On my right wrist is a new addition: a small metal tag, wide as a finger and a shade narrower than a human wrist, held on by a light but tough metal chain. Etched deeply on the tag are terse instructions, alert procedures, and the symbol of a caduceus: in an emergency a paramedic might mistake it for a medical alert bracelet. The resemblance is intentional, but this bracelet does not alert paramedics to an emergency treatment designed to save my life. Instead it describes a biostatis protocol designed to preserve my corpse for cryotransport - or, more succinctly:

If I drop dead, freeze my head and ship me to Arizona.

I am a candidate for cryonic suspension: the freezing of grieviously ill patients in the hope of reviving them later when more advanced technology can cure their ills. The idea is familiar from popular culture - you can't swing a dead cat in LA without hitting an actor that's been frozen, suspended, downloaded into a computer - but few realize that people have been cryonically suspended in reality for over thirty years.

A number of questions leap to mind. Are you serious? Yes, very. How on Earth did people come up with this idea? As we learn more about life and how it works, our idea of death has slowly marched back. Once we believed life required breathing; then we learned to restart breathing and life merely required a beating heart; then we learned to restart hearts and life merely required a functioning brain. Now, we know that death is simply a natural process: when cells are no longer supplied with a source of energy, they stop maintaining their structure in the face of entropy and slowly begin to disintegrate in varied and complex ways.

But the march of entropy is slowed by cold. When a body is frozen, that disintegration stops almost completely, and most of its structure - most of its important structure, despite the damage done by freezing - is preserved. But while a body is frozen in timeless slumber, the march of science is not. As the boundary of life and death continues to be pushed back, the body remains in its frozen state. A cryonicist is simply making a bet: given time - given enough time - the ability of medicine to repair damage to a body will exceed the damage that disease and cold have done to it, and what appeared to be a dead and frozen corpse will once again become alive.

It's a familiar concept - in fiction. Recent popular movies like Artificial Intelligence and Vanilla Sky feature the concept of freezing or chilling someone to preserve their life. Earlier, spacecraft in genre movies like Alien and 2001 routinely put their crews in frozen "hibernation" to reduce the cost of long journeys, and before that, science fiction authors like Larry Niven built large chunks of their careers around words like "corpsicle".

One could argue that this merely dresses up an older fantasy idea with a little scientific gobbledygook to make it sound possible: after all, Rip van Winkle did not need to be frozen to see future wonders. But the idea of preserving and reanimating the dead existed in science before science fiction existed: Benjamin Franklin's speculations on the topic are the most famous example, though Marcus Aurelius' musings about the dissolution of the patterns that made up his body make me suspect that ever since Democritus put forth his atomic hypothesis, philosophers have been wondering whether Humpty Dumpty could be put back together again.

But no matter how far back the history of informed speculation has been, I precisely do want to argue that preservation and reanimation is simply a dressing up of an older fantasy idea: that of the afterlife. Are the elaborate preparations a body undergoes prior to cryonic suspension really so different from the elaborate mummification procedures Egyptian nobility went through prior to being interred in their pyramids? After all, both were and are carried out at great expense by dedicated people who believe seriously that the complex rituals they perform will give their patients a shot at a second life they have never seen. Are these rituals any different to the burial rituals performed by cavemen twenty thousand years earlier?

Really, how is belief in cryonics any different from belief in a religious afterlife?

Speaking as someone who passionately believes in both, I can see a few distinctions. Religion and science are very different beasts. Religion, like the "philosophies" of the ancient Greeks, identifies and preserves deep truths that believers use to structure their pictures of the world and to choose the values that shape their lives. Science, in contrast, collects new knowledge relentlessly and winnows it mercilessly, fine tuning the abilities of its practitioners to explain their world and to technically manipulate it.

In this view, religion is the keeper of very robust knowledge that rarely changes - murder is still wrong, millenia after Moses came down from the mount - but these truths must be accepted on faith because they are not useful for prediction. Science, in contrast, is the keeper of validated knowledge: knowledge backed by argument and evidence and which can be used to predict and act - yet paradoxically, this validated knowledge is subject to change each week as new evidence arrives. Because of these differences, there is a fundamental asymmetry between the two kinds of afterlife.

A religious afterlife is a given. It is not a mere possiblity, but an actuality: a fixture of a believer's universe without which the universe would be meaningless - if not inconceivable. With respect to the elegant arguments of Christian apologists like C.S. Lewis, the afterlife needs no justification: only faith.  A scientific afterlife does not have such ontological luxuries. First, it is not an afterlife at all, but an extension of this life beyond its typical end. Second, a scientific afterlife isn't really scientific, either; it is engineering, a proposal marrying current scientific models with projected technical capabilities. The scientific afterlife offers no guarantees, only possibilities based on knowledge that might be invalid.

