A Peculiar Moon in Lord of the Rings

Lord of the Rings, the fantasy trilogy by J.R.R. Tolkein, takes place in Middle Earth, which has a different geography than our Earth, some different humanoids (Elves, Dwarfs, Hobbits) walking/talking trees (Ents) etc. But the weather, the vegetation and the animal life are mostly similar to ours. In particular, the sun, the moon and the stars seem pretty much the same. The characters are often out and about by night, so the phase and position of the moon is often mentioned. In one scene, however, the moon behaves a bit strangely.

In The Two Towers, Book Four, Chapter 4, Of Herbs and Stewed Rabbits, in the first page of that chapter, "The moon was now three nights from the full, but it did not climb over the mountains until nearly midnight, and the early night was very dark." The mountains are to the east of their location, which would block the early rising moon. Does "three nights from the full" mean the moon is waxing and it is three days before it will be full - or does it mean the moon is waning and it is three days after the full moon? I intuitively interpreted that as the first case: the moon is waxing, it's before the full moon. In Moon Phases in The Lord of the Rings there's an impressively detailed accounting which agrees with that interpretation. But when the moon is waxing, it will typically reach its highest point in the sky before midnight. This really only depends on the fact that the moon is illuminated by light reflected from the sun. In much of the rest of Tolkein, the moon does behave quite normally, for example: "If the Moon gave enough light, we would use it, but alas he sets early and is yet young and pale".

Here's another loony scene however. In the chapter In the house of tom bombadil: "In the dead night, Frodo lay in a dream without light. Then he saw the young moon rising;". Dreams are notoriously full of nonsense, so I guess we can't hold Tolkein responsible for unfortunate lunar behaviour in the bad dream of a little guy with hairy toes.

In societies without widespread artificial lighting, most people were very conscious of the phases of the moon. Today however, this is far from true. Mention the easily observed fact that the full moon typically rises around the same time as the sunset and then sets around sunrise and the expression on people's faces will all too often plainly reveal that this is news to them.

The Darkest Galaxy

A Complete Spectroscopic Survey of the Milky Way Satellite Segue 1: The Darkest Galaxy arXiv preprint.

We present the results of a comprehensive Keck/DEIMOS spectroscopic survey of the ultra-faint Milky Way satellite galaxy Segue 1. We have obtained velocity measurements for 99.1% of the stars within 67 pc (2.3 half-light radii) of the center of Segue 1 that have colors and magnitudes consistent with membership, down to a magnitude limit of r=21.7. Based on photometric, kinematic, and metallicity information, we identify 71 stars as probable Segue 1 members, including some as far out as 87 pc. After correcting for the influence of binary stars using repeated velocity measurements, we determine a velocity dispersion of 3.7^{+1.4}_{-1.1} km/s, with a corresponding mass within the half-light radius of 5.8^{+8.2}_{-3.1} x 10^5 Msun. The stellar kinematics of Segue 1 require very high mass-to-light ratios unless it is far from dynamical equilibrium, even if the period distribution of unresolved binary stars is skewed toward implausibly short periods. With a total luminosity less than that of a single bright red giant and a V-band mass-to-light ratio of 3400 Msun/Lsun, Segue 1 is the darkest galaxy currently known. We critically re-examine recent claims that Segue 1 is a tidally disrupting star cluster and that kinematic samples are contaminated by the Sagittarius stream. The extremely low metallicities ([Fe/H] < -3) of two Segue 1 stars and the large metallicity spread among the members demonstrate conclusively that Segue 1 is a dwarf galaxy, and we find no evidence in favor of tidal effects. We also show that contamination by the Sagittarius stream has been overestimated. Segue 1 has the highest measured dark matter density of any known galaxy and will therefore be a prime testing ground for dark matter physics and galaxy formation on small scales

Quantum Interference

Pairs Rule Quantum Interference in Science.

Quantum interference is one of the most mysterious features of quantum mechanics. In fact, Feynman referred to the double-slit interference experiment for single particles as the "only" mystery in quantum mechanics (1). On page 418 of this issue, Sinha et al. (2) describe a recent experiment that shows that quantum interference from a single photon arises only from pairs of possible paths through an interferometer. There is no need to invoke additional interference terms that might arise from interactions of three or more paths.

The Cyberiad by Stanislaw Lem

I'm in the middle of rereading one of my favorite collections of tales, "The Cyberiad" by Stanislaw Lem, translation by Michael Kandel. Originally in Polish, the English version is filled with delightful word play and whimsy.
"He who has had, has been, but he who hasn't been, has been had"

A Film about East Timor

A Hero's Journey : A documentary film about forgiveness with Xanana Gusmao of East Timor (Timor-Leste) directed by Grace Phan.

FREE FALL: World champion freediver Guillaume Nery special dive at Dean's Blue Hole, the deepest blue hole in the world filmed entirely on breath hold by the french champion Julie Gautier. This video is a FICTION and an ARTISTIC PROJECT. Edited by BLUENERY (c).

Cosmic Acceleration

Cosmology forum: Is dark energy really a mystery? in Nature.

The Universe is expanding. And the expansion seems to be speeding up. To account for that acceleration, a mysterious factor, 'dark energy', is often invoked. A contrary opinion — that this factor isn't at all mysterious — is here given voice, along with counter-arguments against that view.

Topological Insulators

Topological insulators: Star material in Nature.
Topological insulators are a new kind of material which conduct electricity only on their surfaces. There are new, inexpensive compounds based on bismuth which have created a lot of excitement.
Solid-state physics: U-turns strictly prohibited also in Nature.

According to theory, electrons on the surface of a topological insulator are not allowed to make U-turns. This notion, and some of its main consequences, has now been tested experimentally.

North Pacific Deep Water Formation in the last ice age

When Still Waters Ran Deep in Science.

"Deep water" and "bottom water"—the waters that fill the deep parts of ocean basins—form when surface waters become dense and sink. Today, this occurs in the northern North Atlantic and around Antarctica, but not in the North Pacific. There, surface waters do not become dense enough to sink more than a few hundred meters. In the past, however, it seems things were different. Recently, Okazaki et al. offered new insight into the ancient history of the ocean from radiocarbon data and modeling analyses (1). They suggest that deep water formed in the North Pacific at the beginning of the transition out of the last ice age.

The Mystery of Sea-Floor Methane

The Ongoing Mystery of Sea-Floor Methane in Science.

