Cryonics is the speculative practice of freezing a person for long-term preservation with the hope of future revival. The straightforward answer to whether this is possible today is no, as the necessary technology for revival does not yet exist. Current methods focus only on preservation, cooling the body to temperatures where biological decay stops. This field operates on the hope that future scientific advances will resolve the immense damage inherent in the process and allow for successful reanimation.
The Fundamental Biological Barrier of Freezing
Water, which makes up a large portion of the human body, is the primary obstacle to simple preservation at low temperatures. When water freezes, it expands by about nine percent, forming sharp, microscopic ice crystals. These crystals inflict severe mechanical damage, puncturing cellular membranes and connections throughout tissues and organs.
Uncontrolled ice formation also drastically alters the chemical environment outside the cells. As pure water freezes, the remaining liquid becomes a concentrated solution of salts and solutes, leading to osmotic shock. This imbalance pulls water out of the cells, causing them to shrink and dehydrate to a lethal degree. This combination of structural destruction and chemical damage results in the irreversible death of cells and tissues.
Current Techniques for Human Preservation
Cryonics organizations attempt to bypass the damage caused by ice crystal formation through a complex process called vitrification. This technique does not freeze the body in the traditional sense; instead, it aims to turn the body’s water content into an amorphous, glass-like solid. To achieve this, the patient’s blood is removed and replaced with a specialized solution containing high concentrations of Cryoprotective Agents (CPAs) via perfusion.
CPAs, which are medical-grade antifreeze compounds such as glycerol and dimethyl sulfoxide, lower the freezing point of water and increase the viscosity of the solution. These chemical agents are circulated through the circulatory system to penetrate the cells and replace the water molecules. The body is then cooled very rapidly, preventing the water molecules from organizing into crystalline ice structures.
The goal is to reach a glass transition temperature, typically around -120°C, where the entire system solidifies into a glass without any crystalline ice. While this technique mitigates mechanical damage from ice crystals, it introduces chemical toxicity. The high concentration of CPAs required for vitrification is toxic to cells, requiring a balance between chemical damage and thermal damage. Modern cryonics protocols use complex cocktails of CPAs like M22, administered at low temperatures to minimize this toxicity.
The Critical Difference Between Cryonics and Medical Hypothermia
Confusion often arises between the speculative practice of cryonics and the established medical procedure known as therapeutic hypothermia. Therapeutic hypothermia is a reversible, short-term treatment used in hospitals, primarily for patients who have suffered a sudden cardiac arrest. The goal is to lower the patient’s core body temperature by only a few degrees, typically to a range between 32°C and 36°C.
This mild cooling slows the body’s metabolic rate, reducing the brain’s need for oxygen and preventing damaging chemical reactions after blood flow is restored. The procedure lasts only about 24 hours and is a temporary measure designed to limit existing injury, not to reverse death or achieve long-term preservation.
Cryonics, conversely, involves cooling the body to the deep cryogenic temperature of liquid nitrogen, which is -196°C. This is an extreme change in state, requiring the replacement of bodily fluids with toxic chemicals to achieve vitrification. Unlike therapeutic hypothermia, which is a proven medical intervention, cryonics is performed only after a person is legally deceased and is currently irreversible with known technology.
The Unsolved Scientific Problem of Reversing Cryopreservation
While vitrification addresses the initial challenge of ice formation, the more difficult problem is reversing the process and achieving revival. This revival requires rewarming the entire large mass uniformly and rapidly, which is currently impossible without causing catastrophic damage. If the warming rate is too slow, the amorphous glass solid can undergo devitrification, forming lethal ice crystals during the warming phase.
The large size of a human body makes achieving the necessary rapid and uniform warming rate extremely difficult using conventional methods. For instance, the outer layers would warm quickly, while the inner core would lag, creating temperature gradients that cause thermal stress. This stress can lead to macro-fracturing, or cracking, within the vitrified tissue, destroying the delicate structures of the brain and other organs.
Even if the body could be warmed perfectly, the accumulated damage from the initial cryoprotectant toxicity and the mechanical stress of the process would still need to be repaired. This level of repair would require highly advanced, theoretical molecular nanotechnology capable of operating at the cellular and subcellular level. Such technology would need to navigate the entire body, correct nanoscopic structural damage, and restore the brain’s connectome—the precise map of neural connections that stores personality and memory. The complex technology required for this complete restoration does not yet exist outside of scientific speculation.