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Category: particle physics

Teaching thermodynamic laws to AI unlocks a polymer modeling challenge

For more than half a century, materials scientists have struggled with how to simulate the complexity of polymer materials. An individual chain can comprise tens of thousands of atoms, a melt or composite contains billions, and the properties engineers actually care about, such as how an adhesive grips a surface, how a self-assembling block copolymer locks into a nanostructure, or how a biopolymer film stretches without tearing, emerge only over length and time scales that forcible atomistic simulation cannot reach.

The standard workaround is coarse-graining: replacing groups of atoms with simpler mesoscopic particles so the model is fast enough to run. The catch is that this compression almost always sacrifices physics. Conventional coarse-grained polymer models can usually reproduce equilibrium structure or large-scale dynamics, but rarely both, and they routinely fail to capture the entropic and viscous forces that govern how polymers actually flow, relax, and dissipate energy. Those are the forces that dictate mechanical performance, and they are the forces that traditional machine-learning approaches, despite their flexibility, also tend to break.

A research paper recently published in Proceedings of the National Academy of Sciences introduces a new machine-learning framework that lets coarse-grained models achieve both at once. A team from Carnegie Mellon University and the University of Pennsylvania has built an AI architecture that learns coarse-grained dynamics directly from data, whether simulated or experimental, while being mathematically incapable of violating the laws of thermodynamics.

Large Hadron Collider detects strange particle behavior that could rewrite physics

Scientists working at CERN’s Large Hadron Collider may be seeing the strongest hints yet of physics beyond the Standard Model — the decades-old theory that explains the fundamental particles and forces of the universe. By studying incredibly rare particle transformations called “penguin decays,” researchers found behavior that doesn’t fully match theoretical predictions, raising the possibility that unknown particles or forces are influencing the results.

Philosophy Talks 26: Emergence in Process — Prof. Mark H. Bickhard

Date of the talk: 13th November 2024

Abstract:
Emergence can (potentially) integrate across otherwise dual metaphysics of basic substances or atoms on one hand and higher ‘level’ phenomena, including mental phenomena, on the other. But there are strong arguments against the possibility of emergence, such as from Jaegwon Kim. I will argue that such arguments against emergence assume a metaphysics of ‘atoms’ (particles); that that metaphysics is false; that an alternative is a metaphysics of process; and that process metaphysics makes the possibility of emergence coherent and ubiquitous.

Scientists discover atoms suddenly spinning backward in quantum experiment

Scientists have directly watched angular momentum move through a crystal for the very first time — and discovered a bizarre twist along the way. Using ultra-powerful terahertz laser pulses, researchers triggered tiny atomic rotations inside a quantum material and found that the direction of rotation can unexpectedly flip as momentum is transferred. The strange reversal happens because of the crystal’s underlying symmetry, creating an almost impossible-sounding effect where two rotations combine into one spinning the opposite way.

Hydrogen puts quantum wormhole conjecture to the test

A new Physical Review Letters study places constraints on the ER = EPR conjecture, showing that under the authors’ assumptions, the conjecture would imply possible alterations to the hyperfine structure and effective charge of the hydrogen atom—effects that have never been observed.

In 1935, Einstein co-authored two distinct papers. The first proposes the Einstein-Podolsky-Rosen (EPR) paradox describing the quantum entanglement of particles. The second one introduces Einstein-Rosen (ER) bridges connecting distant regions of spacetime, which we today call wormholes.

Nearly a century later, in 2013, physicists Juan Maldacena and Leonard Susskind proposed the ER = EPR conjecture, proposing a link between quantum entanglement and wormholes. This links entanglement, a cornerstone of quantum mechanics, with spacetime connectivity, general relativity. This remains one of the major open questions in modern physics.

‘Butterfly’ molecule spotted at last, completing a 20-year quantum zoo hunt

For two decades, physicists have predicted the existence of a remarkable family of exotic molecules: giant atoms bound to ordinary atoms, with an electron so distant from its nucleus that it sculpts the pair into bizarre and diverse shapes. Reported in Physical Review Letters, the final member of this “quantum zoo” has been spotted. Led by Herwig Ott at RPTU University Kaiserslautern-Landau in Germany, a team of physicists has created and detected the “butterfly” molecule, completing a 20-year hunt for the elusive structure.

The molecules in this quantum zoo belong to a class known as ultralong-range Rydberg molecules. They form when an ordinary atom becomes bound to a Rydberg atom, whose outermost electron has been excited so far from the nucleus that the atom swells to thousands of times its normal size.

The orbital shapes traced out by these distant electrons give each molecule type its character, and its nickname. Some have elaborate lobed structures reminiscent of trilobites; others spread into the winged outline of a butterfly. These molecules are thousands of times more sensitive to electric fields than ordinary molecules, making them especially useful objects for probing the quantum world.

Supercharging solar cells: Quantum dot-molecule hybrid states enable near-maximum efficiency

Solar panels have become more efficient over the years, but even the best designs still lose a large fraction of the energy they absorb. Scientists around the world have been searching for ways to capture more energy from every ray of sunlight and unlock the true potential of solar technology.

In a study published in Nature Photonics, researchers from the University of Osaka and collaborating institutions identified a new mechanism that could help us do exactly that. The study shows how specially designed combinations of molecules and quantum dots can be used to dramatically increase solar cell efficiency beyond currently known limits.

Singlet exciton fission is a photophysical phenomenon in which one particle of light creates two excited energy states instead of one. In theory, this allows solar cells to generate more electricity from the same amount of sunlight. However, the most effective photophysical processes require extra energy and are usually inefficient and difficult to control.

Visualizing how flutter kick vertical vortices generate propulsion and suppress body sway in swimmers

Researchers at University of Tsukuba used advanced techniques to visualize the water flow generated by flutter kicking during front-crawl swimming. They analyzed how this kicking motion generates propulsive force and contributes to body stabilization, demonstrating that the vertical vortices resulting from the alternating left and right leg movements not only impart forward propulsion but also suppress body sway. These results provide a fluid-dynamical explanation of the functional value of the flutter kick.

In competitive swimming, both upper-and lower-limb motions play important roles in propulsion. Extensive research has focused on the dolphin kick used in the butterfly stroke, revealing that this kicking technique generates three-dimensional vortex structures that contribute directly to propulsion. In contrast, the propulsion mechanism of the flutter kick used in the front crawl has remained poorly understood, largely because the alternating motion of the left and right legs induces complex flow patterns.

Therefore, in this study, published in Physics of Fluids, the researchers investigated the flow fields generated by the flutter kick by combining a motion-capture system with particle image velocimetry—an optical method for visualizing and measuring flow.

Tuning into quantum sounds: Acoustic devices simplify quantum sensors

When a singer belts out a tune while a guitar player strums along, sound waves travel through the air, driving collective oscillations of the molecules within. Meanwhile, at the quantum level, something similar is going on. Atoms inside materials, everything from our bodies to metals and more, naturally jiggle around, creating tiny vibrational waves that ripple across the material. These vibrations are known as phonons: the quantum version of sound waves.

Now, physicists at Caltech and Stanford University have developed devices called nanoelectromechanical systems (NEMS) that allow phonons to exhibit their quantum behavior purely through the intrinsic properties of the material that makes up the device. Previously, it was not possible to observe such behavior without the help of an external quantum device, such as a superconducting qubit.

This means that, through this newly discovered mechanism, a solitary NEMS device can, for example, serve as a greatly simplified and very compact quantum sensor or qubit.

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