Tuesday, August 31, 2010

Thursday, August 26, 2010

Collider Physics

There is currently much excitement in physics due to the LHC, the huge new European particle accelerator. This preprint explains the theoretical analysis of such experiments: Introduction to Collider Physics.

Insertion of the vacuum-tank of the CMS detector in the LHC

Fire Tornado


Fire Tornado in Wikipedia.

More Quantum Inequalities

Quantum mechanics: The usefulness of uselessness in Nature.
Bell pointed out that quantum mechanics violates certain inequalities that are true in classical physics. This article discusses other inequalities that even quantum mechanics respects but which distinguish it from "super quantum theories" that would be able to violate these inequalities.

How big is the Proton?

The proton shrinks in size: Tiny change in radius has huge implications - in Nature.

Problems with Quantum Mechanics

Might I say immediately … we always have had a great deal of difficulty in understanding the world view that quantum mechanics represents … I cannot define the real problem, therefore I suspect there’s no real problem, but I am not sure there’s no real problem.

Richard Feynman
Jeremy Bernstein in FAPP and Non-FAPP: A Pedagogical Essay discusses the foundations of quantum mechanics. Bernstein is a very good writer and he explains some aspects of this problematic field quite well. In the end, however, it still seems just as problematic as ever.

FAPP - For All Practical Purposes

Once Bernstein happened to visit physicist Erwin Schroedinger in his Vienna apartment.
There was no cat. He did not like cats.

Wednesday, August 25, 2010

Weak Lensing

Weak lensing, dark matter and dark energy preprint.
Weak gravitational lensing is rapidly becoming one of the principal probes of dark matter and dark energy in the universe. In this brief review we outline how weak lensing helps determine the structure of dark matter halos, measure the expansion rate of the universe, and distinguish between modified gravity and dark energy explanations for the acceleration of the universe. We also discuss requirements on the control of systematic errors so that the systematics do not appreciably degrade the power of weak lensing as a cosmological probe.

Tuesday, August 24, 2010

Nicole Oresme



Nicole Oresme was a sophisticated 14th century French philospher. He discussed and compared Earth-centered and Sun-centered models of the solar system and couldn't find any way to dismiss the Sun-centered model - though he personally didn't believe it. He also used techniques which were very close to Cartesian coordinate systems - over two hundred years before Descartes. See the Nicole Oresme article in the Stanford Encyclopedia of Philosophy.

RRAT's

Transient Radio Neutron Stars preprint.
Here I will review the high time resolution radio sky, focusing on millisecond scales. This is primarily occupied by neutron stars, the well-known radio pulsars and the recently identified group of transient sources known as Rotating RAdio Transients (RRATs). The RRATs appear to be abundant in the Galaxy, which at first glance may be difficult to reconcile with the observed supernova rate. However, as I will discuss, it seems that the RRATs can be explained as pulsars which are either extreme nullers, highly variable or weak/distant. I will re-cap some recent results including a re-analysis of the Parkes Multi-beam Pulsar Survey, which has identified several new sources, as well as the unusual timing behaviour of RRAT J1819-1458. This leads to an examination of where RRATs fit within the evolution of neutron stars post-supernova.

Measuring the mass of solar system planets using pulsar timing

Measuring the mass of solar system planets using pulsar timing
Apparently the pulse time of arrival from pulsars is so accurate it can help determine the masses of the planets of the solar system with accuracy comparable (or better) than data from spacecraft missions. That's because the motions of the other planets cause the Earth to wiggle in its orbit. The pulsar data allowed the researchers to determine the Earth's orbit so well, it could be used to determine the masses of the other planets!
See also Pulsar Signals Could Reveal Solar System Secrets at Science.

Monday, August 23, 2010

Hubble image of SN1987A

HST SN1987A
When I saw this Hubble Space Telescope image of Supernova 1987A on Wikipedia, it was so spectacular at first I thought it must have been just some artist's conception.