Each year, ocean sediments produce a quantity of methane equivalent to about half of the methane emitted to the atmosphere from all natural sources (1). Very little of the methane produced below the sea floor, however, reaches the ocean or the atmosphere; most is consumed by anaerobic microorganisms as it diffuses up through oxygen-poor (anoxic) sediments. Researchers recognized this process, known as anaerobic methane oxidation (AMO), nearly 35 years ago (2), but it remains poorly understood. Investigators have not been able to firmly establish the reaction mechanism, fully understand the factors that control oxidation rates, or isolate the responsible organisms. This represents a gaping hole in our understanding of one of Earth's primary sinks for methane. Recent studies of a rare but intriguing sedimentary environment–sea-floor seeps of methane-rich fluids–have provided new insights into the microorganisms that inhabit methane-rich sediments, but raised new questions regarding reaction mechanisms.

A Low Luminosity Supernova

The Subluminous Supernova 2007qd: A Missing Link in a Family of Low-Luminosity Type Ia Supernovae preprint.

We present multi-band photometry and multi-epoch spectroscopy of the peculiar Type Ia supernova (SN Ia) 2007qd, discovered by the SDSS-II Supernova Survey. It possesses physical properties intermediate to those of the peculiar SN 2002cx and the extremely low-luminosity SN 2008ha. Optical photometry indicates that it had an extraordinarily fast rise time of <= 10 days and a peak absolute B magnitude of -15.4 +/- 0.2 at most, making it one of the most subluminous SN Ia ever observed. Follow-up spectroscopy of SN 2007qd near maximum brightness unambiguously shows the presence of intermediate-mass elements which are likely caused by carbon/oxygen nuclear burning. Near maximum brightness, SN 2007qd had a photospheric velocity of only 2800 km/s, similar to that of SN 2008ha but about 4000 and 7000 km/s less than that of SN 2002cx and normal SN Ia, respectively. We show that the peak luminosities of SN 2002cx-like objects are highly correlated with both their light-curve stretch and photospheric velocities. Its strong apparent connection to other SN 2002cx-like events suggests that SN 2007qd is also a pure deflagration of a white dwarf, although other mechanisms cannot be ruled out. It may be a critical link between SN~2008ha and the other members of the SN 2002cx-like class of objects.

The Stern Gerlach Experiment

The Stern Gerlach Experiment by Jeremy Bernstein, preprint. A history and analysis of the Stern-Gerlach Experiment, a key piece of evidence for quantum mechanics.

Nuclear Reactions

Nuclear Reactions preprint.

Nuclear reactions generate energy in nuclear reactors, in stars, and are responsible for the existence of all elements heavier than hydrogen in the universe. Nuclear reactions denote reactions between nuclei, and between nuclei and other fundamental particles, such as electrons and photons. A short description of the conservation laws and the definition of basic physical quantities is presented, followed by a more detailed account of specific cases: (a) formation and decay of compound nuclei; (b)direct reactions; (c) photon and electron scattering; (d) heavy ion collisions; (e) formation of a quark-gluon plasma; (f) thermonuclear reactions; (g) and reactions with radioactive beams. Whenever necessary, basic equations are introduced to help understand general properties of these reactions. Published in Wiley Encyclopedia of Physics, ISBN-13: 978-3-527-40691-3 - Wiley-VCH, Berlin, 2009.

Missing Baryons

Where are the missing baryons in clusters? preprint.

Observations of clusters of galaxies suggest that they contain significantly fewer baryons (gas plus stars) than the cosmic baryon fraction. This `missing baryon' puzzle is especially surprising for the most massive clusters which are expected to be representative of the cosmic matter content of the universe (baryons and dark matter). Here we show that the baryons may not actually be missing from clusters, but rather are extended to larger radii than typically observed. The baryon deficiency is typically observed in the central regions of clusters (~0.5 the virial radius). However, the observed gas-density profile is significantly shallower than the mass-density profile, implying that the gas is more extended than the mass and that the gas fraction increases with radius. We use the observed density profiles of gas and mass in clusters to extrapolate the measured baryon fraction as a function of radius and as a function of cluster mass. We find that the baryon fraction reaches the cosmic value near the virial radius for all groups and clusters above 5e13 solar masses. This suggests that the baryons are not missing, they are simply located in cluster outskirts. Heating processes (shock-heating of the intracluster gas, plus supernovae and AGN feedback) that cause the gas to expand are likely explanations for these results. Upcoming observations should be able to detect these baryons.

Here are a couple more preprints on the subject:
Evidence for the Missing Baryons in the Angular Correlation of the Diffuse X-ray Background;
The Baryon Content of Cosmic Structures.

Cute Amphibious Robot

The history of Quarks

Memories of Murray and the Quark Model by George Zweig.

Life at Caltech with Murray Gell-Mann in the early 1960's is remembered. Our different paths to quarks, leading to different views of their reality, are described.

Gravity Tricks

Gravitatomagnetic Analogs of Electric Transformers preprint.

Linearized general relativity admits a formulation in terms of gravitoelectric and gravitomagnetic fields that closely parallels the description of the electromagnetic field by Maxwell's equations. For steady mass currents, this formalism has been used to understand gravitomagnetic effects like the Lense-Thirring dragging of inertial frames. For time-varying mass-energy currents, the analog of Faraday's law suggests new effects based on the gravitational equivalent of a transformer where such currents take the place of electrical currents. New experimental possibilities are suggested including a novel coupling mechanism of electromagnetism to gravity, new tests of general relativity in the ultrarelativistic limit using particle beams in the LHC, and searches for a materials exhibiting the gravitational analog of ferromagnetism.

Graphene

Graphene Photonics and Optoelectronics preprint.

The richness of optical and electronic properties of graphene attracts enormous interest. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential to be in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultra-wide-band tunability. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light emitting devices, to touch screens, photodetectors and ultrafast lasers. Here we review the state of the art in this emerging field.

Calculating the Day of the Week

A Method for Accelerating Conway's Doomsday Algorithm preprint.
A simplified version of Conway's Doomsday Algorithm for calculating the day of the week of any calendar date.

The surprising effect of handling objects on subsequent decision-making

Incidental Haptic Sensations Influence Social Judgments and Decisions in Science.

Touch is both the first sense to develop and a critical means of information acquisition and environmental manipulation. Physical touch experiences may create an ontological scaffold for the development of intrapersonal and interpersonal conceptual and metaphorical knowledge, as well as a springboard for the application of this knowledge. In six experiments, holding heavy or light clipboards, solving rough or smooth puzzles, and touching hard or soft objects nonconsciously influenced impressions and decisions formed about unrelated people and situations. Among other effects, heavy objects made job candidates appear more important, rough objects made social interactions appear more difficult, and hard objects increased rigidity in negotiations. Basic tactile sensations are thus shown to influence higher social cognitive processing in dimension-specific and metaphor-specific ways.

Evolution of Microbial Cooperation

A Generalization of Hamilton’s Rule for the Evolution of Microbial Cooperation in Science.

