Cryonics: A Chilling Prospect

by Brian Dunning
December 17, 2024

Spread among several facilities around the world, hundreds of dead people are frozen in capsules cooled with liquid nitrogen — and hundreds more have just their heads in the same cold storage. These are people who have paid a lot of money for what they hope will be a life-extension procedure called cryonics. Their aspiration is that at some point in the future, perhaps the very distant future, technology and medical science will have advanced to the point that we'll know how to safely thaw their body, cure their cause of death, and revive them to resume a healthy life to whatever degree is possible. Today we're going to look at a number of aspects of this controversial technology. How does it work? What's the state of the science? And most importantly, what are the prospects of being revived in the future? And, fair warning: some of you might find parts of this episode a bit too ghoulish for your taste.

If you've heard anything about cryonics, it's probably that although people are already doing it, we don't have proven techniques for any of it yet. The basic problem of freezing human tissue is the formation of ice crystals. Normally, if you freeze living tissue, ice crystals will physically destroy the cells irreparably, and that tissue will die. This is what frostbite is. The destroyed cells become necrotic, and once the damage is done, their loss is unavoidable. Freezing, and particularly thawing, also produce thermal stress fractures, causing larger scale physical damage.

Thus, the avoidance of ice crystals is key to the whole science of cryonics. The idea is to vitrify the tissue. Vitrification means to freeze into a solid glasslike state, devoid of any ice crystals. This is what we do today with the cryopreservation of reproductive cells, like sperm, eggs, and embryos. Depending on what type of tissue is being preserved, and particularly the permeability of the cell walls of that tissue, a cryoprotectant like glycerol or DMSO (dimethyl sulfoxide) might be used, as well as cocktails including ingredients such as formamide, DMSO, propylene glycol, and a colloid.

All of these chemicals bring up the problem of toxicity. Not only does the cryoprotectant have to penetrate the tissue completely in order to allow proper vitrification, it has to be non-toxic to that tissue. It doesn't do much good to vitrify the tissue if the cryoprotectant kills it. We've been able to do this with reproductive cells because they are relatively simple structures and it's been possible to come up with just the right cryoprotectant. An entire human body, however, presents a nearly infinitely more complex problem.

Consider all the many different types of tissue in a human body, and consider that with all the different sensitivities and permeabilities, each may need a different cryoprotectant. In recognition of this problem, cryonics typically focuses on the soft tissues, and then mainly on the brain. Some structures like bones don't seem to have a viable solution, and fluids like blood can be replaced; but if the brain can be kept intact, that's obviously the most important part.

So cryonics also offers the option of preserving only the head. It's cut off, the body is discarded, and right away the vitrification problem is made substantially simpler. It's also easier and cheaper to keep just the head frozen rather than an entire body. We have no idea what technologies there may be at some time in the future for reviving just a brain, a brain and a head, or an entire body. One hope is that just the brain might be enough. Perhaps a new cloned body can be grown and the brain can be transplanted into it; we really have no idea. The whole revival part of the process — the thawing of the vitrified tissue and its revival — is a black box at this point. We can't do it today, so we hope that one day in the future other people will have figured something out.

Luckily, progress is being made. In May of 2024, Chinese scientists published their successful freezing and thawing of brain tissue without loss of function in the journal Cell Reports Methods. Using a cryoprotectant cocktail called MEDY consisting of methylcellulose, ethylene glycol, DMSO, and a compound called Y27632, they successfully vitrified and thawed both brain organoids (lab-grown brain tissue) and actual living human brain tissue "​​without disrupting the neural cytoarchitecture or functional activity." The brain tissue was obtained from a 9-month-old girl who was undergoing a temporal lobectomy to treat her epilepsy. Promising, but all of these tissues measured only 3-4 millimeters, small enough that they were at little risk of thermal stress fractures, much easier to gradually freeze and thaw at internally consistent temperatures, and much easier to saturate with the MEDY cryoprotectant.

