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I was struck by Stephon Alexander's idea of the universe being a neural network ( 11 September, p 47 ). The concept wasn't fleshed out much in the article, and having scant knowledge of astrophysics, I'm not able to see how it would work. But perhaps there is a good example of this on our …

Despite what the preamble to the interview with Alexander said, growing up in the Bronx is typical training for a theoretical physicist. The Bronx High School of Science has produced eight science Nobel laureates – seven in physics and one in chemistry – the most of any secondary school in the world. The American Physical …

In her look at the truth behind widely publicised health targets, Amelia Tait asks who has the time to brush their teeth properly – in other words, for the recommended 2 minutes, twice a day ( 11 September, p 38 ). As an aged member of the underclass who can't afford expensive dentistry and who …

Regardless of how long you should brush your teeth, flossing clears more bacteria. In that regard, given the choice of only brushing or flossing, take the latter. Once proficient, it takes 30 seconds and is painless with proper technique. Also, as far as hydration goes, observing the colour of your urine is a good indicator. …

In your excellent article on net-zero living, there is talk of a future with fewer cars, as many of them will be shared ( 4 September, p 34 ). Really? My impression is that most car owners love their vehicles and regard them as their private space, an extension of their homes. They are reluctant …

Your well-conceived feature "A day in a net-zero life" discusses heat pumps as though they only provide warmth. You seemed to refer to air conditioning as separate tech. However, a heat pump can both heat and cool a home. We have had one for a year. It has operated well through a cool winter and …

Any charges for removing rubbish just create fly-tipping and higher costs ( 25 September, p 18 ). A better way is legislating so those authorities not already using multi-bin sorting for recycling take it up. Supermarkets can also follow the example of a Canadian chain that has recycling bays to sort waste and repay deposits …

With the recent emphasis by the UK government on "nudge" techniques to modify behaviour, I wonder why there has been little research into the motivation behind recycling. I live in Weymouth. Until 2011, we achieved 70 per cent recycling. Then our waste service merged with another authority, whose recycling rate was only about 30 per …

A major problem in trying to recycle plastic is that it is often far from clear if it can be recycled. My local authority can't recycle the large bags in which bird food is delivered, but if I go a few miles to the next local authority, it can be. Then there is the problem …

Of course we waste food ( 25 September, p 42 ). Since the green revolution in the mid-20th century, we have striven to ensure we have plenty of all kinds of food. We can't have "just enough" because it is difficult to predict how much of each type of food we will need and even …