply don't have that technology and our understanding of chemistry leads us to believe that without some new breakthrough discovery in science, it will never be done. Therefore, it's not a simple engineering problem we can throw money and other resources at. It would rely on a scientific discovery to be made that we simply can't predict.

As for the second idea, most of the liquids we can think of that would behave in the right manner as they freeze are actually toxic to us, so while it's possible we wouldn't suffer cell damage, we'd still most likely die.

Bottom line is that in order to successfully cryogenically freeze a person with a high probability of bringing them back, we would either need to be able to replace all the water in all the cells of a human body with something that is both non-toxic AND subject to density increase during freezing; or, we need to find a way for water to react differently to freezing and increase (rather than decrease) in density.

Both are currently outside our known science, which is evident by one simple observation;

We're not doing it yet.

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    $\begingroup$ I'd like point out that dying due to the anti-freeze fluid isn't an issue. If you get frozen you die anyway. The point of cryogenics is to bring preserve the body in a state that bringing them beack from the dead is feasible. $\endgroup$ May 8, 2019 at 11:55
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    $\begingroup$ @TheDyingOfLight well... Yes, true. But without knowing what science will come up with it just seems logical that trying to reanimate a frozen dead person would be easier if you didn't have to simultaneously deal with all that ethelene glycol as well. Generally speaking engineers like to deal with one problem at a time and needing to be reanimated AND detoxified seems to me to be more like two. $\endgroup$
    – Tim B II
    May 8, 2019 at 11:58
  • $\begingroup$ we need to find a way for water to react differently to freezing and increase (rather than decrease) in density - as a side note, amorphous, high-density ice is not outside the known science, even if using it for cryopreservation is not practical. $\endgroup$
    – kfx
    May 8, 2019 at 17:01
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    $\begingroup$ The other problem is that as water freezes, it tends to force other substances out of the forming ice crystals (this is the basis of freeze distillation). Even if water didn't expand when it froze, this would be rather destructive. $\endgroup$
    – Mark
    May 8, 2019 at 22:05
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    $\begingroup$ Or we could find a way to repair the cellular damage as the person thaws, maybe with micro transporters or micro tractor beams or nano-bots. $\endgroup$
    – Chloe
    May 9, 2019 at 2:31

Daiquiri cryonics

This is my favorite low tech method. Blood sugar and blood alcohol (and also acetone) are driven up in tandem. Way up. The person does not die of diabetic coma because her blood alcohol is so high, and does not die of alcohol poisoning because she is so cold that brain metabolism is slowed. You want the body no colder than the freezing point of alcohol. Before she goes to sleep, a left ventricular assist device is implanted; you can use the same line for a dialysis access.

When you revive her, you need to reverse all three in tandem: lower sugar, clear the alcohol and gently warm the body. Oxygen is going to be depleted too so you will need to bring that back artificially until the lungs come on line.

You could do that with current tech using ECMO dialysis. Combination of extracorporeal membrane oxygenation and continuous renal replacement therapy in critically ill patients: a systematic review.

Turn on the LVAD because the heart is too cold to do any work, and will probably not do much but quiver for a while. With the LVAD, blood starts flowing. Dialysis will clear alcohols in the blood and also glucose. You can gradually warm the blood in the machine too. With ECMO you can oxygenate blood on the return circuit but the high sugar content will support anaerobic metabolism for a little while. Lactic acid produced by anaerobic tissues will also be cleared by dialysis.

Once she is warmed up the heart will hopefully take over and you can turn off the LVAD. If not, gentle electricity will be salutary.

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    $\begingroup$ This sounds intriguing, but do you have a scientific source for me as I'm interested in learning more about this method. Your link leads me to some kind of odd forum where people share jokes about the idea. $\endgroup$ May 8, 2019 at 15:31
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    $\begingroup$ Even if not realistic, it's certainly plausible enough for fiction! $\endgroup$
    – Stephen R
    May 8, 2019 at 19:59
  • $\begingroup$ @TheDyingOfLight - I am flattered. The method is my own invention, improved for WB with the addition of machines. You are welcome to add your jokes to the linked halfbakery version. $\endgroup$
    – Willk
    May 8, 2019 at 20:28
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    $\begingroup$ "(...) gentle electricity will be salutary." I just love your posts. $\endgroup$ May 9, 2019 at 0:37
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    $\begingroup$ Is the "gentle electricity" a bolt of lightning from being raised up on a platform during a storm by a cackling mad scientist? $\endgroup$
    – Thorne
    May 9, 2019 at 1:06

As Tim B pointed out it isn't technologically feasable yet to bring someone back from cryogenic sleep (sleep is a marketing euphemism since for all intents and purposes you are dead when frozen). As already said water needs to be removed due to it's freezing causing massive cell damage and other antifreeze fluids it could be replaced with will still cause a lot of damage. Additionally there is a limit on how long someone can be frozen due to the accretion of radiation damage in the body, which is caused by background radiation and the natural decay of radioisotopes within our bodies. In a living person the damage gets repaired naturally, but these repair mechanisms won't work in a (cryogenic sleeper) frozen, mummified corpse.

On that cheerful note let's discuss the technologies which would make (waking up) the reanimation of a long cold body plausible. Since cell damage is the issue at hand any technologie capable of fixing it quickly and on a large scale is fine. The obvious candidate would be medical nano-machines [1], be they biological or mechanical in nature. When we'll have these on a level capable of performing the complex tasks required to bring someone back from (a winter night dream) the land of the dead is yours to choose. Noone could argue against it if you place this level of sophistication somwhere between 2050 and 2200.

