I have question given as: $$\partial_k \varphi = -(C_k+ D_{jk}r_j)$$ where $C_k \,\&\, D_{jk}$ are constants and $D_{jk}$ is symmetric and traceless. I have to find $\varphi$. I am getting : $\varphi = A -C_kr_k - D_{jk}r_jr_{k}$ but answer is: $\varphi = A -C_mr_m - \frac12 D_{sm}r_sr_{m}$ I am ...

Cosmological redshift is based on the idea that the universe is expanding. When the universe doubles in size, or scale factor, the wavelength of light doubles. But the Milky Way is not expanding so my guess is that there is no cosmological redshift within the Milky Way? There is of course Doppler...