The Sachs-Wolfe effect describes CMB temperature fluctuations caused by which phenomenon?
- Doppler shift
- Gravitational redshift/blueshift
- Thomson scattering
- Synchrotron emission
Answer: Gravitational redshift/blueshift
Photons climbing out of potential wells lose energy (redshift); falling in gain energy (blueshift), imprinting primordial density perturbations on CMB.