Two Theories for Cryopreservation

Why cryonics, and the two main methods, with practical discussion and philosophical musings on both.

Epistemic status: Cryonics is a scientific field that is long established, yet long underfunded, and uncertain. I’ve been thinking about this on and off for a few years and remain cautiously optimistic.

Most people who have ever lived, over 90%, have died, and most information we may need to be able to revive them has also gone. We still live in the era where a single accident or disease can swiftly and permanently end your experience of life. If you value your life, and want to continue to live indefinitely, cryogenic preservation of your body is an obvious thing to consider.

Here, I will mostly talk about the two main methods of cryopreservation, with some high-level technical explanation of how they work, and my practical and philosophical musings on these two methods, and what I ultimately decided.

Some of the main considerations I touch on are: chance of biological revival, chance of upload/information recovery, continuity of consciousness, logistical feasibility, and robustness of storage. There are a few main organizations with different tradeoffs, and some more minor and regional ones too. I leave this discussion to another post.

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Why Cryopreservation?

Upon cardiac-arrest, the body loses the ability to provide oxygen to your cells, and they begin to rapidly die. In the past, cardiac-arrest used to be synonymous with death. Nowadays over 100,000 experience cardiac arrest and continue to live.

By analogy, it seems pretty plausible that you could cheat death by preventing your cells from dying over a longer period too. Upon “legal death”, one could preserve your body at low temperatures (keeping all the information intact), and one day bring you back to life.

While one should ideally focus on things that prevent your death in the first place, there are always tradeoffs and tail risks one can not infinitely account for. For example, one could die in an accident, or develop cancer, or get some rare adverse reaction to some disease, amongst other things. One’s body continues to degrade with the uncured ailments of aging, leading to the chance of death with each decade of life increasing exponentially.

For people like me, healthy and in their 20s, the cost of signing up to cryopreservation is also relatively low and affordable, as little as around ~£30/month with little operational overhead to sign up, and with some assumptions has a very high expected-value ROI.

But there are different methods and different organizations, and one can believe different things about it too. So which are these main methods of preservation?

Two theories and methods for cryopreservation

There are two theories on how one might be revived: The first is Biological revival - where your body will be mostly fixed as-is, and you will continue your life in it. The second is Brain upload - where your brain neurons are scanned and simulated by a computer for whole-brain emulation.

Currently, neither is feasible in humans, but there is rapid technological progress on both fronts. Conditioned on AI going well, one of these forms of revival seems quite plausible. Both have tradeoffs, but I leave that to the section on philosophical musings.

Based on these theories, one can make different tradeoffs when doing storage when trying to improve chances of survival, so we now discuss the main methods.

Method 0: Straight Freeze

The simplest, and worst, method for storage is to do a “straight-freeze”. This just involves cooling the normal body to below-freezing temperature. As humans are mostly made of water, and water expands and crystalizes when freezing, this typically causes cells to get severe damage and makes prospects of revival quite slim.

Nobody seriously considers this the best method (unless you are desperate I guess), but it acts as a simple reference we can compare the other methods to.

Method 1: Vitrification

The most common method of cryopreservation, used by organizations such as Alcor since 1976, is to replace the water in the body with an anti-freeze solution (aka: cryoprotective agent) that doesn’t crystalize the same way water does, and then cool down the body to a low temperature by submerging in liquid nitrogen indefinitely, which then turns into a glass-solid by a process called vitrification.

This method basically works pretty well for single-celled organisms (and is similar to how gamete storage works). It has had some studies where people tried to do this with single-organs in animals, but with relatively mixed results as the science is still early. There is promise that this research could one day be used to make the organ donation process significantly better.

This is also the most widely-available method, and it is relatively easy and affordable to sign up.

However there is a tradeoff, that one needs to store in -196°C temperatures indefinitely in dewars, and must top-up the storage containers with fresh liquid nitrogen every couple weeks or so. One can store some on-site supply of liquid nitrogen, but if there is ever a failure in this at any point, then warming would cause the body to degrade as normal again.

Vitrification also has a slight tradeoff that it is not so much a stable solid, but more-so a solid in equilibrium, and that there still may remain some cell movement and degradation. My understanding is that at liquid-nitrogen temperatures this is mostly negligible, but there are concerns in degradation that would from when one may need to inevitably re-warm the body to perform a revival procedure or brain-scan of some sort.

Lastly, basically all the cryoprotective agent solutions also have some tradeoffs in vitrification efficacy, cell toxicity, and perfusion efficacy. There is not, to my understanding, a perfect solution to these yet, but research in cryonics has been pretty underfunded for a long time. The solutions that tend to be used are VM1 and M22.

But there is also another alternative cryopreservation method too.

Method 2: Aldehyde Fixation

The theory for this method is subtly different. Yes, you still need to replace the water in the human body with a different agent. But instead of using an anti-freeze solution, you use a fixative such as glutaraldehyde, which reacts with amino groups in cells, and cross-links the various proteins inside and between cells, to prevent them from moving.

