Conserved charge generates symmetry transformation in Hamiltonian Mechanics

kakarukeys
Messages
187
Reaction score
0
Q is a conserved charge if \{Q, H\} = 0
Show that q+\epsilon\delta q satisfies the equation of motion.
\delta q = \{q, Q\}

I couldn't find the proof. Anybody knows?
My workings:
\delta q = \{q, Q\}
\delta\dot{q} = \{\{q,Q\},H\} = - \{\{Q,H\},q\} - \{\{H,q\},Q\}
\delta\dot{q} = \{\{q,Q\},H\} = \{\{q,H\},Q\}
\delta\dot{q} = \{\{q,Q\},H\} = \{\dot{q},Q\}
Let q' = q+\epsilon\delta q
Show that \dot{q'} = \{q,H\}|_{q'}
L.H.S. is \dot{q}+\epsilon\delta\dot{q}
R.H.S is \{q,H\}+\epsilon\partial_q\{q,H\}\delta q
Therefore we have to prove \{\dot{q},Q\} = \partial_q\{q,H\}\{q,Q\}
...
No clue how to continue
 
Physics news on Phys.org
Solved! I neglected the change in p
 
Thread 'Need help understanding this figure on energy levels'
This figure is from "Introduction to Quantum Mechanics" by Griffiths (3rd edition). It is available to download. It is from page 142. I am hoping the usual people on this site will give me a hand understanding what is going on in the figure. After the equation (4.50) it says "It is customary to introduce the principal quantum number, ##n##, which simply orders the allowed energies, starting with 1 for the ground state. (see the figure)" I still don't understand the figure :( Here is...
Thread 'Understanding how to "tack on" the time wiggle factor'
The last problem I posted on QM made it into advanced homework help, that is why I am putting it here. I am sorry for any hassle imposed on the moderators by myself. Part (a) is quite easy. We get $$\sigma_1 = 2\lambda, \mathbf{v}_1 = \begin{pmatrix} 0 \\ 0 \\ 1 \end{pmatrix} \sigma_2 = \lambda, \mathbf{v}_2 = \begin{pmatrix} 1/\sqrt{2} \\ 1/\sqrt{2} \\ 0 \end{pmatrix} \sigma_3 = -\lambda, \mathbf{v}_3 = \begin{pmatrix} 1/\sqrt{2} \\ -1/\sqrt{2} \\ 0 \end{pmatrix} $$ There are two ways...
Back
Top