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With the Oxford/AstraZeneca vaccine, some evidence suggests that half the current standard dose would be at least as effective 1 May, p 7 . In view of the desperate shortage of vaccines in India at the moment, perhaps we could save lives by stretching supplies of that vaccine, if it were established that a lower …

So trees may have a form of sentience 1 May, p 39 . Now I know that if I have to cut any elder, I must apologise and explain to the plant or face the consequences. Elder may or may not be sentient, but folklore says it is witchy and potentially vengeful. Best not take …

Martin Watson and Tim Johnson worry about a possible black hole orbiting the sun colliding with it or another, similar black hole Letters, 24 April . In order for it to hit the sun, the very large angular momentum that the black hole would have as it orbits would need to be brought close to …

An ultra white paint has been invented and suggested as a means of cooling houses as potently as air conditioning 24 April, p 19 . However, perhaps it could also be used to provide a supply of fresh water. A horizontal, slightly conical metal sheet that was painted white on top would cool and condense …

Is there a flaw in the idea of using super white, cooling paint on buildings in some places? Yes, sunlight will be deflected in summer so less air conditioning will be needed, but what about in winter? Presumably, its effect may mean more heating is needed then.

Steven King worries about possible tsunamis affecting nuclear power plants in the UK Letters, 10 April . However, much of the nature of the Fukushima disaster in Japan resulted from a design that took no account of the possibility that sea defences might be breached. Emergency power supplies were vulnerable to inundation and were rendered …

Claiming that there was once a time when nature was in a perfect, "pristine pre-industrial state", as mentioned in Graham Lawton's column on ecocide, is a fallacy 8 May, p 24 . A preference for one environment or species over another is purely a human judgement; evolution has no inclination for, say, an English bluebell …

You report rising interest in the archaeology of seabeds that were once land 17 April, p 44 . Another reason to think coastal areas would be rich in possible finds is the idea that food supplies were effectively static in these areas. Unlike forests or open plains, where hunter-gatherers would have had to be constantly …

Regarding Brian Reffin Smith's letter reducing to absurdity the equation cited by Carlo Rovelli in his take on quantum theory Letters, 10 April . The equation doesn't deserve ridicule. It is no more controversial than the theory it is part of. Physicists used and accepted such "non-commuting" equations long before Rovelli was born.

In your look at the platypus, you write that its "pelt glows in UV light, which makes no sense for a nocturnal animal" 8 May, p 41 . It only makes no sense if you assume the fluorescence is the function, not just a consequence of a complex chemical structure for some other purpose, perhaps …