The cosmic microwave background (CMB) is the left-over heat from the Big Bang. This radiation provides a picture of the universe when it was only 400,000 years old. Now, 14 billion years later, it has cooled to microwave frequencies and is nearly uniform. The slight variations of 1 part in 100,000 in its temperature reflect initial inhomogeneities in the matter and radiation that later collapsed to form clusters and galaxies. These fluctuations carry information about the origin, composition and evolution of the universe, and theories of the origin of the universe make detailed predictions about their statistical properties.

The CMB is our best hope of uncovering fingerprints of the physics operating at very high-energy scales, inaccessible to Earth-bound particle accelerators. Current cosmological data are, for the first time, precise enough to allow detailed tests of models of the very early universe. The Planck satellite has then dramatically sharpened our view of the early universe, and provided a window into the origin of cosmic structure.

A primordial collision of our Universe with an Exo-Universe would leave a unique imprint in the cosmic microwave background. Physicists in Canada and the US now claim that the prediction can be tested using existing and future space telescopes, contradicting the standard view that the existence of a multiverse is untestable.

via A Collision with Another Universe –Are Signs Lurking in the Big Bang Afterglow?.