Re: Ship's computers

>> If the chips were completely enclosed in a conductive, grounded shield, the
>> EMP could not reach them.  With fibre-optic cables entering the shield, the
>> chips inside would be relatively safe.
>
> Are you sure? If so, why is EMP a problem? Most machines have earthed, metal
> shells, mainly to prevent them from causing radio interference.

That's what the fiber-optic cables are for -- most EMP is carried into
equipment by the wires, which act like antennas.  (BTW, a friend just asked
me about "fiber optic power cables".  A good question...)  For best
protective effect, the metal enclosure should also be spherical -- such a
structure is known as a "Faraday Cage", after EMP pioneer and discoverer of
the solenoid Michael Faraday.  Note that a Faraday Cage doesn't depend on
being "grounded" -- just on the fact that the electrostatic force is an
inverse-square law (in normal space-time, my friend comments.  Relativistic
speeds and jumpspace are an interesting question...)  (Another good question
- -- what does "ground" or "earth" mean in this context, anyway? -- It seems
to me that with the EMP-generating device and its target insulated nearly
perfectly from each other and the rest of the universe, the electromagnetics
get pretty complicated -- particularly since there are probably also a bunch
of charged particles flying around...)

Sigh.  Looks to me like it's time to pitch the "fiber-optic" explanation, and
just describe these computers as "hardened" (in the military sense).
Otherwise, the physics gets too hairy to be fun anymore.  Note as well that
one would expect that there are better ways than EMP to selectively attack
complicated computing machines this far in the future anyway...

					Bart Massey
					..[email removed]
					..[email removed]