Waves & Packets
May. 11, 2013

Reflection from electron mirror confirms Einstein's thought experiment
Max-Planck-Institut für Quantenoptik
A team of physicists has managed to carry out Einstein’s 1905 Gedankenexperiment where he suggested that reflection from a mirror moving close to the speed of light could in principle result in bright light pulses of short wavelengths. As reported in Nature Communications, the team succeeded in generating flashes of extreme UV radiation via the reflection of an IR pulse from a mirror consisting of a dense sheet of electrons accelerated to close to the speed of light. In the experiment the physicists irradiated a nanometer-thin, freestanding foil with a 50 fs, ultra-intense laser pulse. The impinging laser pulse liberated electrons from the carbon atoms of the foil and rapidly accelerated them to close to the speed of light in less than a micrometer forming a dense sheet of electrons capable of acting as a mirror. Radiation reflected from a mirror that is moving is changed in its wavelength as the reflected photons gain momentum from the mirror. Moreover, the time duration of the reflected pulses was on the order of a few hundred attoseconds. This result paves the way for a new method to generate intense, attosecond short flashes of light that can be used to resolve electron motions in atoms.More

NASA's Fermi, Swift see 'shockingly bright' gamma ray burst
A burst of gamma rays from a dying star has been observed by the Fermi and Swift gamma-ray space telescopes. Gamma-ray bursts are the universe's most luminous explosions. This one, with emissions of 95 GeV, was the highest-energy light ever detected from such an event. GeV emissions from the burst lasted for hours, and it remained detectable by the Fermi telescope for the better part of a day, setting a new record for the longest gamma-ray emission from a gamma ray burst. Based on the rapid accurate position from the Swift telescope, the burst subsequently was detected in optical, infrared and radio wavelengths by a record number of ground-based observatories.

In an interview with Waves and Packets, Dr. Soebur Razzaque of the University of Johannesburg stated that GRB 130427A, in addition to having the most energetic photons every detected, it is very nearby (redshift =0.34 compared to typical GRB redshifts of 1 to 2). The burst also exhibited a delay between the arrival time of higher energy photons (above GeV) compared to lower-energy (keV-MeV) photons. With a few hundred gamma-rays with GeV energy each, GRB 130427A is a treasure trove for gamma-ray astrophysicists to learn in more details about the most violent explosions in the universe.


ALPHA reports first direct analysis of how antimatter is affected by gravity
Physics World
Current theoretical arguments predict that hydrogen and antihydrogen atoms have the same mass and should interact with gravity in the same way. Even the tiniest of differences between the behavior of matter and anti-matter is important, as it could shed light on mysteries such as why there is so little antimatter in the universe. Indeed, the ALPHA collaboration at CERN, which has been able to capture anti-hydrogen atoms for periods on the order of 16 minutes, did not find any evidence that gravity acts upon anti-hydrogen any differently than hydrogen. Their analysis is reported in Nature Communications. Over the years CERN has hosted many world-class experiments on antimatter. Two new experiments currently under construction at CERN, AEGIS and GBAR, will also focus on measuring how gravity affects anti-hydrogen. Meanwhile, researchers are still investigating the hyperfine structure and magnetic moment of anti-hydrogen atoms.More

Photonics discovery enable high speed measurement of greenhouse gases from space
The University of Western Australia
Scientists at UWA and NIST have combined forces to build new gas measurement equipment with unparalleled speed, accuracy, precision and spectral coverage. NASA's Jet Propulsion Laboratory has begun using data from the sensor to calibrate carbon monitoring satellites in orbit around Earth and better understand carbon dioxide molecules. The frequency-agile, rapid scanning spectroscopy method, described in Nature Photonics, overcomes the challenges of scanning rate without sacrificing sensitivity. The method uses a high-bandwidth electro-optic modulator to step a selected laser sideband to successive optical cavity modes. It does not reduce the measurement duty cycle, degrade the spectrum's frequency axis or require an unusual cavity configuration. In addition to its application to space-based Earth observation, the method can be used in combustion research.More

