Symmetry breaking in 10-250

by Patrick Henry Winston ’65, SM ’67, PhD ’70 on November 21, 2010 · 1 comment

in Classroom, Prof. Winston's Ideas

Professor Patrick Henry Winston ’65, SM ’67, PhD ’70

Gerry Sussman came by, as he often does. “You don’t look happy,” he said.

PHW: Well, I thought I just got off a pretty good lecture, but they didn’t laugh much at the jokes.

GJS: Everyone has bad days.

PHW: The students have been flat all semester. Maybe I’ve lost a step.

GJS: Everyone has bad years.

Gerry taught 6.001 to extremely large classes for more than 15 years, so I knew he knew what he was talking about.

PHW: It’s strange. You would think with 200 students, the law of averages would dictate that each year would feel the same, but that’s not the way it works. I wonder if it is because the outliers determine the look and feel.

GJS: No, actually, it’s symmetry breaking.

At this point, I vaguely recalled the spinning-coin idea. Inherently, the stable states are lying down, showing heads or tails, but while the coin is spinning, the situation is symmetric, and you can’t tell which state the coin will be in when it falls over.

GJS: The students don’t realize it, but they all want to be like everyone else, so on the first day of class, they are all sensing the overall mood. Within a few minutes, the symmetry breaks spontaneously, and the class falls into a fixed state.

PHW: So if you have a bad first day, you’ve had it, and there is nothing you can do after that.

GJS: Yes.

Come to think of it, that first day wasn’t so great. The OpenCourseWare folks are recording my lectures this year, and it was a little disconcerting to wear a microphone and know each blunder would be a forever blunder.

PHW: So, there is nothing you can do other than put extra effort into the first lecture.

GJS: No, actually, I used to have my UROPs and graduate students come to the first lecture. They were instructed to sit down front, nod approvingly and frequently, and laugh at all the jokes.

Great idea. I knew the standard model of physics would come in handy someday.

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