What was that old saw about the observer altering the state of the subject being studied?

The Heisenberg Uncertainty Principle, I believe.

Sidebar: Werner Heisenberg, a highlu respected physicist, became the head of Nazi Germany's nuclear program. A current theatrical play focused on his 1941 meeting with Neils Bohr in occupied Copenhagen: it is unclear whether he tried to recruit Bohr, or leaked information to Bohr. Documents have been very recently released which may shed light on that meeting.
http://physicsweb.org/article/world/14/11/2