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Adam Vaughan sees hope in the fact that India's prime minister has pledged that the country will achieve net-zero emissions by 2070 ( 6 November, p 10 ). However, promises made by ordinary people, let alone politicians, for 50 years in the future are clearly meaningless. Imagine if Lenin had promised a global utopia by …

Cedric Lynch, Potters Bar, Hertfordshire, UK In your story about the upgrade to the branch of maths called calculus, you say "you could perhaps imagine calculating the rate of change of acceleration too, which would be a third-order derivative" ( 13 November, p 44 ). However, calculating this rate of change can be of more …

In your look at the impact of extra extraction of minerals required to expand renewable energy technologies, such as turbines and electric vehicles, environmental researcher Laura Sonter suggests that "social licence to operate" is important to the minerals industry ( 13 November, p 38 ). Social licence to operate is a mirage conjured up by …

When considering the downsides of mining for minerals that are essential for electrification in pursuit of net zero, I expected to find some reference to the future use of hydrogen. In the near future, we could have hydrogen-fired boilers in our houses and transport powered by modified engines using hydrogen, including jet engines. Where fossil …

You quote Peter Leek at the University of Oxford as saying that the progress IBM has made with its 127-qubit quantum computer is "definitely positive" and "it's good that they're making something with more qubits" ( 20 November, p 7 ). I am not sure that it is good. It seems to me that we …

The plant-based meat options in our supermarkets probably aren't marketed to be seen as healthier than the diet of nuts, vegetables and lentils that vegan pioneer Donald Watson enjoyed ( 30 October, p 38 ). But many are still preferable to the conventionally produced meat these products are designed to replace. A report led by …

Regarding the latest look at quantum theory's implications for reality ( 6 November, p 38 ). If the moon doesn't exist when you aren't looking at it, do I exist when you aren't reading my letter? More seriously, is being alive, even if no one on Earth knows, sufficient qualification for existing when no one …

I would suggest that anyone querying whether things actually exist if you aren't looking at them has never stubbed a toe, reversed a car into an obstruction or suffered some other mishap or injury. Less flippantly, given the severity of climate change and the inadequate attempts to mitigate it, why do people indulge in such …

In "Is reality real ?", Thomas Lewton concludes that unless you hear the forest tree fall, it was never there in the first place. His conclusion is challenged in the same issue by the elephants in "Deciphering Dumbo" ( p 42) that head for an unseen tree whose unheard fall they may have detected by …

I share concerns over increased tree mortality across Europe, but one assertion in your report on this needs to be revised ( 20 November, p 14 ). Your story concludes by citing a much-debated claim that wood harvesting in Europe has risen by 50 per cent since 2016. Subsequent evaluations suggest a substantially smaller value …