Cryonics means freezing someone when they die, so they can be revived with better medical technology in the future.

Another way of saying this is that cryonicists disagree with the legal definition of death. Someone is not dead when their heart has stopped beating, for example. Rather, they are dead when it is impossible – even in principle – to revive someone in their current form. This is known as the ‘information-theoretic criterion of death‘.1 You cannot rearrange a pile of bones into the person they once were, but you can, in principle, revive someone whose heart stopped beating two minutes ago.

Cryonics seems like an obviously good bet. If you don’t sign up to it, you are certainly dead, whether or not cryonics works. If you sign up for cryonics, there are two possibilities: either cryonics doesn’t work, in which case you die, but that would’ve happened if you didn’t sign up to it anyway. Or cryonics does work, then you live. So the only way you could live beyond your natural lifespan is if you sign up to cryonics: by not signing up for it, you are guaranteed permanent death. If you value life, the only rational course of action, therefore, is to sign up to cryonics.

If the above is correct, it is rational to not sign up for cryonics only if:

  1. You believe that P = 0, i.e. cryonics will never work;
  2. You prefer being dead to being alive.

Cryonics will probably work

Freezing biological matter to preserve it (so that when rewarmed, it functions again) has worked already, in smaller cases. It has worked with a rabbit kidney2, which was frozen, rewarmed, transplanted into a new rabbit and functioned normally. It has also worked with, according to Ralph Merkle, “very early human embryos, sperm, skin, bone, red and white blood cells, bone marrow, and others”. There are also well-known cases where people who have been dead for a long period of time were revived, e.g. because they fell into a frozen lake.3 This implies that cryonic freezing has a prima facie chance of working.

Nonetheless, if you talk to the average person – even doctors – about cryonics, they are sceptical. The most common reason for doctors to be sceptical is that cryonics hasn’t been validated using clinical trials, and doctors are, rightly, sceptical of things that haven’t been validated in that way. But cryonics requires a longer time horizon than most clinical trials. We won’t know whether it works for at least 50 years.

We are faced with a bet: will medical technologies in the future will become advanced enough to repair damage to human bodies that we don’t currently know how to deal with? And will cryopreservation keep us in a treatable state until then?

I don’t know of an exact value for P, the probability that cryonics works, but we can confidently state that it’s non-zero. Highly intelligent people are choosing to be cryonically preserved, freezing seems prima facie a good way to preserve people, and medical technology is advancing fast at an accelerating rate.

We should value life

Preferring death to life seems absurd, but it is the source of most people’s distaste for cryonics. People say things like:

  • Death is part of the natural order. It’s a good thing. We shouldn’t fight it.4
  • Life wouldn’t be beautiful if we lived forever. Death makes things beautiful.
  • Living forever would suck: you’d get old, and demented, and weak, but have to go on living in this miserable state.

The third point seems like the most reasonable one. It’d be no fun to be alive and decrepit, because you couldn’t enjoy anything. I’m not worried about this, though: if medical science becomes advanced enough to revive frozen humans, it’s likely good enough to reverse the bad effects of aging too. And if it isn’t, we should remain frozen until it is.

More generally, I find the pro-death arguments baffling. If people really believed that death was good, they wouldn’t cry at funerals, or be sad when their friends died. Nobody wants their family and friends to die. All the cliches about death making life beautiful are just advanced rationalisations for something that’s awful, and bad, and should be stopped.

Paying for a cryonic insurance policy seems like a sane thing to do. It may seem a little crazy, but so did flying across continents in a giant metal container once.

Further reading

Merkle on cryonics

LessWrong’s cryonics wiki

Robin Hanson on cryonics

What is your life worth?’, John Broome


  1. “A person is dead according to the information-theoretic criterion if their memories, personality, hopes, dreams, etc. have been destroyed in the information-theoretic sense. That is, if the structures in the brain that encode memory and personality have been so disrupted that it is no longer possible in principle to restore them to an appropriate functional state, then the person is dead. If the structures that encode memory and personality are sufficiently intact that inference of the memory and personality are feasible in principle, and therefore restoration to an appropriate functional state is likewise feasible in principle, then the person is not dead.” – Ralph Merkle, from here
  2. “ We report here the detailed case history of a rabbit kidney that survived vitrification and subsequent transplantation, a case that demonstrates both the fundamental feasibility of complex system vitrification and the obstacles that must still be overcome, of which the chief one in the case of the kidney is adequate distribution of cryoprotectant to the renal medulla.”
  3. Example 1. Example 2.
  4. Steve Jobs: “Death is very likely the single best invention of Life. It is Life’s change agent. It clears out the old to make way for the new.” (from here.) Jobs was a brilliant man, but he also believed that a fruit-only diet would get rid of his cancer, so we shouldn’t believe everything he said.
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