Wave resolution
Harry Collins does not clarify why the multimillion-dollar hunt for gravitational waves is a worthwhile enterprise (27 November 2010, p 30).
The existence of gravitational radiation was doubted by physicists, including Einstein, through the 1920s and 30s. Einstein’s argument was that gravity is equivalent to acceleration of the reference frame and, consequently, a distortion of space-time. This led to the concept of “ripples” in space-time, as mentioned in your picture caption, which is at odds with the idea of energy-carrying waves and a theory of gravitational field.
Four decades of observing the Hulse-Taylor binary neutron star system mentioned by Collins shows to high accuracy that the system is losing orbital energy. This is interpreted as being because the system emits waves on a real gravitational field, rather than ripples in space-time.
Confirmation of such waves is a major challenge, as the Hulse-Taylor waves are far too weak for detectors. Yet direct detection of gravitational waves is crucial in determining whether the pre-relativity Einstein was right in his concept of gravity as a space-filling field, like the electromagnetic field, or whether the correct one was the later Einstein, who carried his doubts about gravitational waves to the grave.
We are spending many millions on mega-experiments like principally to resolve this fundamental question.
We have named gravitational waves correctly in all instances
Early birds
When discussing the evolutionary transition between dinosaurs and birds (11 December 2010, p 36), surprisingly James O’Donoghue did not mention the gizzard. It could be argued that this muscular stomach used for grinding up food did for birds what the internal combustion engine did for aeroplanes, and the nuclear reactor for submarines.
Effectively the gizzard turbocharged the bird’s digestive system, allowing it to collect and utilise more food energy. It also released birds from the handicap of grinding their food with cumbersome and heavy jaws armed with teeth. This in turn meant great savings in head weight and the neck musculature to support it. Without a working gizzard, long-range powered flight would have been difficult.
From Steven King
Palaeontologist Xing Xu suggests that protofeathers, which could pre-date dinosaurs, may have benefited their owners through their striking appearance.
Another possible advantage of protofeathers would have been to break up a small dinosaur’s outline, thereby providing camouflage, especially if they were coloured correctly.
Both these traits would be advantageous to the creatures’ survival and thus their likelihood to reproduce. Selection may then have resulted in more extravagant growths suitable for warmth, display and flight.
I was also surprised that Xu used the phrase “the first feathers probably evolved for display”. Evolutionists should avoid such teleological language, which risks confusing evolution with Kiplingesque just-so stories.
Crewkerne, Somerset, UK
Pattern of the past
I have no wish to disparage Frank Farris’s creativity with hyperbolic wallpaper (11 December 2010, p 44), but the article inadvertently gave a misleading impression of the mathematical novelty behind his designs. We are told that Farris “found that the Poincarite equivalent of a reflection is… inversion”. I’m sure he did, but he almost certainly found it by consulting the literature: it was published by Eugenio Beltrami in 1868 and was common currency at the end of the 19th century when Henri Poincar茅, Felix Klein and others were studying tiling patterns related to groups of isometries of hyperbolic space.
This extensive area of mathematics remains of central importance in modern research. For example, it is part of the background to Andrew Wiles’s proof of Fermat’s last theorem.
Artistic use of hyperbolic tilings goes back to the Dutch artist M. C. Escher around 1956, using the “disc” model rather than the half-plane. At first he did not appreciate the mathematical connection, but when the geometer H. S. M. Coxeter pointed it out, Escher made explicit use of the mathematics.
I’m sure that Farris explains such things in his elegant presentations. It’s a pity that the article did not.
Neanderthal nurture
While interbreeding is one explanation for the greater homology of Neanderthal DNA with non-African than with African humans (4 December 2010, p 32), there is a simpler alternative explanation.
The genetic divergence between African and non-African humans which has occurred during the 60 or so millennia since their separation may be partly due to drift but, given the timescale, must be due predominantly to differences in adaptation.
The non-African Homo sapiens and Neanderthals would have experienced similar environmental conditions, whilst those experienced by the African branch would have been quite different. Perhaps the extra similarity is due to coexistence rather than cohabitation.
