From: kqb@cbnewsl.cb.att.com (kevin.q.brown)
Subject: Re: How Cold Is Cold Enough?
Organization: AT&T Bell Laboratories
Date: Wed, 22 Jul 1992 23:02:30 GMT
Summary: quantum tunneling does not threaten cryonics

[ The article "How Cold Is Cold Enough?" shows how reaction rate decreases
  dramatically as temperature decreases.  It does not, however, specifically
  address quantum tunnelling as a potential source of unwanted reactions at
  cryogenic temperatures.  The article appended below treats that quantum
  tunneling objection. - KQB ]

---------

Sloppy Science, Continued, Or: Does Quantum Mechanics Threaten Cryonics?
by ALCOR Staff

Cryonics, March 1986 7(3), pp. 29 - 32.
ALCOR Life Extension Foundation, 12327 Doherty St., Riverside, CA 92503

The February, 1986 issue of SCIENTIFIC AMERICAN contains an article
by Soviet scientist Vitalii I. Goldanskii, which concludes with the following
provocative statement:

    "The fact that tunneling allows chemical reactions to occur at
  extremely low temperatures adds yet another reason for doubting the
  possibility of reviving complex organisms that have been frozen a long time."

The basis for this obvious reference to cryonics (not cryobiology:
cryobiologists don't freeze complex organisms for a long time, and the simple
organisms, cells, etc., they do freeze for long times seem to do just fine) is
the existence of what Goldanskii calls the "quantum low temperature limit" on
thermal suppression of chemical reaction rates.  A few words of explanation of
this concept are in order.

Cryonics is predicated on the premise that low temperatures suppress both
chemical and physical reactions virtually completely, which is the reason
indefinite biological preservation is possible.  This notion is well supported
by both experimental work in cryobiology and by the Arrhenius equation, which
reliably predicts vast reductions in chemical reaction rates with
reductions in temperature (see Hixon, CRYONICS, 6(1), 19-25, Jan, 1985)).
In fact, the predictions of the Arrhenius equation are undoubtably
conservative because this equation assumes no changes in the ability of
molecules to diffuse together so as to make reactions possible.  At
temperatures below the glass transition temperature (-130 C or thereabouts),
however, diffusion is for all practical purposes abolished, as all the
reactive molecules are frozen in place.

The reason low temperature suppresses physical and chemical events is
because these events require a certain amount of energy, called the
activation energy, in order to proceed.  At cryogenic temperatures,
thermal energy is so much less than the activation energy that thermal
motions cannot be converted into chemical or physical events.

But quantum mechanics, as usual, makes life more complicated than this.
According to quantum mechanics, atoms and electrons are not just particles
but are also waves, and their positions are not precisely defined.  Because
of this uncertainty in position, there is a finite chance that an electron
or atom will suddenly appear in a location it does not have the energy to
reach.  According to Goldanskii, this effect, in which an atom or electron
"tunnels" through an energy barrier rather than passing over it in the usual
way, could allow chemical reactions of relevance to cryonics to occur at
liquid nitrogen temperatures or even below and might seriously limit the
amount of time someone could be stored pending development of revival
technology.  In fact, Goldanskii presents several examples in which chemical
reaction rates continue unabated as the temperature is lowered from as high
as 120K (-153C) down to 4.2K (-269C).  In one example involving the
polymerization of formaldehyde, the reaction rate at 4.2K was 110 orders of
magnitude higher than the reaction rate predicted by the Arrhenius equation!

Both cryobiologists and cryonicists have long been aware of the time
limits imposed by the free radical reactions caused by cosmic rays,
normal background radiation, etc.  It is known that these reactions
can occur, at least to a point, even at very low temperatures.  But it
is also known that irradiation is less damaging to frozen living
systems than to living ones, even though no repair can occur in the frozen
state.  On the basis of available information, estimates anywhere from
300 to 30,000 years have been proposed for the storage limit imposed by
injury from this source.  In reality, since this type of damage ought to
be easily repairable by a mature nanotechnology, it is actually likely
that the real time limit in the light of such technology is longer than
these conservative guesses which place no burden on future repair.  Since
it is hard to imagine repair technology not being available 1,000 years
from now (the probable minimum available storage time), cryonicists have
justifiably felt that this particular limit is irrelevant.

