( ( photons ( passing ( by ( a ( ( very strong ) ( gravitational field ) ) ) ) ) ) ( ( are ( redshifted ( as ( they ( lose energy ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNS photons)) (VP (VBG passing) (PP (IN by) (NP (DT a) (ADJP (RB very) (JJ strong)) (JJ gravitational) (NN field))))) (VP (VBP are) (VP (VBN redshifted) (SBAR (IN as) (S (NP (PRP they)) (VP (VBP lose) (NP (NN energy))))))) (. .)))
photons passing by a very strong gravitational field are redshifted as they lose energy.
(ROOT (S (NP (JJ Strong) (JJ gravitational) (NNS fields)) (VP (VBP are) (ADJP (JJ capable) (PP (IN of) (S (VP (VBG altering) (NP (NP (DT the) (NN rate)) (PP (IN of) (NP (NN time) (NN passing))))))))) (. .)))