Friday, July 30, 2010

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.

Tuesday, July 27, 2010

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

Saturday, July 24, 2010

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.

Friday, July 23, 2010

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.

Thursday, July 22, 2010

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).

Tuesday, July 20, 2010

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.

Friday, July 16, 2010

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.

Thursday, July 15, 2010

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.

Wednesday, July 14, 2010

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.

Tuesday, July 06, 2010

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.

Thursday, July 01, 2010

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.