Here is a question that I have found in my quantum text which I have been thinking about for a few days and am unable to make sense of.(adsbygoogle = window.adsbygoogle || []).push({});

If there is an operator A whose commutator with the Hamiltonian H is the constant c.

[H,A]=c

Find <A> at t>0, given that the system is in a normalized eigenstate of A at t=0 corresponding to the eigenvalue of a.

-So here is what I am thinking. Please tell me what I am doing wrong.

I know that where p is momentum operator [H,p]=ihdV/dx, and V is some potential in the Hamiltonian

and d<p>/dt=-<dV/dx>

So where [H,A]=c, wouldn't d<A>/dt=0? And then there would be no change in the eigenstate of A with time, and <A>=a which is its initial value at 0, which would be a(Psi) where Psi is my wave function or eigenvector or whatever I need it to be.

Am I understanding the question wrong?

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Time development of Expectation values

**Physics Forums | Science Articles, Homework Help, Discussion**