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Category: particle physics – Page 533

It’s not easy being a “theory of everything.” A TOE has the very tough job of fitting gravity into the quantum laws of nature in such a way that, on large scales, gravity looks like curves in the fabric of space-time, as Albert Einstein described in his general theory of relativity. Somehow, space-time curvature emerges as the collective effect of quantized units of gravitational energy — particles known as gravitons. But naive attempts to calculate how gravitons interact result in nonsensical infinities, indicating the need for a deeper understanding of gravity.

String theory (or, more technically, M-theory) is often described as the leading candidate for the theory of everything in our universe. But there’s no empirical evidence for it, or for any alternative ideas about how gravity might unify with the rest of the fundamental forces. Why, then, is string/M-theory given the edge over the others?

The theory famously posits that gravitons, as well as electrons, photons and everything else, are not point-particles but rather imperceptibly tiny ribbons of energy, or “strings,” that vibrate in different ways. Interest in string theory soared in the mid-1980s, when physicists realized that it gave mathematically consistent descriptions of quantized gravity. But the five known versions of string theory were all “perturbative,” meaning they broke down in some regimes. Theorists could calculate what happens when two graviton strings collide at high energies, but not when there’s a confluence of gravitons extreme enough to form a black hole.

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Japan’s government is facing serious fiscal challenges, but its main science ministry appears hopeful that the nation is ready to once again back basic research in a big way. The Ministry of Education (MEXT) on 31 August announced an ambitious budget request that would allow Japan to compete for the world’s fastest supercomputer, build a replacement x-ray space observatory, and push ahead with a massive new particle detector.

Proposed successor to Super-Kamiokande, exascale computer and x-ray satellite win backing.

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TRULY SUPER. There’s a reason researchers call graphene a “super material.” Even though it’s just a single layer of carbon atoms thick, it’s super strong, super flexible, and super light. It also conducts electricity, and is biodegradable. Now an international team of researchers has found a way to use the super material: to create artificial retinas.

They presented their work Monday at a meeting of the American Chemical Society (ACS).

ARTIFICIAL RETINAS. The retina is the layer of light-sensitive cells at the back of the eye responsible for converting images into impulses that the brain can interpret. And without a functional one, a person simply can’t see.

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The giant CMS detector at the Large Hadron Collider will search for double-Higgs events.

IMAGE: MICHAEL HOCH AND MAXIMILIEN BRICE

For particle physicists eager to explore new frontiers, spotting the Higgs boson has become a bittersweet triumph. Detected in 2012 at the world’s biggest atom smasher, the Large Hadron Collider (LHC), the long-sought particle filled the last gap in the standard model of fundamental particles and forces. But since then, the standard model has stood up to every test, yielding no hints of new physics. Now, the Higgs itself may offer a way out of the impasse. Experimenters at the LHC, located at CERN, the European particle physics laboratory near Geneva, Switzerland, plan to hunt for collisions that produce not just one Higgs boson, but two.

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Quantum particles can be difficult to characterize, and almost impossible to control if they strongly interact with each other—until now.

An international team of researchers led by Princeton physicist Zahid Hasan has discovered a state of matter that can be “tuned” at will—and it’s 10 times more tuneable than existing theories can explain. This level of manipulability opens enormous possibilities for next-generation nanotechnologies and quantum computing.

“We found a new control knob for the quantum topological world,” said Hasan, the Eugene Higgins Professor of Physics. “We expect this is tip of the iceberg. There will be a new subfield of materials or physics grown out of this. … This would be a fantastic playground for nanoscale engineering.”

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Graphene — an ultrathin material consisting of a single layer of interlinked carbon atoms — is considered a promising candidate for the nanoelectronics of the future. In theory, it should allow clock rates up to a thousand times faster than today’s silicon-based electronics. Scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) and the University of Duisburg-Essen (UDE), in cooperation with the Max Planck Institute for Polymer Research (MPI-P), have now shown for the first time that graphene can actually convert electronic signals with frequencies in the gigahertz range — which correspond to today’s clock rates — extremely efficiently into signals with several times higher frequency. The researchers present their results in the scientific journal Nature.

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A system made of just a handful of particles acts just like larger systems, allowing scientists to study quantum behaviour more easily.

Most substances physicists study are made up of huge numbers of particles—so large that there is essentially no difference between the behavioural properties of a drop or a swimming pool’s worth of pure water. Even a single drop can contain more than a quadrillion particles.

This makes understanding their collective behaviour relatively easy. For example, both the water in the drop and in the pool will freeze at 0C and boil at 100C.

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Austrian physicist Erwin Schrödinger (1887−1961), one of the giants of contemporary science, considered entanglement the most interesting property in quantum mechanics. In his view, it was this phenomenon that truly distinguished the quantum world from the classical world. Entanglement occurs when groups of particles or waves are created or interact in such a way that the quantum state of each particle or wave cannot be described independently of the others, however far apart they are. Experiments performed at the University of São Paulo’s Physics Institute (IF-USP) in Brazil have succeeded in entangling six light waves generated by a simple laser light source known as an optical parametric oscillator.

Articles about these experiments have been published in Physical Review Letters and Physical Review A. The experiments are highlighted in a special news feature posted online.

“Our platform is capable of generating a massive of many optical modes with different but well-defined frequencies, as if connecting the nodes of a large network. The states thus produced can be controlled by a single parameter: the power of the external laser that pumps the system,” said Marcelo Martinelli, one of the coordinators of the experiments. Martinelli is a professor at IF-USP and the principal investigator for the project.

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Rice University atomic physicists have verified a key prediction from a 55-year-old theory about one-dimensional electronics that is increasingly relevant thanks to Silicon Valley’s inexorable quest for miniaturization.

“Chipmakers have been shrinking feature sizes on microchips for decades, and device physicists are now exploring the use of nanowires and nanotubes where the channels that electrons pass through are almost one-dimensional,” said Rice experimental physicist Randy Hulet. “That’s important because 1D is a different ballgame in terms of electron conductance. You need a new model, a new way of representing reality, to make sense of it.”

With IBM and others committed to incorporating one-dimensional carbon nanotubes into integrated circuits, chip designs will increasingly need to account for 1D effects that arise from electrons being fermions, antisocial particles that are unwilling to share space.

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