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Mark Lynas's article on the risks of nuclear war was refreshing. The threat of annihilation hangs over us every second of every day, but it seems that politicians and the media prefer to pretend it is all OK( 24 May, p 21 ). As a design engineer, I know too well the impossibility of developing …

While Lynas's hopes and wishes are admirable, with Vladimir Putin threatening the use of nuclear weapons and Donald Trump promising to "drill baby, drill", I fear that the Fermi paradox is secure in its implication that technological civilisations tend to destroy themselves in short order, and that nuclear war and climate change are inevitable. Maybe …

UK governments have long favoured multilateral nuclear disarmament. However, it always seems to boil down to: "You first."

Reading the book review of Out of This World and Into the Next , I saw the term "terraform". The general story behind its use is: "We aren't able to keep Earth's climate under control, so we go to another planet, where we first need to get the climate under control through terraforming." Considering the …

You rightly threw cold water on the romanticism of colonising Mars. Sci-fi offering The Expanse was mentioned as a tonic to such visions. Its Martian colonists sensibly began to flee the Red Planet as soon as green worlds became available (thanks to alien tech). Why abandon our own green world for a hellscape?

I couldn't agree more on the need to reduce town centre traffic. In the UK, motoring bodies like the Automobile Association and Royal Automobile Club tend to resist efforts to cut car use. In Germany, the equivalent body, the ADAC, does the same. At least in Germany there is the ADFC, which pushes back on …

The compelling case to reduce car use is the exact same powerful argument to incentivise the affordable public transport needed to replace individual car use. Unfortunately, rural areas have suffered from inadequate provision for so long that it is virtually impossible to live anywhere other than an urban conurbation without a car. Once you are …

The urban car problem can be solved with app-based ride services that can hold many passengers. Individual city cars could be totally replaced, leaving suburban roads clear for walking and cycling, as well as removing parked cars. An "out-of-town" hire scheme could cover other car journeys. By relinquishing a car (or two), a local family …

Surely what is beneficial in maintaining a healthy brain is continual stimulation via all the senses, not just smell. Some stimulation, such as studying and practising a second language, may be more effective, but only long-term research will elucidate their relative effectiveness. That said, the benefit of developing the olfactory sense looks promising, and little …

So pleasant smells can help reduce chronic inflammation, and being able to smell unpleasant things can help us avoid health threats and stimulate the immune system when necessary. There is also evidence that a declining sense of smell or its loss may be addressed by regularly exposing people to a wide range of scents. However, …

Roger French asks whether anyone is working on using quantum entanglement to achieve instant communication with Mars. But entanglement can't be used to transmit a signal. All it means is that if someone on Earth measures a property of one particle and someone (or an avatar) on Mars measures that property of another particle that …

You report a study that suggests an optimal way to chop onions without crying. Forget slow cuts with sharp blades, black spray paint, electron microscopes and such like – just slice the top and bottom off the onion, soak it in water, chop. No tears. Easy-peasy( 24 May, p 12 ).