Researchers think that the multiverse is not fiction anymore.

Multiverse means that our universe is one of many universes. The reason why researchers and scientists believe that this is true is that logical. About 50 years ago people didn't know that there were other solar systems. Exoplanets were only theories in the 80's. 

About 400 years ago people thought that our Sun was the only star in the universe. Edvin Hubble proved that our galaxy, Milky Way is one of many galaxies. Then researchers found that galaxies form groups, and supergroups. That means that today we think that the universe, where we live is the ultimate supergroup of galactic supergroups. And logically thinking there should be other universes.

We believe that the universe began its existence in an event or series of events called the Big Bang. That event did not begin, because the energy that formed material should come from somewhere. The Big Bang was not one "bang" or explosion. It was a series of events where material took form. Or the energy level that it has today. 

The road from the heliocentric universe to multiverse theory is like matrioshka. We expand our knowledge all the time. And theories travel forward of the observation. 

If we think that the Schwinger effect or wave-particle duality formed all material, we can understand the multiverse's nature better. In interaction where wave movement forms particles, it forms particle-antiparticle pairs. And because they have opposite polarity, that pulls them back together. When material and antimatter face they turn into energy. There was some kind of asymmetry in the young universe. And that asymmetry caused a situation. That there is only one type of material in our universe. When particles hit the atmosphere they form a small number of antimatter particles. 

In the image, an inquisitive person breaks the bubble. 

So what caused that asymmetry? The thing that can explain it is that. Some particles came from another universe. In an antimatter universe, all natural laws are similar to our universe. But the material that forms those universes is mirror material. 

The other universes are harder to see than anything else. Light pollution comes from objects in our universe covering those other universes. 

Those other universes must not be similar to our universe. There is the possibility that antimatter forms those other universes. And if they formed in different times, or if their mass is smaller, that thing causes a situation that those universes are invisible to us.

Multiverse explains things like:

Dark energy

Dark matter 

And even the universe's existence. 

In this model universe is the thing. That formed in the crossing point of energy fields that formed in other universes. Dark energy is energy that comes from other universes. 

Dark matter can form clouds and other structures that are similar to visible material. Those dark matter clouds and dark energy are things, that require new models. 

Sometimes researchers think that dark matter is the source of dark energy. And things like low-mass dark matter objects cause theories that maybe some other universes are invisible to us. 

Multiverse explains dark energy and dark matter. That those things can come from other universes. That is one of the most interesting things in multiverse theory.  In multiverse theory, all universes formed from some kind of Big Bang. And that means there should be other universes forming right now. 

Every single universe's mass can be different in the multiverse. And that means time can travel other ways in them. If the universe expands materia turns into wave movement. And if the universe falls the energy level in it turns higher, which means the material turns "younger" because a high energy level in the environment packs wave movement to those particles. 

That is a key element in time. When the universe expands the particles vaporize and energy travels out from the particles. The universe's accelerates and particles turn into wave movement faster and faster. The reason for that is. The difference in energy levels between a particle and its environment turns higher. That increases the speed of energy flow. 

If the universe turns smaller the energy density in it turns higher. That decreases energy flow from particles. The situation the particle reaches the same energy level as its environment, that thing causes the situation particle to melt in its entirety. So being a particle, it requires a different energy level. 

https://bigthink.com/starts-with-a-bang/scientists-think-multiverse-fiction/