Does quantum tunneling represent an additional, previously unrecognized
source of damage at liquid nitrogen temperature which seriously shortens
the time available for revival techniques to be developed?  Judging from
the data in Goldanskii's article, at least, the answer is an emphatic no!
Goldanskii's suggestion, at least based on the experimental evidence known
to him as reported in his article in SCIENTIFIC AMERICAN, is instead
just one more example of sloppy science, or at least sloppy science writing
similar to others we have considered before in these pages (see CRYONICS,
6(1), 7-11 (Jan. 1985)).  Consider the following problems.

In the first place, every single one of the examples mentioned by
Goldanskii appear to be free radical mediated reactions which can only
be initiated by such means as bombarding the specimens with electron
beams or gamma rays.  Whether you call the resulting reactions tunneling
or not, they have already been assessed by biologists as described above
and found to be essentially irrelevant.  Goldanskii's examples offer no
evidence that biologically relevant, non-free radical mediated chemistry
is known at cryogenic temperatures.  Indeed, biological melecules are
rather inert compared to the types of reagents studied by Goldanskii and
other workers in this field, such as sodium hydroxide solutions and
chlorine gas, and far less likely to react at any temperature.

In the second place, the reactions observed appear to have been obtained using
pure substances as reactants.  For example, the polymerization of formaldehyde
was achieved by irradiating pure formaldehyde.  But this sort of experiment
really says essentially nothing about what might happen to frozen patients
for several reasons.  For one thing, if nothing is present but formaldehyde,
it is not necessary for diffusion to occur in order for a molecule to be
added to the chain, since formaldehyde is always available near the required
site by default.  In contrast, the inability of most molecules of interest in
a frozen patient to diffuse to participate in chemical reactions of any kind
will greatly limit the range of possible events, even given tunneling.
In addition, these molecules will be surrounded by vast excesses of water and
cryoprotectant molecules which will not only shield them from each other but
which will also make tunneling across these barriers virtually impossible.
Goldanskii in fact admits that molecular separation drastically reduces the
potential for tunneling reactions, but he fails to take this into account
in predicting the fate of frozen biological systems.  The final reason using
pure substances as reactants is misleading is that the probability of even
free radical reactions depends on the concentration of potential targets.
If there is nothing in the sample for a gamma ray to hit but formaldehyde,
it will hit formaldehyde.  But if the sample consists of 80% water and
cryoprotectant, most hits will be irrelevant.  Most biological molecules
are present in very low concentrations as opposed to the 100% concentrations
studied by Goldanskii.

The third reason Goldanskii's proposal doesn't wash is that the temperatures
at which Goldanskii observed tunneling are so low as to make the reaction
rates produced by tunneling negligible.  For example, the tunneling
phenomenon in the formaldehyde polymerization reaction began to be 
appreciable only at temperatures below roughly -173C, behaving as predicted
by the Arrhenius equation down to that temperature.  The tunneling
reaction declined with temperature down to about 10K (-263C), at which
temperature it was equivalent to the rate which would have been predicted
by the Arrhenius equation at about 50K (-223C).  Big deal!  If we've been
willing to accept injury on the basis of Arrhenius behavior at -196C, any
tunneling effects of the kind postulated by Goldanskii, even if they did
occur, would not be of concern to us based on numbers like these.  In general,
the reaction rate minimums attributed to quantum tunneling occur at 50K or
below, and probably correspond to Arrhenius behavior at -150C or so, ie. to
reaction rates which need not concern us.

Although it is too bad it has been necessary to spend time rebutting
Goldanskii's comment, perhaps a quote from Goldanskii's own article can be
taken to heart: "The eternity is ours, so why not spend a couple of hours."

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