ELEMENTARY PARTICLE — SCHRODINGER 185 



would be a fairly adequate simile. The idea was very soon abandoned. 

 It seems that both concepts, that of waves and that of particles, have 

 to be modified considerably, so as to attain a true amalgamation. 



3. CURRENT VIEWS: THE NATURE OF WAVES 



The waves, so we are told, must not be regarded as quite real waves. 

 It is true that they produce interference patterns — which is the crucial 

 test that in the case of light had removed all doubts as to the reality of 

 the waves. However, we are now told that all waves, including light, 

 ought rather to be looked upon as ''probability waves." They are only 

 a mathematical device for computing the probability of finding a 

 particle in certain conditions, for instance (in the above example), the 

 probability of an electron hitting the photographic plate within a 

 small specified area. There it is registered by acting on a gi'ain of 

 silver bromide. The interference pattern is to be regarded as a statis- 

 tical registration of the impinging electrons. The waves are in this 

 context sometimes referred to as guiding waves — guiding or directing 

 the particles on their paths. The guidance is not to be regarded as a 

 rigid one ; it merely constitutes a probability. The clear-cut pattern 

 is a statistical result, its clefiniteness being due to the enormous number 

 of particles. 



Here I cannot refrain from mentioning an objection which is too 

 obvious not to occur to the reader. Something that influences the 

 physical behavior of something else must not in any respect be called 

 less real than the something it influences — whatever meaning we may 

 give to the dangerous epithet "real." It is certainly useful to recall 

 at times that all quantitative models or images conceived by the physi- 

 cist are, epistemologically, only mathematical devices for computing 

 observable events, but I cannot see that this applies more to, say, 

 light waves than to, say, oxygen molecules. 



4. CURRENT VIEWS: THE NATURE OF PARTICLES (UNCERTAINTY 



RELATION) 



As regards the modification required in the concept of a particle, 

 the stress is on Heisenberg's uncertainty relation. The so-called 

 classical mechanics hinged on Galileo's and Newton's discovery that 

 the thing which in a moving body is determined at any instant by the 

 other bodies in its environment is only and precisely its acceleration, 

 or, in mathematical terms, the second derivatives with respect to time 

 of the coordinates. The first derivatives, commonly called the ve- 

 locity, are therefore to be included in the description of the momentary 

 state of the body, together with the coordinates themselves which 

 label its momentary place in space or "whereness" (or ubiety, to use 

 an antiquated but convenient word). Thus, to describe the momen- 



