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Andy Coghlan wrote: "What's coming to light for the first time is that euthanasia of charges triggers feelings of guilt, remorse and grief in many carers but most suffer in silence because the subject is taboo, and they feel they have no way to unburden themselves" (29 March, p 8) . This is of immense …

Feedback laments Arthur C. Clarke's lost opportunity for wealth in relation to "his" idea concerning satellites in geostationary orbit (12 April) . I refer you to a letter published in your magazine wherein M. Michael Brody correctly pointed out that the concept was originally postulated by Hermann Noordung (the pseudonym of Captain Herman Potocnik) in …

Robert-Andrew Horton (12 April, p 19) interprets the fact that we select a partner who resembles ourselves as egocentric, and says that this cannot have evolved as we did not have mirrors until recently. Surely most babies grow up surrounded by people with a passing resemblance to what they will likely look like as an …

When Steve Jones talks about Fridtjof Nansen's polar expedition (19 April, p 48) , he implies that the ship Fram accidentally got stuck in the ice, forcing Nansen to leave the ship and try to reach the pole by dog sled. In fact, the expedition got stuck in the ice on purpose as part of …

• Our apologies to Yianna Lambrou of the UN Food and Agriculture Organization for referring to her as "he" (3 May, p 6) .

Your article on improved voting systems neglects an important consideration: politicians take the voting system into account when campaigning (12 April, p 30) . Changing the system will change politicians' behaviour – and quite possibly the entire political landscape. For example, the "antiquated" electoral college system currently in use in the US ensures that politicians …

Lawrence Krauss writes that "the validity of the anthropic principle rests on the assumption that humans are typical life forms" (29 March, p 46) . Why must humans be "typical" to validate it? My understanding of the anthropic principle is that it says humans observe a universe in which fundamental constants have certain values simply …

The fact that stock market traders who started their days with high testosterone tended to make more money does not prove that the high level was the cause and the money-making the effect (19 April, p 12) . It depends on whether there is "autocorrelation" in the profits. If financial success on Mondays, say, means …

If Ian Fairlie is right to be concerned about cancer near nuclear power stations ( 26 April, p 18 ), what about the radioactive materials and other carcinogens released from coal-fired power stations? These are far greater than emissions from comparable nuclear power plants. Has the issue of cancer clusters around coal power plants been …

Paul Mander takes Feedback to task for saying cubic litres involve nine dimensions as this implies cubing a cube and the cube of 3 is not 9 (19 April, p 17) . He should check his maths. The cube of a number n is n × n × n . Cubing this gives ( n …

In a fascinating article, Michio Kaku errs in stating that "precognition... would represent a collapse of the foundations of physics." In a paper I presented at an American Association for the Advancement of Science meeting in California in 2006, I showed how such reaching back in time is not in conflict with physics and logic …

As the World Health Organization develops its strategy to combat alcohol abuse (19 April, p 6) , those involved should consider whether instead of heavy taxation it might be preferable to implement a licensing system, similar to driving licences. "Drinking licences" could be issued at age 16 on completion of a short course describing the …

Edzard Ernst takes a refreshingly practical approach to alternative therapies (26 April, p 44) . Teasing out the genuine benefits of a therapy from the placebo effect can be next to impossible, as the placebo effect itself can bring about a marked improvement to some conditions. The placebo effect must work by somehow stimulating the …

The notion of capturing carbon dioxide and storing it underground (29 March, p 36) should not be equated with the provision of energy from alternative sources. The process itself would consume large amounts of energy, leading to an increase in the production of greenhouse gases. As long as all these pollutants were stored safely underground …

What an excellent article on carbon trading (19 April, p 38) , exposing its mind-boggling complexity, ineffectiveness and cost. Carbon trading hides from the public both the reasons for higher energy costs and the time we have left to solve the problem of carbon emissions. The simplest and cheapest solution would be to impose carbon …

I nodded my head in agreement as I read Saleemul Huq's article on the research that is useful to developing countries affected by climate change (29 March, p 19) . I have been involved in rural development projects in various parts of the world. In most cases the local people have been bemused and amused …