Ehrenfest's Theorem

1. Jul 28, 2005

yukcream

Can anyone tell me what is the Ehrenfest's Theorm in quantum mechanic, I don't understand how it can provide an example for correspondence principle?

2. Jul 28, 2005

Galileo

Are you familiar with the equation of motion:

$$\frac{d}{dt}\langle Q \rangle = \frac{i}{\hbar}\langle [H,Q] \rangle + \langle \frac{\partial Q}{\partial t}\rangle$$

where Q is an observable?
Try putting Q=p (momentum) and Q=r (position).

3. Jul 28, 2005

DaTario

Now I am a bit confused. What's the name of that theorem which forbids static electric and magnetic charges to produce stable equillibrium condition in 3D ?

4. Jul 28, 2005

robphy

Are you looking for Earnshaw's Theorem?

5. Jul 28, 2005

DaTario

hehehehe....thank you a lot... I am getting old, my son...

6. Jul 28, 2005

yukcream

It is just the result of the theorem! Any mathematical divide inside?

7. Jul 28, 2005

Gokul43201

Staff Emeritus
Yes, the mathematics of showing the correspondence principle at work comes from doing what Galileo suggested and arriving at the classical equations of motion.