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The words "…my peers load their plates with only burgers, fries and pizza" define precisely what is at the heart of the obesity crisis. Pretty much no food is inherently bad. However, the sheer amount of it eaten is. In the UK, US and other places where food is relatively cheap, I have witnessed single …

My objections to the many worlds interpretation of quantum theory are that it is necessarily untestable and anyway explains nothing 23 March, p 32 . To be testable, we would have to be able to detect the influence of one of the other copies of our universe on us for at least some tiny period …

It is rather anthropocentric to say that to seek advanced alien life, we should search for clusters of planets that look remarkably similar, a sign of terraforming. Extraterrestrials that are sufficiently evolved to cross space and colonise other worlds might not need to terraform them. They are probably highly adaptable and can do the opposite: …

It is a mistake to pursue unproven high-tech solutions to storing carbon when we already have a proven technology that could be quickly and widely implemented: regenerative agriculture. This uses established techniques to create a living soil that can sequester a great deal of carbon per hectare. Conventionally farmed soil can be improved in three …

In her article on omega fatty acids, Jasmin Fox-Skelly states that the most important thing to do to get more omega-3 in your diet is to eat more oily fish. Vegetarians, vegans and people who don't want to eat fish should note that the fish don't make the DHA and EPA omega-3s they contain themselves: …

6 April, p 36 Kevin Healey, Sydney, Australia Eco-anxiety specialist Caroline Hickman suggests that "if we stopped oil extraction and shifted to renewables, eco-anxiety would almost disappear overnight". Even in the best-case scenario, the climate effects of these measures would take some time to be felt, and by then the focus will undoubtedly have shifted …

I take no issue with the thermal advantages of vines growing on buildings. These plants may cause few problems with certain modern brick or tight-dressed stone walls, but they can grow into, and feed off, the lime cement mortar of older buildings. Likewise, the roots rapidly get behind wooden clapboard walls. 30 March, p 44

Nigel Tuersley's comments on the risks of technological optimism are too true. As well as the throwaway attitude he mentions of thinking we will be able to leave Earth, the argument from some quarters that we will find an engineering fix to climate change is dangerous and used to delay urgently required action. Letters, 20 …

When I taught undergraduates the scientific method, parsimony was a key element. I find this lacking in suggestions that we may live in a simulation. Two scenarios (among perhaps more): our lives are the result of material evolution that gives us the consciousness and intelligence to one day program such a simulation, or another species …

With all this talk of the quantum multiverse, many-worlds and now many-more-worlds, William of Ockham must be spinning in his grave. In multiple universes. 13 April, p 8