Addendum to "Coherent Lagrangian vortices: The black holes of turbulence"

In Haller and Beron-Vera (2013) we developed a variational principle for the detection of coherent Lagrangian vortex boundaries. The solutions of this variational principle turn out to be closed null-geodesics of the Lorentzian metric associated with a generalized Green-Lagrange strain tensor family. This metric interpretation implies a mathematical analogy between coherent Lagrangian vortex boundaries and photon spheres in general relativity. Here we give an improved discussion on this analogy.Comment: Revised 27 June 201

Coherent Lagrangian vortices: The black holes of turbulence

We introduce a simple variational principle for coherent material vortices in two-dimensional turbulence. Vortex boundaries are sought as closed stationary curves of the averaged Lagrangian strain. Solutions to this problem turn out to be mathematically equivalent to photon spheres around black holes in cosmology. The fluidic photon spheres satisfy explicit differential equations whose outermost limit cycles are optimal Lagrangian vortex boundaries. As an application, we uncover super-coherent material eddies in the South Atlantic, which yield specific Lagrangian transport estimates for Agulhas rings.Comment: To appear in JFM Rapid

Kierkegaard’s ‘Repetition’ and Pilgrimage

In 1843, the Danish philosopher Kierkegaard wondered whether it was possible to repeat an experience. He attempted to relive experiences he once had in Berlin by revisiting haunts of his earlier self. After several days, he concluded that his repetition of experience was unsuccessful. Many people make similar attempts at repetition when they make, for example, the pilgrimage to Camino de Santiago multiple times. What could a person hope to gain by this repetition? What prevents successful repetition, suggests Kierkegaard, is beginning with the end in mind rather than traveling merely to collect random impressions. Repetition fails, argues Kierkegaard, when it is tried as some kind of experiment rather than a commitment, and this failure of immersion makes us a passive observer of ourselves. An authentic repetition, he argues, can only happen after one surrenders control of events. One must give something up to get anything back. To experience Berlin again, or to repeat a pilgrimage, one must give up expectations and surrender to whatever unfolds. In this way, the repeat traveler would surrender the objective stance of someone comparing events with earlier ones. Instead, they would be actively engaged, and thus able to actually re-experience something like what happened before. In contrast to passively ‘recollecting’ past events, Kierkegaard advises that a successful ‘repetition’ is to live with a repeatedly renewed commitment to living in the present. Repetition is, paradoxically, not about the past but, rather, about ‘the earnestness of existence.’ Pilgrims, however, often try on identities and roles in attempts to experience what they have heard of in other pilgrim’s stories. It may be that some repeat pilgrims are not so much nostalgically reliving their previous experiences, as trying to experience what others have experienced, and that they themselves did not experience the first time. It will be argued that this imitation of life can never be fully engaged in, and thus, it will always be disappointing because it necessarily involves self-consciously observing oneself in the role

Pilgrimage and Paradigm Shifts: The Role of Experience in Identity Transformations

Some kinds of knowledge can only be acquired by direct experience. Engaging in a pilgrimage can transform a person by allowing them to inhabit different worldviews, or paradigms, that would otherwise remain inaccessible to them. The pilgrim then learns to see the world in a new and different way; has ideas not imagined before the experience, and; may even change their life in ways unforeseen before the pilgrimage. It is uncertain just how, and in what unexpected ways, one might change. Most often these changes are welcomed; however, it is unclear whether one’s prepilgrim- self, before the change, would approve of the end-result. How can one rationally choose to undertake a pilgrimage that might cause change, when one cannot really appreciate whether that change will be for the better until after one has leapt into it? This makes the choice seem irrational and arbitrary. This paper argues that the most likely changes that come about on pilgrimage are a matter of reorientation, rather than a complete metamorphosis (although those happen). Religious experiences that change one’s identity are most often a matter of reorientation of commitment, rather than radical transformation of self. The permanence of the change depends on the commitment to that identity after the change is made

A Changed Understanding of Miracles in Religious Tourism

In this modern age, an unsceptical acceptance of supernatural events–those which cannot be explained as part of the natural order of things–is less common than it once was. This trend is reflected in the declining frequency of miracle-cures certified by the Medical Bureau at Lourdes. Yet miracles past, and the promise of possible miracles in the present, still attract multitudes of religious pilgrims and tourists to sacred sites all over the world. While the frequency of miracles goes down, the appeal of miracles goes on, and the number of religious visitors has not declined. What role do miracles now play in religious tourism? The miracles associated with religious pilgrimage and tourism will be distinguished into two categories. Archaic Miracles are those that occurred in pre-scientific, often medieval, times. These often involve very implausible stories, and have the air of folklore and fairy-tales. Modern Age Miracles occur after the development of science and the Enlightenment commitment to understanding things through reason. This paper will conclude with a ‘compatibilist solution’ between two seemingly contradictory positions–miracles and science. A miraculous event is often taken as one that is contrary to the laws of nature; while religious sceptics reject miracles as unscientific. Yet the scientific demand for complete explanations is too demanding and may be impossible to satisfy. Inspired by a physicist, Marcel Glieser, I explain that there are fundamental limits to our understanding of the universe, which implies that mysteries will always remain. However, an inescapable mystery is no support for supernatural explanations. A modern-day pilgrim need not believe in the supernatural to find meaning in unexplained events, but merely needs to recognise that even ordinary things remain fundamentally unexplained. I defend this ‘wonder of existence’ solution to the problem of miracles, and provide examples, and show how this is relevant to religious tourism

Anharmonic Self-Energy of Phonons: Ab Initio Calculations and Neutron Spin Echo Measurements

We have calculated (ab initio) and measured (by spin-echo techniques) the anharmonic self-energy of phonons at the X-point of the Brillouin zone for isotopically pure germanium. The real part agrees with former, less accurate, high temperature data obtained by inelastic neutron scattering on natural germanium. For the imaginary part our results provide evidence that transverse acoustic phonons at the X-point are very long lived at low temperatures, i.e. their probability of decay approaches zero, as a consequence of an unusual decay mechanism allowed by energy conservation.Comment: 8 pages, 2 figures, pdf fil

Opportunities and Competition in Thick Labor Markets: Evidence from Plant Closures

Since Marshall (1890), it has been widely held in urban economic theory that cities insure workers against the risk of unemployment by offering a larger pool of potential jobs. Using a large administrative panel data set on workers displaced as a result of plant closures, we examine whether positive effects from a higher urban job density are offset by more intense competition between workers. When controlling for the sorting of workers between regions, we find robust evidence that the effect of job competition on unemployment duration exceeds that of job opportunities in absolute value. Our results put the idea of urban risk‐sharing into perspective and provide an explanation for observed longer unemployment durations in cities