This “Week” in the Universe: November 9th – November 22nd

Astrophysics and Gravitation:

Fundamental constants: Big G revisited

Davis, R. (2010). Fundamental constants: Big G revisited Nature, 468 (7321), 181-183 DOI: 10.1038/468181b

Credit: Nature. a, A spherical 'source mass' (ms) is brought near a pendulum's spherical bob (the 'test mass', mt) and causes the bob to move a small distance z from its usual resting position (grey). The gravitational force between the two masses (left side of equation), which depends on Newton's constant (G), can be obtained from a measurement of z provided that k is known (see b). b, The value of k is found by measuring the period (P) of the freely swinging pendulum. To compute the value of G, we need measurements of L, z, ms and P (but not mt). Parks and Faller's experiment was based on four cylindrical source masses of 100 kilograms each, two pendulums and many other refinements.

From the abstract:

Measuring Newton’s constant of gravitation is a difficult task, because gravity is the weakest of all the fundamental forces. An experiment involving two simple pendulums provides a seemingly accurate but surprising value.


For more, see Fundamental constants: Big G revisted.

Galaxy Zoo Supernovae

Galaxy Zoo (2010). Galaxy Zoo Supernovae arXiv arXiv: 1011.2199v2

This paper presents the first results from a new citizen science project: Galaxy Zoo Supernovae which, with 2500 volunteers, has categorized almost 14,000 supernovae candidates.

For more, see Galaxy Zoo paper goes supernova.

“Youngest” Nearby Black Hole

Credits: X-ray: NASA/CXC/SAO/D.Patnaude et al, Optical: ESO/VLT, Infrared: NASA/JPL/Caltech

From the Press Release:

This composite image shows a supernova within the galaxy M100 that may contain the youngest known black hole in our cosmic neighborhood. In this image, Chandra’s X-rays are colored gold, while optical data from ESO’s Very Large Telescope are shown in red, green, and blue, and infrared data from Spitzer are red. The location of the supernova, known as SN 1979C, is labeled… This approximately 30-year age, plus its relatively close distance, makes SN 1979C the nearest example where the birth of a black hole has been observed, if the interpretation by the scientists is correct.

Sure, black holes can have finite age, that seems perfectly reasonable… well no, not really.  The “age” of a black hole is an exceptionally complicated, verging on philosophical, matter that I’ll have to write about.

For more, see Black Hole Baby Spotted Being Born, Youngest nearby black hole found, Youngest Nearby Black Hole.

High Energy Physics and Particles:

Trapped Antihydrogen

Andresen, G., & et al. (2010). Trapped antihydrogen Nature DOI: 10.1038/nature09610

From the abstract:

Antihydrogen, the bound state of an antiproton and a positron, has been produced2, 3 at low energies at CERN (the European Organization for Nuclear Research) since 2002. Antihydrogen is of interest for use in a precision test of nature’s fundamental symmetries. … Here we demonstrate trapping of antihydrogen atoms. …This result opens the door to precision measurements on anti-atoms, which can soon be subjected to the same techniques as developed for hydrogen.

For more, see Antiatoms Bottled for First Time, Antimatter atoms held captive by physicists.

General Relativity, Quantum Gravity, et al.:

Pre-Big-Bang Penrose

V. G. Gurzadyan, & R. Penrose (2010). Concentric circles in WMAP data may provide evidence of violent pre-Big-Bang activity arXiv arXiv: 1011.3706v1

From the abstract:

Conformal cyclic cosmology (CCC) posits the existence of an aeon preceding our Big Bang ‘B’, whose conformal infinity ‘I’ is identified, conformally, with ‘B’, now regarded as a spacelike 3-surface. Black-hole encounters, within bound galactic clusters in that previous aeon, would have the observable effect, in our CMB sky, of families of concentric circles over which the temperature variance is anomalously low, the centre of each such family representing the point of ‘I’ at which the cluster converges… These observational predictions of CCC would not be easily explained within standard inflationary cosmology.

