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Archive for the ‘Physics’ Category

China astronauts return as heroes

After making the country’s first spacewalk, three Chinese astronauts returned safely to Earth on Sunday. They landed in northern China’s Inner Mongolia region.

Mission commander Zhai Zhigang, 41, was watched on television by countless millions around the globe as his 15-minute spacewalk vaulted China into ranks of the United States and the former Soviet Union as the only nations to complete a spacewalk.

China sent its first man into space in 2003 and followed up with a two-man mission in 2005.

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This week a paper puplished arxiv titled :Gravitational fields as generalized string models

We show that Einstein’s main equations for stationary axisymmetric fields in vacuum are equivalent to the motion equations for bosonic strings moving on a special nonflat background. This new representation is based on the analysis of generalized harmonic maps in which the metric of the target space explicitly depends on the parametrization of the base space. It is shown that this representation is valid for any gravitational field which possesses two commuting Killing vector fields. We introduce the concept of dimensional extension which allows us to consider this type of gravitational fields as strings embedded in D-dimensional nonflat backgrounds, even in the limiting case where the Killing vector fields are hypersurface orthogonal.

  Link : http://arxiv.org/abs/0809.4495

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I have just gone through the press release from CERN. They said that investigations at CERN following a large helium leak into sector 3-4 of the Large Hadron Collider (LHC) tunnel have indicated that the most likely cause of the incident was a faulty electrical connection between two of the accelerator’s magnets. Before a full understanding of the incident can be established, however, the sector has to be brought to room temperature and the magnets involved opened up for inspection. This will take three to four weeks. Full details of this investigation will be made available once it is complete.

The time necessary for the investigation and repairs precludes a restart before CERN’s obligatory winter maintenance period, bringing the date for restart of the accelerator complex to early spring 2009. LHC beams will then follow.

Original press release 

More about LHC incident at the New York Times, BBC News, and the London Times. And more from the BBC.

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Today is 10th september,2008 and LHC has started up. Beam is in the LHC now. So CERN is really hot. Two blogs have started live bloging to keep us updated – Cosmic Variance and symmetry breaking . You can also get updates in the blog of  Tommaso Dorigo. Here is the plan for tomorrow . Best of luck for LHC.

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According to Loop quantum gravity (LQG), loops are the quantum excitations of the gravitational
field and they are space. Because there is no background space. Only loops over loops and these loops intersect each other just like a net. Interesting fact is that, the points at which loops intersect, i mean at the nodes “quanta of space” ( also called elements of space or grains of space)was found! Two adjacent quanta or elements of space are separated by a surface, and the area of this surface is also quantized. Nodes carry quantum numbers of volume elements and links carry quantum numbers of area elements. These quantum numbers and their algebra looked like the spin angular momentum numbers of elementary particles. So they are called spin network.

Here are few selected articles which should work well to understand spin network.

Useful articles for Quantum Mechanics :

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String 2008 starts today

Today String 2008 is going to start at CERN. This conferense will end on 23rd of this month. Last year it was held in Madrid, Spain. This conference is the largest and most important one on String Theory. Almost 400 physicists are participating. Here is the scheduale. CERN will provide live webcast . Lubos Motl is updating String 2008 in his blog.

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Gravitational wave is a prediction of Einstein’s General Relativity . Gravitational waves are disturbance in curvature of space-time caused by the motions of matter and they propagate as a wave, traveling outward from a moving object or system of objects. Important examples of systems which emit gravitational waves are binary star systems, where the two stars in the binary are white dwarfs, neutron stars, or black holes.

Gravitational waves propagate through space-time at the same speed of light . It does not only propagate through space but also matter. Here is video on Gravitational wave you will like to enjoy:

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