Quantum
Early History | Planck's Contribution | Einstein's Contribution | Bohr Atom | Wave Mechanics | Matrix Mechanics | Quantum Meaning | Uncertainty | Quantum Results | Developments | The Future | Two Holes | Quantum Time Waits for No Cosmos

At the turn of the century, physicists did not yet clearly recognize that these and other difficulties in physics were in any way related. The first development that led to the solution of these difficulties was Planck's introduction of the concept of the quantum, as a result of physicists' studies of blackbody radiation during the closing years of the 19th century. (The term blackbody refers to an ideal body or surface that absorbs all radiant energy without any reflection.) A body at a moderately high temperature—a "red heat"—gives off most of its radiation in the low frequency (red and infrared) regions; a body at a higher temperature—"white heat"—gives off comparatively more radiation in higher frequencies (yellow, green, or blue). During the 1890s physicists conducted detailed quantitative studies of these phenomena and expressed their results in a series of curves or graphs. The classical, or prequantum, theory predicted an altogether different set of curves from those actually observed. What Planck did was to devise a mathematical formula that described the curves exactly; he then deduced a physical hypothesis that could explain the formula. His hypothesis was that energy is radiated only in quanta of energy hu, where u is the frequency and h is the quantum action, now known as Planck's constant.

Quantum
Early History | Planck's Contribution | Einstein's Contribution | Bohr Atom | Wave Mechanics | Matrix Mechanics | Quantum Meaning | Uncertainty | Quantum Results | Developments | The Future | Two Holes | Quantum Time Waits for No Cosmos