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.


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