Introduction to Cryonics

Cryonics is an effort to save lives by using temperatures so cold that a person beyond help by today’s medicine can be preserved for decades or centuries until a future medical technology can restore that person to full health.

Cryonics sounds like science fiction, but is based on modern science. It’s an experiment in the most literal sense of the word. The question you have to ask yourself is this: would you rather be in the experimental group, or the control group?

Cryonics is justified by three facts that are not well known:

1) Life can be stopped and restarted if its basic structure is preserved.

Human embryos are routinely preserved for years at temperatures that completely stop the chemistry of life. Adult humans have survived cooling to temperatures that stop the heart, brain, and all other organs from functioning for up to an hour. These and many other lessons of biology teach us that life is a particular structure of matter. Life can be stopped and restarted if cell structure and chemistry are preserved sufficiently well.

2) Vitrification (not freezing) can preserve biological structure very well.

Adding high concentrations of chemicals called cryoprotectants to cells permits tissue to be cooled to very low temperatures with little or no ice formation. The state of no ice formation at temperatures below -120°C is called vitrification. It is now possible to physically vitrify organs as large as the human brain, achieving excellent structural preservation without freezing.

3) Methods for repairing structure at the molecular level can now be foreseen.

The emerging science of nanotechnology will eventually lead to devices capable of extensive tissue repair and regeneration, including repair of individual cells one molecule at a time. This future nanomedicine could theoretically recover any preserved person in which the basic brain structures encoding memory and personality remain inferable, which typically occurs well after spontaneous function has been lost.


  • If survival of structure means survival of the person;
  • If cold can preserve essential structure with sufficient fidelity;
  • If foreseeable technology can repair injuries of the preservation process;

Then cryonics should work, even though it cannot be demonstrated to work today. That is the scientific justification for cryonics. It is a justification that grows stronger with every new advance in preservation technology.

Preventing Death

Death occurs when the chemistry of life becomes so disorganized that normal operation cannot be restored. (Death is not when life turns off. People can and have survived being “turned off”.) How much chemical disorder can be survived depends on medical technology. A hundred years ago, cardiac arrest was irreversible. People were called dead when their heart stopped beating. Today death is believed to occur 4 to 6 minutes after the heart stops beating because after several minutes it is difficult to resuscitate the brain. However, with new experimental treatments, more than 10 minutes of warm cardiac arrest can now be survived without brain injury. Future technologies for molecular repair may extend the frontiers of resuscitation beyond 60 minutes or more, making today’s beliefs about when death occurs obsolete.

Ultimately, real death occurs when cell structure and chemistry become so disorganized that no technology could restore the original state. This is called the information-theoretic criterion for death. Any other definition of death is arbitrary and subject to continual revision as technology changes. That is certainly the case for death pronounced on the basis of absent “vital signs” today, which is not real death at all.

The object of cryonics is to prevent death by preserving sufficient cell structure and chemistry so that recovery (including recovery of memory and personality) remains possible by foreseeable technology. If indeed cryonics patients are recoverable in the future, then clearly they were never really dead in the first place. Today’s physicians will simply have been wrong about when death occurs, as they have been so many times in the past. The argument that cryonics cannot work because cryonics patients are dead is a circular argument.

Cryonics Today

More than one hundred people have been cryopreserved since the first case in 1967. More than one thousand people have made legal and financial arrangements for cryonics with one of several organizations, usually by means of affordable life insurance. Alcor is the largest organization, and distinguished among cryonics organizations by its advanced technology and advocacy of a medical approach to cryonics.

Alcor procedures ideally begin within moments of cardiac arrest. Blood circulation and breathing are artificially restored, and a series of medications are administered to protect the brain from lack of oxygen. Rapid cooling also begins, which further protects the brain. The goal is to keep the brain alive by present-day criteria for as long as possible into the procedure. It is not always possible to respond so rapidly and aggressively, but that is Alcor’s ideal, and it has been achieved in many cases.

In 2001 Alcor adapted published breakthroughs in the field of organ preservation to achieve what we believe is ice-free preservation (vitrification) of the human brain. This is a method of stabilizing the physical basis of the human mind for practically unlimited periods of time. The procedure involves partly replacing water in cells with a mixture of chemicals that prevent ice formation. Kidneys have fully recovered after exposure to the same chemicals in published studies.

Alcor’s future goals include expanding ice-free cryopreservation (vitrification) beyond the brain to include the entire human body, and reducing the biochemical alterations of the process to move closer to demonstrable reversibility. Based on the remarkable progress being made in conventional organ banking research, we believe that demonstrably reversible preservation of the human brain is a medical objective that could be achieved in the natural lifetime of most people living today.

To learn more, please read our list of Frequently Asked Questions and the many other articles in the Alcor Library.

Dramatic Advances in Brain Tissue Preservation

Figure 1: Pre-1992 freezing damage in brain tissue after treatment with 3 molar glycerol. This light micrograph prepared by “freeze substitution” in the frozen state shows extensive ice crystal damage. This is the kind of damage that many commentators assume is common in cryonics patients. Their assumption is outdated and incorrect.

brain electron micrograph

Figure 2: Pre-1992 freezing damage in brain tissue after treatment with 4 molar glycerol. This electron micrograph prepared after thawing shows tears surrounding a capillary, and a naked cell nucleus with no cell membrane (dark rounded object). There seems to be less damage in frozen-thawed tissue than in tissue imaged in the frozen state.

Figure 3: 1992-2001 freezing damage in brain tissue after treatment with 7.5 molar glycerol. This electron micrograph prepared after thawing shows tears surrounding a capillary, but otherwise good structural preservation.  With this protocol, ice damage occurs at intervals throughout the brain, but with most of the volume remaining ice-free.

brain electron micrograph

Figure 4: Today brain tissue preserved with a modern vitrification solution shows virtually no freezing damage. Whole neurons are visible with intact membranes and well defined structure. This is the excellent brain preservation which Alcor can now achieve in human patients. Most “experts” who complain about damage caused by cryonics procedures are unaware that such preservation is now possible.