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Ax 4 in page 19 of Ticciati's QFT textbook.

  1. Mar 11, 2012 #1


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    The axiom says:
    "The interaction between two observations is constrained by causality
    [tex]|x-y|^2 <0 \Rightarrow [\phi(x),\phi(y)]=0[/tex]

    But |x-y|^2<0 is always false that means the if the condition applies then by simple logic the consequnet of the condition can occur or not occur, I don't understand this.
  2. jcsd
  3. Mar 11, 2012 #2
    The statement is about a timelike distance four-vector in Minkowski space. Its squared length is negative in the case of a -+++ metric.
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