Immortalist Philosophy

by Max More

Possibility and Prediction

In making a case for the reasonableness of cryonics, we sometimes hear from poorly informed scientists that cryonics is "impossible". What this actually means seems to be this: "I do not understand how frozen people could ever be revived. It is not now possible and I am unable to see how it could be done."

Cryonicists are generally good at poking holes in this way of thinking. We standardly point out that just because someone is unable to see how something could be done may show not that it's impossible, but that the person's foresight or breadth of knowledge is poor. I'd like to sharpen up the typical cryonicist's answer to the pessimist.

Possibility can be divided into several types. A minimal list will include technical possibility, empirical (or scientific) possibility, and logical possibility. Unfortunately these divisions are not as neat or straightforward as some people like to think.

To say that a goal, such as reaching the moon, is technically possible is to say that it can be accomplished with current technology. Even this is vague: Does it mean possible with machines currently in existence? Or machines either in existence or on the drawing board? Or possible with technology that exists somewhere in the universe, whether or not we know of it?

To say that a goal is scientifically or empirically possible, is to say that it's achievement is not ruled out by the known regularities of nature. A goal may be technically impossible, such as going to Alpha Centauri and back in ten years, or moving one galaxy out of the way of another, but it's still empirically possible if it is not ruled out by a basic scientific principle. It's hard to give clear examples of scientifically impossible goals, but perpetual motion is usually regarded as one because of the Second Law of Thermodynamics.

To say that something is logically possible is to say only that there is no contradiction involved in claiming that it can be done. It seems that we can consistently conceive of a perpetual motion machine even though it's empirically impossible. We cannot conceive of 2+2 not being equal to 4, nor of something both existing and not existing at the same time and in the same respect.

The strongest possible objection to something is to show that it's logically impossible. This means that we cannot really even have a coherent idea of what it would mean for something to be the case. Demonstrating that a goal is empirically impossible establishes that, with our current scientific understanding, the goal, even though coherently conceivable, could never be achieved, no matter how long we tried. Showing that something is technically impossible is much less bothersome. It means only that we need to develop new technology to do it. So long as we can show that the goal requires only new technology which is empirically possible we can expect to one day accomplish it, assuming that intelligent life continues, and that the technology is not beyond the capacities of our brains (or of future artificial ultra-intelligence).

Unfortunately, relatively tidy and useful though this conceptual scheme is, a satisfactory account is much more complicated. Philosophers of science and language have challenged the logical vs empirical possibility distinction. It's more a matter of degree than an absolute division. Since logical possibility is taken to depend on the logical relation of the concepts involved, and the concepts may be fundamentally revised when science is revised, what previously seemed logically impossible might become logically and, perhaps, empirically possible (and vice versa). For example, in Euclidean geometry it is logically impossible for the internal angles of a triangle to diverge from the Euclidean sum of 180 degrees. Thanks to Einstein and curved space-time, new geometries have been developed in which the internal angles can add up to other than 180. Similarly, in Newtonian physics it would have been logically impossible for an object to have more than one length or velocity, but special relativity implies that one object can have different lengths or velocities depending on the frame of reference.

Even if something, say backwards time travel, is empirically impossible, there is still some hope. Empirical possibility and impossibility is relative to the prevailing paradigm. That is, while our science may rule out a goal, a radically different future science may allow the achievement of that goal after all. The change in our views about what is possible need not be in the preferred direction however: Relativistic physics imposes limits on velocity not present in classical physics, and quantum mechanics tells us that we cannot have precise knowledge of a particle's position and velocity simultaneously. To say that something is possible in the sense that a conceptual revolution might render it conceivable is a rather weak and unsatisfactory kind of possibility.

Cryonicists like to rely on the distinction between what is technically possible now, and what is empirically possible and therefore eventually likely to be technically achievable. Eric Drexler, in arguing for the achievability of nanotechnology, claims that complex nanomachines violate no physical laws and so are constructable even though we cannot currently do this. Assuming that he has the empirical facts correct, I agree that his statement is reasonable if the claim is that we therefore have good reason to believe that advanced nanotech (and thus reactivation of biostasis patients) is likely to be achievable, I do not think we can conclude that it is definitely possible or inevitable (even ignoring non-technological factors).

Firstly, some things may be empirically possible but too difficult to ever figure out. Perhaps our brains are too limited to ever solve certain problems. Of course no one could be justified in claiming that this is definitely true of some goal. That would require omniscience - a demonstration that every idea and technique that will ever be discovered will be insufficient. We optimists can also cite vast amounts of inductive evidence from the history of science to show that nay-sayers have frequently turned out to be wrong. (See Michael Flynn's "Sixty Astounding Years," in ANALOG January 1990.) Furthermore, we can project the continuous increase in our species ability to control energy and to achieve increasing conceptual subtlety. We can hypothesize that intelligence enhancement technology and artificial ultra-intelligence will abolish the current limits of our brains. Still, we cannot guarantee that anything empirically possible will eventually be achieved.

Secondly, some things may appear to be empirically possible, but only because we haven't fully grasped all the implications of all relevant areas of science. Advanced nanotech assembler technology might just turn out to be impossible for unforseen reasons. In arguing for the plausibility of cryonics, we should therefore make a case for its possibility and probability rather than its uncertainty. To assert that it will inevitably work would be to fall into the intellectual vice of faith. As it is, it's people like Arthur Rowe, who claim that cryonics is impossible, who are taking the position of the devout believer.

I cannot here review the scientific evidence in favor of cryonics. Given that cryonic suspension and our scenarios for eventual revival do not involve anything more than an improved ability to manipulate molecules, and given the apparently unstoppable advance of physical science, what we are doing is probably workable. Perhaps the greatest weakness in our case lies in our relative ignorance of the condition of suspension patients and the integrity of their personality. We need more studies of the microstructure of suspended brain tissue. We also need to know more about the way in which memory and personality are stored. One way of demonstrating our commitment to reason and therefore to strengthening our position with the scientific and critical public is to pursue and examine such research diligently.

Perhaps we can focus more on this goal now that our legal position is more secure.