Strings: Reality in 10 or 11 dimensions? |
| When people first began thinking about
quarks, a pertinent question was why isolated
quarks had not been observed. One idea was that quarks might be the ends
of strings. If a particle was a string and the quarks were just the ends of the string, then one could understand why one never found one quark without the other. A string is essentially a 1-dimensional object in a space of 4 dimensions (counting time as a dimension). Physicists turned to topology; the mathematics of knots and surfaces, to find what the implications might be of using strings instead of particles in their calculations.Surprisingly, strings simplified calculations. At about this same time, physicists working with other mathematical theories of particles and forces rediscovered an idea from the 1920s. In 1919, Theodor Kaluza had found a way to derive electromagnetism from Einstein's theory of general relativity, but Kaluza's derivation requires 5 dimensions and we only observe4. In 1926 Oskar Klein developed an explanation of why the fifth dimension is invisible-it curls up into a tiny circle-but very few people were impressed. In the late 1970s, however, Eugene Cremmer and Bernard Julia found that another theory that had been discarded because it was so complicated became very simple if the universe has 11 dimensions with 7 of them curled up in the way Klein suggested. The string theorists were not to be left out of this promising idea. Already they had incorporated another theory, called supersymmetry, into string theory, resulting in superstring theory. Now they tried putting their superstrings into spaces with more dimensions. The complicated mathematics of superstrings shows that they work best in Kaluza-Klein spaces of 9 or 10 dimensions, however, not 11. Theoretical "particle" physicists at this point have worked themselves into this dilemma: In many ways it makes sense for the universe to be a Kaluza-Klein space of 11 dimensions, but the calculations are difficult and peculiar. Superstring theory makes the calculations easy and normal, but does not seem to describe the universe. Still, many physicists, and not just the ones worliiing on superstring theory, think that it may finally be recognized as the ultimate reality. |
Alexander Hellemans and Bryan Bunch
"Timetables of Science" p594
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