Hamilton’s rule states that cooperation will evolve if the fitness cost to actors is less than the benefit to recipients multiplied by their genetic relatedness. This rule makes many simplifying assumptions, however, and does not accurately describe social evolution in organisms such as microbes where selection is both strong and nonadditive. We derived a generalization of Hamilton’s rule and measured its parameters in Myxococcus xanthus bacteria. Nonadditivity made cooperative sporulation remarkably resistant to exploitation by cheater strains. Selection was driven by higher-order moments of population structure, not relatedness. These results provide an empirically testable cooperation principle applicable to both microbes and multicellular organisms and show how nonlinear interactions among cells insulate bacteria against cheaters.

Ice Age Terminations

The Last Glacial Termination in Science.

A major puzzle of paleoclimatology is why, after a long interval of cooling climate, each late Quaternary ice age ended with a relatively short warming leg called a termination. We here offer a comprehensive hypothesis of how Earth emerged from the last global ice age. A prerequisite was the growth of very large Northern Hemisphere ice sheets, whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation. The Southern Hemisphere westerlies shifted poleward during each northern stadial, producing pulses of ocean upwelling and warming that together accounted for much of the termination in the Southern Ocean and Antarctica. Rising atmospheric CO2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres.

Velocities in Globular Clusters

Testing Newtonian gravity in the low acceleration regime with globular clusters: the case of omega Centauri revisited preprint.

Stellar kinematics in the external regions of globular clusters can be used to probe the validity of Newton's law in the low acceleration regimes without the complication of non-baryonic dark matter. Indeed, in contrast with what happens when studying galaxies, in globular clusters a systematic deviation of the velocity dispersion profile from the expected Keplerian falloff would provide indication of a breakdown of Newtonian dynamics rather than the existence of dark matter. We perform a detailed analysis of the velocity dispersion in the globular cluster omega Centauri in order to investigate whether it does decrease monotonically with distance as recently claimed by Sollima et al. (2009), or whether it converges toward a constant value as claimed by Scarpa Marconi and Gilmozzi (2003B). We combine measurements from these two works to almost double the data available at large radii, in this way obtaining an improved determination of the velocity dispersion profile in the low acceleration regime. We found the inner region of omega Centauri is clearly rotating, while the rotational velocity tend to vanish, and is consistent with no rotation at all, in the external regions. The cluster velocity dispersion at large radii from the center is found to be sensibly constant. The main conclusion of this work is that strong similarities are emerging between globular clusters and elliptical galaxies, for in both classes of objects the velocity dispersion tends to remain constant at large radii. In the case of galaxies, this is ascribed to the presence of a massive halo of dark matter, something physically unlikely in the case of globular clusters. Such similarity, if confirmed, is best explained by a breakdown of Newtonian dynamics below a critical acceleration

Omega Centauri ESO

While this paper asserts that globular clusters cannot contain dark matter, it didn't actually seem to provide the reason why not. Upon googling, I didn't stumble upon a really definitive explanation of this, and it seemed that other researchers may disagree.

Quantum Lithography

On the efficiency of quantum lithography - preprint.

Quantum lithography promises, in principle, unlimited feature resolution, independent of wavelength. However, in the literature at least two different theoretical descriptions of quantum lithography exist. They differ in to which extent they predict that the photons retain spatial correlation, and while both predict the same feature size, they differ vastly in predicting how efficiently a quantum lithographic pattern can be exposed.
Until recently, essentially all experiments reported have been performed in such a way that it is difficult to distinguish between the two theoretical explanations. However, recently an experiment was performed which gives different outcomes for the two theories. We comment on the experiment and show that the model that fits the data unfortunately indicates that the trade-off between resolution and efficiency in quantum lithography is very unfavorable.

Magnetic resonance force microscopy

Force-detected nuclear magnetic resonance: Recent advances and future challenges, preprint.

We review recent efforts to detect small numbers of nuclear spins using magnetic resonance force microscopy. Magnetic resonance force microscopy (MRFM) is a scanning probe technique that relies on the mechanical measurement of the weak magnetic force between a microscopic magnet and the magnetic moments in a sample. Spurred by the recent progress in fabricating ultrasensitive force detectors, MRFM has rapidly improved its capability over the last decade. Today it boasts a spin sensitivity that surpasses conventional, inductive nuclear magnetic resonance detectors by about eight orders of magnitude. In this review we touch on the origins of this technique and focus on its recent application to nanoscale nuclear spin ensembles, in particular on the imaging of nanoscale objects with a three-dimensional (3D) spatial resolution better than 10 nm. We consider the experimental advances driving this work and highlight the underlying physical principles and limitations of the method. Finally, we discuss the challenges that must be met in order to advance the technique towards single nuclear spin sensitivity -- and perhaps -- to 3D microscopy of molecules with atomic resolution

Neutrinoless Double Beta Decay

Nuclear Double Beta Decay, Fundamental Particle Physics, Hot Dark Matter, And Dark Energy preprint.

Nuclear double beta decay, an extremely rare radioactive decay process, is - in one of its variants - one of the most exciting means of research into particle physics beyond the standard model. The large progress in sensitivity of experiments searching for neutrinoless double beta decay in the last two decades - based largely on the use of large amounts of enriched source material in "active source experiments" - has lead to the observation of the occurrence of this process in nature (on a 6.4 sigma level), with the largest half-life ever observed for a nuclear decay process (2.2 x 10^{25} y). This has fundamental consequences for particle physics - violation of lepton number, Majorana nature of the neutrino. These results are independent of any information on nuclear matrix elements (NME)*. It further leads to sharp restrictions for SUSY theories, sneutrino mass, right-handed W-boson mass, superheavy neutrino masses, compositeness, leptoquarks, violation of Lorentz invariance and equivalence principle in the neutrino sector. The masses of light-neutrinos are found to be degenerate, and to be at least 0.22 +- 0.02 eV. This fixes the contribution of neutrinos as hot dark matter to >=4.7% of the total observed dark matter. The neutrino mass determined might solve also the dark energy puzzle. *{It is briefly discussed how important NME for 0nubb decay really are.}

Dark Matter: A Primer

Dark Matter: A Primer preprint.

Dark matter is one of the greatest unsolved mysteries in cosmology at the present time. About 80% of the universe's gravitating matter is non-luminous, and its nature and distribution are for the most part unknown. In this paper, we will outline the history, astrophysical evidence, candidates, and detection methods of dark matter, with the goal to give the reader an accessible but rigorous introduction to the puzzle of dark matter. This review targets advanced students and researchers new to the field of dark matter, and includes an extensive list of references for further study

see also this previous post: Dark Matter Review Article.

