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You report a call for everyone to "think like a hacker" to improve online security ( 20 May, p 43 ). Leaving the muddied epithet of who is a hacker aside, cybersecurity is now, more than ever, a complex activity that involves people ranging from the developers of hardware and software through to the day-to-day …

Simon Ings's stance in his review of the documentary A Crack in the Mountain appears laudable at first. The film relates the beauty and tragedy of Hang Son Doong cave in Vietnam. The local government could ruin this part of a UNESCO World Heritage Site by installing a cable car to carry 1000 tourists an …

There is a big difference between racing herbivores and carnivores. Herbivores usually run fast to flee predators. So horses may be stressed when racing. Dogs enjoy running: when they catch prey, they are often excited. Ultimately, racing and hunting (and pedigree) animals are inbred to varying degrees. Unless they are used as breeding stock, they …

Hotspots for ultra-high-energy cosmic rays seem to centre on galaxies Centaurus A and M82 ( 3 June, p 46 ).

You say that carbon cuts alone won't be enough to reverse catastrophic climate change. I agree. Measures introduced so far will have very little effect. Emissions continue to rise, even accelerating. This is doomsday unless something drastic is done. Fiddling with carbon capture is never going to hack it. We don't have time for such …

Chris Impey doubts the prospects of communicating with aliens, saying that despite sharing 99 per cent of our DNA with chimps, we can't communicate with them. However, humans have been making themselves understood by chimps for 50 years. We have been communicating with other animals, and they with us, for thousands of years ( 27 …

Impey doesn't mention another reason for caution in contacting aliens, even if they are assumed to be benevolent. They might freely make technologies available to us that are far more advanced than our own, thinking that they could only help us. They may assume that we don't suffer from the dysfunction and conflicts that plague …

The reason we can't communicate with chimps is because they aren't sufficiently intelligent, but this has no bearing whatsoever on whether we could communicate with an alien species clever enough to detect our messages.

Michael Le Page says that brain organoids grown in labs are nothing like real brains, that they are "bunches of brain cells just a few millimetres across that are nowhere near even a simple animal brain" ( 10 June, p 21 ). Even so, that is a lot bigger than many animal brains. The whole …

I do believe a basic bag-filling algorithm, of the sort described by Peter Rowlett as "a simple rule a computer program can mindlessly apply", is already being used by the supermarkets that deliver to my home. Considering no factor other than filling space, sliced bread is routinely squashed out of all recognition by bottles, jars …