In special relativity, we introduced the momentum of a particle in a given Lorentz frame as p" = (E,p'), where E is the energy of the particle and p¹ is the relativistic 3-momentum. Explain why, in general relativity, the energy of a particle measured by an observer is given, irrespective of the coordinate system used, by -p Uobs, where p" is the momentum of the particle and uobs is the velocity of the observer in those coordinates.

In special relativity, we introduced the momentum of a particle in a given Lorentz frame as p" = (E,p'), where E is the energy of the particle and p¹ is the relativistic 3-momentum. Explain why, in general relativity, the energy of a particle measured by an observer is given, irrespective of the coordinate system used, by -p Uobs, where p" is the momentum of the particle and uobs is the velocity of the observer in those coordinates.