High-energy X-rays shine light on mystery of Picasso's paints
Argonne National Lab
The Art Institute of Chicago teamed up with Argonne National Laboratory to help unravel a decades-long debate among art scholars over whether or not Picasso was one of the first master painters to use common house paint rather than traditional artists' paint. Many art conservators and historians have tried over the years to use traditional optical and electron microscopes to study this question, but those methods failed because they would not let them see deeply enough into the layers of paint or with enough resolution to distinguish between binders and fillers in paint and the actual pigment. But the hard X-ray nanoprobe at Advanced Photon Source and Center for Nanoscale Materials is able to scan a painting with high spatial resolution and micro-focusing abilities. These capabilities combine to give the probe the unique ability to identify individual chemical elements and distinguish between the size of paint particles crushed by hand in artists' studios and those crushed even smaller by manufacturing equipment.

Using the nanoprobe, scientists were able to determine that Picasso used enamel paint to create in 1931 The Red Armchair, on display at the Art Institute of Chicago. They were also able to determine the paint brand and from what manufacturing region the paint originated. The results are published in Applied Physics A: Materials Science & Processing.


US PAPER experiment in South Africa closes in on Epoch of Ionization
One of the most exciting topics in modern cosmology is determining the exact timing and sequence of events that kicked of the Epoch of Reionization. About 300,000 years after the Big Bang the original primordial plasma cooled down enough that protons and electrons combined to form neutral hydrogen atoms, creating the Cosmic Microwave Background and marking the beginning of the so-called ‘dark ages’. At some time thereafter, something, presumably the collapse of hydrogen clouds and subsequent ignition of the first stars and galaxies, must have happened to convert all of that neutral matter back into an ionized state that we see today. Radiation from the first stars could have provided enough energy to ionize hydrogen, and when that process occurred 21 cm photons were emitted. There are several experiments to detect these 21 cm photons. The Precision Array for Probing the Epoch of Reionization (PAPER) experiment is a low-frequency radio interferometer located in the Karoo Desert, not far from the KAT-7 array, as well as a companion array near NRAO Green Bank. The PAPER team has reported new results that place a new upper limit of the amount neutral hydrogen at redshift = 7.7. The result means that at the time indicated by this redshift there was not enough neutral hydrogen to produce a signal stronger than 52 mK at these lengthscales, and that there was large-scale heating of the neutral intergalactic medium during reionization.More

Does photophoresis explain the density of Mercury and other rocky planets?
Mercury's high density has been a longstanding puzzle in planetary science. Its density means that it must have significantly higher iron abundance than Venus, Earth, Mars, or the asteroids, probably in the form of a large iron core. A common popular explanation is that a giant impact came along late in the formation process and stripped the silicate mantle off of Mercury, leaving behind an iron-rich planet. But that theory has been challenged by data from the NASA MESSENGER. A new theory, proposed in a paper posted onto arXiv, suggest that radiation heating of particles in the planetary disk sorts material on the basis of thermal conductivity. This photophoretic process would lead to iron particles ending up closer to radiation source, while silicate particles would transported further away. Photophoresis would thus naturally create a composition gradient in the disk, with metal-enrichment in the inner parts and silicate-enrichment in the outer parts. This could explain the iron-enrichment of Mercury, as well as the apparent slight iron-enrichment of other rocky exoplanets.More

New cold atom based detector could help detect gravitational waves
Physics World
A modified form of an atom interferometer could present a cheaper and easier method to detect gravitational waves than current laser interferometers. Gravitational waves are tiny perturbations in the curvature of space–time that arise from accelerating masses — according to Einstein's general theory of relativity. International teams, LIGO and VIRGO, are trying to detect these waves using long-baseline laser interferometers. A group of physicists at Stanford University are proposing that instead of measuring the difference in phase between two beams of light, as in the LIGO and VIRGO instruments, an atom interferometer be used to measure the change in the phase of a matter wave made of atoms in a superposition of quantum states. An atom interferometer can be created by repeatedly exciting and de-exciting one half of the wavefunction using a laser while holding the other half in the ground state. As explained in Physical Review Letters, the wavelength of an atom shortens when the atom is in its excited state, creating a phase shift between the two halves of the wavefunction that depends on how long the first half has spent in the excited state.More

