Editor's pick: Dark dimples in baby galaxies
The issues with dark matter that Stuart Clark describes got me thinking (2 April, p 30). Gravity results from the warping of space-time caused by mass.
Aside from the effect of mass, however, is it possible that space-time itself did not start out smooth but instead incorporated persistent warping in the form of dimples and wrinkles? These distortions would have the effect of gravity without needing corresponding matter. They could explain the observed excess gravitation towards matter observed in galaxies and large structures without recourse to dark matter.
Under this model, the early galaxies would have coalesced in the dimples, which themselves would have been aligned by the wrinkles to form large-scale structures – filaments and walls. As well as the excess of gravity, this could account for the rapid formation of galaxies and the observations of structures that are larger than expected.
If, however, dark matter were the explanation, you would still have to explain how it coalesced so quickly and at such large scales. Little in nature is formed in a perfectly uniform state, so why should space-time be different?
Something fishy about that fact
In your interview with Timothy Leighton, he says “if you buy a farmed salmon today from North America, chances are it will have eaten a greater weight of antibiotics during its life than its own body weight” (26 March, p 32). The inherent improbability of this, given the efficacy of antibiotics and standard ratios of drug dose to organism weight, not to mention the relative costs of salmon and antibiotics, is stark.
Luton, Bedfordshire, UK
The editor writes:
• Leighton based this on public statements by the UK's Chief Medical Officer, which have been widely reproduced. We asked the Department of Health, which says: “The Chief Medical Officer's original comment in 2014 was based on information that was supplied to her verbally, and we now understand that this information may be unreliable.”
First class post
You will always be yourself as long as there are people to remember who you were
Claire Davies , which explores the loss of the self (newscientist.com/article/2086643)
When predicting the world fails
Anil Ananthaswamy describes the hypothesis that perception is founded on prediction (9 April, p 42). This is supported by my own experience that brain injury can cause perceptual disturbance in two ways.
It can leave the processing of sensory data intact, but still disrupt the generation of predictive perceptual models. And it can disrupt the confident recall of memories needed to fluently generate these models.
The result of these twin effects is a confusing state in which the processing of incoming sound and light signals functions perfectly but cognition becomes defective at precipitating out perceptions of objects and their states. For example, I remember early in my rehabilitation having to examine domestic switches and controls for an inordinate length of time, despite their being visually fully apparent to me, to determine whether they were “on” or “off”.
Evolution in word selection
Evolution is contested by those who know no better (26 March, p 5). But most of the population of the world is unlikely to grasp the basic process of evolution until science commentators regularly use language that describes its function. Currently, too many reports of evolution – more elsewhere than in New 杏吧原创 – tell of a species “choosing” to adapt or “deciding” to grow this feature or discard that.
Maybe it is more cumbersome to say that a population is descended only from those whose forebears had the feature in question, or that those with this feature failed to breed. However, as long as people see the language of “choosing”, they will continue to ask: “Will the next generation have smaller fingers, 'cos, like, everybody uses mobile phones?”
Is overeating making corals sick?
Ruth Gates mentions corals expelling their microalgae colonies because of the increase in temperature from global warming (9 April, p 26). Perhaps the corals are “vomiting” because of accidental overindulgence, rather than actively ejecting the microalgae. Might the increase in food due to raised temperatures be the real coral killer?
Barnsley, South Yorkshire, UK
Ruth Gates writes:
• The “vomiting” is not related to an abundance of food. Under normal conditions, corals carefully regulate the number of symbionts or microalgae in their tissue. The microalgae live inside the corals' cells, so they are ejected into the stomach, then bundled in a mucus ball, which is essentially vomited from the coral's mouth when it contracts. This happens more rapidly when the animal suffers environmental stress.
A natural history of other morality
Michael Tomasello's book A Natural History of Human Morality is definitely a must-read for all ages, but especially for educators (12 March, p 42). But it raises an obvious question: is there non-human morality?
The real roots of monogamy
David Barash is right to debunk the proposal that sexually transmitted infections explain monogamy (23 April, p 20). But he falls into another trap when he says that polygyny – men having more than one female partner – is a default human mating system. It seems to me that polygyny is the product of the development of agriculture, which enabled some men to become rich and afford more than one “wife”. Battles over land killed many young men, leaving a surplus of women who would otherwise get no partner.
Hunter-gatherer societies weren't like that. The most widespread such societies to survive into modern times are those of Indigenous Australians: in these societies, marriage was monogamous, and men couldn't become rich because all wealth was shared.
Your android is not paranoid enough
Aviva Rutkin reports machines teaching themselves to grapple with the real world (19 March, p 20). Impressive though progress is, I don't believe an artificially intelligent entity will be judged quasi-human until it professes to feeling very depressed, in spite of having a brain the size of a planet.
Wide-eyed and very far away
You report Mike Brown saying that from the distance of the Oort cloud “the sun appears so small that you could completely block it out with the head of a pin” (19 March, p 30). Since in such dim light the iris of the eye would be larger than a pinhead, a pin could not block out even a point source.
Trust no one when it comes to free will
Alun Anderson's review of The Mind Club by Daniel Wegner and Kurt Gray was fascinating, almost persuading me to buy the book (23 April, p 44). Then it occurred to me that their ideas applied to themselves: their interpretation of evidence depends on the “roiling, preconscious electrical activity” of their brains. How do we know that this produced sound conclusions?
In 1927, J. B. S. Haldane “If my mental processes are determined wholly by the motions of atoms in my brain, I have no reason to suppose that my beliefs are true. They may be sound chemically, but that does not make them sound logically.” Neuroscience has progressed since Haldane's time, but surely we cannot trust the conclusion that we have no free will when it is made by people who self-confessedly have no free will and are therefore not free to come to any other conclusion.
Interstellar probes work both ways
Billionaire Yuri Milner and physicist Stephen Hawking suggest that sending a probe to Alpha Centauri is practical, and it will take only 20 years to get there (16 April, p 9). If true, this would mean that the likelihood of intelligent life elsewhere in the galaxy is very much diminished. It would lead me to expect our own solar system to be full of tiny alien probes sending messages back to their own systems, which we would doubtless be able to intercept.
Costs and benefits of HIV prevention
You compare the cost of Truvada, used as a prophylactic against HIV, with that of treating people who are HIV-positive (2 April, p 5): “it costs £380,000 to treat an HIV-positive person for life, versus £4700 to supply Truvada for a year, so you'd have to take the drug for 80 years before it became more expensive”. This is only true if everyone taking Truvada would otherwise become HIV positive. Even in high risk populations the risk of infection is not 100 per cent.
Berlin, Germany
The editor writes:
• That was a first approximation. One model compares the cost of this drug with the saving made through treating fewer HIV infections. It shows an overall saving when the drug is given to men who have sex with men if 5 per cent of them get HIV a year (, ). This is roughly similar to the proportion of new HIV cases in gay men attending STI clinics who have had condomless sex as receptive partners in the past year.
For the record
• The US Centers for Disease Control and Prevention in fact that 25.3 million adults in the US suffer from daily (chronic) pain (Letters, 23 April).
• The person developing a device to distinguish types of infections is called Ravi Verma (30 April, p 16).