Making Rope

The ancient art of laying rope

We describe a geometrical property of helical structures and show how it accounts for the early art of ropemaking. Helices have a maximum number of rotations that can be added to them -- and it is shown that for an $N$-ply this is a geometrical feature, not a material property. This geometrical insight explains why nearly identically appearing ropes can be made from very different materials and it is also the reason behind the unyielding nature of ropes. The maximally rotated strands behave as zero-twist structures. Under strain they neither rotate one or the other way. The necessity for the rope to be stretched while being laid, known from Egyptian tomb scenes, follows straightforwardly, as does the function of the top, an old tool for laying ropes. The repetitive structures of twisted metal wires in Viking arm and neck rings are discussed in the light of the new insight arising for the understanding of zero-twist structures. They are maximally rotated structures.

Field Testing Sexual Selection in Crickets

Dance Like No One Is Watching, Sing Like No One Is Listening? in Science.

Genetic paternity testing and field observations of crickets challenge conventional wisdom about sex differences and fitness.

Freshwater Outburst from Lake Superior as a Trigger for the Cold Event 9300 Years Ago in Science.

Paleoclimate proxy records reveal a pervasive cooling event with a Northern Hemispheric extent ~9300 years ago. Coeval changes in the oceanic circulation of the North Atlantic imply freshwater forcing. However, the source, magnitude, and routing of meltwater have remained unknown. Located in central North America, Lake Superior is a key site for regulating the outflow of glacial meltwater to the oceans. Here, we show evidence for an ~45-meter rapid lake-level fall in this basin, centered on 9300 calibrated years before the present, due to the failure of a glacial drift dam on the southeast corner of the lake. We ascribe the widespread climate anomaly ~9300 years ago to this freshwater outburst delivered to the North Atlantic Ocean through the Lake Huron–North Bay–Ottawa River–St. Lawrence River valleys

The Lamb Shift

The Lamb Shift—Yesterday, Today, and Tomorrow in Science.
"Quantum field effects are magnified by collective interactions between many atoms."

The Local Void

Local difficulty for Big Bang in Nature.

The relativistic Big Bang theory of cosmic evolution gives a good description of our expanding Universe on the grand scale. But closer to home, where we can observe galactic properties in detail, its predictions go awry. For instance, some of the largest galaxies in our neighbourhood are found in less crowded regions, contrary to standard-model predictions. And the region known as the Local Void contains many fewer galaxies than expected. The observations of nearby galaxies are more understandable if it is assumed that matter forms more rapidly into galaxies and clusters than current theory allows. Jim Peebles and Adi Nusser outline recent efforts by cosmologists to adapt fundamental theory to let new physics operate on the scale of galaxies, yet preserve the properties of the present model on cosmological scales

The Center of the Galaxy

The Massive Black Hole and Nuclear Star Cluster in the Center of the Milky Way

The Galactic Center is an excellent laboratory for studying phenomena and physical occurring in many other galactic nuclei. The Center of our Milky Way is by far the closest galactic nucleus, and observations with exquisite resolution and sensitivity cover 18 orders of magnitude in energy of electromagnetic radiation. Theoretical simulations have become increasingly more powerful in explaining these measurements. This review summarizes the recent progress in observational and theoretical work on the central parsec, with a strong emphasis on the current empirical evidence for a central massive black hole and on the properties of the surrounding dense star cluster. We present the current evidence, from the analysis of the orbits of more than two dozen stars and from the measurements of the size and motion of the central compact radio source, Sgr A*, that this radio source must be a massive black hole of about 4.4 x 10^6 Solar Masses, beyond any reasonable doubt. We report what is known about the structure and evolution of the dense nuclear star cluster surrounding this black hole, including the astounding fact that stars have been forming in the vicinity of Sgr A* recently, apparently with a top-heavy stellar mass function. We discuss a dense concentration of fainter stars centered in the immediate vicinity of the massive black hole, three of which have orbital peri-bothroi of less than one light day. This 'S-star cluster' appears to consist mainly of young early-type stars, in contrast to the predicted properties of an equilibrium 'stellar cusp' around a black hole. This constitutes a remarkable and presently not fully understood 'paradox of youth'. We also summarize more briefly what is known about the emission properties of the accreting gas onto Sgr A* and how this emission is beginning to delineate the physical properties in the hot accretion zone around the event horizon.

Chandra image of Sgr A*

Quadracoptor Perching

Solar System Dating

Astronomy with Radioactivities: (An Introduction to Astrophysics with
Decaying Isotopes)

This chapter presents a (partial) review of the information we can derive on the early history of the Solar System from radioactive nuclei of very different half-life, which were recognized to have been present alive in pristine solids. In fact, radioactivities open for us a unique window on the evolution of the solar nebula and provide tools for understanding the crucial events that determined and accompanied the formation of the Sun. Discussing these topics will require consideration of (at least) the following issues. i) The determination of an age for solar system bodies, as it emerged especially from the application of radioactive dating. ii) A synthetic account of the measurements that proved the presence of radioactive nuclei (especially those of half-life lower than about 100 Myr) in the Early Solar System (hereafter ESS). iii) An explanation of their existence in terms of galactic nucleosynthesis, and/or of local processes (either exotic or in-situ) preceding and accompanying the formation of the Sun. This will also need some reference to the present scenarios for star formation, as applied to the ESS

Grand Unified Theories

The Algebra of Grand Unified Theories

The Standard Model of particle physics may seem complicated and arbitrary, but it has hidden patterns that are revealed by the relationship between three "grand unified theories": theories that unify forces and particles by extending the Standard Model symmetry group U(1) x SU(2) x SU(3) to a larger group. These three theories are Georgi and Glashow's SU(5) theory, Georgi's theory based on the group Spin(10), and the Pati-Salam model based on the group SU(2) x SU(2) x SU(4). In this expository account for mathematicians, we explain only the portion of these theories that involves finite-dimensional group representations. This allows us to reduce the prerequisites to a bare minimum while still giving a taste of the profound puzzles that physicists are struggling to solve.

Flow My Tears, the Policeman Said

Flow My Tears, the Policeman Said is a paranoid science fiction novel by Philip K. Dick.

Scrutinizing him, she said, 'Maybe your're not a celebrity; maybe I've reverted back to my delusional period. They said I probably would, sometime. Sooner or later. Maybe it's later now.'
'That,' he pointed out, 'would make me a hallucination of yours. Try harder; I don't feel completely real.'
She laughed.

The Big Sleep

The Big Sleep is a detective novel by Raymond Chandler.

"You know what Canino will do? Beat my teeth out and kick me in the stomach for mumbling."

See The Simple of Art of Murder for a previous post about Raymond Chandler.

