Consider a free particle with rest mass m moving along a geodesic in some curved spacetime with metric gμν:
S=−m∫dτ=−m∫(dτdλ)dλ=∫L dλ
L=−mdτdλ=−m(−gμνdxμdλdxνdλ)1/2
The canonical 4-momentum Pα can be derived from the Lagrangian L using the following calculation: Pα=∂L∂(dxα/dλ)=m2dλdτ(gανdxνdλ+gμαdxμdλ)=m gανdxνdτ=m dxαdτ
Thus, expressed in contravariant form, we have derived an expression for the 4-momentum Pα given by
Pα=m dxαdτ
Is it correct to interpret the components of Pα in the following manner:
P0 is the energy of the particle,
Pi is the 3-momentum of the particle in the ∂i direction?
In other words is Pα the energy-momentum vector with respect to a local orthonormal basis?
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