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Michael Brooks raises an important point about how we regard causality in his look at the paradoxes of a quantum universe (3 August, p 32) . Scientists should not uncritically accept principles enunciated by philosophers, such as Immanuel Kant's conception of the causality principle as a universal. This was never claimed by Kant's contemporary David …

It is blindingly obvious what is happening with "entangled" photons – two photons produced by splitting a single photon using a half-silvered mirror – that seem to exchange information at superluminal speeds. In some extra dimension which we cannot see, the photons aren't divided; they are still a single particle. Swanage, Dorset, UK

I am facing treatment-resistant depression myself, and being of a scientific mind, have already tried some of the new approaches you describe (27 July, p 34) , including the drug ketamine. I hope to have repetitive transcranial magnetic stimulation (rTMS) soon. Sadly, for me, large or small doses of ketamine bring only half a day …

In your feature on vagal nerve stimulation, HeartMath's Inner Balance Sensor was described and, apparently, recommended (13 July, p 46) . I bought it. Two weeks later, Feedback looked at the fruitloopy nature of an article by someone from HeartMath (27 July) . It seems disappointing that Â鶹´«Ã½ has become a pitchman for fruitloopery. …

Your look at whether modifying the US food stamps programme could combat obesity (newscientist.com/article/mg21929284.800) took me back to 1965, when I was a student in Philadelphia. My friends and I used to go to the federal building for free cornmeal, flour, oat flakes, red kidney beans, cooking oil, rice and other basic foodstuffs. Then President …

I read Feedback's item about the sign at a beach in Western Australia bearing the words "WARNING. Water" with interest (13 July) . I too have seen the sign, and it left me speechless. Despite the fact that someone was killed by a shark a few months earlier at the same beach, I did not …

I question the International Energy Agency's claim that there are "well-developed procedures" to ensure that major hydroelectric schemes are sustainable (6 July, p 6) . Negative environmental and social impacts of large dams often outweigh the economic benefits. Ensuring better management is hard in developing countries. An example is the poor use of environmental assessments …

David Flint is right to worry that the risk of methane from fracking leaking into the atmosphere may be underestimated (6 July, p 29) . However, his estimate that a leak of 0.7 per cent of the methane in shale gas would cancel out any benefit to climate that fracking has over simply burning coal …

Eye disorders are proving excellent early targets for stem cell therapies, notably restoring damaged corneas and in clinical trials for age-related macular degeneration, as your report on the transplanting of lab-grown photoreceptor cells into the eyes of blind mice indicates (27 July, p 11) . The big challenge will be to transfer the three-dimensional cell-culture …

In a relativistic look at the BBC's Science Hour radio show, prompted by its 55-minute duration, you remarked that the listener "needs to keep re-tuning his radio, since the signal from the moving radio station would be shifted in frequency as well". (Feedback, 20 July) . But if the transmitter moves at a constant rate, …

Jeff Hecht's look at distracted driving was very interesting (20 July, p 24) . Here in Australia we have accepted laws to curb use of phones while driving, which will save many lives. I cannot believe that parts of the US are so far behind in terms of legislation, but it makes some sense in …

The early days of Biosphere 2 demonstrate the folly of the more mystically inclined ecologists in seeing a purpose in evolution and geological history (27 July, p 41) . Why else, unless convinced that this planet has become the way it is in order for humans to live on it, would you build a self-contained …

Anil Ananthaswamy, in his discussion of shifting wind patterns on a warming Earth, points out that the margins of Hadley cells in the atmosphere of the mid-Cretaceous were at about latitude 27° "contrary to expectation" (20 July, p 34) . Perhaps this is because an extra set of cells developed, so there were four in …

So a giant "methane burp" as the Arctic warms could apparently worsen global warming and cost the world an estimated $60 trillion (27 July, p 16) . The solution may not be rocket science... or maybe it is. Surely the world's superpowers now have the technical expertise to monitor this by satellite. And if it …

Tiffany O'Callaghan reports on the cultural cues our voices give (13 July, p 38) . I testify in US federal courts as an expert witness on computer software issues and I have an English accent, having grown up in London and attended a private school in the UK. I have been told that US jurors …