Analysis of the cosmic microwave background radiation has demonstrated that there are at least four large ring-shaped structures in the universe, each about four degrees wide - eight times the apparent diameter of the sun or full moon. This is far too great to have been caused by known astrophysical processes. The most logical explanation, according to most cosmologists, is that these are other universes that have collided with ours.
Are these indeed other universes?
The spots show all the features that universes that collide with ours would show.
Already in 2007, a huge gaping hole, a billion light-years across, was found in which the background temperature turned out to be lower than in the rest of the universe. There are hardly any galaxies in the hole.
A lower background temperature means that the engulfed universe was expanded further than ours, ie older, when it collided with ours. One of the other three areas has a higher background temperature than the rest of the universe. So this was of a younger age when the collision took place.
In any case, it is remarkable that there is no spherical symmetry: the spots are not perfectly round. In many cosmological theories this spherical symmetry is assumed. If these theories are indeed other universes, they can be thrown away in their current form.
Waiting for confirmation
The Planck satellite of the European space agency ESA is currently carrying out measurements. These were completed in 2012. Planck measures polarization, the direction in which photons from the cosmic background radiation vibrate. This is zero from standard cosmic background radiation: all directions occur at random. Due to the violent distortion of spacetime upon collision, if the 'spots' are indeed remnants of sister universes, the polarization direction will also deviate in a certain way.
Consequences for us
The existence of alternate universes has huge implications. No longer will we be trapped in this universe, which, according to almost all cosmological theories, is ultimately doomed. We may be able to find a way to escape to a young universe and build a new existence there.