And those possibilities are tentative: engineering makes no guarantees. No matter how carefully a system is prepared, there is always some chance, some tiny epsilon, of failure. And even if a cryonic system could be guaranteed to function correctly every time, there is no guarantee that circumstances would enable the technique to be applied to any given person. With all the things that can go wrong at the end of someone's life, what chance does anyone have of cryonic survival even if the machines could work perfectly?

I have argued that cryonics is engineering, and engineers are taught to begin with rule-of-thumb estimation, ballparking the range of reasonable answers before detailed calculation begins. The technique is so valuable everyone can learn to do it - pick a rough model of the phenomenon, find reasonable estimates of each value, and run the numbers. It may be wrong, but it is a start that is more valuable than pure intuition because it helps improve your understanding of the problem. As a start, you can do this yourself to estimate the success rate of cryonics.

Choose a simple assumption - for example, you might argue that you need to have a whole brain in order to have a reasonable shot of being reanimated as the same person. With that assumption, now ballpark the number of people who die each year, and the number of people who die in ways unsuited for even the best cryonic suspension - murder victims who are autopsied, traffic victims who are burned, Alzheimer's victims who "die" before they die - and you may find the result to be sobering.

But engineers - whether they are civil engineers accounting for wind shear on a bridge or software engineers modeling the cost of manipulating a priority queue - are taught to go beyond the back of the envelope and to methodically identify the factors relevant to the problem based on known models of the phenomena and to then analyze how those factors impact the solution. And based on the models at hand, an engineering analysis supports the idea that reanimation of a cryonically suspended corpse is possible - while achieving it will require the development of novel technologies, it violates no known fundamental limits of physical law.

However, applying the same kind of mental discipline reveals that while that cryonic suspension is possible it will be extremely difficult to achieve technically. Moreover, cryonics requires so many factors to work in concert that it appears extraordinarily unlikely to succeed in any given instance - the epsilon of error in the equation grows to dominate the other factors. Nerve cells begin to degrade rapidly after blood flow stops. Freezing destroys the very structure it is designed to preserve, turning tissue into an frozen mulch of ice crystals. And the mathematics of reconstructing those trillions of cells is daunting, to say the least.

How could this ever work?

But the beauty of engineering is that once a technical challenge has been identified, it can be addressed. Procedures that ensure cryosuspension begins as soon as possible can minimize nerve damage. Cooling the body slowly can "vitrify" the tissue, preventing ice crystals from forming by turning cells into perfectly preserved glass. And to rebuild those cells, science is actively pursuing nanotechnology to manipulate matter on an atomic scale. Which brings us back to the cryonicist's bet - that technology will improve to the point that even an imperfectly preserved corpse can be animated by a sufficiently advanced technology.

This bet is not "magical", but is grounded in the nature of science as a self-improving enterprise. While scientific knowledge is volatile, it is not ephemeral. Scientific knowledge is ruthlessly revised every day, and the result of centuries of this effort is that over time the bulk of scientific knowledge gets more and more accurate. Similarly, the capabilities of engineers building on that science grow more and more powerful.

As a consequence, many seemingly implausible dreams put forth by informed scientists have a way of becoming true. Davinci's dreams of flight have long since been achieved and surpassed. Kepler's fantasies of space travel were longer in coming, but they too have been realized. Archimedes spoke of moving worlds, and scientists now seriously debate how to move asteriods from their orbits to preserve life against a catastrophe like that which killed the dinosaurs. And preserving life brings us back to the dreams of Ben Franklin.

Religious faith in the afterlife is, in a sense, easy: I do wait in joyful hope for the coming of the Kingdom, and that hope is a sustaining one. Scientific faith in cryonic suspension and nanotechnological reanimation is much more challenging: for it to be meaningful you must accept that you will to die. Opting for cryonic suspension is a pragmatic choice, based on the scientific evidence, that gives you a razor-thin chance to prolong your life by an unknown amount --- but you will still die, even if you are revived; just later, rather than sooner.

The same laws that make cryonic suspension even remotely feasible mean that even if you are reanimated you will still die. Your odds will be better, but modern science predicts that all life must inevitably come to an end. Even if you choose not to buy our current cosmological theories, which predict that all matter in the universe will ultimately fly apart into cold, isolated particles, utterly alone, you must face statistics. You are a system. There is a nonzero probability that any system can break down. Given a long enough time any system that can break down inevitably will break down. Logically...

This means you.

By hook or by crook, you will still die, one day, when your heart stops ... or the stars grow cold.

But to see the stars grow cold! Even a long shot at such an incredible adventure seems worth it for most who sign up. To paraphrase Tyler Durden from Fight Club: You have to realize that one day you will die. Until you know that, you are useless. When you know that, you can do anything.

If you can't face that, don't put on the tag.

See you in 15 ... or perhaps 15,000,000?
- The Centaur
Renaissance Engineer