X-Message-Number: 4721 From: Ralph Merkle <> Subject: SCI.CRYONICS Cold Start Date: Sat, 5 Aug 1995 06:51:00 PDT "Cold Start," by Ralph C. Merkle, Cryonics 11(11), November 1990, page 11. There are basically two ways to build a brain. The conventional method takes place in liquid at about 98.6 degrees. The other way takes place when everything is frozen solid at perhaps 140 Kelvins. There's a lot to recommend the first method. It's traditional. We know it works. Why change a good thing? Well, there are reasons why solid-phase construction might be more convenient. The biggest reason: things don't slosh around -- they stay where the're put. There are also no chemical reactions. This is important if building a brain takes a few months or years. The chemicals used in the early phases of construction might otherwise go stale. That said, we should make it perfectly clear that liquid phase construction should be quite feasible and might prove better (though it's a bit hard to say just at the moment). The fact that airplanes work doesn't mean that helicopters don't, and vice versa. Which brings us, at last, to the point of this article. Suppose you've actually built a brain, and suppose further that you've built it using solid-phase construction at 140 Kelvins, you've still got one last problem: how do we warm it up? We'd like to warm it up fast. The more rapidly we can warm it up, the less time there is for recrystallization damage and other bad things to happen. Ideally, it should instantaneously reach 98.6 degrees Fahrenheit without spending any time at the intermediate temperatures that cause damage. Which brings us to a modest proposal: put 10^15 "heating pellets" into the brain as you build it, each one about one micron away from its neighbors. When you want to warm the brain, trigger all the heating pellets at once. Heat need only flow from the pellets to the surrounding tissue, a distance of less than 1 micron. The heat can travel this short distance in almost no time (well, a few microseconds or less). The heating pellets can contain highly reactive chemicals (they need to react at 140 Kelvins!) to provide the energy. The pellets can be large enough to hold a molecular size "trigger" mechanism. And there'd better be a tough outer casing around the reacting chemicals to prevent them from escaping into the tissue. We need to know two things: how much energy is required to warm up the brain? And how much energy can we get from a chemical reaction? We can approximate the energy required to heat the brain by the energy required to heat 1.4 kilograms of ice from 140 Kelvins to 310 Kelvins. The heat of fusion of water is 333 kilojoules/kilogram, the specific heat capacity of ice is 2220 joules/kilogram-Kelvin, and the specific heat capacity of water is 4190 joules/kilogram-Kelvin[1]. (We neglect the fact that the heat capacity of ice is lower at lower temperatures. This just means we'll conservatively overestimate the energy required for heating). To go from 140 K to 273 K (the melting point of water) requires (273-140) x 2220 x 1.4 or 4.4 x 10^5 joules. Melting takes 333 x 1.4 kilojoules, while a further increase of 37 Kelvins requires 37 x 4190 x 1.4 joules. This totals about 10^6 joules (about as much energy as in a "diet meal with 240 calories"). The reaction of hydrogen gas with flurine gas (to name simply one possibility) proceeds rapidly down to about 20 Kelvins. The production of one mole of HF (20 grams) will produce about 2.7 x 10^5 joules[2]. Production of 75 grams of HF from H2 and F2 would generate the 10^6 joules needed to heat a 1400 gram brain. Heating would be finished in a few microseconds -- rapid enough to prevent ice formation (and almost anything else) from taking place during rewarming and eliminating rewarming damage. Extra credit problems: what should you make the "tough outer casing" from to contain the HF (Hydrogen Fluoride)? What pressure will the casing have to withstand? (assume that you can occupy 10% of the total volume of the brain with heating pellets). Find chemicals that react at 140 kelvins which produce a relatively innocuous compound (2H2 + O2 would be ideal, except they don't react at that temperature). Catalysts may be used to help your reaction take place. 1. "Fundamentals of Physics," Third Edition Extended, by David Halliday and Robert Resnick, Wiley 1988. 2. "General Chemistry" Second Edition, by Donald A. McQuarrie and Peter A. Rock, Freeman 1987. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=4721