A Simple Heart

A Simple Heart is a story by Gustave Flaubert, it's one of my favorites. Sad, funny, droll - a person, place and time that has no particular intrinsic interest but despite that (or perhaps because of it) a great story.

Terahertz Lenses

X-Ray Vision, Without the Radiation in Science. "X-ray–like imaging without the harmful radiation and cell phones with more bandwidth are closer to reality now that researchers have developed a novel type of lens that works with terahertz frequencies. The new lens is a metamaterial, an artificial material with a structure made from many tiny parts, and it could drastically expand what lenses can do. "

The Heart of the World

The Heart of the World is a short silent film by Guy Maddin in the manner of Metropolis.

The Inner Core

Hemispherical anisotropic patterns of the Earth’s inner core in PNAS.

It has been shown that the Earth’s inner core has an axisymmetric anisotropic structure with seismic waves traveling ∼3% faster along polar paths than along equatorial directions. Hemispherical anisotropic patterns of the solid Earth’s core are rather complex, and the commonly used hexagonal-close-packed iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice-preferred orientation of a body-centered-cubic iron aggregate, having a fraction of their [111] crystal axes parallel to the Earth’s rotation axis. This is compelling evidence for the presence of a body-centered-cubic Fe phase at the top of the Earth’s inner core

Ultrasmall Archaea

Enigmatic, ultrasmall, uncultivated Archaea in PNAS.

Metagenomics has provided access to genomes of as yet uncultivated microorganisms in natural environments, yet there are gaps in our knowledge—particularly for Archaea—that occur at relatively low abundance and in extreme environments. Ultrasmall cells (< 500 nm in diameter) from lineages without cultivated representatives that branch near the crenarchaeal>/euryarchaeal divide have been detected in a variety of acidic ecosystems.

Manta Rays

Once again I've had the good fortune to visit the Manta Rays of San Benedicto Island, in the Pacific off the coast of Mexico. Thanks again to Gregory Colbert, his film crew and friends, and the crew of the Nautilus Explorer for another wonderful trip.
I haven't been able to find a reference to the tubes just above the corners of the manta's mouth pictured below. Thanks to Sten Johansson of the Nautilus Explorer for the photos and for pointing out this interesting feature. Please comment if you can identify these structures, a reference or link to the literature would be especially welcome!

Newton and the Counterfeiter

Newton and the Counterfeiter: The Unknown Detective Career of the World's Greatest Scientist a book by Thomas Levenson is about Isaac Newton and William Chaloner a notorious counterfeiter that Newton prosecuted when he was Warden of the Royal Mint.
While Newton was perhaps the greatest scientific genius of all time, and even a very competent functionary - as detailed in this book - he was strictly mortal in the realm of financial investments. He lost a fortune in the South Sea Bubble of 1720 which rankled him greatly, admitting "that he could not calculate the madness of the people."

Paleocene-Eocene Thermal Maximum

Did Monster Eruptions Warm the World? in Science.
The Paleocene-Eocene Thermal Maximum occured 55 million years ago. Temperatures rose over 5C and there were mass extinctions - many classes of current mammals arose afterwards. Researchers have recently found evidence of massive undersea volcanic eruptions near Iceland from that time period. The volcanic release of methane may have caused the warming.

Dark Matter Review Article

Dark Matter in Modern Cosmology preprint.

The presence of Dark Matter (DM) is required in the universe regulated by the standard general relativistic theory of gravitation. The nature of DM is however still elusive to any experimental search. We discuss here the process of accumulation of evidence for the presence of DM in the universe, the astrophysical probes for the leading DM scenarios that can be obtained through a multi-frequency analysis of cosmic structures on large scales, and the strategies related to the multi-messenger and multi-experiment astrophysical search for the nature of the DM.

Cosmic microwave background anisotropies

Lecture notes on the physics of cosmic microwave background anisotropies

We review the theory of the temperature anisotropy and polarization of the cosmic microwave background (CMB) radiation, and describe what we have learned from current CMB observations. In particular, we discuss how the CMB is being used to provide precise measurements of the composition and geometry of the observable universe, and to constrain the physics of the early universe. We also briefly review the physics of the small-scale CMB fluctuations generated during and after the epoch of reionization, and which are the target of a new breed of arcminute-resolution instruments

Dark Energy

Why all these prejudices against a constant?

The expansion of the observed universe appears to be accelerating. A simple explanation of this phenomenon is provided by the non-vanishing of the cosmological constant in the Einstein equations. Arguments are commonly presented to the effect that this simple explanation is not viable or not sufficient, and therefore we are facing the "great mystery" of the "nature of a dark energy". We argue that these arguments are unconvincing, or ill-founded

.

Galaxy Structure

The Universal Faber-Jackson Relation

In the context of modified Newtonian dynamics, the fundamental plane, as the observational signature of the Newtonian virial theorem, is defined by high surface brightness objects that deviate from being purely isothermal: the line-of-sight velocity dispersion should slowly decline with radius as observed in luminous elliptical galaxies. All high surface brightness objects (e.g. globular clusters, ultra-compact dwarfs) will lie, more or less, on the fundamental plane defined by elliptical galaxies, but low surface brightness objects (dwarf spheroidals) would be expected to deviate from this relation. This is borne out by observations. With MOND, the Faber-Jackson relation (the power-law relation between luminosity and velocity dispersion), ranging from globular clusters to clusters of galaxies and including both high and low surface brightness objects, is the more fundamental and universal scaling relation in spite of its larger scatter. Faber-Jackson reflects the presence of an additional dimensional constant (the MOND acceleration) in the structure equation

The mass distribution in Spirals

In the past years a wealth of observations has unraveled the structural properties of the Dark and Luminous mass distribution in spirals. These have pointed out to an intriguing scenario not easily explained by present theories of galaxy formation. The investigation of individual and coadded objects has shown that the spiral rotation curves follow, from their centers out to their virial radii, a Universal profile (URC) that arises from the tuned combination of a stellar disk and of a dark halo. The importance of the latter component decreases with galaxy mass. Individual objects, on the other hand, have clearly revealed that the dark halos encompassing the luminous discs have a constant density core. This resulting observational scenario poses important challenges to presently favored theoretical

DSLR with nice HD Video Capabilities

"The Last 3 Minutes"

"The Last 3 Minutes" From Shane Hurlbut, ASC from Shane Hurlbut, ASC on Vimeo.

shot with the Canon 5D Mark II DSLR. Try to watch in full screen mode with HD on by following the link that's mentioned.

