One of the reasons that I chose the name Planck's Constant for this blog is that the concept represents one true certainty in a universe filled with uncertainty. Time, mass and energy can all change; however Planck's Constant absolutely defines the size of the lanes that the momentum must travel in.
In its simplest terms, if Planck's Constant were equal to say 5 feet, then all waves would be either 5, 10, 15 or some other multiple of 5 feet long. There would be no waves in between. It is this concept due to Planck and Einstein that led Niels Bohr to conjecture that an atom could exist only in a discrete set of stable energy states. Neils was one of the Jewish Nobel Prize Laureates in Physics that I blogged about in Muslim Inventions - Nobel Prizes.
This may all be rather ponderous for non-scientific types, but please bear with me. All of this can more easily be explained by the simple expedient of an illustration.
Here is the definition of a wave for Engineers:
Please proceed with caution - wave mechanics may injure sqeamish eyes.