Consider that this level of medical technologie won't appear in a vacuum as beeing able to repair damaged cells at the rate needed for successful revival of a (sleeping beauty) slightly rotten corpse will make extreme longjevity or outright biological immortality possible. Going over Aubery de Grey's SENS approach [2] [3] medical nanotechnology will fix all of the issues.

Finally this video by Youtuber Isaac Arthur goes into furtjer detail on cryogenics [4].

A good overview of the modern state of cryogenics is given in this article [5]. There are frogs in nature which use glucose [6] as an antifreeze to replace dangerous water. While somewhat successful experiments haves been done with frozen rat organs none of the possesses is completly safe or reaches the temperature of 77 Kelvin where all biological processes would stop.

[1] https://www.microscopemaster.com/nanobots.html

[2] https://www.sens.org/our-research/intro-to-sens-research/

[3] https://youtu.be/RDpjv2z3dyE

[4] https://youtu.be/fM-JHvg-ZCM

[5] http://discovermagazine.com/2005/feb/biology-of-cryogenics

[6] https://en.m.wikipedia.org/wiki/Glucose

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    $\begingroup$ since for all intents and purposes you are dead when frozen There was a 365 Tomorrows story a while back that utilized that as a key plot point. They found a way to travel FTL, but it didn't work on living tissue. But dead things were just objects, so they cryogenically froze people, sent them through, and then resuscitated them. $\endgroup$ May 8, 2019 at 15:23
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    $\begingroup$ Currently reading "Playgrounds of the mind" by Larry Niven and there was a short story called "The Defenseless Dead" where people who had been frozen since the 1970's for various reasons (illness, visit the future, ...) and people of the future wanted to live longer lives, so they were making rules which would invalidate some of these people from being brought back (the procedure wasnt perfect, about 2/3 made it, but parts seemed 100%) and so for awhile it was an easy organ bank. $\endgroup$
    – Fering
    May 8, 2019 at 16:20


There are many possible developments in tech which would allow this, (OK , first, going along with the question's assertion that the freezing process has already occurred - thus excluding some modification akin to the adaptation in some frogs re. antifreeze in their cells):

Scanning tech close to the atomic-level - coupled with the ability to reproduce matter.

Basically, as soon as we develop teleportation tech, (and a high level of software editing to repair freeze-related damage) then we can focus those beams on the frozen individual, upload their physiological data (eg. all their brain's grey and white-matter data - all their life's experience, mental associations), plus their body (maybe with a few repairs/improvements). Then simply re-materialize them in their prime.

Time travel, coupled with mind-reading tech and cloning.

After death, their frozen remains can be discarded (they were only there for the family's viewing anyhow, PR style).

A person/bot is sent back to the most convenient time before death to retrieve the memories. For dementia patients, this could be pre-diagnosis, for murder suspects, just before the act (to ascertain mental state) or just after to get an exact view how it went. Memory editing by the state/third parties could be an issue in this society, I'd hate to be hacked - again. Anyway, the cloning wouuld produce a new body, an imprint of the mind would be uploaded to the blank-slate.

Nano, coupled with advanced AI.

Molecular level issues with cell integrity could perhaps be sorted out by the bots, reversal of blood clotting, cell membrane rupture, proteins being shredded by ice crystals. These minor issues could be repaired on an atom-by-atom basis (see "The World's Smallest Movie"). They could be repaired if the process is supervised by a splendidly intelligent AI, in communication with all the bots-in-the-bod, supervising the various stages of repair and reanimation.


One of the posts above talked about using alcohol. I'd propose we Cryo-freeze folks by first giving them genetic therapy that grants them traits of koi/carp. Carp, according to this article have the ability to survive in icy water by turning lactic acid (what happens when you exercise) into alcohol. https://www.foxnews.com/science/scientists-discover-how-some-fish-survive-in-icy-water

*> Per the BBC, goldfish and crucian carp developed the ability to

survive months in icy lakes and ponds using the unique ability to convert lactic acid into alcohol.

As water freezes and oxygen levels dwindle, lactic acids produced from eating carbohydrates are unable to escape a fish's body. These trapped lactic acids would kill the fish in minutes were it not for an evolutionary trait that allows them to convert the acids into alcohol, which is then released through their gills.*

This is where the scifi twist happens. This genetic therapy also gives our characters GILLS! This allows our characters to be frozen at near cryogenic temperatures while retaining the ability to breathe under water.

Folks wishing to prolong their life our stored under water in a cold facility or climate (free).

The drawback here and the low cost method of defrost would be that these folks would remain near "merfolk" until they could afford the genetic treatment to become an air breathing human again. Just like Amazon Glacial cloud storage, you can put your data (or body) in for free but when you want to reverse the operation it's going to cost you.

A method of the plot could also be how the cryo company raised rates and now have a ransom group of merfolk from 100 years ago.

  • $\begingroup$ This doesn't seem like it would actually freeze the person or the fish. The fish just gets to live in really cold water. It might look like the fish has been frozen because the whole lake's been frozen over, but it hasn't turned into a solid block of ice. $\endgroup$
    – Pimgd
    May 9, 2019 at 8:48
  • $\begingroup$ Yes I guess this would slow functions down to minimum and then we'd have to maintain a medically induced coma. Might not be 100% suspended animation but if it could be done for 100yrs with minimal aging it could be a viable plot device. $\endgroup$
    – Matt D
    May 9, 2019 at 17:20

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