I have a question concerning the nature of Ms. Wu's experiment confirming parity violation. I'm very familiar with this experiment and its outcomes, but the setup of the experiment itself, alludes me. Wu found that the electron's emitted from the Cobalt-60 atom always went in the direction opposite to their spin. My misunderstanding; I do not understand what was the independent variable of the experiment. What did she change to observe that parity was violated? http://www.doublexscience.org/wp-content/uploads/2014/01/Wu_experiment.png This picture accurately describes my dilemma. The "parity transformation" is what I don't get, it seems theoretical and not practical or even experimental. Yes, we expect that the electrons in the mirrored world would fly in the direction described by the top right of the image. How do we know the electrons don't do that? Without something changing in the experiment, could you know? The image also shows the magnetic field pointed in the same direction so she couldn't have changed that? I understand parity operations and why this result would violate, I just don't see how it was done experimentally. However, perhaps I don't see how they did it experimentally because I'm misunderstanding parity operations.