BATTLE OF THE ALCHEMISTS COMPTON 273 



Think for a moment what this ignorance implies. All of the 

 positive electricity, most of the negative electricity, most of the mass, 

 and by far the greater part of the energy of the world reside in 

 atomic nuclei. We must therefore confess that we know as yet very 

 little about most of the world of matter, electricity, and energy. 

 This should make us rather careful about making such statements as 

 one recently published by a leading exponent of the new school of 

 theoretical physicists, who wrote: "The underlying physical laws 

 necessary for the mathematical theory of a large part of physics 

 and the whole of chemistry are thus completely known. * * * " 

 It should also warn us against such rash statements as " the break- 

 down of the law of causality " and " the law of conservation of 

 energy does not apply to individual processes but only statistically as 

 an average." It would be far better simply to admit that, successful 

 as we have been in describing by equations much of the behavior of 

 those extranuclear electrons that move in orbits far outside the 

 nuclei, we are still grossly ignorant of the most powerful elements 

 of our material world. 



A very crude analogy will illustrate the relative advancement of 

 our present state of knowledge of atoms. Liken the nucleus to a 

 building and the extranuclear electrons to a group of pebbles resting 

 on the steps of a fire escape on the outside of the building. As 

 we observe these pebbles, we notice that, from time to time, a pebble 

 falls from one step to another. We do not understand why it falls, 

 and make various attempts to hypothecate some model or mecha- 

 nism which will explain the dropping of these pebbles. Bohr, Som- 

 merfeld, Langmuir all take their turn, but none of them invents a 

 mechanism that satisfies all of the observations. We become dis- 

 couraged with model building. Finally a brilliant young man, 

 Heisenberg, proposes that we do away with models entirely and con- 

 centrate entirely upon the observable quantities — the steps, the 

 pebbles, and their falling. He finds a mathematical expression which 

 accurately correlates the height of the steps (energy levels) with the 

 probability that a pebble will fall (radiate) from one step to an- 

 other. To the mathematician this accurate formulation of the mathe- 

 matical relationship between the observable quantities is a complete 

 and satisfactory explanation or theory. The physicist, however, 

 guided perhaps by instinct (which is the accumulated wisdom of the 

 ages) rather than by formal logic, is not satisfied. He feels im- 

 pressed but a bit confused by the logic of the mathematician, and 

 also a bit distrustful. Down in his heart he feels that there must 

 be something more than a law of probability which makes those 

 pebbles drop. He goes to investigate. He finds the door of the 



