This lecture starts with a review of Noether’s theorem, which links continuous symmetries with conserved quantities (charges). The model of a closed string is developed following the earlier procedure for open strings. The energy spectrum is similar but with a new constraint called the level matching rule linking the energy of waves in each direction around the string that is connected to Noether’s theorem.
- Why is charge quantized?
- Noether’s theorem and conserved charges
- A model of closed strings
- The energy spectrum of closed strings
- The level matching rule