Letters archive

Tom Stafford notes the ability of a cellular automaton to generate an endless, unpredictable set of behaviours, given the right rules and starting conditions – importantly, not the same starting conditions ( 6 April, p 34 ). I am not clear why this should give comfort to those who believe that free will isn't a …

Stafford's fascinating article on free will argues that if a simple model like a cellular automaton can generate complex, non-linear states, then animals can't be mere mechanistic machines. He suggests that we need choice to navigate and respond to the non-predictable conditions that our complex world generates. I agree. But this might seem to skirt …

Melanie Rimmer is unimpressed with the size of the prize for solving the "P=NP" problem in mathematics ( 20 April, p 15 ) Couldn't you use it to steal all the secrets? Seems that would net you more than £1M

While the article on functional disorders was enlightening ( 6 April, p 28 ), as a scientist I find myself uneasy at the idea that no physical cause can be found. Given that the brain is a physical object, anything that happens in the brain has a physical cause. It may be that functional symptoms …

No one who has had the misfortune to suffer from an invisible illness would use the word "think" so carelessly, as in saying that "we can think ourselves ill". We understand "thinking" to mean consciously having thoughts. People with functional disorders are at the mercy of some neurological dysfunction, which is a little more complicated …

Tony Green notes that according to his kettle, the cup he uses for coffee holds two cups, but his coffee maker thinks it is three (Letters, 2 March ). You report that the UK's National Health Service recommends servings of 80 grams. A standard US serving of fruit , vegetables, meat and fish is 4 …

Madeleine Finlay reports some clean-up solutions for space debris ( 30 March, p 26 ). Who will pay for this? Does the "polluter pays" principle apply in space? I suspect that any clean-up attempts will be funded by national governments, and therefore by you and me. But what about privately funded space missions? How can …

Two questions come to mind on the use of cross-laminated timber (CLT) in buildings ( 16 March, p 33 ). Does it burn well? And do termites eat it? The editor writes: • Tests by the US Forest Service show CLT resisting fire and indeed blasts ( bit.ly/NS-CLT1 ). Early work suggests that it is …

Nick Blackstock reports seeing black leopards in Kenya in 1956 (Letters, 30 March ). I worked in that country during the early 1960s with Gurner van Someren, a member of a noted East African family of naturalists, who in the 1940s sought to prove that black leopards were a separate species. In his role as …

• The proof of the efficiency of a new method of multiplication works only for numbers with more than 10 to the power of 200 trillion trillion trillion digits ( 6 April, p 12 ).