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We know that large language model chatbots can't be trusted to always tell us the truth. We now find that it is hard to get them to "unlearn" concepts and facts without retraining on "cleaned" data, a wholly impractical task ( 4 November, p 40 ). One wonders what the next problem could be. I …

A novel by Jack Vance pre-empts, to some extent, the language-shapes-mindset view of Caleb Everett in his book A Myriad of Tongues . Vance's The Languages of Pao tells the story of the placid people of the planet Pao ( 4 November, p 29 ). These people have been invaded, so they adopt three new …

Previous research I was involved in showed that aerosol sprays don't linger, as James Wong found with water sprayed on plants. I don't spray my water-loving plants and haven't done for years. A stack of Maranta , moth orchids, Nepenthes and Venus flytraps are kept damp with regular light watering at a north facing window …

I loved Alice Klein's piece about South Australia's transition to renewables. I would say it had a bit of unexpected help. South Australia formerly had a major automotive industry. Holden, once Australia's largest car-maker, ran a huge factory in the Adelaide suburb of Elizabeth. From 2013, it started ramping down production, finally shutting in 2017. …

Robert Peck writes that "the fundamental truth is that open, uncensored debate is still the best way to expose and defeat falsehoods". This only holds true when those debating are truly rational. With 8 billion of us, there are now many who have low levels of rationality and high levels of bias. There are also …

When it comes to ultra-processed foods, I find myself cooked into a corner. I have made my grandson's birthday cake using the finest ingredients: dark chocolate, butter, cream, organic flour and so on, but it required a lot of processing by me. Am I condemning him to a life of health misery? I think the …

For the solution to puzzle #243 ( 21 October, p 47 ), fewer than 31 customers at a time means there won't be a clash.

The concept of quantised space-time may be the key to understanding the multiverse – and the requirement that the plethora of universes must display a wide range of properties that fortuitously result in a limited number being relatively stable and life-friendly ( 28 October, p 30 ). If the fundamental constituents of space-time were to …

You published a timely article about preserving us from the possibility of being wiped out by Martian microbes brought back to Earth in study samples. I hope sufficient steps are being taken to prevent Earth microbes from contaminating Mars and elsewhere that we visit ( 4 November, p 21 ). It would be a tragedy …

Further to Bryn Glover's call for names for the opening chapter of the proposed next geological epoch – the human-induced Anthropocene – I would suggest that an appropriate title for its first age might be "The End" ( Letters, 4 November ).