[ExI] Ultra-cryonics

[Anders Sandberg]

Short version: ultra-cryonics is probably not worth the effort because 
it is hard and expensive to reach the outer system, and the preservation 
benefits are offset by risk and radiation.


Chemical reaction rates follow the Arrhenius equation, r=A*exp(-E/kT), 
where A is a constant, E the activation energy, k the Boltzmann constant 
constant and T the temperature. If you want the ratio between r at 
temperature T1 and T0, it is r(T1)/r(T0) = exp(-(E/k)(1/T1 - 1/T0)). So 
if we have a reaction where E is a few tens of kJ/mol (seems typical for 
biochemistry) I get E/k around 1000, going from T=300 K to 77 K would 
give us a rate reduction of 0.00006 - more than four orders of 
magnitude. Going down to 4 K gives 107 orders of magnitude(!).

This is also why it might not be much use in doing ultra-cryonics: fast 
reactions you can stop this way will already have happened before you 
chill the body deep enough. Still, I was a bit annoyed at seeing a mere 
four or five orders of magnitude for standard cryonics: that would make 
a few decades equivalent to a day of chemical decay. However, I suspect 
the lack of liquid diffusion and the non-linearities in the real world 
(A is temperature dependent to some extent) might make things better - 
it would be interesting to do the calculation carefully for a few 
example enzymatic and non-enzymatic reactions important for body 
deterioration.

On 19/03/2013 01:51, David Lubkin wrote:
> Would any measures be required to safely cool a patient to 50°K or to
> as low as 4°K beyond what we do today to cool him down to LN
> temperatures?
>
> Would our current suspension procedures have to be (or ought they be)
> modified for new patients, knowing they would be stored at a lower
> or much lower temperature than LN?

I would assume there is not much change, since the big problem is 
getting core temperatures down fast, and get them below freezing without 
ice crystal formation: the final temperature is not a part of the analysis.

However, the amount of strain due to thermal contraction is roughly 
proportional to the temperature difference. Going to 4 rather than 77 K 
means 32% more strain. The yield strength goes up a bit for materials as 
you cool them, but which one wins depends a lot on the material - I 
suspect things are really complicated because of the different thermal 
expansions of different components. See http://goo.gl/CBB21 for more fun 
materials physics.

One obvious problem is that launching something into the Kuiper or Oort 
cloud is going to require a rocket. A dangerous, vibrating, occasionally 
exploding rocket.

Launch safety is a real thing. Looking at 
http://www.spacelaunchreport.com/log2012.html shows around 7.7% of 
launch failures. Is the improved storage viability worth a fairly high 
chance of getting incinerated?

I don't know what vibrations a frozen body can handle. The early Saturn 
launches had 5 G vibrations at 11 Hz, and looking at figure 1 of 
http://www.scielo.cl/pdf/ingeniare/v14n3/art09.pdf suggests that the 
space shuttle is a bit milder. A frozen body has a higher speed of sound 
(~3890 m/s for bubble free ice at -20, 
http://www.physik.rwth-aachen.de/fileadmin/user_upload/www_physik/Institute/Inst_3B/Forschung/IceCube/publications/aachen_SpeedOfSound_preprint.pdf 
vs 1540 m/s in soft tissue) so the new resonant frequencies would be a 
few times higher. So there are some definite issues here about whether 
this shaking might cause cracking.

Cosmic rays are definitely something to consider. Long-term storage 
means that you integrate the radiation flux across the storage time. In 
interplanetary space cosmic rays would give humans 400-900 mSv per year.

The biological effect on a frozen body will be somewhat different to an 
active body. In active bodies, when you reach a few Sieverts you get to 
fatal acute doses, so that suggests the viability of storage is just a 
few years if the effect is like getting all the damage at once. In 
active bodies self-repair can do some pretty nifty things: Albert 
Stevens survived 64 Sv over 21 years after being injected with plutonium 
in 1945. But I suspect a frozen body just accumulates damage. Adding a 
lot of shielding seems to be a good idea: if going to the outer system, 
you might want to bury the body inside a Kuiper belt object.

BTW, going for the Oort cloud also means you will be outside the 
termination shock, which apparently reduces the < 1 GeV rays by 90%.



-- 
Anders Sandberg,
Future of Humanity Institute
Oxford Martin School
Faculty of Philosophy
Oxford University