\input buslet
\jmclet
\vskip 30pt
\address 
Prof. Petr Beckmann
Box 2298
Boulder, CO 80306

\body
Dear Petr:

I hope you are well recovered from your bicycle accident. I admire your ability
to overcome misfortune.

I have three disagreements:

1. While escape velocity is 11.2 km/sec, orbital velocity = escape velocity
/ $\sqrt2$ = 8km/sec. Only a small increment in this is required to achieve orbital
altitude .

2. The probabilistic argument on evolution is not so clear. An eye
appearing all at once indeed has negligible probability, even though this
probability is not readily calculated because it isn't known how genes
encode structure -- via proteins perhaps, but then how do the proteins
encode structure.  However, there may have been intermediate light
sensitive organs far less elaborate than an eye that were probable enough
to arise by chance, advantageous enough to be selected, and subject to
further improvement without starting over. One imagines a chain of
intermediate forms, each an improvement on the preceding. Since we don't
see fossils of the intermediate forms, they are supposed to have existed
for a relatively short time.  A light sensitive organ that doesn't form an
image is one possible intermediate. A hard problem is to find
intermediates on the way to a lens.

The mathematics goes like this.  Suppose $n$ structures are involved in
an eye, and each has a probability $p$ of arising by chance.
If only the combination is useful to an animal, then the combination
must arise before it can be confirmed by natural selection and this
has probability $p↑n$ which may be very small.  If the structures are
independently useful, then they can arise in parallel, and can be combined
by matings.  If the structures are only sequentially useful, i.e. the previous
ones must be present before the next one can usefully arise, then it takes
$n$ times as long to get the combination.

3. Your explanation of a nuclear explosion doesn't agree with what I read
in a mischievous book published by NRDC. The conventional explosion
compresses the nuclear material but doesn't hold it together against the
nuclear explosion.  This is accomplished by inertia.  The fission reaction
in U235 or Pu239 has a doubling time of around $10↑{-8}$ seconds once the
device is well compressed.  A computation of the velocities corresponding
to the chemical energy of the chemical explosion indicates that the bomb
should stay together for something like $10↑{-5}$ seconds.  It is
important that the nuclear reaction should not generate enough energy to
oppose the compression until then. Pu240 is spontaneously fissionable so
if a bomb contains too much of it, the neutron multiplication will start
at a high enough level so that there will be too much multiplication
before the device is compressed.

There is an optimal time for the rate of nuclear fission to reach a high
level, and I understand that a neutron generating trigger is used.  An
example from before WWII is a radium, beryllium combination radium emits
alpha particles which have very short range. Alpha particles react with
beryllium to produce neutrons.  If the conventional explosions bring the
radium and beryllium in contact at just the right time, a pulse of
neutrons will occur just when wanted.

Even though all this (indeed more accurate and complete versions) is well
known and published, I suggest you not publish these facts. Nuclear bomb
threats by nuts are rather common. However, the nuts are almost always too
lazy to look up the published information on how bombs work, and
conversation with an expert establishes that the guy doesn't have a bomb.
If nuts and terrorists learn the importance of making their threats
technically credible, a city may have to be evacuated some day.  This is
why I consider the NRDC book mischievous, unless it contains a major piece
of wrong information.

Incidentally, the things exploded in Nevada are always called devices
rather than bombs. This may be just a euphemism, but I suspect that the
terminology reflects the fact that usually they aren't bombs in the sense
of something that could be put in an airplane and dropped or put in a
missile.  The additional apparatus to make it a bomb is usually
superfluous for the underground test, expensive, and complicates the
security problems.  While complete bombs are also tested, there are
presumably security reasons not to distinguish these tests from the others
in public announcements.

I have no classified information, so some of the above may be wrong.

\closing
Best regards,    

John McCarthy    
\annotations
%\vskip 1in
%Enclosure
\vskip 1in
JMC/ra 
\endletter
\end