This is the gold-standard for preserving neural tissue in neuroscience experiments, and has the best results for electron-microscopy prep. It also has the benefit that once the procedure is done, results are stable for a pretty long time. One can preserve indefinitely at dry-ice temperatures (-78.5°C), and temporary time where the body reaches room temperature again are not catastrophic.

Freezing at -196°C may still lead to more stable/less chance of degradation in the long term, but it would mostly be redundant and unnecessary.

It is also a procedure that has only become available as of much more recently, by only one organization called Nectome in Portland, Oregon . Though the team seems to be quite good.

And the procedure has limitations, in that the procedure needs to be done immediately after death for good preservation quality, (Nectome found the critical window is around 12 minutes post-legal-death to start washout perfusion), and so is reserved for MAiD patients only.

Lastly, the procedure is essentially irreversible. Hopes for biological revival become much more slim. Though prospects for information being fully preserved for future whole-brain emulation seem significantly higher with this procedure.

Given these tradeoffs for these two different methods and theories for cryonics, what should we choose?

My Philosophical Musings

Perhaps my philosophical musings are relatively uninformed and irrelevant, but I raise these unresolved concerns anyway. That is, I think the choice mostly depends partly on what you think counts as survival.

My main current concern is on continuity of consciousness with whole-brain uploading (as opposed to biological revival) that have not yet been adequately addressed for my own comfort.

To a large extent, I do care more to preserve my own experience of living. It would be nice if there were an exact copy of me that continued to keep living after I died, but to me, it would not be the same as my personal self continuing to live.

And I emotionally feel like having a whole-brain emulation would not lead to my personal self continuing to live.

Yes I know there are already strange parts to life. The fact that we go to sleep every night, then wake up, and have periods where we were not conscious in the middle - this seems fine to me, if only by being used to it. The fact that we may already be in a simulation that could be paused and restarted, and there could be multiple copies of me - on a more fundamental level. The fact that I wouldn’t mind my neurons being replaced one-by-one with mechanical versions as some kind of Ship of Thesius, and that this already happens biologically to some extent anyway.

Perhaps there is some ratio of [number of lifeyears of copies of myself] to [lifeyears of my actual self] that I should just take the tradeoff anyway. But I continue to cling on to some level of person-affecting ethics.

In the end, I still emotionally feel that a continuation of my physical substrate is still needed for the sense of self that is experienced to be my own, and that making a copy of me, then disassembling me separately, does not feel like living my own life. And I do value my own life specifically.

Additionally, even if this were to be resolved, I then have some concerns on S-risk enabled by whole-brain emulation too. Sure, there could be a million copies of myself living lives of perfect bliss, but what if the cost of this is that one-in-a-million copies get sometimes subjected to perfectly optimized torture instead? I feel utilitarian to some extent, maybe it’s worth it, but if I were the one experiencing that optimized torture, would I still feel like it was worth it? what if the ratio was different. I don’t really buy into anti-natalism as a whole, but these thoughts do keep me worrying sometimes too.

Maybe this is a form of cope too, but to some extent, I feel that biological revival at least gives me a possible way out from all the torture, in a way that having digitally-backed-up bits seems much more resilient. but I’m not sure either.

I overall do feel positive about cryopreservation, but I hold these philosophical concerns nonetheless.

So what do I personally do?

Most of my current risk of death still comes from highly time-sensitive accidents or diseases, so vitrification providers remain the main option.

But what about in the future? I guess one can try to weigh up one’s concerns, conditioned on vitrification vs aldehyde-fixation:

• [chance of biological revival] and [chance of brain upload],

• [future lifespan given biological revival] and [future lifespan given brain upload]

• [chance of continuity-of-consciousness given biological revival] and [chance of continuity of consciousness given brain upload].

All the numbers for this would be made up, but it can still be a useful exercise. One can try to weigh up how much you value continuity-of-consciousness for yourself specifically VS for other people too, and try to use this as a more impartial way of making this decision for yourself too, or vice-versa.

With my current weighing up of these factors:

• I still emotionally prefer the odds of continuity of consciousness from biological revival via vitrification (after seeing the EBF storage facility in Switzerland)

• Intellectually, I prefer the higher odds of physical revival as a whole (with brain upload) via aldehyde fixation (after seeing a talk by Borys Wróbel in 2024).

But it seems possible that I may change my mind on this in the future or with persuasion from other people. And I don’t think I can really fault anyone who chooses to go one way or another.

And remember, that in my opinion, It is significantly better to have signed up at all and change provider later, than to procrastinate indefinitely and not get around to signing up.

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Once you have a view on the method, the remaining question is which provider best matches your budget, geography, and logistics

• Tomorrow / Alcor: mainstream, all-inclusive SST + SP vitrification providers

• Cryonics Institute/American Cryonics Society/KrioRus/others: some common lower-cost vitrification providers.

• Nectome: new provider for aldehyde fixation, MAiD-only

I plan to give a detailed discussion on the tradeoff of these in tomorrow’s post.

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