## Volume elements in position and momentum space

Volume elements in position and momentum space

This entry was posted in Uncategorized. Bookmark the permalink.

### 2 Responses to Volume elements in position and momentum space

Hi there,

I think the fact that the 4-momentum is orthogonal to the mass hyperboloid follow from the fact that p^2=-m^2 and that it is constrained to lie on this as time passes.

For example (assuming a non-zero rest mass so I can use proper time τ) the 4-momentum travels on a path along the mass hyperboloid as time passes, so p = p(τ). The 4-vector dp/dτ is tangent to this path and thus the hyperboloid. Taking the proper time derivative of p^2=-m^2 gives p•dp/dτ=0, meaning that p is orthogonal to the hyperboloid.

Let me know what you think.

Like

• growescience says:

That’s great thanks. I was trying for ages to figure out how to find a tangent to the hyperboloid in the Minkowski metric, completely forgetting that it’s just dp/dτ. I’ve added your comment to the original post.

Like