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Record-breaking temperatures in the air and oceans highlight two extremely urgent challenges ( 1 June, p 8 ). Despite the Paris deal for a 1.5°C warming limit and undertakings at subsequent COP meetings, total energy-related annual carbon dioxide emissions continue to rise, approaching 37 gigatonnes in 2023. Drastic action to reduce our dependence on fossil …

Your intriguing article about retrocausality poses the question of whether quantum information could be sent back in time. Surely the answer must be yes. How else could we explain the fact that electrons sent through a double slit, one at a time, create an interference pattern on a screen beyond? Each electron must be sending …

You report that time could be a quantum illusion. Maybe it is the other way round. Perhaps space-time is fundamental and the simplest way a universe with time can be predictable, but not deterministic, is for it to obey the rules of quantum mechanics.

Yes, there is a problem with salt addiction, but it is social rather than biological. A liking for salty food is far from universal and is probably acquired rather than innate. In family homes and in restaurants, the salt shaker is a ubiquitous presence on the table. Many people add salt to their food before …

Alex Wilkins's review of books on artificial intelligence mentions Ray Kurzweil's prediction that the Turing test of machine intelligence will be passed by 2029, along with his belief that the singularity – when AI will surpass human intelligence – is nigh ( 1 June, p 28 ). I don't think this is just a question …

In your interview with Sophie Attwood, it was good to read about the simplicity of effective interventions to modify our unsustainable eating habits. However, the final quote that "8 billion people are eating three meals a day" is debatable ( 1 June, p 37 ). According to a recent UN report, close to a billion …

Even if we ignore the various technical doubts about carbon offsetting, whether offsetting a flight makes flying acceptable depends upon what activity you think of as coming first ( 11 May, p 22 ). The usual view is that the climate-negative activity of flying is being compensated for by offsetting. But an alternative view is …

Bernd-Juergen Fischer rightly points out that a simulation of the universe would only need to take account of the inner world of the subjective "I" and whomever and whatever they interact with ( Letters, 1 June ). Taking that concept further, most of the universe would need only be stored as a vague set of …

Graham Lawton writes that wooden buildings don't give off heat like brick buildings after soaking in warmth all day ( 8 June, p 24 ). But I have seen an effect. In winter, I put the heating on after the house has dropped to around 12 ° C (54 ° F). The room temperature stagnates …

David Werdegar says language is necessary for thought. Long ago in this magazine, a reader posed the question: "Do you think in language?" The consensus was: "No, I think in thoughts." Never mind hominids, chimps have thoughts such as those we would word as "If I crush these leaves into a sponge, I will be …