Letters archive

Everyone who has studied the science and history of marijuana use agrees that prohibition does more harm than good and should end. The votes to legalise it in the states of Colorado and Washington (17 November 2012, p 6) are great steps towards a more rational policy for the US and the rest of the …

While engineers continue to be surprised by the endurance of Moore's Law, which says that computing power doubles roughly every 18 months, we can be certain that Silas Beane's descendants will never get to simulate the universe on a lattice resolution of 10 -27 metres (15 December 2012, p 33) . Today's state-of-the-art memory chips …

If Harold de Vladar is right that game theory can help define the risk of signalling extraterrestrials, one wonders if all attempts at contact are suicidal (15 December 2012, p 11). Unless an alien civilisation is just a few centuries ahead of us technically – unlikely given the age of the universe – on receipt …

Further to your look at the vote against mandatory labelling of genetically modified food in California (17 November 2012, p 28) , nothing Californians eat is natural. The defeated proposal, known as Prop 37, was another attempt by practitioners of the politics of fear to codify a false dichotomy in our labelling regulations. RIP Prop …

"This book will anger many environmentalists," says Fred Pearce in his careful review of Dieter Helm's The Carbon Crunch (17 November 2012, p 51) . It would be more accurate to say that the book will anger anyone with logic, as its arguments are nonsensical. Helm says that existing clean energy technology is expensive, uneconomic …

You reported research suggesting that Earth might once have had a planetary ring, like Saturn (8 December 2012, p 18) . Is it possible that major meteorite impacts on the moon produced such a ring of debris? If so, could the effect on climate have caused the "snowball Earth" events about 2.3 billion years ago?

The rise of small personal drones brings many issues (8 December 2012, p 42) , including for wildlife. I fear that birds in areas where drones will be used could be in for a tough time, especially in war zones, where they might be shot down by mistake.

Regarding the article on flood risks for the world's deltas, there are some further factors worth raising as they help mitigate subsidence (1 December 2012, p 40) . First, Holocene sediments in some deltas include sandy layers – as in Bangladesh – which provide aquifers but do not create subsidence by compaction when the water …

MacGregor Campbell need not worry about the manufacturer of his kettle claiming copyright when he prints a new handle (15 December 2012, p 46) . They are more likely to be concerned that the kettle's planned obsolescence has been foiled. They would prefer Campbell to buy a new kettle.

Your editorial discusses the American Psychiatric Association's failure to agree a new system of diagnosing personality disorders for the next edition of its handbook, DSM-5 (8 December 2012, p 5) . While improving the system would help to ensure that the correct diagnosis is given, the problem of inadequate availability of psychotherapy has not gone …

The inventors of a new train in Japan were not the first to think of gravity-aided public transport (8 December 2012, p 22) . At least some London Underground lines have stations higher than the tracks either side, so that gravity helps to slow the trains' approach and accelerate them as they leave. Clever people, …

I was surprised there was no reference to the Gulf Stream in your look at possible climate change in Europe by 2050 (1 December 2012, p 8) . It clearly has considerable influence on the UK's climate, and I seem to remember an article some years ago discussing the possibility of it ceasing completely. • …

Richard Price's letter decrying the description of a voltage in terms of that generated by AA batteries rather than SI units (8 December 2012, p 32) reminded me of how Richard Feynman tried to make physics understandable. He used many figures of speech to help us visualise things. In his book What Do You Care …

• In our look at the mystery of matter (5 January, p 36) , artwork should have been credited to Daniel Stolle.