There are worse ways to die than by freezing. To be sure, it’s extremely unpleasant, but only for a while. At first, the cold gnaws at your skin, which soon goes slightly numb, the blood shunted away from the surface to protect your inner organs. Your body shakes as it tries to gin up heat, your heartbeat quickens, your breath comes faster, but the farther your body temperature drops from its usual 98-plus degrees, the less you feel or understand. At about five degrees below normal, you develop amnesia. As more warmth seeps out, you grow apathetic, then fall into a stupor. Just before you lose consciousness, you may engage in a mysterious activity called "paradoxical undressing"—ripping your clothes off—probably because at this point the blood floods back to your skin and you are suddenly very hot. Your kidneys start to fail. Urine may flow out of you, though you probably won’t notice; nor will you be aware that your breathing has now slowed while carbon monoxide builds up inside you. Your metabolism sputters like an engine out of gas. Your heartbeat becomes erratic. When your temperature sinks to about 75 degrees, your heart stops. Very shortly after that, your brain flatlines.
One of the ironies of hypothermia, the extreme loss of body heat, is that the attendant shutdown of somatic processes can save as well as kill you. A stilled heart and brain need little oxygen. A stalled metabolism slows the breakdown of cells and organs. This is why the frozen can sometimes be brought back to life. It’s also the reason doctors deliberately chill the living; it buys them time to operate on people suffering from cardiac arrest, extreme bodily trauma, and stroke. The virtues of cooling the injured have been known since the Greek physician Hippocrates recommended packing wounded soldiers in snow and ice, but the modern science of therapeutic freezing dates back around 80 years. Emergency-room physicians at the University of Pittsburgh Medical Center are preparing to take the procedure further by removing the blood of people likely to die from knife and gunshot wounds and pumping icy saltwater into their veins, reducing their body temperatures to 50 degrees. This is an unprecedented degree of frigidity, to be imposed with record swiftness. These doctors will flash-freeze their patients to apparent death in order to then have a better chance of keeping them alive.
Innovations like this move us steadily toward a goal that science-fiction writers and not a few scientists have been dreaming of for more than a century—suspended animation by hypothermic means. It was around the end of the 1800s that freezing characters and waking them up in the far future became a common plot device. How far is the fiction from reality today? “I think we’re quite a distance,” says Lance Becker, a leading hypothermia researcher at the University of Pennsylvania. But long-term cryogenic preservation is “theoretically quite possible,” he continues, “and I have no doubt that at some point we will do it.” If the handful of labs that work seriously on the problem pooled their efforts, he suspects, they’d make “very substantial progress.”
The philosophical implication of any advance in therapeutic hypothermia is stark. “If you imagine that there is life, and then a borderline, and then there’s death,” Becker told me, “I think that what we’re going to learn is that there is now a space in between.”
To be clear: cryogenic preservation is not cryonic preservation. Cryonics is the freezing and storing of the dead—or usually just their heads, because of the cost—in the hope that future breakthroughs will make resurrection possible. People who buy and sell cryonic services traffic in magical thinking, not science. In all probability, cryonically pickled brains have already turned to mush.
Freezing the living, by contrast, has empirical research behind it, and the Pittsburgh protocol (bioethicist Arthur Caplan calls it “the Slurpee method”) is not the only form under investigation. Researchers have also been looking at using toxins and oxygen deprivation as a way to cheat death. Mark B. Roth, a biochemist at the Fred Hutchinson Cancer Research Center in Seattle, has found that by giving mice very small doses of hydrogen sulfide (the poisonous chemical that makes rotten eggs smell so bad) or depriving other animals of all but the tiniest amounts of oxygen (a state called hypoxia), he can effectively put the animals into advanced hibernation. Exposed, next, to otherwise lethal cold, they survive for up to 24 hours. Roth has not tested his methods on humans, but several instances of accidental hypothermia plus hypoxia suggest that he’s on to something. In 1999, a 29-year-old Norwegian skier submerged in freezing-cold water for 80 minutes without oxygen and no or little blood flow was revived after three hours, her body temperature having fallen to an astonishing 56.7 degrees. This year, a 15-year-old stowed away in the wheel well of an airplane in San Jose, California, lost consciousness in the thin air and intense cold of 38,000 feet, then stumbled out onto the tarmac in Maui.
So far, no mammal not pre-programmed to hibernate has been frozen for more than several hours and survived, but if humans could decelerate their metabolism the way Arctic squirrels, bats, and bears do, we too might be able to endure the perils of such prolonged slumber: the starvation, the suspension of immunological activity that makes a body susceptible to infection, the immobility that usually destroys muscle tone. Only one primate species is known to hibernate, the fat-tailed dwarf lemur of Madagascar; a few members of a related species in Africa have been made to enter the short-term state of hibernation known as torpor, but only very rarely, or when deprived of food and water in a laboratory. Hibernation is an adaptation to adverse conditions, which means that there must be genes for it. Since we share 98 percent of our genes with lemurs, some researchers suspect we have some of the right ones; we just have to figure out how to switch them on. (Understanding the molecular changes underlying hibernation may do more than inch us toward immortality; it could further the science of resuscitation in the here and now.)
But human refrigeration poses legal and moral as well as scientific challenges. The most urgent involves pinpointing the moment of death. The law currently regards you as dead when doctors can find no activity in the brain stem, but it is vague about how and when to determine that the brain is permanently inoperative or merely dormant. American Academy of Neurology (AAN) guidelines instruct doctors not to start looking for signs of death until a frozen patient has regained a normal temperature; a saying goes, “You’re not dead till you’re warm and dead.” But hospitals vary widely in how long they wait afterrewarming—some as little as six hours, others as much as a week—to make the determination. In 2011, a journal reported the case of a 55-year-old man in respiratory and cardiac arrest who had been cooled down, warmed up, then declared dead after 78 hours. While lying on an operating table the next day, about to have his organs removed, he started to cough. He never regained consciousness, but the takeaway was clear. “The AAN criteria are without a doubt outdated and no longer accurate,” Becker told me.
Now push your imagination further to a time when we can put ourselves on ice for decades or more. Weary of coping with a chronic disease, eager to see how your grandchildren turn out, or curious about life on Jupiter, you ask your doctor to freeze you. (This couldn’t happen today, because it would be considered assisted suicide, but laws can change.) As soon as she says yes, you’d better ask yourself another question: Now that you can jump ahead in time, are you sure you really want to?
We assume that it’s better to be alive than dead. “People are attracted to the possibility of long-term suspended animation or freezing, followed by the resumption of conscious life, because they can regard it from within simply as a continuation of their present life,” writes the philosopher Thomas Nagel in a now-classic essay about death. (It’s called, simply, “Death.”) But life is about more than sheer physical or even mental existence. It’s also about having adequate relationships and living in a tolerable society. If you are revived after, say, 100 years, your new life will in no way resemble your old one. You may find yourself in a glorious utopia or a world of trouble, but existence as you knew it will have been irrevocably discontinued. And unless key members of your social circle froze themselves with you, you’re going to be very lonely.
These scenarios get milked for comedy in Woody Allen’s Sleeper and for tragedy in Planet of the Apes. But the tableau I find the creepiest, and also, weirdly, the most appealing, is conjured by the novelist Margaret Atwood in an essay about cryogenics. A handful of people survive a series of civilization-ending catastrophes, and some of them encounter a preserved head, which they immediately recognize as dinner. Yucky, yes, but it’s what I’d want to happen if that head were mine. I would rather be a post-apocalyptic man’s meal than wake up in his predicament.