Physicist: There is no new energy or matter (or even new universes), it’s just that how it’s distributed depends on who’s asking, and in what “world” they’re doing the asking. If you go online (or read some kind of book or something) you generally find the Many Worlds Interpretation presented as the universe “splitting”. The many (like: many, many) different versions of the universe branch apart, and come together all over the place. When a particle (or whatever) is in multiple states its energy and matter is distributed among those various states. So, for example, 50% chance of each path means equal division of the energy and matter of the particle.