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There is an easily verifiable proof that time travel is impossible, which I was able to demonstrate only the other night in The Angel pub in London's St Giles High Street. I took several sheets of blank paper and at the top of the first I wrote "Plans For Time Machine". Under this I wrote …

Jeremy Leggett's article promoting solar power contains several statements, unfortunately not backed by facts, that imply that solar power is relatively cheap and that economists are conspiring to make it sound expensive (6 September, p 23) . As an exercise I costed a system that would take my house off the grid. Last month I …

I'm afraid I have to disagree with John Fisher and Tony Woodhouse's opinions on the spread of viruses (20 September, p 26) . The most common cause of viral infection is human error. Opening an email which is from either an unknown sender, or has a subject which seems less than genuine, spreads viruses by …

Peter Wienand's response to Tony Straka raises doubts about the authority of the Bridgeman vs Corel case and argues for copyright associated with photographic reproductions of art works in the public domain (20 September, p 26) . While some may disagree with the finding of the case, many others agree with it as being consistent …

Graham Lawton exaggerates the virtues of the five-factor model in his article on personality (13 September, p 30) . He states that "the score you get on one has no bearing on the others". I am afraid that this is not so. In the manual of their revised NEO Personality Inventory, Paul Costa and Robert …

I am confused by the assertion in your article on personality that agriculture emerged as part of radical technological advances 40,000 ago, and that it affected our genes. While certain genes may have been changing, it would not have been anything to do with farming, as this did not appear until at least 30,000 years …

When a person feels faint, or has indeed fainted, first aiders are trained to raise that person's legs so as to increase the blood flow to the brain – and the recovery is quite dramatic. While an inflatable "shock sheet" sounds like a good idea (13 September, p 24) , would there also be some …

I was surprised by the complexity of the idea of linking several cell phones to gather the last remnants of available battery power for emergency calls (13 September, p 22) . If cellphones already have technology to shut them down before all battery power is entirely drained, wouldn't it make much more sense to program …

Your correspondent Ian McKinley points out that 10 13 years would be required to transmute the iodine using a laser (20 September, p 27) . This is obviously a ridiculous proposition. Scientists are intelligent people, and would accomplish the task in just one year, using 10 13 lasers.

• In our editorial on contaminated cell lines (20 September, p 5) we mistakenly called Walter Nelson Rees "William" Nelson Rees.

Philip Stott quotes two recent papers as supposedly implying that carbon emissions should not be reduced. However, neither of the papers quoted support that position (20 September, p 25) . The first paper, by Ján Veizer and Nir Shaviv, is a speculative study on climate forcings over hundreds of millions of years, for which we …

Stott claims that the paper by Shaviv and Veizer is important science that did not get enough attention from media and policy makers. The opposite is true: it received a disproportionate amount of media coverage due to the strong but unfounded claims the authors made in their press releases. Shaviv and Veizer claim to have …

The paradoxes referred to when time travel is discussed always seem to involve sentient beings (20 September, p 28) . Someone goes back in time and alters the time line or carries information back with them. Is it possible to specify a significant paradox involving only non-sentient objects – say a rock, or an electron? …