ELEMENTARY PARTICLE — SCHRODINGER 193 



and membership is now attached to other persons : the electrons have 

 gone over into other states. Wliether you can, in a loose way, speak 

 of a certain membership going over from Dick to Tom, thence from 

 Tom to Harry, etc., depends on the circumstances. They may suggest 

 this view, or they may not, but never in an absolute fashion. In this 

 our simile is perfect, for it is the same with an electron. Moreover, 

 it is quite appropriate to consider the number of members as fluctuat- 

 ing. Indeed, electrons too are created and annihilated. 



The example may seem odd and inverted. One might think, "Why 

 cannot the people be the electrons and various clubs their states? 

 That would be so much more natural." The physicist regrets, but he 

 camiot oblige. And this is just the salient point : the actual statistical 

 behavior of electrons cannot be illustrated by any simile that rep- 

 resents them by identifiable things. That is why it follows from their 

 actual statistical behavior that they are not identifiable things. 



The (b), illustrating Einstein-Bose statistics, is competent for light 

 quanta (photons), inter alia. It hardly needs discussion. It does not 

 strike us as so strange for the very reason that it includes light, i. e., 

 eJectromagnetic energy; and energy, in prequantum times, had always 

 been thought of in very much the way our simile represents it, viz, as 

 having quantity, but no individuality. 



11, RESTRICTED NOTION OF IDENTITY 



The most delicate question is that of the states of, say, an electron. 

 They are, of course, to be defined not classically, but in the light of 

 the uncertainty relation. The rigorous treatment referred to at the 

 end of section 6 is not really based on the notion of "state of one elec- 

 tron" but on that of "state of the assembly of electrons." The whole 

 list of members of the club, as it were, has to be envisaged together — 

 or rather several membership lists, corresponding to the several kinds 

 of particles that go to compose the physical system under considera- 

 tion. I mention this, not to go into details about it, but because, taken 

 rigorously, the club simile has two flaws. First, the possible states 

 of an electron (which we had assimiliated to the persons eligible for 

 membership) are not absolutely defined; they depend on the arrange- 

 ment of the — actual or imagined — experiment. Given this arrange- 

 ment, the states are well-defined individuals, which the electrons are 

 not. They also form — and this is the second flaw of the simile — a 

 well-ordered manifold. That is, there is a meaning in speaking of 

 neighboring states as against such as are more remote from each other. 

 Moreover, I believe it is true to say that this order can be conceived in 

 such a fashion that, as a rule, whenever one occupied state ceases to be 

 occupied, a neighboring state becomes occupied. 



