MadSci Network: Physics |
Excellent question Andre. The basic premise of string theory is that everything reduces to strings and everything comes from strings. These strings come in two flavors - open (like a dangling piece of string) and closed (like a rubber band if you will). One can excite modes on these strings (very analogous to playing musical notes, except in a highly multidimensional space -- more on that later) which give rise to all the observed matter and the force carriers (the W/Z meson and the photon (govern the electroweak force), the gluon (the strong nuclear force), and perhaps most important, the graviton - the quantum force carrier particle for quantum gravity. It provides a natural framework for the emergence of the correct particle needed to describe quantum gravity. This gave string theory a big boost in interest since a quantum mechanical description of gravity is the missing link of physics - the standard model (modern quantum mechanics) cannot describe gravity. General Relativity (Einstein's theory of gravity) does a marvelous job of describing gravity - but it is strictly classical, and breaks down in regions where quantum physics should become important (say, the interior of a black hole). The price one pays for this little miricle is mathematics. The current theory holds there are 11 dimensions - 3 normal space, 1 time, 6 tightly curled up dimensions, and a stretching of a string into a membrane for the 11th dimension. If this doesn't make your head spin, I don't know what will. String theory (or more correctly, M-theory or sometime superstring theory) is in its infancy. We do not know the exact starting equations for the theory and we do not generally have exact solutions for the equations we do have. Furthermore, the exact geometry of this tightly curled up 6 dimensions is still debated as there are various geometries which work (Calibi Yau geometry) and they can't all be right. Now these extra 6 dimensions are very tightly curled up (roughly 0.1 micro-nano-nano-nanometers (10^-30 cm), so that a nanometer is a huge distance in comparison. Vibrational modes of the strings can make use of these extra dimensions, but to the physical world - they are invisible. Imagine if you will a power line at a distance. At long range, the power line looks 1-dimensional. If you get up very close, you can see it is 3- dimensional. So to answer your question about the speed of light, the photon would travel at the regular speed of light in our 4-dimensional space-time. To make a photon, strings would vibrate in these extra dimensions. But light would not actually propogate in the curled up dimensions. There is an interesting side to this multidimensional situation. There is a superstring theory which allows gravitons to exert influence through the extra dimensions - perhaps offering a new theoretical framework for dark matter and dark energy. Still, I must caution that there is still much that is not understood about string theory and the theory itself is not proven. There is tantalizing evidence starting to emerge which support string theory - but the road ahead is long and foggy. for more info: http://www.superstringtheory.com/ http://www.strings.ph.qmw.ac.uk/WhatIs/Nutshell.html
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