The November 2004 issue included "Holes in the Missile Shield," by Richard L. Garwin, a topic that attracted volleys of letters from all sides. David Caccia of Honokaa, Hawaii, found an additional hole in the shield: "If an enemy nation could produce only a few nuclear weapons, would it risk sending them on rockets, which have a considerable chance of malfunctioning? And even if the launch was successful, the country could expect retaliation. Wouldn't it rather transport a weapon to one of our cities in a shipping container, which would have a much better chance of reaching its target and also leave no trace of its sender after detonation?" But Taras Wolansky of Kerhonkson, N.Y., saw a hole in one of the arguments against a defense system: "The Soviets went to great lengths to prevent the [Reagan administration's] Strategic Defense Initiative. Perhaps they understood that to make use of those 'easy' countermeasures, they would have to rebuild their entire ICBM arsenal every time the Americans tweaked their detectors." Other stimulating queries and observations on more topics follow.

I enjoyed "Black Hole Computers," by Seth Lloyd and Y. Jack Ng, but have two questions: When the radius of the space being measured in the sidebar "Computing Spacetime" doubles, wouldn't the maximum number of satellites allowed in it increase eightfold rather than double, allowing the same spacing of satellites without exceeding the critical density?

Also, what would be the effect of relativistic time dilation on a particle (and its encoded information) from the perspective of a frame of reference outside a black hole? Would relativistic time dilation cause the particle and its information to appear to "freeze" on the surface of the event horizon from the perspective of an outside observer, thereby conserving the amount of information available to the universe outside the black hole?
Michael Sklar
Huntington Woods, Mich.