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The J. Doyne Farmer interview on conceptualising the economy as a complex system with emergent behaviour was fascinating. As an ex-teacher, what I particularly enjoyed was the grass-zebra-lion analogy, comparing the interdependence of specialised entities in an ecosystem to those in the economy. Although an oversimplification, it was very easy to understand and was capable …

Dark matter remains quite an enigma. If it exists, we have to confront a situation where the big bang created two separate types of matter – the normal matter we see today or its precursor (making up around 20 per cent of the total) and dark matter (about 80 per cent). Alternatively, we may need …

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

Thomas Metzinger's book, The Elephant and the Blind , has been made available as open access ( 27 April, p 28 ).

Chanda Prescod-Weinstein laments the shift to broad-spectrum white LEDs in towns and cities because of the impact on the night sky. However, go to any sizeable theatre today and you will see from the stage lights that LEDs can be any colour. It isn't obvious why most LED road lighting is white, and it isn't …

Prescod-Weinstein regrets that when street lighting was converted to LEDs there was no requirement that the white light be filtered to a single frequency, which would make it easier for astronomers to deal with. But that would defeat the purpose of converting to LEDs – their efficiency. Filtering out most of the frequencies would drastically …

In many countries, such as India, power generation is indeed moving noticeably away from fossil fuels, with significant reductions in carbon emissions for that sector. ( 4 May, p 8 ) However, the overall energy consumption and carbon emissions of many nations is changing far more slowly, if at all, due to continued reliance on …

Thank you for the article on indoor climbing walls and the concerns about inhaling chemicals in the rubber dust released by the shoes used in such facilities. It was excellent, and this is something I have worried about for a while. ( 11 May, p 10 ) In a similar vein, I also have concerns …

The statement that "plastic, rightly demonised as a scourge of the modern world, could be fantastic again" seems to go too far in its criticism of the material. ( 27 April, p 36 ) It takes less energy to make a plastic bottle than a glass one. Additionally, plastic films play a crucial role in …