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2 votes
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The value of the volume form on an orthonormal frame

When applying the two constructions to the volume form the former produces the annoying factors you noticed: $$dx^1 \wedge \cdots \wedge dx^n\left(\frac{\partial}{\partial x^1}, \ldots, \frac{\partial} …
Valter Moretti's user avatar
3 votes
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Liouville Theorem analogue in generalized velocities?

.$$ Therefore, the canonical volume in terms of Lagrangian variables is $$dp\wedge dq = q d\dot{q} \wedge dq\:.$$ Since the left-hand side is preserved by solutions of the equation of motion and $q=q(t … So the apparantly natural volume constructed out of Lagrangian variables is not constant in time on the motion of the system, differently from the canonical volume. …
Valter Moretti's user avatar
17 votes
Accepted

Is a canonical transformation equivalent to a transformation that preserves volume and orien...

they are not equivalent since (for time-independent transformations) canonical is equivalent to $$\sum_{k=1}^n dq^k\wedge dp_k = \sum_{k=1}^n dQ^k\wedge dP_k\tag{1}$$ whereas conservation of oriented volume
Valter Moretti's user avatar
16 votes
Accepted

Liouville's theorem and conservation of phase space volume

If $Q_k\equiv 0$, even if $H$ explicitely depend on time, the solutions of Hamilton equations preserve, in time, the canonical volume: $$dq^1 \wedge \cdots \wedge dq^n \wedge dp_1 \wedge \cdots \wedge … d p_n\:.$$ In the presence of dissipative forces which cannot be included in the Lagrangian, the term $Q_k$ show up and the volume above generally fails to be preserved. …
Valter Moretti's user avatar