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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 …

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 …

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 …

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

I thoroughly enjoyed the excellent interview about dinosaurs and pterosaurs with Dave Hone, and it reminded me of my introduction to dinosaurs in the UK National History Museum when I was 10, some 70 years ago ( 2 May, p 40 ). My mother and aunt had taken my cousin and me on our first …

I found the article on the essence of reality very interesting. However, it isn't difficult to conceive of things being equally real whether we are considering our normal perceptions of the world ("red tomatoes") or more abstract concepts, such as quantum fields. We know that light consists of a continuous range of frequencies. However, our …

I can't pretend to explain how we experience time, but I'm sure it isn't what Tim Redman proposes. We don't observe something happening and say, "Oh, the entropy is increasing, so time must be flowing in a positive direction." True, the arrow of time can be related to a global increase in entropy, but we …

I have to agree with Tim Redman. Time is a human construct for measuring the "now" of successive events. Relativistic events appear so because the working parts of measuring instruments, namely clocks, are what are affected.

Regarding the article "Unlocking consciousness", it seems to me that the excellent and wonderful work of Nao Tsuchiya et al. is about perception, not consciousness. If we could map a cat's colour perception, I think we would find a similar web of contrasts and similarities. I think a cat is aware of colour, but I …