One Hedge Fund that made money fueling the Bubble

The Magnetar Trade: How One Hedge Fund Helped Keep the Bubble Going at ProPublica.
"A hedge fund, Magnetar, helped create arcane mortgage-based instruments, pushed for risky things to go inside them and then bet against the investments"

More about the mathematician Perelman

He Conquered the Conjecture by John Allen Paulos in the New York Review of Books is a review of Perfect Rigor: A Genius and the Mathematical Breakthrough of the Century by Masha Gessen a biography of the Russian mathematician Grigoriy Perelman who recently solved a long-standing problem in topology, the Poincaré conjecture.

Markets, Theory and Reality

Hedging America by Robert M. Solow in the magazine The New Republic. Solow is a Nobel Prize winning economist who also happened to teach my macroeconomics class at MIT many a moon ago. The article discusses the theory behind markets and how the reality from time to time falls conspicuously short.

The Economics of Dueling

The Deadliest of Games: The Institution of Dueling.

Recent historical research indicates that ritualistic dueling had a rational basis. Basically, under certain social and economic conditions, individuals must ght in order to maintain their personal credit and social standing. We use a repeated two-player sequential game with random matching to show how the institution of dueling could have functioned as a costly but incentive-compatible means by which individuals could demonstrate their good faith dealings by defending their "honor".

More Evidence for Cosmic Acceleration

Astrophysics: Cosmic acceleration confirmed in Nature.
Evidence for the accelerated expansion of the Universe from weak lensing tomography with COSMOS: astrophics preprint.

Why was the ancient Earth so warm?

Early Earth: Faint young Sun redux Early in the Earth's history (several billion years ago) it is thought that the Sun was dimmer, so much so that the oceans would have been frozen. However there is ample evidence that the oceans were mostly liquid during that period. Greenhouse gases in the atmosphere may have kept the Earth warm. But there's a new theory that the Earth's surface may have also been darker in the past, allowing it to retain more heat from the fainter sun and resulting in warmer temperatures.

Prospects for Personal Genomics

Multiple personal genomes await by J. Craig Venter in Nature. Gene sequencing pioneer Venter reviews the current state of the art. One difficult problem is due to chromosomes occuring in pairs, one from each parent. Apparently it isn't easy to distinguish the two copies and the differences between them.

Ice Age Flood went to the Arctic not Atlantic

River reveals chilling tracks of ancient flood in Nature. After the end of the last ice age there was another cool period, the Younger Dryas, 13,000 years ago. One theory was that a huge freshwater lake in Canada, formed from melted glaciers, suddenly drained into the North Atlantic, disrupted the warm water conveyer belt there, resulting in a resumption of cold conditions in the Northern Hemisphere. But now it appears that instead Lake Agassiz drained north into the Arctic Ocean. Did that flood still cause the Younger Dryas cold period?

Chemistry of the Ancient Oceans

Ocean Chemistry and Early Animals in Science. Animal life requires oxygen. What stages took place before the current oxygenated ocean chemistry and animal communities beccame established around 542 million years ago?

Quark Masses

Mass of the Common Quark Finally Nailed Down in Science.
Currently there are six known flavors of quarks, each with a different mass. The masses haven't been known with much accuracy, in part because quarks are never found in isolation, they are are always found bound with other quarks. The binding interaction is so strong that most of the mass of the bound particle (like a proton or neutron) is due to the energy of interaction. These new theorectical calculations may give the quark masses to a greater degree of accuracy.

Powerful People are Better Liars

Powerful Lies an article from Columbia Business School.
"Most people become stressed when lying, but new research shows that people with power feel just fine when lying — and are better at getting away with it."

Arthropod Phylogeny

Arthropod relationships revealed by phylogenomic analysis of nuclear protein-coding sequences in Nature.

The evolutionary interrelationships of arthropods has long been a matter of dispute. A new phylogeny applies an arsenal of techniques to more than 41,000 base pairs of DNA from 75 arthropod species. The results support the idea that insects are land–living crustaceans, that crustaceans comprise a diverse assemblage of at last three distinct arthropod types, and that myriapods (millipedes and centipedes) comprise the closest relatives of this great 'pancrustacean' group

See also Surprising New Branches on Arthropod Family Tree
The the newly defined sister group to the Hexapoda (insects and related species) is the Xenocarida or strange shrimp some unusual recently discovered marine crustaceans. So insects are actually more closely related to some oddball marine crustaceans than other terrestrial arthropods such as spiders.

High Energy Cosmic Rays

Cosmic-ray theory unravels in Nature.

Astrophysicists ponder whether ultrahigh-energy particles really do come from the centre of galaxies

Could they be iron nuclei instead of protons?

Pregnant fathers selective abortion

Evolutionary biology: Pregnant fathers in charge in Nature.

Pipefish and related species provide rare examples of extreme male parental care. Controlled breeding experiments allow the resulting conflicts of interest between female, male and offspring to be explored

The Golden Ratio found in a magnet

Solid-state physics: Golden ratio seen in a magnet

The golden ratio — an exact 'magic' number often claimed to be observed when taking ratios of distances in ancient and modern architecture, sculpture and painting — has been spotted in a magnetic compound

Sterile Neutrinos

Hunt for the sterile neutrino heats up in Nature.

Neutrinos like to keep to themselves. These ghostly particles are so reluctant to interact with ordinary matter that billions zip harmlessly through each person every day, and it takes giant, specialized detectors to capture even a handful of them. Now astronomers are finding hints of an even more elusive type of neutrino, one so shy that it could never be detected directly: the sterile neutrino

Fairness Behaviour Across Societies

Fairness in Modern Society in Science.

Experiments in psychology and economics have demonstrated that in industrialized societies all over the world, a substantial fraction of individuals will be fair in anonymous interactions and will punish unfairness (1, 2). However, it has not been clear whether this benevolent, prosocial behavior depends on innate human psychology or norms peculiar to industrialized societies. Henrich et al. explored the motivation for fairness in anonymous interactions across dramatically diverse societies and on page 1480 of this issue (3), they report that this behavior increases with the level of the society's market integration, measured as households' average percentage of calories that are purchased.

Controlling Turbulence

Controlling Turbulence in Science.

Pipes feature strongly in the infrastructure of everyday life, from domestic water pipes to oil and natural gas conduits. A primary consequence of the onset of turbulence in the fluid flowing through the pipes is the dramatically increased power required to pump stuff at the same rate. Thus, the incentives to understand and control the transition process are strong. However, more than 100 years after Osborne Reynolds's seminal experiments on the transition of flow through a pipe from a laminar (smooth) to a turbulent state, the exact physical mechanism that drives this phenomenon still vexes the fluid mechanics community. On page 1491 of this issue, Hof et al. (1) describe a mechanism that feeds energy into a turbulent flow system, allowing the onset of the transition to be manipulated and even the suppression of the turbulence

Is Depression Adaptive?

