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BBC Horizon (2011) - What is Reality? (complete, uncut) 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?

Quantum time travel: Black hole not required - physics-math - 22 November 2010

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. If it weren't for a computer screen in the corner, the room's interior could almost date from that time. The office belongs to Seth Lloyd, one of the world's leading theorists on quantum mechanics. We are talking about a paper he and his colleagues circulated a month or so earlier describing a subtle new twist on time travel.

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.

How to create temperatures below absolute zero - physics-math - 01 December 2010

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.

Negative-temperature systems have the opposite behaviour. Creating negative-temperature systems to see what other "bizarro world" properties they might have is tricky. More From New Scientist Promoted Stories Recommended by. Topologist Predicts New Form of Matter : Physics. Topologist Predicts New Form of Matter  Back in 1970, a young physicist working in the Soviet Union made a counterintutive prediction.

Topologist Predicts New Form of Matter 

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. Large Hadron Collider - How does it work? Delayed choice quantum eraser. A delayed choice quantum eraser, first performed by Yoon-Ho Kim, R.

Delayed choice quantum eraser

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. The experiment was designed to investigate peculiar consequences of the well-known double slit experiment in quantum mechanics as well as the consequences of quantum entanglement. The delayed choice quantum eraser experiment investigates a paradox. Delayed choice experiments have uniformly confirmed the seeming ability of measurements made on photons in the present to alter events occurring in the past. Introduction[edit] In the basic double slit experiment, a beam of light (usually from a laser) is directed perpendicularly towards a wall pierced by two parallel slit apertures. Which-path information and the visibility of interference fringes are hence complementary quantities.

How Quantum Suicide Works". ­­A man sits down before a gun, which is pointed at his head.

How Quantum Suicide Works"

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. Depending on the measurement, the gun will either fire, or it won't. If the quantum particle is measured as spinning in a clockwise motion, the gun will fire. If the quark is spinning counterclockwise, the gun won't go off. Nervously, the man takes a breath and pulls the trigger. Go back in time to the beginning of the experiment. But, wait. 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.

Einstein's sceptics: Who were the relativity deniers? - physics-math - 18 November 2010

"Every coachman and every waiter is debating whether relativity theory is correct. Belief in this matter depends on political affiliation. " Einstein's general theory of relativity, published in 1915, received an overwhelming public response - not all of it positive. Numerous accounts which appeared during the 1920s claimed to show relativity was wrong, and Einstein received many letters from laypeople who claimed to have found the ultimate refutation of his theory.

Many of today's physicists and astronomers (not to mention science journalists) continue to receive this kind of mail. Best ever image from a neodymium rare-earth magnet. Jamie Condliffe, reporter (Image: Linden Gledhill/Cognisys) Is it a robo-hedgehog?

Best ever image from a neodymium rare-earth magnet

A Lady Gaga headpiece? Or merely a new way to juice lemons?