Who said: "There is no central arbiter of truth in open distributed systems."
The exact quotation seems to be:


  "Pluralism: There is no central arbiter of truth in the system."


See:


http://archive.org/stream/byte-magazine-1985-04/1985_04_BYTE_10-04_Artificial_Intelligence#page/n237/mode/2up


(p. 239, 2nd bullet point.)