A very interesting, and easily misinterpreted paper, co-authored by the great Roger Penrose is the major buzz of this week.  It doesn’t imply anything about “before the universe” knowledge, which would be unphysical, but it does say that if we lived in a certain type of cyclic universe, with multiple contractions and expansions (initiated by “Big Bangs”) throughout its history, we might be able to see evidence of those contraction/expansion cycles in the CMB.  Do we see that evidence? Maybe.  Pattern matching in the CMB is able to show a lot of people a lot of different results that don’t fit in to the standard inflationary scheme, but none with a very high level of confidence.  Basically, inflation isn’t quite right, we might live in a cyclic universe, but we also might not.

For more, see Penrose claims to have glimpsed universe before Big Bang, Have we found the universe that existed before the Big Bang? (I’ll answer that one: No).

Hawking Radiation from Ultrashort Laser Pulse Filaments

Belgiorno, F., Cacciatori, S., Clerici, M., Gorini, V., Ortenzi, G., Rizzi, L., Rubino, E., Sala, V., & Faccio, D. (2010). Hawking Radiation from Ultrashort Laser Pulse Filaments Physical Review Letters, 105 (20) DOI: 10.1103/PhysRevLett.105.203901

Abstract:

Event horizons of astrophysical black holes and gravitational analogues have been predicted to excite the quantum vacuum and give rise to the emission of quanta, known as Hawking radiation. We experimentally create such a gravitational analogue using ultrashort laser pulse filaments and our measurements demonstrate a spontaneous emission of photons that confirms theoretical predictions.

For more, see Physicists Create Black Hole ‘Light’ in Lab, New horizons for Hawking radiation.

Introduction to Supergeometry

Alberto S. Cattaneo, & Florian Schaetz (2010). Introduction to supergeometry arXiv arXiv: 1011.3401v1

The abstract:

These notes are based on a series of lectures given by the first author at the school of `Poisson 2010′, held at IMPA, Rio de Janeiro. They contain an exposition of the theory of super- and graded manifolds, cohomological vector fields, graded symplectic structures, reduction and the AKSZ-formalism.

Coarse graining theories with gauge symmetries

Benjamin Bahr, Bianca Dittrich, & Song He (2010). Coarse graining theories with gauge symmetries arXiv arXiv: 1011.3667v1

The abstract:

Discretizations of continuum theories often do not preserve the gauge symmetry content. This occurs in particular for diffeomorphism symmetry in general relativity, which leads to severe difficulties both in canonical and covariant quantization approaches. We discuss here the method of perfect actions, which attempts to restore gauge symmetries by mirroring exactly continuum physics on a lattice via a coarse graining process. Analytical results can only be obtained via a perturbative approach, for which we consider the first steps, namely the coarse graining of the linearized theory. The linearized gauge symmetries are exact also in the discretized theory, hence we develop a formalism to deal with gauge systems. Finally we provide a discretization of linearized gravity as well as a coarse graining map and show that with this choice the 3D linearized gravity action is invariant under coarse graining.

The Fluid/Gravity Correspondence

Veronika E. Hubeny (2010). The Fluid/Gravity Correspondence: a new perspective on the Membrane Paradigm arXiv arXiv: 1011.4948v1

From the abstract:

This talk gives an overview of the recently-formulated Fluid/Gravity correspondence, which was developed in the context of gauge/gravity duality. Mathematically, it posits that Einstein’s equations (with negative cosmological constant) in d+1 dimensions capture the (generalized) Navier-Stokes equations in d dimensions. Given an arbitrary fluid dynamical solution, we can systematically construct a corresponding asymptotically AdS black hole spacetime with a regular horizon whose properties mimic that of the fluid flow. Apart from an overview of this construction, we describe some of its applications. The presentation is intended for a broad audience of relativists, and does not assume prior knowledge of string theory or gauge/gravity duality.

This is just beautiful.

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