Big black holes An alternative explanation of why ultramassive black holes reaching 10 billion solar masses seem to go dormant (“Ultramassive: As big as it gets,” SN: 10/25/08, p. 18) could be that in these black holes, the violent activity associated with smaller black holes is completely contained within the event horizon and thus removed from any observation. The tidal forces at the event horizon, which cause the observable effects, actually diminish as the mass and radius of the black hole increase. At a 30-billion-kilometer event horizon, the tidal force is so weak that the largest stars and gas clouds could approach and disappear within, with little distortion and no fireworks. The ultramassive black hole would sit in quiet darkness, outwardly passive, while violent internal processes were shrouded by a natural cloak of invisibility. But the black hole would be continuously and inconspicuously absorbing its surrounding galactic material, growing ever larger and more massive. More missing mass? Charles Wilkinson, Beltsville, Md.
Robot humor and intelligence I was struck by Leo’s seriousness in “Body in mind” (SN: 10/25/08, p. 24). Instead of opening the cookie box that actually contained the cookie, many people would have made the interaction into a game by opening the requested box and pretending to be surprised when it contained no cookies. Let’s hope scientists never figure out how to give robots a sense of humor. The result could only be mischief, and eventually some small percentage of mischief would turn destructive, as it does for humans. Gail Smith, Seattle, Wash.
I was intrigued by the ideas discussed in “Body in mind” since I have long thought that there is an overemphasis on algorithms in efforts to create artificial intelligence. I remember arguing with a student of Stephen Hawking’s in Cambridge in 1978 that sensors and actuators are essential to intelligence, artificial or otherwise. Antonio Damasio makes a persuasive case for the inseparability of emotion and reason in his book Descartes’ Error. As aptly summarized in three words in John Kent Harrisons’ movie Beautiful Dreamers: “Feeling precedes thinking.” Peter Eisenhardt, Altadena, Calif.
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To be or not to be free It’s hard to convince humans that we don’t have free will when ideas are constantly welling up in our minds (“The decider,” SN: 12/6/08, p. 28). The brain is a high-gain analog computer — that’s how we recognize images so quickly. A biomolecular machine with such high gain is bound to be chaotic. This means that we have ideas that are in the abstract deterministic, but are not predictable in any practical sense. Hence, we have real-world free will. Tom Jaquish, Fort Wayne, Ind.
In regard to “The decider,” is the real issue understanding human accountability in light of modern neuroscience? For those, like myself, who are unwilling to concede responsibility for some thoughts and actions, there is perhaps a concession offered by science. The brain is a complex system. Technically, this means that any future state, such as a decision, is so dependent upon the infinitely precise details of the preceding state of the brain and all its influences, it is generally impossible to predict.
Might it be that somehow deep within mechanistic brain processes there does exist a human ability to really choose, but it will forever elude scientific probing by hiding in the imperceptibly precise details of an infinitely connected world? In other words, might humans be bound to play out their lives in a physical medium that simultaneously provides freedom while masking the reality of that freedom?
This possibility seems consistent with the idea that moral agency is nullified not only in a purely mechanistic world, but also in one where truth is fully transparent and consequent choice unavoidable. Nick Weir, Phoenixville, Pa.
I was disappointed to read “The decider.” Tom Siegfried makes it very clear that he believes in the philosophy of materialism, and the essay suggests that he also believes that modern science supports that philosophy. Siegfried should know that materialism is not a part of the physical sciences. It is metaphysical. Materialism has been disproved as well as Cartesian dualism. You do a disservice to your readers by presenting philosophy as science. Samuel Mistretta, Baton Rouge, La.
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My instruction as an engineer included the admonition to perform a “sanity check” at the end of solving a problem as a way to catch errors. The logical end of considering the brain as simply a machine (paragraph three in “The decider”) is the obvious nullification of the concepts “meaning,” “responsibility” and “justice.” Without such concepts there is no basis for a criminal justice system or for concern over human rights — both of which seem entirely reasonable ideas. I think the issue here is an untestable assumption of philosophy masquerading as science. Gary Wernsing, Beverly, Mass.
Regarding “The decider”: We are an arrangement of atoms, and the result is self-awareness and the universe reflecting upon itself. What a miracle! From here, what a small step it is to aver volition, both weak and strong. Arthur Koestler’s The Ghost in the Machine lives on. C.W. Folse, New Orleans, La.