The bright side of being blue:
Depression as an adaptation for analyzing complex problems
by Paul W. Andrews and J. Anderson Thomson, Jr.

Depression ranks as the primary emotional condition for which help is sought. Depressed people often have severe, complex problems, and rumination is a common feature. Depressed people often believe that their ruminations give them insight into their problems, but clinicians often view depressive rumination as pathological because it is difficult to disrupt and interferes with the ability to concentrate on other things. Abundant evidence indicates that depressive rumination involves the analysis of episode-related problems. Because analysis is time consuming and requires sustained processing, disruption would interfere with problem-solving. The analytical rumination (AR) hypothesis proposes that depression is an adaptation that evolved as a response to complex problems and whose function is to minimize disruption of rumination and sustain analysis of complex problems. It accomplishes this by giving episode-related problems priority access to limited processing resources, by reducing the desire to engage in distracting activities (anhedonia), and by producing psychomotor changes that reduce exposure to distracting stimuli. Because processing resources are limited, the inability to concentrate on other things is a tradeoff that must be made to sustain analysis of the triggering problem. The analytical rumination hypothesis is supported by evidence from many levels, including genes, neurotransmitters and their receptors, neurophysiology, neuroanatomy, neuroenergetics, pharmacology, cognition and behavior, and the efficacy of treatments. In addition, we address and provide explanations for puzzling findings in the cognitive and behavioral genetics literatures on depression. In the process, we challenge the belief that serotonin transmission is low in depression. Finally, we discuss implications of the hypothesis for understanding and treating depression.

see also Depression’s Upside in the New York Times.

First Clay Mathematics Prize Awarded

The First Clay Mathematic Prize was awarded to Grigoriy Perelman for solving the Poincare Conjecture.

Books

Too Big to Fail by Andrew Ross Sorkin a dense account of the 2008 financial crisis.
Drive by Daniel H. Pink, about research into human motivation.
Lanark by Alasdair Gray, a Kafkasque novel.
Empire of Illusion by Chris Hedges, a polemic against corporations and popular culture which I would not recommend.
Shop Class as Soulcraft: An Inquiry Into the Value of Work by Matthew B. Crawford a charming book celebrating manual work and craftsmanship.

Happy Baby on the Silver Bank

photos by Mike Murphy

Dancers on the Silver Bank

photos by Mike Murphy
The humpback whale courtship display is one of the most spectacular in nature. The female is almost always the active one (the "dancer" or "valentine") while the male watches passively - a reversal of the usual norm in the animal kingdom. Occasionally the male begins to join in, which started to happen at the end of the this encounter on the Silver Bank two weeks ago, but I don't believe we got a picture of that part alas.

Humpback Twister

A twisting water formation is sometimes formed by the tip of a humpback whale's pectorial fin and then spins off. Frequently seen, but not so often photographed this clearly - taken by Mike Murphy last week on the Silver Bank.


photo by Tom Conlin

Video of the photographer by Tom Conlin - the still above was taken from the video.

A Very Friendly Whale

photo by John Munro
I'm back on the Silver Bank with Tom Conlin of Aquatic Adventures aboard the Turks and Caicos Explorer II. We encountered a very friendly female humpback whale with her male escort, who is blowing bubbles at us from below.

Economics Rap

A Book about Prices

Priceless: The Myth of Fair Value (and How to Take Advantage of It) by William Poundstone is an entertaining summary of the recent scientific literature about prices and uncertainty. Unfortunately it also reinforces one's dismay over the limitations of human reasoning ability in real-life practical situations.

Cooking as Courtship

Cooking as Courtship: a manual of sorts, exploring the ins and outs of love and friendship in the context of food - a charming book, also available in blog format.

Comparison of Human and Chimpanzee Y Chromosomes

Chimpanzee and human Y chromosomes are remarkably divergent in structure and gene content in Nature.

The human Y chromosome began to evolve from an autosome hundreds of millions of years ago, acquiring a sex-determining function and undergoing a series of inversions that suppressed crossing over with the X chromosome. Little is known about the recent evolution of the Y chromosome because only the human Y chromosome has been fully sequenced. Prevailing theories hold that Y chromosomes evolve by gene loss, the pace of which slows over time, eventually leading to a paucity of genes, and stasis. These theories have been buttressed by partial sequence data from newly emergent plant and animal Y chromosomes, but they have not been tested in older, highly evolved Y chromosomes such as that of humans. Here we finished sequencing of the male-specific region of the Y chromosome (MSY) in our closest living relative, the chimpanzee, achieving levels of accuracy and completion previously reached for the human MSY. By comparing the MSYs of the two species we show that they differ radically in sequence structure and gene content, indicating rapid evolution during the past 6 million years. The chimpanzee MSY contains twice as many massive palindromes as the human MSY, yet it has lost large fractions of the MSY protein-coding genes and gene families present in the last common ancestor. We suggest that the extraordinary divergence of the chimpanzee and human MSYs was driven by four synergistic factors: the prominent role of the MSY in sperm production, ‘genetic hitchhiking’ effects in the absence of meiotic crossing over, frequent ectopic recombination within the MSY, and species differences in mating behaviour. Although genetic decay may be the principal dynamic in the evolution of newly emergent Y chromosomes, wholesale renovation is the paramount theme in the continuing evolution of chimpanzee, human and perhaps other older MSYs.

Chromosome Segregation

Towards building a chromosome segregation machine in Nature.

All organisms, from bacteria to humans, face the daunting task of replicating, packaging and segregating up to two metres (about 6 × 10^9 base pairs) of DNA when each cell divides. This task is carried out up to a trillion times during the development of a human from a single fertilized cell. The strategy by which DNA is replicated is now well understood. But when it comes to packaging and segregating a genome, the mechanisms are only beginning to be understood and are often as variable as the organisms in which they are studied.

Quantum Computers

Physics: Quantum computing in Nature.

The race is on to build a computer that exploits quantum mechanics. Such a machine could solve problems in physics, mathematics and cryptography that were once thought intractable, revolutionizing information technology and illuminating the foundations of physics. But when?

Martian Methane

Planetary science: A whiff of mystery on Mars in Nature.
Methane has been discovered in the Martian atmosphere. Could that be a sign of life?

No Anomalies in the Cosmic Microwave Background

Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Are There Cosmic Microwave Background Anomalies?

