Cryostasis, as depicted in science fiction, where a person is frozen alive and woken up later, is not real. But a related practice called cryonics does exist, and over 500 people have already been preserved in liquid nitrogen after legal death, with thousands more signed up. The gap between what’s real and what movies promise is enormous, but the science behind it is more nuanced than a simple yes or no.
What Actually Exists Today
Cryonics is the real-world practice closest to what most people mean by “cryostasis.” It involves preserving a human body (or just the head) at extremely low temperatures after legal death, with the hope that future technology will be able to revive and heal them. Nobody has ever been revived from cryopreservation, and no technology currently exists to do so.
Two organizations dominate the field in the United States. Alcor, based in Scottsdale, Arizona, has 234 patients in cryopreservation and 1,444 living members. The Cryonics Institute in Clinton Township, Michigan, houses 250 patients in its facility. A newer company, Tomorrow Biostasis, operates out of Berlin and stores patients at a facility in Rafz, Switzerland, while also expanding into the U.S. market. Between 1,500 and 5,500 people worldwide have signed up for future preservation.
One critical legal detail separates cryonics from science fiction: the preservation process cannot begin until a person is legally dead. Starting it on a living person would be considered homicide. So cryonics teams stand by during a patient’s final hours, ready to begin the moment death is declared, because every minute of delay causes more cellular damage.
How the Preservation Process Works
The biggest enemy of long-term preservation isn’t cold itself. It’s ice. When water inside cells freezes, it forms sharp crystals that tear through cell membranes and destroy tissue from the inside out. Cryonics organizations avoid this through a process called vitrification, which replaces the water in tissues with chemical solutions that solidify into a glass-like state instead of forming ice crystals.
Vitrification eliminates mechanical injury from ice and removes the need to find perfect cooling and warming rates, which has historically been one of the hardest problems in cryopreservation. The tradeoff is that the chemicals used to prevent freezing are themselves toxic in high concentrations. Getting enough of the solution into tissues to prevent ice, without poisoning the cells in the process, is a delicate balance that current techniques don’t fully solve for whole human bodies.
Once vitrified, patients are stored in large stainless steel containers called dewars, submerged in liquid nitrogen at around minus 196 degrees Celsius (minus 321 Fahrenheit). At that temperature, all biological activity effectively stops. Research on heart valve tissue stored in liquid nitrogen for up to 13 years found no significant loss of cell viability beyond what occurred during the initial freezing and thawing process. The structure of the tissue, both in the leaflets and vascular walls, remained well preserved. This suggests that once something is successfully vitrified and cooled, storage time itself isn’t a major source of damage.
Why Revival Remains Impossible
Preserving small, simple tissues is very different from preserving and then reviving an entire human body. Several problems stack on top of each other. First, current vitrification techniques don’t penetrate evenly through large organs, let alone a whole body. The brain, which is what cryonics patients are really betting on preserving, contains roughly 86 billion neurons connected by trillions of synapses. Even minor uneven cooling can cause thermal stress fractures, essentially tiny cracks in the vitrified tissue.
Second, the damage that occurs between legal death and the start of preservation is significant. Brain cells begin deteriorating within minutes of blood flow stopping. Even with a standby team ready to act immediately, some degradation is unavoidable. Third, nobody knows how to reverse vitrification in a large organ without causing the very ice formation the process was designed to prevent. Warming must be perfectly uniform, and that becomes exponentially harder as the tissue gets larger.
The most detailed revival proposals rely on molecular nanotechnology: hypothetical microscopic machines that could operate inside the body at extremely low temperatures, repairing damage atom by atom before warming begins. One scenario describes nanorobots clearing the circulatory system at liquid nitrogen temperatures (a process compared to “drilling a tunnel”), stabilizing fractures with nanometer-thick support sheets, and even replacing damaged chromosomes inside individual cells. These proposals are internally consistent and detailed, but they depend on technology that does not yet exist and may not for decades, if ever.
Animals That Survive Freezing
Nature does offer proof that some organisms can survive extreme cold. Wood frogs survive winter with up to 65% of their body water frozen solid, then thaw and hop away in spring. Tardigrades, microscopic animals barely half a millimeter long, survive temperatures near absolute zero by entering a state called cryptobiosis. They’ve even survived exposure to the vacuum of space in low Earth orbit.
Researchers studying tardigrades have found that specialized proteins play key roles in their survival. Some of these proteins act as molecular shields, protecting cell structures from damage. Others help stabilize muscle filaments, locking the animal’s body into a rigid state that maintains structural integrity while metabolism essentially shuts down. Tardigrades also produce a sugar called trehalose that helps protect cells during desiccation and freezing. The exact mechanisms are still not fully understood, but the combination of structural reinforcement and chemical protection allows these animals to enter a reversible state of suspended animation.
The catch is that tardigrades are tiny, simple organisms. Scaling their survival strategies up to a 70-kilogram human with a complex brain is not a straightforward engineering problem. It’s closer to a fundamental biological puzzle that hasn’t been solved.
What It Costs
Cryopreservation is expensive, though the range is wide. At the Cryonics Institute, basic preservation starts at $28,000 to $35,000, but adding a standby team and field cryoprotection (chemical treatment at the site of death rather than at the facility) pushes the cost to $106,000 to $128,000. Alcor charges $80,000 for neuropreservation (head only) and $220,000 for whole-body preservation. Most members fund their arrangements through life insurance policies, naming the cryonics organization as the beneficiary.
These fees cover not just the initial preservation but also indefinite storage. The organizations maintain trust funds designed to keep patients in liquid nitrogen for as long as it takes. Whether those funds and institutions will survive the decades or centuries needed for revival technology to emerge is another open question entirely.
The Honest Bottom Line
Cryostasis as science fiction portrays it, freezing a living person and waking them up later, is not real. Cryonics, the practice of preserving legally dead people at ultra-low temperatures, is real and actively practiced. The preservation side of the equation works reasonably well for small tissues and is improving for larger structures. The revival side doesn’t exist at all. People who sign up for cryonics are making a bet: that the information encoded in their brain’s structure survives the preservation process, and that some future civilization will develop the technology and motivation to bring them back. It’s a bet with no guaranteed odds, but it’s not pure fantasy either. The science of cryopreservation is genuine, even if its most ambitious application remains firmly in the realm of hope.