Six of the ten dimensions are compactified: they are curled up on themselves on very small scales (on the order of 10-33 cm) (1,4). To account for these strings, a theory called superstring theory postulates that space and time exist in ten dimensions. The different vibrational states of the strings correspond to the particles. They can be closed or open-ended and can have different modes of vibration, similar to how a guitar string can vibrate differently depending on how and where you pluck it. These vibrating strings are quantum mechanical entities that can exist in different states. String theory attempts to explain the universe in terms of tiny, vibrating, "strings" that represent the fundamental particles postulated by the Standard Theory of particle physics: bosons, which are force-carrying particles like photons, and muons, particles that make up matter such as the electron (3). This property of string theory makes it hard to confirm through the use of experimental physics. Theoretical calculations on the currently-favored string theory postulate that the strong and weak forces come together at temperatures that are eighteen orders of magnitude above what physicists can currently experiment with using particle accelerators (2). Physicists and mathematicians are currently trying to unify the two theories into an all-encompassing quantum theory, called string theory, that can account for the four main forces: gravity, electromagnetism, the strong force and the weak force (1).Ī theory of particle physics, the Standard Theory, seeks to unify the latter three, while string theory goes one step farther: trying to also incorporate a quantum theory of gravity. Two theories currently shape the world of physics: quantum mechanical theory, which involves small particles, and gravitational theory, which involves large particles.