Deformed nuclei could point to physics beyond the Standard Model
The University of York
Most nuclei that exist naturally are observed to be prolate spheroids. While the latest theories are able to predict this, the same theories have predicted that for some particular combinations of protons and neutrons, nuclei can also assume very asymmetric shapes, like a pear, where there is more mass at one end of the nucleus than the other. But observations of nuclei having this shape have only recently been made. In a report published in Nature, physicists at CERN’s ISOLDE facility have observed pear-shaped nuclei in radon-220 and radium-224. This was done by revealing octupole moments in the in the gamma ray emissions from the atoms after being excited and subsequently decaying to the ground state. The implications of these results are profound. The Standard Model predicts that nuclei have a vanishing small electric dipole moment, which methods used heretofore have not captured. The technique used in this current work may increase sensitivity leading to quantitative measurements. Furthermore, pear-shaped nuclei are good places to look for CPT violation beyond that allowed by the Standard Model, and thus perhaps an explanation of there is more anti-matter than matter in the universe.More

A new scheme for ultrashort, extremely high energies X-ray pulses
RIKEN Research
Takashi Tanaka from the RIKEN SPring-8 Center has proposed a theoretical pulse-amplification scheme that allows for the production of ultra-short x-ray pulses at extremely high energies. His proposed solution, detailed in Physical Review Letters, involves shortening the electron pulse used to generate the x-rays by filtering out all but the middle part of the pulse, rejecting the weakest leading and trailing pulse components. The filtered electron pulse is then sent on a curved path—helped by a matching optical laser that stabilizes the electron movements—to divide the electron pulse into a series of small ‘bunches’. These electron bunches are then converted into weak x-ray laser pulses, which are sent through a delay line that shifts the leading ‘target’ pulse so as to coincide with the last of the corresponding electron bunches. In a further amplification process, the target pulse is strengthened using a laser, leaving the rest of the pulses unaltered. Repetition of this last step a number of times amplifies the target pulse by many orders of magnitude. If feasible and implemented, this scheme would further enhance the utility of x-ray free electron lasers in studying materials, chemical reactions, and important protein structures, like the photosynthetic center, G-protein receptors, and Trypanosoma brucei cathepsin B, which is involved in the transmission of African sleeping sickness.More

National Society of Black Physicists jobs board postings
Deputy Division Director, Division of Physics (PHY)
NASA Postdoctoral Fellowships
Assistant Editor, Physical Review D

Reflection from electron mirror confirms Einstein's thought experiment
Max-Planck-Institut für Quantenoptik
A team of physicists has managed to carry out Einstein’s 1905 Gedankenexperiment where he suggested that reflection from a mirror moving close to the speed of light could in principle result in bright light pulses of short wavelengths.More

Einstein's gravity theory passes toughest test yet
National Radio Astronomy Observatory
A newly-discovered system containing a pulsar and its white-dwarf companion has put gravitational theories to the most extreme test yet. The two objects orbit each other once every two and a half hours.More

LHCb experiment observes new matter-antimatter difference
CERN Press Office
The LHCb collaboration has made the first observation of matter-antimatter asymmetry in the decays of strange B mesons. Matter and antimatter are thought to have existed in equal amounts at the beginning of the universe, but today the universe appears to be composed essentially of matter.More

Latest research from European Journal of Physics
IOP Publisher
Whether or not to run in the rain

Analysis of LED data for the measurement of Planck's constant in the undergraduate laboratory

Entropic forces—making the connection between mechanics and thermodynamics in an exactly soluble model

What is what we call the 'quantum field'? Answering from a teaching perspective by taking the foundations into account

Derivation of the harmonic oscillator propagator using the Feynman path integral and recursive relationsMore

Latest research from Physical Review Special Topics — Physics Education Research
American Physical Society
Relativity concept inventory: Development, analysis, and results

Students' epistemological beliefs, expectations, and learning physics: An international comparison

Introducing Taiwanese undergraduate students to the nature of science through Nobel Prize stories

Exploring the context of change: Understanding the kinetics of a studio physics implementation effort

Female physicist doctoral experiencesMore