Swathed in darkness
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 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 (). 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 mega-matter could 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.
According to general relativity, a black hole used to be defined by its singularity 鈥� 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
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 fishing cannot continue. This film comes at an extremely opportune time for the UK 鈥� when the Marine and Coastal Access Bill is working its way through Parliament.
The bill will provide a once-in-a-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.
Chiropractic case
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 high-velocity manipulation of the neck.
Chiropractic does cause minor transitory adverse reactions, but the evidence that it is life-threatening 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.
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
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 of world-war veterans did not doubt the legitimacy of the conflict, but some did. Equally, while some of today’s veterans question the justification for the war they were involved in, the majority do not.
More importantly, the post-battle symptoms we see in soldiers today are nothing new, and indeed are remarkably similar to those reported by veterans of the Somme and Ypres. Even veterans who thought the first world war was justified suffered from shell shock and other psychological difficulties.
The greatest cause of long-term trauma is not linked to the perceived legitimacy of a conflict, but rather to the nature of the fighting, including factors such as having a safe retreat, a visible enemy and feeling achievement related to military goals.
It helps no one to misidentify the causes of post-traumatic stress disorder. Trying to use it as a lever to criticise the unjust wars of today is as much an injustice as the conflicts themselves.
Weaker apart?
Prompted by your essay on C. P. Snow (2 May, p 26), David Roser commented on the poor communication between related disciplines at his university (30 May, p 20).
I am a first-year student studying anthropology, sociology, psychology and philosophy. All the courses deal with concepts of “the person”, but with little overlap. Raising this with tutors often leads to entertaining but dismissive observations about the other disciplines.
This may be because I am studying at quite a low level, but I worry that not only are the scientists not talking to the arts faculty, but even within the arts, the schools pooh-pooh each other.
Despite all the high words, C. P. Snow probably had it right, in perpetuity.
Like bugs
David Attenborough uses the example of termites working blindly in a nest to illustrate that humans may also lack a sensory mechanism 鈥� the one they need to perceive a creator (16 May, p 28). However, should the termites sense him, there is no reason why they would impute him to be their creator, and scientific observers would know for sure he was not.
Still, I believe most atheists would agree that there may exist vastly more intelligent life forms outside our human termite nest, of which we remain unaware.
Fiery spectre
In her article on medical research into death by fire, Linda Geddes states that it is a myth that bodies usually sit up as they burn (23 May, p 32).
As an apprentice electrician in the mid-1950s, I was working one day on a thermostat control in a newly built crematorium. An operator directed me to look through a furnace’s inspection window, where I saw a skeleton sitting up surrounded by flames from the gas burners. While I watched in amazement, the skull fell off and the bones collapsed.
Soon afterwards, the tray was removed and when the ashes had cooled down, the bones were ground up in a large electric mincing machine. My will now states that I wish to be buried.
Nanoversal science
Frederick Blundun argues that an intelligent being would inevitably develop Newtonian dynamics (23 May, p 25).
However, the universe experienced by a microscopic or nanoscale intelligence would be dominated by fluid dynamics, chaotic turbulence and fractal boundaries. They would be likely to develop a theory of relativistic quantum dynamics long before they developed the technology to manipulate what would be, to them, the extremely large apparatus required to measure gravitational interactions.
With a relativistic theory that pre-dates their ability to accurately measure gravity, they would move straight to general relativity. Possibly they might conceive of Newtonian dynamics in an attempt to imagine how the universe might appear to a macroscopic intelligence like us.
With regard to religions, they could not conceive of the Olympian gods or the God of the Abrahamic tradition, because these concepts are not based on any of the measurable attributes of the universe.
Stressful lives
I was fascinated by the link found between brain physiology during conflict and post-traumatic stress disorder in soldiers, reported by Peter Aldhous (9 May, p 40).
Is it possible that potential interventions and treatments mentioned in the article could be applied far more widely? I suggest that most mental distress, unless drug related, is caused by extreme and overwhelming stresses at various points in a person’s life, and is a consequence of this stress overload.
Future hopes
Never mind Ray Kurzweil’s singularities in 2045 (9 May, p 26); when will we all have personal helicopters and more leisure time? Any futurologist who doesn’t promise these isn’t playing the game properly.
For the record
鈥� We mistakenly suggested that greater gender inequality increases the instance of female mathematicians in a country. Of course that should have been gender equality (6 June, p 7).
鈥� Some corals live in water flowing at a rate of 10 metres per second. However, we should not have implied that this was a minimum flow rate for coral survival (9 May, p 37).