64 THE RUNNING-DOWN OF THE UNIVERSE 



in sorting the cards. I allow you to shuffle them because 

 you can do that absent-mindedly. 



Secondly, it is not quite true that the original order 

 never comes back. There is a ghost of a chance that 

 some day a thoroughly shuffled pack will be found to 

 have come back to the original order. That is because 

 of the comparatively small number of cards in the pack. 

 In our applications the units are so numerous that this 

 kind of contingency can be disregarded. 



We shall put forward the contention that — 



Whenever anything happens which cannot be undone, 

 it is always reducible to the introduction of a random 

 element analogous to that introduced by shuffling. 



Shuffling is the only thing which Nature cannot undo. 

 When Humpty Dumpty had a great fall — 



All the king's horses and all the king's men 

 Cannot put Humpty Dumpty together again. 



Something had happened which could not be undone. 

 The fall could have been undone. It is not necessary to 

 invoke the king's horses and the king's men; if there 

 had been a perfectly elastic mat underneath, that would 

 have sufficed. At the end of his fall Humpty Dumpty 

 had kinetic energy which, properly directed, was just 

 sufficient to bounce him back on to the wall again. But, 

 the elastic mat being absent, an irrevocable event hap- 

 pened at the end of the fall — namely, the introduction 

 of a random element into Humpty Dumpty. 



But why should we suppose that shuffling is the only 

 process that cannot be undone? 



The Moving Finger writes; and, having writ, 

 Moves on: nor all thy Piety and Wit 

 Can lure it back to cancel half a Line. 



