Does an exciting but controversial new model of quantum gravity reproduce Einstein's theory of general relativity? Scientists at Texas A&M University in the US explore this question in a paper appearing in Physical Review Letters and highlighted with a Viewpoint in the August 24th issue of Physics.
"If it ain't broke, don't fix it," sums up fairly well how many scientists have viewed Einstein's theory of general relativity. The theory, which Einstein developed in the early 20th century, says that matter curves spacetime, and it is this curvature which deflects massive bodies – an effect that we interpret as the influence of gravity. The theory has been tested to extremely high accuracy and without it, our satellite global positioning system would be off by about 10 km per day.
Despite the success of general relativity, one of the most important problems in modern physics is finding a theory of quantum gravity that reconciles the continuous nature of gravitational fields with the inherent 'graininess' of quantum mechanics. Recently, Petr Hoøava at Lawrence Berkeley Lab proposed such a model for quantum gravity that has received widespread interest, in no small part because it is one of the few models that could be experimentally tested. In Hoøava's model, Lorentz symmetry, which says that physics is the same regardless of the reference frame, is violated at small distance scales, but remerges over longer distance scales
The team at Texas A&M, which includes Hong Lu, Jianwei Mei and Christopher Pope, report their investigations into how the modifications proposed in Hoøava's theory will broadly affect the solutions of general relativity. One aspect of their study is that it leads to an important caveat, described by Horatiu Nastase in a Viewpoint commentary in Physics (physics.aps.org). Lu et al.'s calculations, explains Nastase, suggest that Hoøava's model only reproduces general relativity on unobservable scales, "larger than the size of the Universe".
Lu et al.'s paper is an important contribution to testing the Hoøava model and shows that a good deal of work remains to understand its full implications.
Also in Physics this week:
Nuclear Physics and Astrophysics: Cosmic alchemy in the laboratory
Michael Wiescher writes a Trends article in Physics (http://physics.aps.org/articles/v2/69) on how advances in experimental techniques that measure nuclear reactions that occur in stars are opening new opportunities for understanding the stellar and chemical evolution of our UniverseQuantum electronics: Attempting to mimic the physics of black holes
About APS Physics
APS Physics (http://physics.aps.org) publishes expert written commentaries and highlights of papers appearing in the journals of the American Physical Society.
Seeing the quantum future... literally
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Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
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At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
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Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
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Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.
Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...
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