I am looking at the derivation of the Heisenberg Uncertainty Principle presented here: http://socrates.berkeley.edu/~jemoore/p137a/uncertaintynotes.pdf [Broken] and am confused about line (21)... I do not understand why [itex]AB[/itex] and [itex]BA[/itex] are complex conjugates of each other... (I'm still in high school so I don't really have much of a background in the algebra of operators). If I assume what is written in line 21, I think I get the following lines- if [itex]AB[/itex] and [itex]BA[/itex] are complex conjugates, then [itex]|\langle AB-BA \rangle |^2 = |2\langle AB\rangle |^2 = 4|\langle AB\rangle |^2[/itex] I think... The expected value signs are what is confusing me most... Thank you for any help!