The string symphony.

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Two foundation pillars General relativity Description of stars, galaxies, expansion of the universe… Quantum mechanics Description of molecules, atoms, and all the way down to subatomic particles like electrons and quarks. But they can not both be right!

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« Why questions » in QM Why do the particles have the masses that they have? Why are there only three families of the particles? Why are there four fundamental forces? Why do the forces have such different properties ? Why? Why? Why?

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Why strings? The oscillations of the strings determine all properties of the particles that we can observe like mass, electric charge, etc. The scale of the length of the strings is over meters . They represent the end of the line - the last of the Russian matrioshka dolls - in the numerous layers of substructure in the microscopic world.

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Extra dimensions In 1919 a little-known Polish mathematician named Theodor Kaluza from the University of Konigsberg had the temerity to challenge the obvious - he suggested that the universe might not actually have three spatial dimensions - it might have more.

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The garden hose universe From big distance the thickness of the hose will be difficult to discern. But by using a pair of binoculars you can zoom in on the hose and observe its girth directly.

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The garden hose universe This example underscores a subtle and important feature of spatial dimensions : they come in two varieties. They can be large, extended, and therefore directly manifest, or they can be small, curled up, and much more difficult to detect.

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Extra dimensions in String Theory Bosonic string theory requires 26 spacetime dimensions. When supersymmetry was included the number of spacetime dimensions reduced to 10 . In 1984, Philip Candelas, Gary Horowitz, Andrew Strominger , and Edward Witten showed that the shape of the six curled-up dimensions in String Theory is Calabi-Yau shape.

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SUSY and String Theory There are five ways to include SUSY in String Theory: The type I theory The type IIA theory The type IIB theory The H eterotic type SO(32) The Heterotic type Troubles with bosonic string theory : there is no place for matter particles , and this theory contains non-existent particle - tachyon . By 1971 or so, it was found that there exist the new symmetry associated with spin. It is known as supersymmetry (SUSY)

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Strings 95 At the string conference in March 1995 at the University of Southern California w hen his appointed hour to speak had arrived, Edward Witten strode to the podium and delivered a lecture that ignited the second superstring revolution .

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M-Theory Witten suggested that the five string theories are all just different ways of describing the same underlying physics or the same theoretical framework. These framework was named M - Theory .

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M-Theory 11 dimensions Supergravity N- B ranes

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Experimental proof Currently it is very very difficult to obtain the direct experimental evidence of the theory and we can not be sure that String Theory is correct!!!

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Experimental proof However we can try to get some circumstantial evidence. One of them we already have - string theory predict gravity, and we can observe it! So far we have not found the superpartners of the particles. But it is expected that they can be found already on the Large Hadron Collider (LHC). There is a possibility that extra dimensions are not too small.

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The future of String Theory Edward Witten once called string theory “a bit of 21st century physics that somehow dropped into the 20th century .” So we can expect a lot of new amazing discoveries in this majestic cosmic symphony.

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THE END