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30 December 2020
From Charles Sawyer, Byron Bay, New South Wales, Australia
The "something obvious" Matthew Allan is missing in how to steer a solar-powered space vessel is the resultant force felt by an object when light reflects from it ( 28 November 2020, Letters ). If it uses a mirror set at a non-right angle to the light as a sail, the reflected photons will create …
30 December 2020
From Alec Cawley, Newbury, Berkshire, UK
An equivalent of solar sailing on the sea, into which the keel bites to allow the ship to tack upwind, is gravity. The mathematics is more complicated, but sailing a spacecraft using solar wind and gravity is similar to sailing on wind and open ocean.
6 January 2021
From Ronald Gibson, Irvine, California, US
Your article on overpopulation is too little and definitely too late ( 14 November 2020, p 34 ). I once had the chance to ask M. King Hubbert, he of peak oil theory fame, if he thought we had enough time to salvage our future, considering overpopulation and its effects on the planet's diminishing geologic …
6 January 2021
From Tony Osborn, Downham Market, Norfolk, UK
We, the deist gods, widely believed to have existed since before time began and ever constantly watching over our cosmic creation, have recently become very interested, even concerned. Our worries are centred on the tiny planet Earth, currently suffering from a potentially serious infection of humanitis. The cause seems to be a relatively recently evolved …
6 January 2021
From Geoff Vaughan, Lowton, Greater Manchester, UK
Sylvia Terbeck presents two versions of the trolley problem: one in which you divert a trolley that will kill five people so it only kills one other person, and another in which you push someone into the path of the trolley to stop it ( 31 October 2020, p 23 ). This addresses the problem …
6 January 2021
From Sam Edge, Ringwood, Hampshire, UK
Thanks for the early Christmas present of the Kari Leibowitz interview on positive mindsets ( 5 December 2020, p 40 ). What a refreshing article. I wish more doctors and therapists, not to mention friends and relatives, were more like Leibowitz. I wonder how much of the damage of, say, being "clinically obese" can be …
6 January 2021
From Jim Ainsworth, Kingsland, Herefordshire, UK
The interview with Leibowitz was full of sage advice. Of particular interest must be the fact that we have some control over our own mindset and can change it for the better, just by thinking positively. It would seem that the arts and sciences may be at one on this. John Milton summed up the …
6 January 2021
From James Weatherly, Scappoose, Oregon, US
Michael Le Page writes about the exciting news that an AI system has learned how to predict how proteins fold ( 5 December 2020, p 15 ). That is all well and good and I am sure it will help the human condition immeasurably, but when will the great scientific minds teach a robot to …
6 January 2021
From Mike Bell, Woolacombe, Devon, UK
After reading about efforts to put a quantum twist on Einstein's theories of space and time, I think I am getting a torsion headache ( 28 November 2020, p 34 ).
6 January 2021
Bureau of Land Management and American Wild Horse Campaign birth control programmes for wild horses in the US are separate entities ( 19/26 December 2020, p 12 ).
