The multiverse theory was developed to explain the differing observational results of two observers in two different frames of reference without violating the law of causality.
Author Ngo Quang Ha has proven the Lorentz transformation is wrong.
After reconstructing the Lorentz transformation to ensure compliance with causality, the multiverse theory is no longer necessary.
The book (in English) is available on Amazon: https://www.amazon.com/dp/B0HCGYPFK1