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In "Welcome to the fuzzy-verse", philosopher Eddy Keming Chen misstates the relationship of physics and mathematics ( 5 September, p 36 ). The universe is what it is, and the fundamental laws of physics are really just expressions of the patterns we observe there – they don't explain anything. What they can do is help …

I was inspired by Graham Lawton's description of Rob Jackson's plea to restore the atmosphere to its pre-industrial state ( 22 August, p 24 ). We absolutely must do this. Any plan or course of action that falls short of full reinstatement to pre-industrial conditions, with the associated thermal equilibrium of the planet that is …

In his look at the benefits of "social capital", inspired by the pandemic lockdown, David Robson argues that "in recent decades, a raft of research has shown that individuals with richer social worlds tend to have better mental well-being and lower stress, and to perform better at work" ( 15 August, p 32 ). Does …

Could there be an alternative to a coronavirus vaccine to achieve herd immunity if we could come up with a test to predict who would be asymptomatic? Many people would probably fall into this category ( 5 September, p 7 ). They might have something in common other than their underlying good health that could …

You report on an analysis that found voting by mail would have little effect on US election results ( 5 September, p 20 ). It seems to assume that Democrats and Republicans would vote by post in similar numbers. In fact, a recent poll indicates that a significantly higher proportion of those who support the …

From River Axe-the-Tax, Manchester, UK Simon Goodman expresses concern about Russian plans to roll out a coronavirus vaccine without the usual stage III clinical trials, rightly saying that these can help spot harm ( Letters, 19 September ). Similar concerns have to be raised about Donald Trump's desire for a vaccine to be released before …

From Brian Reffin Smith, Berlin, Germany So many of the questions and answers within Eddy Keming Chen's article "Welcome to the fuzzy-verse" seem, perhaps paradoxically given the article's emphasis on mathematics, to be due to human choice, and hence to become impossibly vague ( 5 September, p 36 ). We can choose to think about …

From Patrick Davey, Dublin, Ireland Your article explores how the rate of carbon absorption by forests may alter as the climate changes ( 15 August, p 38 ). While I was working in Uganda with Mountains of the Moon University, one of our central projects involved growing roses. We were about 300 metres higher than …

From Jim Ainsworth, Kingsland, Herefordshire, UK As to which came first when life arose – structural integrity, metabolism or reproduction – Michael Marshall explains that it is possible all three happened at once ( 8 August, p 34 ). He adds that metabolism is the trickiest system to account for, since it involves "creating entire …

From Paul Wood, Hamilton, New Zealand You report that baby titanosaurs had a sharp horn on their snout, something that was absent in any adult fossils, but offer few possible reasons for this difference ( 5 September, p 20 ). Perhaps it was there to help them break out of their egg, just as birds …