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Category: particle physics – Page 281

face_with_colon_three circa 2012.

It is shown that the idea of a photon rocket through the complete annihilation of matter with antimatter, first proposed by Sänger, is not a utopian scheme as it is widely believed. Its feasibility appears to be possible by the radiative collapse of a relativistic high current pinch discharge in a hydrogen–antihydrogen ambiplasma down to a radius determined by Heisenberg’s uncertainty principle. Through this collapse to ultrahigh densities the proton–antiproton pairs in the center of the pinch can become the upper gigaelectron volt laser level for the transition into a coherent gamma ray beam by proton–antiproton annihilation, with the magnetic field of the collapsed pinch discharge absorbing the recoil momentum of the beam and transmitting it by the Moessbauer effect to the spacecraft. The gamma ray laser beam is launched as a photon avalanche from one end of the pinch discharge channel. Because of the enormous technical problems to produce and store large amounts of anti-matter, such a propulsion concept may find its first realization in small unmanned space probes to explore nearby solar systems. The laboratory demonstration of a gigaelectron volt gamma ray laser by comparison requiring small amounts of anti-matter may be much closer.

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A team of researchers at Universität Heidelberg has built an early universe analog in their laboratory using chilled potassium atoms. In their paper published in the journal Nature, the group describes their simulator and how it might be used. Silke Weinfurtner, with the University of Nottingham, has published a News & Views piece in the same journal issue outlining the work done by the team in Germany.

Understanding what occurred during the first few moments after the Big Bang is difficult due to the lack of evidence left behind. That leaves astrophysicists with nothing but theory to describe what might have happened. To give credence to their theories, scientists have built models that theoretically represent the conditions being described. In this new effort, the researchers used a new approach to build a in their laboratory to simulate conditions just after the Big Bang.

Beginning with the theory that that the Big Bang gave rise to an , the researchers sought to create what they describe as a “quantum field simulator.” Since most theories suggest it was likely that the was very cold, near absolute zero, the researchers created an environment that was very cold. They then added potassium atoms to represent the universe they were trying to simulate.

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The scientists said their spacetime simulation “agrees very well with theory.”

A team of physicists used a “quantum field simulator” to simulate a tiny expanding universe made out of ultracold atoms, a report from VICE

Simulating spacetime.

Pixelparticle/iStock.

The scientists conducted the experiment to simulate the early rapid expansion of the universe following the Big Bang. Their work could lead to accurate representations of the universe in future experiments, allowing for the testing of countless models of the early evolution of the cosmos.

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A tantalizing signal reported by the XENON1T dark matter experiment has sparked theorists to investigate explanations involving new physics.

On June 16, 2020, the collaboration running XENON1T—one of the world’s most sensitive dark matter detectors—reported a signal it couldn’t explain (see today’s accompanying article, Viewpoint: Dark Matter Detector Delivers Enigmatic Signal). The signal has yet to reach the “5-sigma” bar for discovery, and a mundane explanation could still be the culprit. But theorists have been quick to explore whether exotic particles or interactions might be involved. Physical Review Letters followed a special procedure to get a coherent expert review of the proposals it received. Now, the journal is publishing five papers that represent the breadth of theories being pursued.

All of the reported scenarios explain two aspects of the signal, which was produced in the huge vat of ultrapure xenon that makes up XENON1T’s detector. First, the signal looks like it came from particles that collided mostly with the xenon atoms’ electrons. And second, each of these interactions dumped a few keV into the atom.

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Scientists used the IceCube Neutrino Observatory, a special telescope that extends for more than a mile under the Antarctic ice at the South Pole, to capture roughly 80 astrophysical neutrinos from a galaxy known as NGC 1,068, or Messier 77, which has an extremely active galactic core. The finding suggests that these active galaxies provide “a substantial contribution” to the abundance of astrophysical neutrinos, and therefore cosmic rays, that permeate through the universe, according to a study published on Thursday in Science.

“This is a very exciting result because for the first time, we actually understand that astrophysical neutrinos can be related to this very special type of galaxy,” said Theo Glauch, an experimental physicist at the Technical University of Munich and a co-author of the new study, in a call with Motherboard. “We physicists call them active galaxies because they’re very different from, for example, our Milky Way.”

Unlike our own galaxy, which is currently dormant, NGC 1,068 contains “an extremely bright environment which we can only study in neutrinos,” Glauch added. “Neutrinos are the only particles that can directly escape from the processes that drive this extremely high luminosity in the core of those galaxies.”

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After several years of developing the theoretical ideas, University of Illinois Urbana-Champaign researchers have validated multiple novel predictions about the fundamental mechanism of transport of atoms and molecules (penetrants) in chemically complex molecular and polymer liquid matrices.

The study from Materials Science and Engineering (MatSE) Professor Ken Schweizer and Dr. Baicheng Mei, published recently in Proceedings of the National Academy of Sciences (PNAS), extended the theory and tested it against a large amount of experimental data. MatSE Associate Professor Chris Evans and graduate student Grant Sheridan collaborated on this research by providing additional experimental measurements.

“We developed an advanced, state-of-the art theory to predict how move through complex media, especially in polymer liquids,” Schweizer said. “The theory abstracted what the important features are of the chemically complex molecules and of the polymeric medium that they’re moving through that control their rate of transport.”

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Chirality is the breaking of reflection and inversion symmetries. Simply put, it is when an object’s mirror images cannot be superimposed over each other. A common example are your two hands—while mirror images of each other, they can never overlap. Chirality appears at all levels in nature and is ubiquitous.

In addition to static , chirality can also occur due to dynamic motion including rotation. With this in mind, we can distinguish true and false chirality. A system is truly chiral if—when translating—space inversion does not equate to time reversal combined with a proper spatial rotation.

Phonons are quanta (or small packets) of energy associated with the vibration of atoms in a . Recently, phonons with chiral properties have been theorized and experimentally discovered in two-dimensional (2D) materials such as tungsten diselenide. The discovered chiral phonons are rotating—yet not propagating—atomic motions. But, truly chiral phonons would be atomic motions that are both rotating and propagating, and these have never been observed in three-dimensional (3D) bulk systems.

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The observation of the onset of turbulence in a gas of bosons allows researchers to explore how turbulence comes to life.

Despite over a century of trying, physicists have yet to develop a complete theory of turbulence—the complex, chaotic motion of a fluid. Now Maciej Gałka of the University of Cambridge and colleagues have taken a step in that direction by witnessing the onset of turbulence in a quantum gas and observing its evolution over roughly 100 ms [1]. The finding could help scientists answer open questions in turbulence, which is observed in systems ranging from ocean waves to star interiors.

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