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Quantum time travel: Black hole not required - physics-math - 22 November 2010 You don't need to set the universe in a spin to see time travel in action – so what happened when a photon with a quantum gun went back to kill itself? CHATTING about time travel in a room overlooking a verdant quadrangle at the Massachusetts Institute of Technology seems strangely appropriate. The building dates from 1916 and looks its age: the high ceilings, echoing corridors and musty offices with heavy wooden doors have changed little in that time. Quantum time travel: Black hole not required - physics-math - 22 November 2010
How to create temperatures below absolute zero - physics-math - 01 December 2010 How to create temperatures below absolute zero - physics-math - 01 December 2010 ABSOLUTE zero sounds like an unbreachable limit beyond which it is impossible to explore. In fact there is a weird realm of negative temperatures that not only exists in theory, but has also proved accessible in practice. An improved way of getting there, outlined last week, could reveal new states of matter. Temperature is defined by how the addition or removal of energy affects the amount of disorder, or entropy, in a system. For systems at familiar, positive temperatures, adding energy increases disorder: heating up an ice crystal makes it melt into a more disordered liquid, for example. Keep removing energy, and you will get closer and closer to zero on the absolute or kelvin scale (-273.15 °C), where the system's energy and entropy are at a minimum.
If you haven't completed a quarter of quantum, then please try /r/AskPhysics first, especially for basic, or philosophical physics questions. What job opportunities are available in physics? MIT phys courses, HyperPhysics Before you submit: The aim of /r/Physics is to build a subreddit frequented by physicists, scientists, and those with a passion for physics. Papers from physics journals (free or otherwise) are encouraged. Topologist Predicts New Form of Matter : Physics Topologist Predicts New Form of Matter : Physics
Topologist Predicts New Form of Matter  Topologist Predicts New Form of Matter  Back in 1970, a young physicist working in the Soviet Union made a counterintutive prediction. Vitaly Efimov, now at the University of Washington in the US, showed that quantum objects that cannot form into pairs could nevertheless form into triplets. In 2006, a group in Austria found the first example of such a so-called Efimov state in a cold gas of cesium atoms.
Delayed choice quantum eraser A delayed choice quantum eraser, first performed by Yoon-Ho Kim, R. Yu, S.P. Kulik, Y.H. Shih and Marlan O. Scully,[1] and reported in early 1999, is an elaboration on the quantum eraser experiment that incorporates concepts considered in Wheeler's delayed choice experiment. Delayed choice quantum eraser
­­A man sits down before a gun, which is pointed at his head. This is no ordinary gun; i­t's rigged to a machine that measures the spin of a quantum particle. Each time the trigger is pulled, the spin of the quantum particle -- or quark -- is measured. How Quantum Suicide Works"

How Quantum Suicide Works"

Einstein's sceptics: Who were the relativity deniers? - physics-math - 18 November 2010 When people don't like what science tells them, they resort to conspiracy theories, mud-slinging and plausible pseudoscience – as Einstein discovered "THIS world is a strange madhouse," remarked Albert Einstein in 1920 in a letter to his close friend, the mathematician Marcel Grossmann. "Every coachman and every waiter is debating whether relativity theory is correct. Belief in this matter depends on political affiliation." Einstein's sceptics: Who were the relativity deniers? - physics-math - 18 November 2010
Short Sharp Science: Best ever image from a neodymium rare-earth magnet Short Sharp Science: Best ever image from a neodymium rare-earth magnet Jamie Condliffe, reporter (Image: Linden Gledhill/Cognisys) Is it a robo-hedgehog?