There is also the totally different option called mind uploading, something that a number of companies are currently studying. Can your mind, including your consciousness, be uploaded into some sort of storage system, to be later restored into a new brain? Or could it even be transferred into a digital brain emulation, inside of which it could remain conscious and interact? Could such an entity live out an immortal life inside of a virtual reality populated with all the other such entities? Could that consciousness be loaded into a robotic body? A robotic horse? A jet airplane? So far, mind uploading — and the interesting variety of things that could be done with such a virtual human consciousness — is purely speculative, as well as profoundly controversial.

Mind uploading also raises the question of what philosopher Derek Parfit termed the "teletransportation paradox." There seems to be no way to know that if your consciousness could successfully be moved from one entity into another, would it really be you, and not just a copy of you? For example, every time Captain Kirk beamed somewhere, his body was obliterated, converted to energy, and reconstructed somewhere else. From our perspective, he continued being Captain Kirk with no observable interruption. But how do we know the original Captain Kirk's conscious self didn't terminate and die, and an entirely new conscious self was created, with the same thoughts and memories, and unaware that he had only been created seconds ago? If I want to become immortal, it doesn't do me any good if I'm obliterated and some digital twin brother goes on to live out the rest of my life.

Unfortunately nobody has ever come up with a method to scientifically or empirically test a transferred consciousness (should such a thing ever become possible) to see if the true original consciousness was retained, or if a new copy of it was made and the original destroyed. So far this has remained in the domain of philosophers' thought experiments. Oblivion is a risk that all mind uploaders may always have to chance — whereas, with cryonic preservation and potential revival, there would be no teletransportation and that's at least one problem you wouldn't have to worry about.

There is also an alternate method of preserving the brain, hopefully indefinitely, by embalming it instead of freezing it, and thus avoiding the (so far) intractable problem of freezing and thawing without significant physical damage. The problem here is that the subject has to be alive and under general anesthesia to have their brain thoroughly penetrated by the embalming fluid, which is necessarily fatal. The hope is that one day the preserved (but unrevivable) brain can be somehow scanned in order to replicate it at the atomic level, or perhaps digitally. But of course, then we have the teletransportation paradox again.

Many people stress the risks involved with all of these techniques. What if there's a natural disaster or a war or a blackout and the company loses all their power? What if their building blows up? What if someone trips over a wire and pulls your plug? It's also true that most cryonics companies that have ever existed have gone out of business and their frozen corpses thawed and disposed of. Obviously there are a million things that can go wrong, and potentially a very long time in which any of them might happen. But these are little different from the risks we all face every day just living in the world. Every time we get into a car we risk death. Our house might burn down any night while we're asleep. We could get hit by a meteor. There is no such thing as a risk free life; the risks involved in your stasis state are the same, it's just a different set of dangers.

It's little wonder that few in the scientific community consider cryonics a seriously viable option for life extension, at least with today's technology. With such great risk and so little potential for any upside, how should we regard it? One way of evaluating cryonics is as a variation on Pascal's Wager. Imagine a 2x2 grid; the two columns represent "cryonics works" and "cryonics doesn't work"; the two rows represent "You go for it" and "You don't." There are four possibilities:

Two of those possibilities result in no important outcome, but the other two are tremendous loss and tremendous gain. The difference is that in one case you went for it, and in the other you didn't. So the only smart bet for Pascal is to go for it. You've got nothing to lose except some money. But it's kind of a lot of money — usually in the hundreds of thousands of dollars; if you're wealthy enough that you can spend it without a problem, there is no reason not to become a cryonics customer. Of course, that's only for someone who wants the potential upside, and also who has no philosophical, moral, religious, or other objections to it.

My personal conclusion — which nobody should take as guidance or as a recommendation — is that even price-independent, I wouldn't do it (though I probably would do a mind upload once I was on my deathbed). The big stumbling block for me is the impracticality of properly vitrifying a complete brain, let alone a complete body, without substantial physical damage, and I wouldn't want to be revived only to find myself horribly mentally or physically compromised. But what if that changes? What if a brain or body can be successfully vitrified in my lifetime? I'd probably take another look at it. But my read is that for now, the potential for upside just isn't there yet.

By Brian Dunning
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