Over the weekend, Robert Ettinger, founder of the cryonics movement, died at his home in Michigan and was quickly frozen. "We're obviously sad," said his son David in an obituary in The Washington Post. But "we were able to freeze him under optimum conditions, so he's got another chance."

For the uninitiated: Cryonics is the preservation of dead people -- "patients" in cryonics-speak -- at very low temperatures in preparation for a time when medical advances allow them to be thawed and brought back to life. At the top of the page, take a look at the facilities, machines, and people that are working to keep more than 100 people and several dozen animals frozen in the suburbs of Detroit.

A dream of a world where death can be undone raises some nasty ethical problems, but cryonicists are not to be deterred. In a New Yorker profile of Ettinger two years ago (subscription required), Jill Lepore wrote:

But if no one ever dies, won't there be too many people on the planet? "The people could simply agree to share the available space in shifts, Ettinger suggested, "going into suspended animation from time to time to make room for others." There will be no childbirth. Fetuses will be incubated in jars. "Essentially, motherhood will be abolished." Then, too, eugenics will help keep the birthrate down, and deformed babies could be frozen against the day that someone might actually want them, or figure out how to fix them. "Cretins," for instance, or babies born with cerebral palsy. For the weak-minded, who might find making such a decision difficult, Ettinger offered a philosophical rule of thumb: Ask yourself, "If the child were already frozen and it were within my power to return him to deformed life, would I do so? If the answer is negative, then probably the freezer is where he belongs."

Regardless of your position on the movement's moral standing or the odds you'd give of anyone ever being revived, it is clear that cryonics presents an immense technological challenge. How do you freeze a body for hundreds of years? Machines break, electricity fails, people shirk their responsibilities. If a body warms up, even for a short while, decomposition will set in and any hope of awakening will be dashed. (For a fantastic look at the difficulties faced when trying to keep bodies frozen, check out this episode of This American Life.)