If we take a set of real numbers and square a negative it can not be found in the possible set of real numbers thus signifying a parallel universe could not be found within a given universe. A parallel universe is one that exists within a universe as distinct universe. There could be infinite universes that could exist out of the infinity while there could be a set of well defined universes in different time-space that might exist with a given universe as parallel universes.
The greater the energy, the greater the contraction of space as defined by Lorentz transformation and slower the time would run relative to an observer. In a given second there are more seconds in the case of time running slower so consequently it is gaining time to run the given distance, meaning the distance would already be covered when our time is run out hence we could not see the parallel universe but if we experience a time running slower we could be a witness to the pa”rallel universe. As the motion of sun is relative to the observer on the earth, the parallel universe might contain a replica of the sun as defined by Lorentz transformation if the observer is experiencing slower time passage.
So we have a universe in where exists another parallel universe in different or same space dimensions. It is to be noted the energy of parallel universe is substantially more.