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Superstring Theory


M-theory

The problem with determining a correct Calabi-Yau space is related to the perturbative method used to perform the calculation. In this approximation scheme, each possible Calabi-Yau shape appears to be on equal footing with every other; none is fundamentally singled out by the equations. It is simply not possible to select one Calabi-Yau space from the many others. One of the new approaches to non-perturbative string theory involves M-theory and duality, which in fact force us to reconsider the central role played by strings in supersymmetry. In particular, duality allows us to show that the five previously mentioned superstring theories are nothing but different solutions of a single theory, called "M-theory". In this revised picture, the various string theories are different vacua of the M-theory. While perturbation theory only probes the vicinity of each vacua, duality allows us to make non-perturbative correlations across different vacua. Furthermore, M-theory indicates that the "true home" of the theory may actually be the eleventh dimension, where we find new, exotic objects, such as super membranes and 5-branes. The complete "action" of M-theory is unknown, but is believed to contain membranes (2-branes) and 5-branes. Closed strings in lower dimensions can be viewed as compactifications of these membranes.

It is shown in 2008 by the Hubble space telescope that the two images in CSL-1 were two different, deceptively similar galaxies. Thus like so many exotic objects concocted by theorists, cosmic string remains just a hypothetical entity.

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