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With reference to the interesting article by Ciarán Gilligan-Lee on quantum cause and effect, I would point out something that I have often noted, but that is always overlooked ( 29 November, p 36 ). History can be understood in quantum terms. The future is nothing but a series of probabilities, the present is where …

Richard Black asks if a hearing aid can be designed with software to selectively amplify sounds coming from the direction you are facing. I can tell him that my hearing aid does exactly that ( Letters, 22 November ). Instead of picking up all the sounds entering the ear and amplifying select frequencies, my hearing …

David Flint says biomass carbon capture would require too much land area. He favours using chemical plants to capture carbon dioxide from the air. I would like to point out that, every year, about 440 gigatonnes of carbon dioxide enter the atmosphere from rotting vegetation, whereas we have about 1100 gigatonnes more carbon dioxide in …

As a contributor to the documentary Blue Planet Red , I would like to address the criticism in Simon Ings's review that xenon-129's presence in the Martian atmosphere implies ancient nuclear conflict only if you ignore the well-understood process by which a now-extinct isotope, iodine-129, would have decayed to xenon-129 in Mars's rapidly cooling lithosphere …

You report that a study by Satoshi Kojima and his colleagues may have solved the mystery of why birds sing at dawn, suggesting singing is suppressed by darkness, leading to a build-up of motivation that is released when the dawn breaks. This may explain the mechanism that mediates the diurnal pattern of singing, but it …

Regarding the feature Songs from the caves, the Lascaux cave paintings in France include a star map of the Taurus region of the sky with a bull painted around the Hyades, just as the constellation is depicted today ( 22 November, p 34 ). Dated at 17,000 years old, surely this is the oldest provable …

The Torino scale assigns asteroids a score of 0 to 10 based on their size, energy and probability of hitting Earth ( 15 November, p 38 ).

I cannot agree more with Anthony Laverty's article on the need to curb the trend towards big cars. Not only are they more lethal in a crash, they are also more likely to be involved in accidents because of larger blind spots and longer braking distances. I call for regulations to inconvenience big car owners …

Laverty perfectly sums up what can only be described as the biggest environmental crisis ever to hit UK roads, and beyond. Let's hope this subject gathers much-needed momentum.

In reference to Claudia Canavan's article, "Time for a new you", I have been applying the Myers-Briggs Type Indicator – which categorises people into 16 personality types – for over 30 years ( 27 September, p 23 ). Despite often being dismissed, it has always "said" everyone is both an extrovert and introvert (just not …