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You report that spraying salt water into the atmosphere over the Pacific to brighten clouds for nine months a year for 30 years to save California from extreme heat could eventually cause dire temperature increases in Europe as a side effect ( 29 June, p 11 ). However, other studies are more hopeful about such …

The idea of our cosmic insignificance is a matter of emotion rather than reason. We all feel it, but it does, after all, involve equating physical size with significance. This is absurd, as we don't say an elephant is more significant than a human, or a mountain than an elephant. What happens is that, when …

What a magnificent photograph of the Milky Way seemingly emerging from the summit of Aoraki/Mount Cook in Aotearoa/New Zealand. In it, our galaxy also seems to be looking down on the rapidly retreating terminus of the Hooker glacier and the equally rapidly expanding Hooker Lake. By 2016, this lake had lengthened from nothing to 2.5 …

You outline research showing how varying stride length while walking helps burn more calories. However, it does more than that. It enhances muscle tone and overall fitness. This is the idea behind fartlek, a training method for runners. Practitioners vary their pace (and thus their stride length) while running through woodland or open country, switching …

You raise the idea of paying people to lose weight. Use of financial incentives isn't new. American football player William "The Refrigerator" Perry had a clause in his contract with the Chicago Bears stating he would be penalised if his body weight went above a certain level ( 29 June, p 12 ).

When it comes to obesity, some people claim healthy food costs more. This is false. I cook all my food, mostly vegan, and it costs just a fraction of what most people spend on their unhealthy food.

There is one vagus nerve on each side of the human neck ( 29 June, p 19 ).

Carl Zetie highlights the issue of those who say that a change of attitudes, not the use of weight-loss drugs, is the way to tackle obesity ( Letters, 6 July ). As has been pointed out many times, one reason why our ancestors avoided this problem was the struggle they had in accessing food. Hunting …

In your look at life in the universe, you say that almost all the stars that will ever exist have already been born, and they have been around long enough for life to arise on planets that orbit them. But we don't know that they have been around long enough for life to come about …

On exercises to stave off lower back pain, I discovered that regular hip waggling (twerking?) during tooth cleaning with my 2-minute cycle electric brush resulted in the pain completely disappearing. The only downside is that I have to make sure no one sees me – even at 90, I look incredibly sexy( 29 June, p …