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.