SHUFFLING 65 



When there is no shuffling, is the Moving Finger stayed? 

 The answer of physics is unhesitatingly Yes. To judge 

 of this we must examine those operations of Nature in 

 which no increase of the random element can possibly 

 occur. These fall into two groups. Firstly, we can 

 study those laws of Nature which control the behaviour 

 of a single unit. Clearly no shuffling can occur in these 

 problems; you cannot take the King of Spades away 

 from the pack and shuffle him. Secondly, we can study 

 the processes of Nature in a crowd which is already so 

 completely shuffled that there is no room for any further 

 increase of the random element. If our contention is 

 right, everything that occurs in these conditions is 

 capable of being undone. We shall consider the first 

 condition immediately; the second must be deferred 

 until p. 78. 



Any change occurring to a body which can be treated 

 as a single unit can be undone. The laws of Nature 

 admit of the undoing as easily as of the doing. The 

 earth describing its orbit is controlled by laws of motion 

 and of gravitation; these admit of the earth's actual mo- 

 tion, but they also admit of the precisely opposite 

 motion. In the same field of force the earth could retrace 

 its steps; it merely depends on how it was started off. It 

 may be objected that we have no right to dismiss the 

 starting-off as an inessential part of the problem; it may 

 be as much a part of the coherent scheme of Nature as 

 the laws controlling the subsequent motion. Indeed, as- 

 tronomers have theories explaining why the eight planets 

 all started to move the same way round the sun. But 

 that is a problem of eight planets, not of a single 

 individual — a problem of the pack, not of the isolated 

 card. So long as the earth's motion is treated as an 

 isolated problem, no one would dream of putting into 



