Swathed in darkness

OPINION LETTERS Swathed in darkness From Max Wallis, Cardiff Centre for Astrobiology, Cardiff University Stephen Battersby is unfair to Albert Einstein in saying his relativity theory fails if Sagittarius A* turns out not to be a black hole (23 May, p 28). At the British Gravity meeting in April, long-time guru of black holes, Kip Thorne, reminded us that J. Robert Oppenheimer and his student Hartland Snyder predicted black holes in their 1939 paper (Physical Review, vol 56, p 455). Einstein in fact rejected the idea of black holes in his own paper that year (Annals of Mathematics, vol 40, p 922), insisting that matter cannot travel faster than light. Einstein argued that matter cannot cross the event horizon, where light slows to zero speed to an outside observer or, were you able to follow its path, plunges into an infinitely deep hole. An alternative to the black hole solution to Einstein’s equation would mean that black holes don’t exist. Instead, contracting megamattercould simply pile up at the event horizon. Light would still be distorted but there would be no outburst from gas swirls crossing

the horizon or falling down the hole. The “collapsar” that follows from Einstein’s reasoning is not as glamorous as a black hole, but let’s be ready to give him credit if one is indeed found later this year. Cardiff, UK From Christopher Game According to general relativity, a black hole used to be defined by its singularity – a point of infinite density. But Battersby now tells us that its defining characteristic is the presence of an event horizon, a thing no longer specific to general relativity. The true believers of the general relativity religion will never admit they are mistaken. They just move the goalposts. Kew, Victoria, Australia

Thanks for all the fish From Helen Phillips, Natural England Linda Geddes’s review of End of the Line, a documentary on the effects of overfishing, hits the mark (6 June, p 48). For decades, the marine environment has been damaged by over-exploitation. The lesson to take from End of the Line is that unregulated

Enigma Number 1550

Eightmanband GWYN OWEN The letters of EIGHTMAN represent different digits. When representing a number, ENIGMA is the product of GGG and TTT. Furthermore, a six-digit number using the letters of ENIGMA in a different order is the product of GGG and HHH. Please send in the number EIGHTMAN.

WIN £15 will be awarded to the sender of the first correct answer opened on Wednesday 22 July. The Editor’s decision is final. Please send entries to Enigma 1550, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, or to [email protected] (please include your postal address). Answer to 1544 Spanish squares: The numerical value of the square root of (CERO x UNO x NUEVE) is 812224 The winner Richard Harvey of Ancaster, Ontario, Canada

24 | NewScientist | 20 June 2009

fishing cannot continue. This film comes at an extremely opportune time for the UK – when the Marine and Coastal Access Bill is working its way through Parliament. The bill will provide a once-ina-lifetime opportunity to rescue our seas, an incredibly precious resource, from additional harm. It aims to restore fish stocks

while helping the fishing industry to move towards a more sustainable future. As End of the Line shows, this level of protection cannot come quickly enough if we are to avert an environmental disaster of unprecedented dimensions. London, UK

Chiropractic case From George Lewith, www.cam-research-group.co.uk The recent opinion piece by Edzard Ernst fails to give a balanced view of chiropractic (30 May, p 22). Since its origins in the middle of the 19th century, chiropractic has changed considerably. It no longer espouses a vitalistic philosophy. Equally, conventional medicine has changed and no longer bleeds dehydrated cholera patients to death. The evidence base for chiropractic is limited and more research is needed; much the same is true of general practice, where perhaps only 15 to 20 per cent of the interventions used are based on sound evidence. Chiropractors do not claim incontrovertible evidence for

the use of chiropractic in children, only that there is evidence for their claims. Ernst implies that chiropractic is the cause of stroke based on inconclusive case reports. The post-mortem evidence suggests that vertebrobasilar stroke is an inflammatory arterial condition, and substantial case-controlled studies (10 million people over 10 years) indicate that it is equally likely to occur after a visit to a family doctor as after a highvelocity manipulation of the neck. Chiropractic does cause minor transitory adverse reactions, but the evidence that it is lifethreatening and damages the vertebral arteries is certainly inconclusive. The way in which the evidence is quoted in Ernst’s article implies causation from coincidental association, a common epidemiological trap. Southampton, UK From Byron Rigby The libel case about chiropractic, on which David Allen Green comments, (16 May, p 24) could have been avoided by the use of scientific, courteous language. “Bogus” is not a scientific term. Why use it? “Unverified” would have been just as good. As Green says, “it may be that the statements that led to these actions were indeed libellous”. Even so, he is right in saying that the “reverse burden of proof” is obnoxious if one has to wait and pay for a court appearance to prove a statement was defensible. Bundoora, Victoria, Australia

Shocking wars From Taz Wake While it is likely that there was less public support for the wars in Vietnam, Afghanistan and Iraq than for the first and second world wars (16 May, p 26), Stephen Wealthall wrongly assumes that this is reflected in prevailing attitudes in the military. As Wealthall states, the majority