29Q REALITY 



"spherical". But which is the real truth? Disregard 

 the fact that I introduced A and A' to you as though 

 they were not the same particles, because that begs the 

 question; imagine that you have actually had this 

 adventure in a world you had not been told about. You 

 cannot find out the answer. Can you conceive what the 

 question means ? I cannot. All that turns on the answer 

 is whether we shall provide two separate haloes for A 

 and A' or whether one will suffice. 



Descriptions of the phenomena of atomic physics 

 have an extraordinary vividness. We see the atoms with 

 their girdles of circulating electrons darting hither and 

 thither, colliding and rebounding. Free electrons torn 

 from the girdles hurry away a hundred times faster, 

 curving sharply round the atoms with side slips and 

 hairbreadth escapes. The truants are caught and 

 attached to the girdles and the escaping energy shakes 

 the aether into vibration. X-rays impinge on the atoms 

 and toss the electrons into higher orbits. We see these 

 electrons falling back again, sometimes by steps, some- 

 times with a rush, caught in a cul-de-sac of metasta- 

 bility, hesitating before "forbidden passages". Behind 

 it all the quantum h regulates each change with mathe- 

 matical precision. This is the sort of picture that appeals 

 to our understanding — no insubstantial pageant to fade 

 like a dream. 



The spectacle is so fascinating that we have perhaps 

 forgotten that there was a time when we wanted to be 

 told what an electron is. The question was never 

 answered. No familiar conceptions can be woven round 

 the electron; it belongs to the waiting list. Similarly 

 the description of the processes must be taken with a 

 grain of salt. The tossing up of the electron is a con- 

 ventional way of depicting a particular change of state 



