text: Planck was one of the people who was thinking of energy as being delivered in discrete amounts or bundles.  This was one of the clues that lead Einstein to conclude in his 'Photo-electric Effect' experiments that, again, energy was being absorbed at only very specific frequencies and possibly in specific bundles of energy.\n\nThen you get to thinking of light as photons to carry the energy and materials seem to only absorb special kinds of bundles of energy and some guys in Stockholm start thinking that energy changes in atoms occur in discrete quanta.  Neils Bohr and friends were trying to come up with equations to describe the orbit of the electron around the nucleus and put some of the Planck stuff together with the Einstein stuff and came up with the idea that electrons could only change orbits according to the energy quanta that they absorbed and emitted.\n\nFrom all this we get the basics of quantum mechanics, sub-atomic orbital mechanics, lasers, fluorescent lights, bunches of stuff :).