Wednesday, December 29, 2004

String Theory

I just happened upon an excellent website designed to explain to novices like me everything you wanted to know about theoretical physics-well almost. It'll keep me busy for a while.
From The Official String Theory Web Site:

Relativistic quantum field theory has worked very well to describe the observed
behaviors and properties of elementary particles. But the theory itself only works well when gravity is so weak that it can be neglected. Particle theory only works when we pretend gravity doesn't exist. General relativity has yielded a wealth of insight into the Universe, the orbits of planets, the evolution of stars and galaxies, the Big Bang and recently observed black holes and gravitational lenses. However, the theory itself only works when we pretend that the Universe is purely classical and that quantum mechanics is not needed in our description of Nature. String theory is believed to close this gap.


Think of a guitar string that has been tuned by stretching the string under tension across the guitar. Depending on how the string is plucked and how much tension is in the string, different musical notes will be created by the string. These musical notes could be said to be excitation modes of that guitar string under tension. In a similar manner, in string theory, the elementary particles we observe in particle accelerators could be thought of as the "musical notes" or excitation modes of elementary strings.


If string theory is to be a theory of quantum gravity, then the average size of a string should be somewhere near the length scale of quantum gravity, called the Planck length, which is about 10-33 centimeters, or about a millionth of a billionth of a billionth of a billionth of a centimeter. Unfortunately, this means that strings are way too small to see by current or expected particle physics technology (or financing!!) and so string theorists must devise more clever methods to test the theory than just looking for little strings in particle experiments.


This period in string history has been given the name the second string revolution. And now the biggest rush in string research is to collapse the table above into one theory, which some people want to call M theory, for it is the Mother of all theories. Stay tuned to this web site, we may some day soon be changing the name to The Official M Theory Web Site!

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