MODERN PHYSICS JEANS 87 



but the motion was quite inconsistent with the mechanistic deter- 

 minism of the Newtonian mechanics. The electron did not move 

 continuously through space and time, but jumped, and its jumps were 

 not governed by the laws of mechanics, but to all appearance, as Ein- 

 stein showed more fully 4 years later, by the laws of probability. Of 

 1,000 identical atoms, 100 might make the jump, while the other 900 

 would not. Before the jumps occurred, there was nothing to show 

 which atoms were going to jumjD. Thus the particle picture conspicu- 

 ously failed to provide an answer to the question, " What will happen 

 next?" 



Bohr's concepts were revolutionary, but it was soon found they 

 were not revolutionary enough, for they failed to explain more com- 

 plicated spectra, as well as certain other phenomena. 



Then Heisenberg showed that the hydrogen spectrum — and, as we 

 now believe, all other spectra as well — could be explained by the mo- 

 tion of something which was rather like an electron, but did not move 

 in space and time. Its position was not specified by the usual coordi- 

 nates a?, y, 3 of coordinate geometry, but by the mathematical abstrac- 

 tion known as a " matrix." His ideas were rather too abstract even for 

 mathematicians, the majority of whom had quite forgotten what 

 matrices were. It seemed likely that Heisenberg had unravelled the 

 secret of the structure of matter, and yet his solution was so far re- 

 moved from the concepts of ordinaiy life that another parable had to 

 be invented to make it comprehensible. 



The wave parable serves this purpose ; it does not describe the uni- 

 verse as a collection of particles but as a system of waves. The uni- 

 verse is no longer a deluge of shot from a battery of machine guns, 

 but a stormy sea with the sea taken away and only the abstract quality 

 of storminess left — or the grin of the Cheshire cat if we can think of 

 a grin as undulatory. This parable was not devised by Heisenberg, 

 but by de Broglie and Schrodinger. At first they thought their waves 

 merely provided a superior model of an ordinary electron; later it 

 was established that they were a sort of parable to explain Heisen- 

 berg's pseudoelectron. 



Now the pseudoelectron of Heisenberg did not claim to account for 

 the spectrum emitted by a single atom of gas, which is something 

 entirely beyond our knowledge or experience, but only that emitted 

 by a whole assembly of similar atoms; it was not a picture of one 

 electron in one atom, but of all the electrons in all the atoms. 



In the same way the waves of the wave parable do not picture indi- 

 vidual electrons, but a community of electrons — a crowd— as for in- 

 stance the electrons whose motion constitutes a current of electricity. 



In this particular instance the waves can be represented as traveling 

 through ordinary space. Except for traveling at a different speed, 



