MIT 3.60 Lec 10a Symmetry, Structure, Tensor Properties of Materials
PROFESSOR: All right, I feel almost as though I should introduce myself all over again. It's been a week and a half since we had a lecture. So let me begin by reminding you of what we were doing. We had derived all of the plane groups, and for better or worse had put them behind us. And then we moved into three dimensions, where things get a lot more involved and a lot more complicated, and to say the least, a lot more numerous. And the first question we asked was to say, when we're in a three-dimensional space, we can combine a first rotation operation with a second rotation operation, B beta If we're to begin by deriving point groups-- that is to say, the least [INAUDIBLE] point in this three-dimensional space is not going to move. [INAUDIBLE] two axes to intersect a point. For a space group, they could be parallel to one another. But that's gonna be an infinite set of symmetry elements and operations that extends through all space. Then we asked the que...