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The idea of "honest placebos" isn't new. Â鶹´«Ã½ reported they were effective against irritable bowel syndrome ( 9 March 2016 ). They have appeared in fiction, too. In Stephen King's It , Eddie finds out his asthma inhaler contains a placebo, but continues to use it ( 5 April, p 20 ).

I enjoyed Rowan Hooper's piece imagining the future use of mechanical avatars on Mars. However, an important factor was missed: distance. Currently, communication can go no faster than light speed, which means that any instruction from a human host on Earth to an avatar on Mars would take at least several minutes to arrive, and …

You report that warming soils "could" sequester more carbon than we thought, offsetting some of the carbon release expected as climate change alters peat bogs and permafrost. And an earlier article says the contribution of large animals to carbon removal "may have" been underestimated ( 29 March, p 39 ). While there might be some …

If thousands of quakes are rocking the northern part of Mars during its summer, then, presumably, only its southern hemisphere may be a relatively safe place to establish a self-sustaining human mission. Hopefully this has been taken into account in any plan for a Mars community ( 22 March, p 13 ).

  From Maggie Cobbett, Ripon, North Yorkshire, UK Your special issue on quantum theory took me back to 1974, when I had the honour of shaking Werner Heisenberg's hand. He was guest of honour at the new Heisenberg Gymnasium in Dortmund, Germany, where I was teaching English( 19 April, p 29 ). As I joined …

  I have always loved Carlo Rovelli's brilliant writing. Doesn't his book The Order of Time move you to tears in the final chapter? And his history of quantum theory was illuminating, but Erwin Schrödinger might be turning in his grave as a result. However, I suspect if we flipped up the lid and looked …

Your article about quantum Darwinism delved into a new attempt to explain how a classical reality common to us all emerges from the quantum realm. It seems to me that our subjective experience of living in this universe can give us great insight( 12 April, p 8 ). It appears self-evident that the future is …

I read with interest about the "middle-class microdoser" of the weight-loss drug Wegovy, who lost 20 kilograms of body weight over nine months. That is a long time to be eating less than his body needed each day. He reflected on becoming grumpy over that time and wondered if it was a side effect of …

Letters, various dates From Michael Wigley, Bissoe, Cornwall, UK There has been a lot of coverage, mainly negative, on the idea of humans colonising Mars. However, there is a long history of scientists saying something is impossible, only for it to be achieved. And even if we try and fail, it is likely to be …

If Mel Earp's old code is running in my smart TV, could they pop round and fix it so I can keep watching Netflix? The screen is perfect, the 5.1 sound is impeccable, and digital TV, satellite and BBC iPlayer are all fine, but Netflix isn't working and there is no update available( Letters, 12 …