Material universal bubbles (like our universe) are supposed to be entangled with at least ONE anti-material universal bubble.
If we live in such a 12 fold multiverse, we should be able to detect 5 traces of our neighbouring universes as warmer patches inside the cosmic microwave background (CMB) radiation.
Is Our Universe Inside a Bubble?
First Observational Test of the 'Multiverse'
Physicists are now searching for disk-like patterns in the cosmic microwave background (CMB) radiation -- relic heat radiation left over from the Big Bang -- which could provide tell-tale evidence of collisions between other universes and our own.