Redshift Factor in a Symptotic Stationary Flat Space

[johnstrass]

I am reading Wald's book. There is a problem confused me: page 158, problem 4,(b). An symptotic statoinary flat space, two stationary observer connected with a rope. One observer A is at finite r and the other B is at infinity. Observer B is really stationary by other forces and holding the rope in order for A to be stationary. Use the energy conservation argument to proof the force asserted through the rope on B differ from the force on A from the rope by a redshift factor. How to think in the problem? Thanks.

 

[cesiumfrog]

Haven't looked in the book yet, but..

By conservation of momentum, you would expect the rope to be tensioned, but not accelerate, if some "observer" C is applying equal and opposite streams of photons against (solar parachutes attached to) each end of the rope. But A & B would differ in the flux of momentum they measure impinging at their respective end.