The Many Faces of Planck's Constant h
Peter Marquardt
Max Planck's 150th anniversary (April 23rd, 2008) is a welcome opportunity to devote some thoughts to the history and the role of his "quantum of action", h, which he hesitatingly established in 1900. Many-fold are the occurrences of h in physics ranging from the radiation law (the "cradle of quantum physics") and Planck's units to some aspects of nanotechnology. Quantization is considered a first-rate revolution in physics, but is there really a continental divide between "classical" and "post-classical" physics? The problem with the quantum is quite similar to that with relativity: Giving preference to mathematical reasoning ala Heisenberg, 20th century physics arrived at questionable conclusions in spite of numerically correct results. Some unorthodox views are in order to give h back to physics. True physical aspects seek answers asking questions off the beaten path. What is quantized? Obviously it is not energy, but action. What possibly links the two ingredients of action together? Why should there be a quantum at all? It might be due to some stability criterion and a compromise between two counteracting variables. What is the interplay of the variables that occur in formulas containing h? The "constant of least action" may still be good for some surprises.
