- #1

jstrunk

- 55

- 2

**Summary::**The problem solutions contain a lot of unjustified steps, making them pointless.

I am trying to use Griffiths Introduction to Quantum Mechanics.

He states that the wave function ##\psi## approaches 0 as x approaches infinity to make normalization work.

I can accept that.

But then I can't solve the problems in the book so I peak at some of the solutions

that people have provided online and they are making assumptions like these:

$$x\left[ {{\psi ^*}\frac{{\partial \psi }}{{\partial x}} - \frac{{\partial {\psi ^*}}}{{\partial x}}\psi } \right]_{ - \infty }^\infty = 0$$

$$\left. {\frac{{\partial \psi }}{{\partial x}}\frac{{\partial {\psi ^*}}}{{\partial x}}} \right|_{ - \infty }^\infty = 0$$

Griffiths never mentioned these identities, much less justified them.

I don't see any point in trying to doing the exercises if you can just make up anything you

want and stick it in your solution so you get the answer you need.

I understand that in learning a new subject you sometimes have to take some things on faith

at the beginning, knowing they will be explained later. But Griffiths hasn't said these will

be explained later. In fact, I don't even know if he used these identities in his solutions. He doesn't

provide solutions. I found these in other people's solutions.

If there was a finite list of these identities that I was allowed to use in the exercises, and I was

sure that proofs exist for each of them, then I could continue trying to use Griffiths.

If not, I need to find a different book.

I know a lot of people learned quantum mechanics from this textbook.

How do people cope with this problem? Does the professor fill the gaps? That doesn't help me

because I am doing this on my own.