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Name and address supplied You report on institutional racism in science ( 27 June, p 14 ). I am a white woman in a fairly senior support role at a university, but I have seen racism and sexism in my own institution. It isn't just the hurdles that BAME students have to overcome or the …

When discussing why there hasn't yet been another wave of the coronavirus in the UK, you say one explanation that can be ruled out is herd immunity as the level required for this virus has been estimated at 60 per cent, while studies suggest that "just 1 to 10 per cent of people have antibodies …

Kevin Hand, in reference to moons in our solar system with ice-capped oceans, says the presence of microbial life in a range of extreme environments on Earth suggests that "if life emerges easily wherever the conditions are right, then these alien oceans beyond Earth should be inhabited" ( 20 June, p 40 ). This would …

Jason Wright may not be able to think of a reason why the Odd Radio Circles (ORCs) recently found by astronomers might be created by aliens, but there may be one ( 11 July, p 14 ). We know that when our civilisation began broadcasting radio waves, these also spread out from our planet in …

One major difference between leaders of countries and leaders of more traditional, small-scale societies is that the latter have to interact with their followers in person and command their respect or they won't remain leader for very long. National political leaders don't necessarily require the same qualities. With a good team behind them to help …

The solution to the problems of developing a coronavirus contact tracing app in the UK for multiple devices could be to develop a single wearable packaged as a watch, brooch or key fob ( Letters, 4 July ). It would have to be backed up by a central database, but that would be under NHS …

I was a little surprised that Claudia de Rham's article on new ideas about gravity made no mention of dark energy ( 11 July, p30 ). It seemed to be the logical next step to wonder, if gravitons have mass, and thus have finite range, whether there is any need, in considering the expansion of …

If gravity does have mass, as de Rham suggests, how does it escape a black hole?

Further to your story "Circles in space are like nothing we've ever seen" about inexplicable radio signals spotted by astronomers ( 11 July, p14 ). Could they result from gravitational lensing of other objects?

You say that "half of the deaths of large tropical trees are down to lightning" ( 27 June, p40 ). One way to reduce this toll could be to fit such trees with cheap lightning conductors.