The Physics arXiv Blog
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How fast could Usain Bolt have run the 100m?
You’ll probably have seen footage of “the greatest 100m performance in the history of the event” as Michael Johnson put it. But if not, here’s short description: In the Olympic final of the 100 metres in Beijing, the Jamaican sprinter Usain Bolt accelerated away from the field and then, with victory assured but with 20…
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Predicting mine collapse
Northern France is riddled with limestone mines that occasionally collapse creating a ring-shaped crater on the surface that can cause serious damage to nearby buildings. Is there any way to predict these failures and thereby attempt to prevent them? If there is, Siavash Ghabezloo and Ahmad Pouya from the Laboratoire Centrale des Ponts et Chaussées…
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Orbiting observatory finds dark matter, but what kind?
The world of cosmology is abuzz with rumours that an orbiting observatory called PAMELA has discovered dark matter. Last month, the PAMELA team gave a few selected physicists a sneak preview of their results at a conference in Stockholm. Here’s the deal. The PAMELA people say their experiment has seen more positrons than can be…
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Rot ‘n’ decay (part 2)
More highlights from the arXiv this week: Quantum Computing with Alkaline Earth Atoms Graphene Nanodevices: Bridging Nanoelectronics and Subwavelength Optics Observation of Quantum Capacitance of Individual Single Walled Carbon Nanotubes Inferring Basic Parameters of the Geodynamo from Sequences of Polarity Reversals Can Matter Wave Interferometer Detect Translational Speed?
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Rot ‘n’ decay
The best of the rest from the physics arXiv this week: Gravitational Time Advancement and its Possible Detection How Hard Is Bribery in Elections? On the Stability of Black Holes at the LHC The Flavour of Inflation Dante, Astrology and Astronomy
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Do nuclear decay rates depend on our distance from the sun?
Here’s an interesting conundrum involving nuclear decay rates. We think that the decay rates of elements are constant regardless of the ambient conditions (except in a few special cases where beta decay can be influenced by powerful electric fields). So that makes it hard to explain the curious periodic variations in the decay rates of…
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Why Galileo underestimated the distance to the stars
“Galileo argued that with a good telescope one could measure the angular sizes of stars, and that the stars typically measured a few arc-seconds in diameter,” says Chris Graney at Jefferson Community College in Louisvile in good ol’ Kentucky. That doesn’t sound right. We know today that stars appear as point sources of light, so…
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The sound of a bouncing basketball
“A basketball bounced on a stiff surface produces a characteristic loud thump, followed by high pitched ringing,” says Joanthan Katz at Washington University in St Louis. The question is why and, conveniently, Katz provides the answer on the arXiv today. He assumes first that a basketball is an inextensible but perfectly flexible hollow sphere. From…
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The ultimate black hole size limit
We have a pretty good idea that a supermassive black hole is sitting at the center of our galaxy. By supermassive, astronomers mean about 6 millions times as massive as our sun. That’s pretty big by any standards but how big can black holes get Is there any limit to how big these monsters can…
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Why aluminum should replace cesium as the standard of time
The second is defined as 9,192,631,770 vibrations of a cesium atom and measured in a device known as a fountain clock. These work by cooling a tiny cloud of cesium atoms to a temperature close to zero, tossing it up in the air and zapping it with microwaves as it falls. Then you watch the…