Saturday, August 21, 2010

Picophytoplankton

Targeted metagenomics and ecology of globally important uncultured eukaryotic phytoplankton in PNAS.

Small (2-3μm) uncultured photosynthetic eukaryotic plankton (picophytoplankton) are a substantial component of the biomass and primary production in the oceans. Pico-prymnesiophytes genomes seem to be a mosaic, with the chloroplast and nuclear genomes from different lineages.

Friday, August 20, 2010

The Pioneer Anomaly

The Pioneer Anomaly preprint.
Radio-metric Doppler tracking data received from the Pioneer 10 and 11 spacecraft from heliocentric distances of 20-70 AU has consistently indicated the presence of a small, anomalous, blue-shifted frequency drift uniformly changing with a rate of ~6 x 10^{-9} Hz/s. Ultimately, the drift was interpreted as a constant sunward deceleration of each particular spacecraft at the level of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2. This apparent violation of the Newton's gravitational inverse-square law has become known as the Pioneer anomaly; the nature of this anomaly remains unexplained. In this review, we summarize the current knowledge of the physical properties of the anomaly and the conditions that led to its detection and characterization. We review various mechanisms proposed to explain the anomaly and discuss the current state of efforts to determine its nature. A comprehensive new investigation of the anomalous behavior of the two Pioneers has begun recently. The new efforts rely on the much-extended set of radio-metric Doppler data for both spacecraft in conjunction with the newly available complete record of their telemetry files and a large archive of original project documentation. As the new study is yet to report its findings, this review provides the necessary background for the new results to appear in the near future. In particular, we provide a significant amount of information on the design, operations and behavior of the two Pioneers during their entire missions, including descriptions of various data formats and techniques used for their navigation and radio-science data analysis. As most of this information was recovered relatively recently, it was not used in the previous studies of the Pioneer anomaly, but it is critical for the new investigation.

Thursday, August 19, 2010

The Birthplace of the Sun

The Astrophysical Environment of the Solar Birthplace preprint.
Our Sun, like all stars, formed within a cold molecular cloud. Astronomical observations and theory provide considerable detail into this process. Yet cosmochemical observations of short lived radionuclides in primitive meteorites, in particular 60Fe, provide unequivocal evidence that the early solar system inherited fresh nucleosynthetic material from the core of a hot, massive star, almost certainly ejected in a supernova explosion. I give a short introduction to the fields of star formation and meteoritics and discuss how the reconciliation of their disparate clues to our origin places strong constraints on the environment of the Solar birthplace. Direct injection of supernova ejecta into a protoplanetary disk or a dense molecular core is unlikely since their small sizes require placement unusually close to the massive star. Lower density molecular cloud clumps can capture more ejecta but the radionuclides decay during the slow gravitational collapse. The most likely scenario is on the largest scales via the formation of enriched molecular clouds at the intersection of colliding supernova bubbles in spiral arms.

Saturday, August 14, 2010

The Earth's Inner Core

Earth's Moving, Melting Core in Science.
Strange forces are at work 5000 kilometers below Earth's surface. The inner core is acting in ways that scientists can't explain. Theoretically, the core should be drawing iron from its molten surroundings and crystallizing it into solid metal. But that alone doesn't account for a number of odd observations—unless, as a few scientists speculate, the core is also melting.

Tuesday, August 10, 2010

P is not equal to NP?

Vinay Deolalikar a research scientist at HP labs, has a preprint (on his web page) which is a preliminary draft of a proof that P is not equal to NP. Claimed resolutions of P=NP are rife on the internet. However, this draft preprint is from a reputable researcher. The P=NP question is one of the most important research problems of our time. Any proof of this importance will have to be carefully checked by the research community. We shall see!

See how this process has been playing out as of August 16, 2010: Step 1: Post Elusive Proof. Step 2: Watch Fireworks. in the New York Times.

See also A Tale of A Serious Attempt At P≠NP by Computer Scientist Richard J. Lipton at CACM.