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.

“If you imagine that there is life, and then a borderline, and then there’s death, I think that what we’re going to learn is that there is now a space in between.”

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.