Letters archive

There is a relatively simple solution to the question of dark matter – the unseen mass thought to be exerting an additional gravitational effect on galaxies( 11 February, p 46 ). In his book The Elegant Universe: Superstrings, hidden dimensions, and the quest for the ultimate theory , Brian Greene explains that string theory postulates …

You say that £870 million a year is the supposed beneficial impact on the UK's health thanks to rivers and lakes encouraging physical activity and relaxation. I wonder if there is another, hidden cost that should be added in due to polluted waters( Leader, 18 February ). Back in 1995, I swam in a river …

Your story on using moon dust to create a sunshield for Earth implies that the 1 million tonnes of dust needed would have to be replaced at the rate of 200,000 tonnes a day. While you mention the possible use of a railgun to propel the dust into space, there would need to be infrastructure …

"Into the void" suggests we may risk an increase in cosmic rays as our planet passes into a new area of interstellar space in about 2000 years. We entered the area we are currently in around 60,000 years ago. I suggest calculating when previous transitions occurred to see if they tally with events in Earth's …

I was glad to see Mark Jacobson rectifying some of the overblown optimism around carbon capture and storage, direct air capture, "blue hydrogen" and so on( 18 February, p 27 ). He didn't mention electrification of vehicles, but there are significant problems with this as well, on a global scale. I think these downsides should …

Jacobson makes the point that we will only achieve our climate goals on the short timescales necessary if we use existing technologies. I and most people would agree. Unfortunately, he then includes a yet-to-be developed technology as one of the solutions. Storage for renewables, despite what he says, is nowhere near ready to help support …

We hear more and more about fermented foods and how good they are for our microbiome and hence our immune system. But it is frustrating to always hear kimchi given as the example( 4 February, p 41 ). What about our centuries-old European tradition of fermenting cabbage or root vegetables to provide nutrients and, above …

You report doubts about the "wood wide web", in which trees communicate and share resources via buried fungi. I think it is more likely that the fungi are in charge, actively encouraging certain types of tree to grow in certain spots. The fungi could favour mixed woodland species and discourage monocultures( 18 February, p 10 …

Is a 4°C temperature rise by 2100 ruled out? Graham Lawton assures us that the current models say so. However, I wonder if there is an assumption that climate feedbacks will be constrained. The models don't include release of methane from permafrost at the observed and rapidly rising level. In the past few years, anthropogenic …

Kayt Sukel reports on people scheduling set periods when they are allowed to worry as a way of managing and reducing paranoia. I suggested another approach to someone, that they give up worrying for Lent, as they were always fretting about something. They felt so much better that they did this every year( 11 February, …