At the surface of the Sun, Photon versus first space string "friction" could be the cause of Classical Gravitational Red Shift like energy loss, which I have named it Quantum Frictional Red Shift (QFRS)
Quantum Frictional Red Shift
φ = Photon Energy Loss in Quantum Frictional Red Shift
e = First String Vibrating energy
θ = Angle Between Photon & String
λ = Photon (EM) Wave Length
R = Sun's Radius
Ff = Frictional Force in Quantum Friction
h= Planck Constant
mc= Photon Momentum
QFRS
de Broglie Equation
Frictional Force in Quantum Friction
h= Planck Constant
mc= Photon Momentum
"e" could be replaced by covariant Hamiltonian in String Theory: