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Amelia Tait's article on the struggle to get motivated rang a bell with me ( 29 May, p 41 ). When I retired just over 11 years ago, I fully intended to fill my retirement with a whole series of projects. However, first of all I thought I would just relax a little, until several …

I was glad to read that the United Nations, and hopefully national governments, are starting to take the damage commercial farming does to the environment with nitrogen fertilisers seriously ( 15 May, p 41 ). I'm not sanguine about anything being done in the UK in the near future, however, as the agrochemical and farming …

A number of people quoted in the article on the hypothesis of quantum superdeterminism criticise it by saying it would make free will untenable ( 15 May, p 36 ). Setting aside that this criticism confuses the desirable with the real, free will doesn't need determinism (quantum or otherwise) to make it untenable. All it …

You report that a passenger's expectation of jet lag is the strongest predictor of how severe it turns out to be ( 15 May, p 16 ). As a business traveller, many of my trips follow the same route, with similar departure and arrival times. My expectations are informed only by previous experience. I can …

In your look at Japan's promotion of a hydrogen economy to coincide with the Olympics, you mention the Suiso Frontier bulk carrier vessel, which will ship liquid hydrogen from Australia to Japan ( 29 May, p 18 ). It will carry 1250 cubic metres of the stuff, although some will boil off en route. To …

I was with you all the way in your leader on the need for change to tackle the climate emergency, and I also agreed with a lot of what Graham Lawton said in his article ( p 40 ) about trying to make sure our pensions are invested in an ethical way that helps, rather …

Your leader concludes that "capitalism created climate change". Sure, but only if you classify China and the former Soviet Union as capitalist economies. China is building more coal-fired power stations than the rest of the world combined and has plans for even more. As for the Soviet Union, take this analysis from Alexander Prishchepov at …

Quite apart from the evidence suggesting we need a massive economic shift away from carbon emissions right now to have any chance of stopping runaway global warming, capitalism isn't about meeting people's needs, let alone environmental ones. Economic growth is a tenet of capitalism and contradictory to the constraints of living on Earth. The statement …

The quantum internet may not solve all our security problems ( 29 May, p 36 ). While any technology that reduces the ability of states and criminals to conduct surveillance and sabotage is to be welcomed, quantum communications are unlikely to be enough without a lot more technical work. Another possibility is post-quantum cryptography. This …

Michael Overholt wonders why a small primordial black hole wouldn't grow into a giant during the time when the universe was young ( Letters, 5 June ). At that point, the universe consisted of gas or plasma that was fairly uniform. Although the black hole could attract gas near it, gas further away would have …