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Discussing how soon we may have a vaccine against covid-19, Carrie Arnold writes of "the stark realisation during the West African Ebola outbreak that Big Pharma could no longer be relied upon to solely underwrite expensive vaccine research" ( 21 March, p 44 ). I take umbrage at this. As you have reported, pharmaceutical firms …

Footpaths should be added after people have used an area for a while so users decide where the paths should be, suggests Frank Bover ( Letters, 21 March ). This method has been used for decades by planners of new universities and college campuses. Michigan State University has paths designed this way: an aerial view …

You have previously reported a mathematical model of the interactions between walkers and developing shortcuts ( 5 July 1997, p 11 ). It is a good idea, although I suspect that architects will still strive to please their clients rather than the end users.

I can confirm that the pedestrian method works. When I was an overseas volunteer at a school in the Pacific Islands in 1976, I was given the task of laying concrete footpaths between the buildings before the onset of the wet season. I ignored the headmaster's planned layout and waited for a few weeks to …

Adam Vaughan discusses plans to plant trees to lock away carbon dioxide ( 29 February, p 20 ). These won't work here in Australia. In the most recent bush-fire season, around 126,000 square kilometres of vegetation and more than a billion animals were burned. We have to address the main causes of climate change. Time …

Donna Lu reports new lightweight materials made of gallium, indium and glass bubbles ( 14 March, p 12 ). In the same issue, Layal Liverpool describes a gold-coated fabric that can emit light in different patterns ( p 18 ). These seem remarkable from a technological point of view, but I wonder how recyclable such …

Richard Webb's discussion of efforts to make large amounts of anti-atoms in an antimatter factory made interesting reading ( 29 February, p 44 ). I remember when physicist Richard Feynman suggested in the early 1970s that, when we map matter and antimatter creation and annihilation, the antimatter could be portrayed as normal matter going backwards …

Webb asks whether matter and antimatter repel each other gravitationally. The majority of physicists have long felt they have good reason to believe that antimatter reacts to gravity in the same way as matter. In 1958, Leonard Schiff pointed out that experiments looking for a difference between the gravitational and the inertial masses of atoms …

You report that one mechanism by which silver prevents harmful bacteria spreading has been clarified ( 7 March, p 15 ). In 1989, and again in 2009, I was too ill to work. It seemed to me that the cause was bacteria and fungi growing in air conditioning ducts in relatively new buildings. When I …

Your exploration of the problems of reality is fun and fascinating, but it deals with two very different concepts: accepting reality and understanding how it all works ( 1 February, p 34 ). To give a simple analogy: at our farm, because I am a biologist, I understand a lot about how the grass, trees …