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First, it was Y2K. Now, it's proofing the security of our technology against quantum computing (well covered by Karmela Padavic-Callaghan). Both challenges continue to add evidence that ignorance, wilful or otherwise, isn't bliss in cyberland ( 25 April, p 10 ). However, perhaps one change we can make is to demote the language we assign …

On the subject of the pluriverse, the delayed-choice experiment may point to a remarkable conclusion: conscious realisation is itself a real fact, and it is this fact that fixes physical reality by converting virtual possibility into determinate actuality ( 21 March, p 28 ). Before we know which path a particle takes in the double-slit …

Matthew Stevens rightly points out that, in a few millennia's time, it will be difficult to read nanometric information etched into glass, given that, by then, the necessary reading technologies will probably have been forgotten. But there is a very simple solution: engrave th information onto the glass, but then carve the instructions for building …

Your correspondent Erik Foxcroft would be interested to find out if other people can imagine smells or tastes. I can do so vividly: if I can't get to sleep, I do a mental walk through my old school, where each room (classroom, lab, gym, storeroom) has a different smell. Or I imagine an all-you-can-eat buffet …

Thank you for your excellent article about Chernobyl. I was involved with a safety case for a new building at Sellafield in 1986 when the accident happened. I always wanted to visit, and in 2018 I was lucky enough to visit the site and see all the most interesting aspects as described by your reporter …

Keith Joshi mentions the idea of "lazy evaluation" in a simulation of the universe. I have a similar hypothesis about the interior of black holes. Since such interiors are outside of what we can ever observe, it could be that physics there is undefined. There's no need for it ( Letters, 25 April ).

Regarding the piece on household butlers, the cost of garden maintenance is so high around here that I would love a robot to do it. At least with simple things like mowing. It could also spray weeds as is done in agriculture, but only on the lawn and not in the flower beds, where it …

The chimpanzee civil war has been held to show war as a pre-human activity, but is civil war the same thing as war? It may be argued that war defined the start of civilisation: one group of people reacting to another in opposition and possibly cooperating with others. Surely civilisation was when humans realised they …

Concerning David Robson's piece "Why is it so hard to change your mind?": like many people, I'm extremely open minded ( 25 April, p 17 ). I'm willing to listen to anyone's point of view, even though I know they're wrong!

C. H. Johnson was playing rugby (25 April, p 46)