String theory and superstring theory are closely related, with superstring theory being a specific formulation or extension of string theory. The key difference lies in the incorporation of supersymmetry in superstring theory. Here's a breakdown of their distinctions:
String Theory: String theory postulates that the fundamental building blocks of the universe are not point-like particles but tiny, one-dimensional objects called strings. These strings can vibrate at different frequencies, giving rise to different particles with distinct properties such as mass and charge. String theory suggests that the universe has more than the familiar three spatial dimensions, proposing the existence of additional compactified dimensions.
String theory encompasses several different versions, including Type I, Type IIA, Type IIB, heterotic SO(32), and heterotic E8×E8. These versions differ in their characteristic properties and predictions. However, all versions of string theory share the common feature of strings as the fundamental entities.
Superstring Theory: Superstring theory extends the concepts of string theory by incorporating supersymmetry, a theoretical framework that introduces a symmetry between bosons (particles with integer spin) and fermions (particles with half-integer spin). Supersymmetry predicts the existence of superpartners for each particle, where each particle has a superpartner with different spin statistics.
In superstring theory, the strings are described by supersymmetric quantum mechanical equations. The addition of supersymmetry introduces new mathematical structures and symmetries that allow for more consistent and mathematically elegant theories. It also helps address some of the challenges encountered in traditional string theory, such as the cancellation of certain quantum anomalies.
Superstring theory has multiple variants, including Type I, Type IIA, Type IIB, heterotic SO(32), and heterotic E8×E8, just like string theory. However, these variants now incorporate supersymmetry, making them "superstring" theories.
In summary, the main difference between string theory and superstring theory is that superstring theory includes supersymmetry as a fundamental aspect, which leads to the prediction of superpartners for each particle. Superstring theory can be seen as a more refined and mathematically consistent version of string theory.