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Prof. Petr Beckmann
Box 2298
Boulder, CO 80306

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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.

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Best regards,    

John McCarthy    
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JMC/ra 
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