Pruss versus Deleuze on whether there are sufficient reasons for an approximate universe

Further down, Delueze has a better explanation than Pruss for the times the universe seems arbitrary (why is pi irrational?).   Just below, Pruss wins out on making sense of why the world contains order and not just disorder. Are either correct?

"Now, suppose that there is some dimensionless constant α, say the fine-structure constant, which needs to be in some narrowish range to have a universe looking like ours in terms of whether stars form, etc. Simplify to suppose that there is only one such constant (in our world, there are probably more). Suppose also, as might well be the case, that this constant is a typical real number in that it is not capable of a finite description (in the way that e, π, 1, −8489/919074/7 are)—to express it needs something an infinite decimal expansion. The best system will then not contain a statement of the exact value for α. An exact value would require an infinitely long statement, and that would destroy the brevity of the best system. But specifying no value at all would militate against informativeness. By specifying a value to sufficient precision to ensure fine-tuning, the best system thereby also specifies that there are stars, etc.

"Suppose the correct value of α is 0.0029735.... That's too much precision to include in the best system—it goes against brevity. But including in the best system that 0.0029<α<0.0030 might be very informative—suppose, for instance, that it implies fine-tuning for stars, for instance.

"But then on the best-systems account of laws, it would be a required by law that the first four digits of α after the decimal point be 0029, but there would be no law for the further digits. But surely that is wrong. Surely either all the digits of α are law-required or none of them are.

-- Alexander Pruss' blog, July 2013

"Difference is not diversity. Diversity is given, but difference is that by which the given is given, that by which the given is given as diverse. Difference is not phenomenon but the noumenon closest to the phenomenon. It is therefore true that God makes the world by calculating, but his calculations never work out exactly, and this inexactitute or injustice in the result, this irreducible inequality, forms the condition of the world. The world ‘happens’ while God calculates; if the calculations were exact, there would be no world. The world can be regarded as a ‘remainder’, and the real in the world understood in terms of fractional or even incommensurable numbers. Every phenomenon refers to an inequality by which it is conditioned. Every diversity and every change refers to a difference which is its sufficient condition."

-- Giles Deleuze, Difference and Repetition, 1995 (English translation,Paul Patton)

High Altitude Flight and MRI Brain Lesions

In the past ten years, there have been several studies showing a small but significant increase in white matter brain lesions in professional and other high frequency divers. At least one such study correlated the increase in lesions to the number of accents from depth at over 10 meters per minute. This may implicate nitrogen micro-bubbles due to rapid decompression as a scuba diver ascends quickly as the cause, rather than the more ordinary arteriosclerosis seen with aging in the brain.

This past month, a similar study was published (it had been also announced at the AAN meeting in March 2013). This one was done in Air Force pilots rather than divers. In particular, the study looked at brain MRI scans in U2 spy plane pilots, who use a partially pressurized cabin with supplemental oxygen in a very high altitude, almost space-like low pressure environment during their flights. Once again, an increase in white matter brain lesions not explainable by atherosclerosis was seen. Micro-bubbles forming during the plane's ascent? Probably. Additionally, though there were no discernible cognitive consequences in the diver studies, the affected pilots had a slight decrease in some tests of cognition.

Although there had been a theory that venous bubbles forming in the body outside the head were being shunted through an atrial defect in the heart on the way to the brain, such as via a patent ductus arteriosus, recent studies have not shown that patent ductus arteriosus or atrial septal defect correlated with these lesions in divers as much as those rapid ascents do.

So, whenever possible, always ascend slowly when coming up from a dive, folks.



White matter hyperintensities on MRI in high-altitude U-2 pilots

Authors: Stephen McGuire, MD, Paul Sherman, MD, Leonardo Profenna, MD, MPH, Patrick Grogan, MD, John Sladky, MD, Anthony Brown, MD, Andrew Robinson, MD, Laura Rowland, PhD, Elliot Hong, MD, Beenish Patel, BS, David Tate, PhD, Elaine S. Kawano, BA, Peter Fox, MD and Peter Kochunov, PhD

doi: 10.1212/WNL.0b013e3182a1ab12

Neurology August 20, 2013 vol. 81 no. 8 729-735

Objective: To demonstrate that U-2 pilot occupational exposure to hypobaria leads to increased incidence of white matter hyperintensities (WMH) with a more uniform distribution throughout the brain irrespective of clinical neurologic decompression sickness history.

Methods: We evaluated imaging findings in 102 U-2 pilots and 91 controls matched for age, health, and education levels. Three-dimensional, T2-weighted, high-resolution (1-mm isotropic) imaging data were collected using fluid-attenuated inversion recovery sequence on a 3-tesla MRI scanner. Whole-brain and regional WMH volume and number were compared between groups using a 2-tailed Wilcoxon rank sum test.

Results: U-2 pilots demonstrated an increase in volume (394%; p = 0.004) and number (295%; p < 0.001) of WMH. Analysis of regional distribution demonstrated WMH more uniformly distributed throughout the brain in U-2 pilots compared with mainly frontal distribution in controls.

Conclusion: Pilots with occupational exposure to hypobaria showed a significant increase in WMH lesion volume and number. Unlike the healthy controls with predominantly WMH in the frontal white matter, WMH in pilots were more uniformly distributed throughout the brain. This is consistent with our hypothesized pattern of damage produced by interaction between microemboli and cerebral tissue, leading to thrombosis, coagulation, inflammation, and/or activation of innate immune response, although further studies will be necessary to clarify the pathologic mechanisms responsible.

On the Vagueness of Species

Current evolutionary theory claims that all life is historically descended from a single starting organism or group of organisms (but see reasonable dissenters here). If all species are ancestrally related, there are probably not any distinct boundaries between species if we take a really long view (from the viewpoint of hundreds of millions of years).

Yet, looking at things over just hundreds of years, species are almost completely divided into what seem to be natural kinds of life: an ohia lehua tree seems a very different kind from a tiger shark, though both are alive.

Where species boundaries break down in the present is when we look for ways to determine when one kind of ohia tree is the same species as another ohia tree. Often, as soon as we establish criteria for a particular species of tree, we find a tree which fits just outside our definition. At such times, is this a new species, or just a variant within the species?

 Simple essentialism about ohia species does not work.

What kind of universals can be used, then, for species? Vague ones. If physics holds a core of unavoidable uncertainty -- for example, we cannot sometimes know where a particle going at a known velocity is located -- why should we expect biology to have any absolutely working definition of an empirical concept such as where the line between ohia lehua species can be located?

Vagueness is not just an artifact of our language. It is a feature of the world we see.

Hula as Cardiac Rehabilitation

At the American Psychological Association this week, the traditional Hawaiian dance, hula, was put through its paces in a study presented yesterday. See this pdf. Turns out that hula is comparable to tennis or basketball in cardiovascular training benefits for those who have had heart problems.

Dancing the hula: good for the heart.

Artificially Sweetened Soft Drinks May Increase the Risk of Stroke

This week JAMA published an epidemiological study of 451,743 Europeans from 10 countries which suggested there is an increased risk of m...