Letters archive

As Adam Vaughan writes, it is now clear that we have to reduce our greenhouse gas emissions to zero ( 27 April, p 20 ). But the question of when depends on who we mean by "we". The Intergovernmental Panel on Climate Change special report shows that global emissions should reach net zero by about …

If another human species has been discovered on the island of Luzon in the Philippines, how did it get there, and when? There were five or six periods of low sea level in the mid-to-late Pleistocene ( 13 April, p 9 ). In the two most recent of these, levels were about 120 metres below …

Chris Stokel-Walker says there is little evidence that banning Chinese company Huawei from supplying 5G mobile technology is the right approach ( 4 May, p 11 ). But when deciding this, we shouldn't be seeking evidence to test a hypothesis. We should use the precautionary principle: don't do something if it might be disastrous. The …

What is the motivation of the US in trying to stop Huawei selling 5G infrastructure to the UK and others? There is a body of opinion that it is to get US companies to dominate the market, and to enforce the spread of US spyware, not Chinese. The US National Security Agency has reportedly meddled …

Chris Baraniuk concludes that it is one thing to hack an artificial intelligence controlling a vehicle in a car park, and quite another to hack an AI controlling a weapon ( 27 April, p 34 ). But what about a weapon such as a driverless car that is doing 50 kilometres per hour on a …

• Wet, wet, wet: It is the class of space rocks that includes Itokawa that may have brought half as much water as is in Earth's oceans ( 11 May, p 18 ). • Mind like a sieve: The reason that Harald Helfgott's prime number-finding algorithm is purelytheoretical is that he hasn't optimised it ( …

Chris Stokel-Walker describes the nightmare of not being able to make a cup of tea while your kettle updates itself ( 11 May, p 23 ). This does raise an important question: why do we put up with things that are so badly engineered that they need fixes after we have bought them? A bicycle …

You say there is no evidence that Chinese network equipment firm Huawei has mishandled data ( 4 May, p 11 ). But, for example, Le Monde reported last year that equipment installed in the Chinese-built headquarters of the African Union in Addis Ababa, Ethiopia, transmitted data every night from midnight to 2 am to servers …

You report a plan to send a swarm of 1-gram devices towards Alpha Centauri at 20 per cent of light speed ( 13 April, p 32 ). Each will have kinetic energy equivalent to half a kiloton of TNT explosive, comparable to a small nuclear device. Any entity on the receiving end may get the …

I applaud your series on becoming a maker (How to be a maker, 11 May ). We are in danger of forgetting the basics. But to imply that you can get a painful shock from a 9-volt battery is absurd – unless you connect it to your teeth, or have a coil with large inductance …