X-Message-Number: 25553
From: 
Date: Sat, 15 Jan 2005 12:08:50 EST
Subject: indiscernibles again

Henri Kluytmans wrote mostly good stuff, but I again take issue with the  
following:
 

>when  a system possesses the same physical properties, and exhibits 
>the same  physical behavior as the original, then there is no difference 
>between  it and the original. According to physics those systems are  
>interchangable

 
This is sometimes called the "identity of indiscernibles." But it is  crucial 
to recognize two things:
 
1. There is an assumption here that a difference in location is not a  

significant difference. This may or may not be true, depending on the  
particulars 
and on the criteria of significance. We know for SURE that a  difference in 
location also implies other differences--we just don't always know  how 
significant, in a particular context, those differences may be.
 
2. "Interchangeable" is a relative term, even if we ignore the  objective vs. 
subjective question. Two hydrogen atoms are the "same" in most  respects, but 
if they have different locations or/and different momenta you  cannot 

substitute one for the other. They are not interchangeable and not  
indistinguishable.
 
Robert Ettinger


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