- #1
thegreenlaser
- 525
- 16
In Lagrangian/Hamiltonian mechanics, what is it that makes phase space special compared to configuration space? As a simple example, if I use ## q ## as my generalized position and ## v = \dot{q} ## as my generalized momentum, then the Hamiltonian
[tex] H = \frac{1}{2} v^2 + \frac{1}{m} V(q) [/tex]
gives the correct dynamics. Yet we always seem make a big deal out of transitioning from configuration space ## (q, \dot{q} ) ## to phase space ## (q, m \dot{q} ) ##. Is there something about the phase space coordinates ## (q, \dot{q} ) ## that doesn't work? (From a mathematical point of view, is it maybe impossible to set up a symplectic structure with those coordinates?)
To put it another way, if I arbitrarily pick variables to be my generalized momentum and position and I can find a Hamiltonian which gives the correct dynamics in terms of those variables, is that sufficient to guarantee I've set up a phase space correctly (symplectic structure and all)?
[tex] H = \frac{1}{2} v^2 + \frac{1}{m} V(q) [/tex]
gives the correct dynamics. Yet we always seem make a big deal out of transitioning from configuration space ## (q, \dot{q} ) ## to phase space ## (q, m \dot{q} ) ##. Is there something about the phase space coordinates ## (q, \dot{q} ) ## that doesn't work? (From a mathematical point of view, is it maybe impossible to set up a symplectic structure with those coordinates?)
To put it another way, if I arbitrarily pick variables to be my generalized momentum and position and I can find a Hamiltonian which gives the correct dynamics in terms of those variables, is that sufficient to guarantee I've set up a phase space correctly (symplectic structure and all)?