The CMB was first detected by the Holmdel Horn Antenna in 1964. The accelerating expansion of our universe through dark energy was originally conjectured in 1921, along with Kaluza-Klein theory as a precursor to string theory. Among this radiation one can find that the universe at its birth emitted many different kinds of particles, including lots of energy and matter. Both dark energy and the relic radiation can be measured together and directly related to each other due to the wavelengths of light that eventually red-shift over time. Today, the CMB sits around us everywhere in the sky as a microwave echo of energy from the abyss that was once emitted by the universe when it was only in its youth.
Dark energy, similar to vacuum energy in otherwise empty space, is thought to expand space from every point and in every direction. The CMB's photons emerged from a dark universe the same way as dark energy expands the particular space that it's inherent to. Experiments such as the Fermilab Holometer are currently working to find evidence that would show the universe itself is a giant hologram. This would eventually shed light on dark energy and also support modern interpretations of string theory, including M-theory, with its 11 dimensions of reality.

A 6-dimensional Calabi–Yau manifold, as known to superstring theory and mirror symmetry (Image: Wolfram).