2IO Science Religion and Reality 



previously shown my matter to be unreal. If once wc could 

 demonstrate the unreality of any element in B, the whole structure 

 would collapse ; but we cannot do this so long as we keep to the 

 cycle, because the cycle of unreal quantities is just as perfect as the 

 cycle of real quantities. The unreal stars of B emit unreal light, 

 which falls on unreal retinas and ultimately reaches unreal brains. 

 At last there is a chance to expose the deception, for the next step 

 takes us outside the cycle. Is the brain disturbance translated 

 into consciousness ? That will test whether the brain is real or 

 unreal ; for there is no question about our consciousness being real 

 or unreal — it is just " our consciousness." 



Actuality — that which distinguishes this world from many 

 other possible worlds consistent with the laws of nature — is not 

 susceptible of definition without trespassing beyond the frontiers 

 of physics. I fear that the word " actuality " is one of those high- 

 sounding phrases with metaphysical associations obnoxious to 

 science. But most of the terms of physics have metaphysical 

 associations which the physicist must learn to disregard. So I 

 would emphasise that the word actuality is here used with a very 

 definite meaning definable in terms of experience. It is that dis- 

 tinctive property of the world A — the world around us which we 

 study experimentally — which is not possessed by the other worlds 

 which might have occurred consistently with all the laws of nature. 

 And since experience does certainly tell us that we have to do with 

 one particular world and not the whole group of possible worlds, 

 actuality denotes something which is significant and detectable by 

 experience. 



Actuality is recognised as tremendously important by the 

 experimental physicist. But it does not appear in the scheme of 

 the theoretical physicist. And it is quite natural that it should not 

 appear. The experimental physicist deals with the particular 

 cases ; the theoretical physicist generalises ; he refines away that 

 which is special and particular and seeks to obtain the general laws 

 of nature. So that he eliminates the reference to one particular 

 and actual world and arrives at a theory which applies to all possible 

 conditions that might occur — this, of course, includes the actual 

 world as a special case. The theoretical physicist thus necessarily 

 excludes actuality from his purview, though he arranges that it 

 can be added as an afterthought ; and we can see how admirably 

 the device of the vicious circle of definition is adapted to this 



