Cryonics is the practice of storing human bodies at extremely low temperatures for the purpose of one day bringing them back to life. The first person to be cryogenically frozen was Dr. James Bedford, a 73-year-old psychologist who was frozen in 1967.
Cryonics began in 1964 with a book titled "The Prospect of Immortality" by physics teacher Robert Ettinger. Ettinger proposed that a person could be frozen and revived once the technology to safely thaw a human body had been developed. In 1967, psychologist Dr. James Bedford became the first person to be cryogenically frozen. By early 2004, the Alcor Life Extension Foundation, one of the world's largest cryonics companies, had 59 patients in cryosuspension.
Cryonic freezing begins once the patient is legally dead. Technicians replace the body's water with a chemical mixture called a cryoprotectant, which prevents cells from being destroyed during freezing. The body is then cooled on dry ice to a temperature of -130 degrees Celsius. Finally, the body is placed in a tank of liquid nitrogen and stored at a temperature of around -196 degrees Celsius.
Cryonics practitioners freeze bodies before brain death occurs for the purpose of potentially reviving them in the future. However, no cryogenically frozen body has ever been revived, and the technology to revive cryonics patients does not currently exist, as of 2015. Since cryonics can cost as much as $150,000, some critics allege that cryonics companies are misleading people by selling them a promise of immortality that can't be delivered. However, cryobiologists hope that nanotechnology may someday allow frozen bodies to be revived by using microscopic machines to repair cell damage caused by freezing, disease and aging.