From Bryn Glover
A good candidate for the cause of the disappearance of the Neanderthals 鈥� especially as their mixing and breeding with our ancestors has now been established as a fact 鈥� has to be the capacity for genocide that persists in Homo sapiens. Apparent today, particularly between rival tribal and religious groupings, this tendency would certainly have been exacerbated by clashes involving sexual jealousy.
How likely is it that we’ve actually discovered our first example of a Nazi-like “final solution”?
Cracoe, North Yorkshire, UK
Pee it out
In my experience, it is not only frogs that can pass foreign objects in their urine (11 December 2010, p 16). As a gynaecologist, I have applied hundreds of pairs of Filshie clips 鈥� small self-locking clips made of titanium and silicone rubber 鈥� to Fallopian tubes for female sterilisation. Several years ago one of my patients, upon whom I had performed this procedure, came and showed me something she had just passed through her urethra in the shower.
It was a Filshie clip. An X-ray confirmed only one remained.
Philosophical denial
Scepticism towards Einstein’s theory of relativity is not confined to irrational conservatives (13 November 2010, p 48). In his later years, the philosopher Karl Popper became increasingly troubled by relativity. I argue that, for Popper, inconsistencies in Einstein’s presentation of his theory gave a rational explanation for persistent opposition to it (, vol 41, p 354).
Popper himself ended up preferring Hendrik Lorentz’s version of relativity, which retained absolute space and time.
Farming Skippy
The reason that marsupials such as kangaroos are not farmed in Australia (9 October 2010, p 42) is not because it is too difficult, but rather that in various states it is either illegal to do so or discouraged. In the past, considerable work has been done on farming marsupials.
I was familiar with a project to domesticate the eastern wallaroo, or euro (), which used sheep netting fences with an electric fence on the top and bottom. The initial stock, having been obtained from sources including zoos and those hand reared as pets, were quiet to start with. Joeys born to this stock tended to be quiet too, but any that jumped the fence were shot for being too bouncy.
The marsupials were handled like deer, in a darkened shed under red lights. Although euros are not as large as “big red” kangaroos, breeding males had to be treated with respect in the breeding season. Excess males were castrated to prevent fights.
Conveniently, the animals’ pouch reflex means that when they have a bag put over their head, they curl up and relax, and can be transported to the abattoir with little stress.
The domestication project was working well when a ban was introduced. All the specially bred stock were subsequently sent to slaughter.
We have the perfect animal to provide healthy meat with less damage to the environment, but we aren’t allowed to farm them. Instead, they are expensively fenced out of farmland, and shot or poisoned so we can run sheep and cattle.
From Lionel Delaney
I disagree with the arguments put forward by Dror Ben Ami against shooting and eating kangaroos (20 November 2010, p 30).
Animals that lower a farmer’s profitability are treated as pests and farmers try to reduce their numbers to make a living from their land. Make the animal valuable to the people who have to pay for its existence and they will protect it or, in the kangaroo’s case, conserve it.
Kangaroos make good, tasty meat. To shoot them and let them rot is crazy, but that is the present system for grey kangaroos.
Rylstone, New South Wales, Australia
From Bernie Masters
Kangaroo numbers are much higher now than at the time of European settlement in 1788. Provision of pasture and watering points by farmers for their livestock has allowed the total population of kangaroos to increase, albeit with fluctuations due to seasonal climate variability.
Kangaroos used to be rarer, making them a sought-after source of food for Indigenous Australian people. One woman I spoke to recalled seeing her first kangaroo in the Tuart Forest National Park, Western Australia, on her 21st birthday in 1965. Now, between 500 and 1000 kangaroos are shot in this park each year following a population explosion.
Kangaroo grazing is listed as a threat to local biodiversity under federal government laws in some parts of Australia because it has such a detrimental effect on native bushland.
Capel, Western Australia
Dreams come true
Apparently red dwarfs are “more bountiful than expected” (4 December 2010, p 7).
Should these be the stars I wish upon, then?
For the record
鈥� An unfortunate last-minute editing error made plant biologist a “he” (25 December 2010, p 45). Apologies.
鈥� A sentence in our article on networked bacteria was meant to read “Electrosynthesis could also produce industrial inorganic compounds like caustic soda…”. Caustic soda is not, of course, organic (18 December 2010, p 38).