The effect of → gravitational potentials
on the → anisotropy
of the → cosmic microwave background radiation,
in which photons from the → CMB
are gravitationally → redshifted,
causing the CMB spectrum to appear uneven. This effect is the predominant source
of fluctuations in the CMB for angular scales above about 10 degrees.
It involves two parts: the effect of the potential at the
→ surface of last scattering, which is the ordinary
Sachs-Wolfe effect. And the integrated Sachs-Wolfe (ISW) effec,
which is caused by the time variation of gravitational potentials as the
photons travel through them. A photon traveling through a decaying
→ potential well (wall) gains (loses) energy.
Without → dark energy the photon is
→ blueshifted and then
→ redshifted, so that both effects compensate
each other. On the other hand, in an → accelerating Universe
driven by dark energy the photon gets more blueshifted.
See also → Rees-Sciama effect.
See also: Rainer Kurt Sachs (1932- ) & Arthur Michael Wolfe (1939- ), 1967,
ApJ 147, 73; → effect.
