Strings and Fundamental Physics
The basic idea, simple and revolutionary at the same time, to replace the concept of a point particle with a one-dimensional string, has opened up a whole new field of research. Even today, four decades later, its multifaceted consequences are still not f
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String Theory 101 Neil Lambert
1.1 Introduction: Why String Theory? The so-called Standard Model of Particle Physics is the most successful scientific theory of Nature in the sense that no other theory has such a high level of accuracy over such a complete range of physical phenomena using such a modest number of assumptions and parameters. It is unreasonably good and was never intended to be so successful. Since its formulation around 1970 there has not been a single experimental result that has produced even the slightest disagreement. Nothing, despite an enormous amount of effort. But there are skeletons in the closet. Let me mention just three. The first is the following: Where does the Standard Model come from? For example it has quite a few parameters which are only fixed by experimental observation. What fixes these? It postulates a certain spectrum of fundamental particle states but why these? In particular these particle states form three families, each of which is a copy of the others, differing only in their masses. Furthermore only the lightest family seems to have much to do with life in the universe as we know it, so why the repetition? It is somewhat analogous to Mendelev’s periodic table of the elements. There is clearly a discernible structure but this wasn’t understood until the discovery of quantum mechanics. We are looking for the underlying principle that gives the somewhat bizarre and apparently ad hoc structure of the Standard Model. Moreover the Standard Model also doesn’t contain Dark Matter that constitutes most of the ‘stuff’ in the observable universe. The second problem is that, for all its strengths, the Standard Model does not include gravity. For that we must use General Relativity which is a classical theory and as such is incompatible with the rules of quantum mechanics. Observationally N. Lambert (B) Theory Division, CERN, 1211 Geneva 23, Switzerland e-mail: [email protected]
M. Baumgartl et al. (eds.), Strings and Fundamental Physics, Lecture Notes in Physics 851, DOI: 10.1007/978-3-642-25947-0_1, © Springer-Verlag Berlin Heidelberg 2012
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this is not a problem since the effect of gravity, at the energy scales which we probe, is smaller by a factor of 10−40 than the effects of the subnuclear forces which the Standard Model describes. You can experimentally test this assertion by lifting up a piece of paper with your little finger. You will see that the electromagnetic forces at work in your little finger can easily overcome the gravitational force of the entire earth which acts to pull the paper to the floor. However this is clearly a problem theoretically. We can’t claim to understand the universe physically until we can provide one theory which consistently describes gravity and the subnuclear forces. If we do try to include gravity into QFT then we encounter problems. A serious one is that the result is non-renormalizable, apparently producing an infinite series of divergences which must be subtracted by inventing an infinite series of new interactions,
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