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Elementary Particles and the World of Planck Scale

Realm of Planck Scale

Soon after Max Planck introduced the Planck constant h in 1899 to account for the spectrum of blackbody radiation, he realized that the only way to construct a unit of length out of h = 6.625x10-27 erg-sec, the velocity of light c = 3x1010 cm/sec, and the gravitational constant G = 6.67x10-8 cm3/sec2-gm, is LPL = (Gh/c3)1/2. This is the now famous Planck length. Since h is related to Quantum Theory, c and G emerge from the Special and General Relativity respectively, it implies that any length scale in a Quantum Gravity Theory would involve LPL, which is extremely short at 4x10-33 cm.

Subsequently, it transpires that the realm of Planck scale would involve entities with size of the order 10-33 cm and associated with high energy phenomena at 1019 Gev. Such environment is considered to occur at the moment of Big Bang - a most favorable theory for the creation of this universe. Theoretically, both quantum theory and general relativity are required to formulate a correct description - hence the many theories of "Quantum Gravity". All of them have evaded observational confirmation so far and current technology does not generate such high energy to probe at such tiny region. Some examples are shown in Figure 15-32, they are more or less conjectures as explained briefly below.