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Regarding your look at the Fukushima nuclear power plant accident 10 years on, I wasn't surprised by the small impact of radiation on life expectancy ( 13 March, p 18 ). A 2011 study of survivors of the atomic bombings of Hiroshima and Nagasaki found that those who got an amount of radiation of less …

Julian Barbour suggests that time may flow in two directions, highlighting that the physics of a billiard ball collision appears the same with time flowing forwards or backwards ( 6 March, p 46 ). That doesn't work if the event is seen as a whole: balls would jump out of pockets and self-assemble in the …

Perhaps at the big bang, time did move backwards and forwards. Our universe moved forwards and the antiverse, with antimatter, moved backwards. This would explain a flaw in the big bang theory over what happened to the antimatter, which should have appeared in equal amounts to matter. Antimatter may experience antitime and antigravity, so in …

The article on the laser thruster to power satellites was fascinating, and got me thinking about another application ( 13 March, p 12 ). Would it be possible to use the same principle to deorbit defunct satellites or push space junk into lower orbits so it burns up in the atmosphere?

Rowan Hooper's plan to eradicate world poverty by spending $1 trillion doesn't mention corruption, which is said to waste far more than $1 trillion per year ( 27 February, p 38 ). Well-overseen pilot projects, like those he cites, may not scale up to well-overseen megaprojects. Do we simply assume that corruption will be obliterated …

Your report on the impact of the pandemic on children's health is all well and good, but we need an investigation into why we have seen a big spike in mental illness in the past few decades ( 6 March, p 8 ). The recent mental health decline seems attributable to the lockdown conditions affecting …

I, too, fear that the strategy of targeting covid-19 vaccinations at vulnerable people first may well turn out to have been the wrong decision, a possibility suggested in Michael Le Page's report 13 March, p 9 . Even if we do get away with it and no new variants emerge that nullify all the vaccination …

One year into the pandemic, I welcome your article looking at the psychological and health impacts of repeated lockdowns on children 6 March, p 8 . Perhaps now is also the time to consider another possible health implication. I have always been a supporter of the hygiene hypothesis to explain the rise in the prevalence …

Further to the debate on the merits of a hydrogen economy 6 February, p 44 . For cars, an electric vehicle getting renewable energy from the grid wins out. There are energy losses from the electricity transmission and distribution systems (maybe 2 per cent for transmission and up to 10 per cent for distribution). Charging …

To expand on Marc Smith-Evans's point about using offshore wind turbine structures as reefs to aid fish stocks, structures associated with oil and gas production in the North Sea (and elsewhere) have long been seen as wildlife havens Letters, 6 March . In other areas of the world, there have been very successful "rigs-to-reefs" programmes, …