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You accurately report the recent NASA Senior Review evaluation for Gravity Probe B (online news, 20 May) , but not the true complexities of the situation. There are two distinct issues. First, the actual progress of the GP-B data analysis; and second, the long standing lack of a clear "home" for fundamental physics missions within …

I was very interested by commentary by Lawrence Krauss on the statement by 95 scientists outlining a series of unilateral steps that the US could take to reduce the global threat of nuclear weapons (10 May, p 54) . I fully agree with the steps outlined, but I think there are further steps that should …

The debate about the legal time limit on abortion is not, or should not be, about the instances of fetuses surviving premature birth before 24 weeks (17 May, p 6) . It should concern the likelihood that fetuses suffer pain after 20 weeks of age. The editor writes: • Most neurologists who study the fetal …

Phil Stracchino objects to instant run-off voting (preferential voting) on the grounds that in some cases a candidate who is acceptable to most voters will be eliminated by a low score of first preferences (3 May, p 20) . The same would apply to first-past-the-post voting, which would give a result at least as bad …

I very much enjoyed Stuart Kauffman's article and sympathised with his expression of a need to "build a sense of the sacred that encompasses all life and the planet itself" (10 May, p 52) . He describes his project as "a reinvention of 'God' ", but his ideas already have a name: pantheism. From Steve …

Had I been able to comment on Richard Weller's article on the classification of cosmetics (3 May, p 18) before it was published, I may have been able to forestall some misunderstandings. It is true that cosmetics companies employ extremely competent scientists who perform high-quality research. Much of that research is published in peer-reviewed scientific …

A few years ago (24 November 2001, p 34) you published an article about research by Sue Scott and Christopher Duncan which theorised that the Black Death was not, as has been believed for the past hundred years or so, bubonic plague. I have since found considerable information on the subject, particularly in the work …

Could the rise in numbers of inedible whales in a declining population (10 May, p 41) be a predictable survival strategy? It would be interesting to discover whether "stinky whale" syndrome is an environmental response or a hereditary trait. That might be an opportunity for a genuinely useful piece of scientific whaling.

Feedback is puzzled by why anyone would want a duffel bag waterproof to a depth of 300 feet (3 May) . It would be of immense use for holding exactly the items that Feedback suggests – the box of matches, sandwiches and change of underwear – for a cave-diver, who might reach an air-filled passage, …

What's really scary is if a "flash gun" made up of nothing but LEDs, some electronics and a battery – something that looks like a torch – can live up to the claims that it can "knock people flat" (10 May, p 38) . Five minutes after it comes onto the market someone will figure …

Harro Drexler takes it as read that a carbon tax should be applied at the point where the fossil fuels are extracted (17 May, p 22) . This is far from clear. What if the fuel is not used to produce carbon dioxide but, say, plastics which may be recycled indefinitely? What about non-fossil fuels? …

Robert Matthews's examination of Karl Popper's criterion that scientific hypotheses are defined by their falsifiability, and of alternatives like Bayesian probability, provides an illuminating view for modern physics (10 May, p 44) . Particularly at very large and very small scales, physics sometimes lacks the comfortingly straightforward Newtonian cause and effect that is so easily …

I see Ning Zeng is considering burying wood to lock up carbon dioxide (3 May, p 32) . I agree with him that we should be growing the wood, but has he not realised that the burying has already been done by nature long ago in the form of coal? Why not simply leave the …

• The map with the article "Vote of no confidence" showed Minnesota with 32 votes in the electoral college that selects a US president (12 April, p 30) . It has 10.