A simple six-parameter LCDM model provides a successful fit to WMAP data, both when the data are analyzed alone and in combination with other cosmological data. Even so, it is appropriate to search for any hints of deviations from the now standard model of cosmology, which includes inflation, dark energy, dark matter, baryons, and neutrinos. The cosmological community has subjected the WMAP data to extensive and varied analyses. While there is widespread agreement as to the overall success of the six-parameter LCDM model, various "anomalies" have been reported relative to that model. In this paper we examine potential anomalies and present analyses and assessments of their significance. In most cases we find that claimed anomalies depend on posterior selection of some aspect or subset of the data. Compared with sky simulations based on the best fit model, one can select for low probability features of the WMAP data. Low probability features are expected, but it is not usually straightforward to determine whether any particular low probability feature is the result of the a posteriori selection or of non-standard cosmology. We examine in detail the properties of the power spectrum with respect to the LCDM model. We examine several potential or previously claimed anomalies in the sky maps and power spectra, including cold spots, low quadrupole power, quadropole-octupole alignment, hemispherical or dipole power asymmetry, and quadrupole power asymmetry. We conclude that there is no compelling evidence for deviations from the LCDM model, which is generally an acceptable statistical fit to WMAP and other cosmological data.

My previous blog posts on the Axis of Evil anomaly here and here.
A diagram of the WMAP spacecraft:

The Perry Bible Fellowship

The Perry Bible Fellowship is a webcomic which can be found here. It is irreverent, to put it mildly.

The Reason Why the Earth is at the Center of the Universe

I'm reading Galileo at Work: His Scientific Biography by Stillman Drake. Galileo had literary interests as well as scientific. When he was younger (before he had even adopted the Copernican system) he was invited to lecture on Dante's Inferno. "Galileo expounded on God's reasons for having placed [the earth] at the center of the universe --- namely, to have it as far as possible from the sight of the blessed residents of Heaven, least they be offended by its grossness."
'In the midway of this our mortal life, I found me in a gloomy wood, astray'

Alternatives to dark matter

Alternatives to dark matter: Modified gravity as an alternative to dark matter by Jacob D. Bekenstein.

The premier alternative to the dark matter paradigm is modified gravity. Following an introduction to the relevant phenomenology of galaxies, I review the MOND paradigm, an effective summary of the observations which any theory must reproduce. A simple nonlinear modified gravity theory does justice to MOND at the nonrelativistic level, but cannot be elevated to the relativistic level in a unique way. I go in detail into the covariant tensor-vector-theory (TeVeS) which not only recovers MOND but can also deal in detail with gravitational lensing and cosmology. Problems with MOND and TeVeS at the level of clusters of galaxies are given attention. I also summarize the status of TeVeS cosmology

The Crab Canon by J.S.Bach

There's a discusion of the video here: This Week's Finds in Mathematical Physics (Week 291).

Group Extensions

Some notes on group extensions by Fields Medallist Terance Tao, contains a "high-concept" overview of methods for extending mathematical spaces, a typical and powerful technique.

Minature Heat Engine and Refrigerator

Piezoresistive heat engine and refrigerator

Heat engines provide most of our mechanical power and are essential for long-range transportation. However, whereas significant progress has been made in the miniaturization of motors driven by electrostatic forces, it has proven difficult to reduce the size of conventional liquid or gas driven heat engines below 10^7 um^3. Here we demonstrate an all-silicon reciprocating heat engine with a volume of less than 0.5 um^3. The device draws heat from a DC current using the piezoresistive effect and converts it into mechanical energy by expanding and contracting at different temperatures. It is shown that the engine can even increase the mechanical energy of a resonator when its motion is governed by random thermal fluctuations. When the thermodynamic cycle of the heat engine is reversed, it operates as a refrigerator or heat pump that can reduce motional noise in mechanical systems. In contrast to the Peltier effect, the direction of the thermal current does not depend on the direction of the electrical current.

Dense Stars

Dense matter in compact stars - A pedagogical introduction

Cold and dense nuclear and/or quark matter can be found in the interior of compact stars. It is very challenging to determine the ground state and properties of this matter because of the strong-coupling nature of QCD. I give a pedagogical introduction to microscopic calculations based on phenomenological models, effective theories, and perturbative QCD. I discuss how the results of these calculations can be related to astrophysical observations to potentially rule out or confirm candidate phases of dense matter.

Logicomix

Logicomix is a graphic novel which features a fictionalized life story of the Philosopher/Logician Bertrand Russell. I thought the story was quite charming and did manage to give some nice hints about the controversies in the foundations of mathematics, including Russells' Paradox, one of my favorites. I've never tried to read Principia Mathematica (Russell and Whitehead's magnum opus) myself, though I once had a meeting at a professor's office who showed me a copy - he was a big fan of the work - it looked pretty hairy!

Necker Cube Illusion

Necker Cube.

Nucleon Excitations

Nucleon Excitations

The mass pattern of The mass pattern of nucleon and Delta resonances is compared with predictions based on quark models, the Skyrme model, AdS/QCD, and the conjecture of chiral symmetry restoration. and $\Delta$ resonances is compared with predictions based on quark models, the Skyrme model, AdS/QCD, and the conjecture of chiral symmetry restoration.

Baryon Spectroscopy and the Origin of Mass

The proton mass arises from spontaneous breaking of chiral symmetry and the formation of constituent quarks. Their dynamics cannot be tested by proton tomography but only by studying excited baryons. However, the number of excited baryons is much smaller than expected within quark models; even worse, the existence of many known states has been challenged in a recent analysis which includes - compared to older analyses - high-precision data from meson factories. Hence $\pi N$ elastic scattering data do not provide a well-founded starting point of any phenomenological analysis of the baryon excitation spectrum. Photoproduction experiments now start to fill in this hole. Often, they confirm the old findings and even suggest a few new states. These results encourage attempts to compare the pattern of observed baryon resonances with predictions from quark models, from models generating baryons dynamically from meson-nucleon scattering amplitudes, from models based on gravitational theories, and with the conjecture that chiral symmetry may be restored at high excitation energies. Best agreement is found with a simple mass formula derived within AdS/QCD. Consequences for our understanding of QCD are discussed as well as experiments which may help to decide on the validity of models.

Zipf's Law

On the Universality of Zipf's Law

Zipf's law is the most common statistical distribution displaying scaling behavior. Cities, populations and firms are just a few of the examples of this seemingly universal law. Although many different models have been proposed, no general theoretical explanation has been shown to exist for its universality. Here we show that Zipf's law is, in fact, an inevitable outcome of a very general class of stochastic systems. Borrowing concepts from Algorithmic Information Theory, our derivation is based on the properties of the symbolic sequence obtained through successive observations over a system with an unbounded number of possible states. Specifically, we assume that the complexity of the description of the system provided by the sequence of observations is the one expected for a system evolving to a stable state between order and disorder. This result is obtained from a small set of mild, physically relevant assumptions. The general nature of our derivation and its model-free basis would explain the ubiquity of such a law in real systems.