L1.2 Setting up the perturbative equations
PROFESSOR: So here it is. Suppose you have a serious expansion in lambda. So this is the state-- when lambda is equal to 0, this should be the state. But when lambda is different from 0, that will not be the state. We'll have lambda correction. So this is the first-order correction to this state. So that's why I put the 1. And you should think of it first order-- oh! --because it comes with a lambda. This is the second-order correction to the state, because it comes with a lambda squared. And the same thing here. So the superscript is telling you what order in lambda you are working-- to what accuracy. So what is the most urgent thing to find the first order of corrections? If you find them, and we still have time [LAUGH] for the second order, you go more and more. OK, let's continue. Let's solve some of this. So our next task is to solve this problem. And here we go. Let's solve that. So what am I going to do? I'm going to just write this equation...