There is a theory of a multiverse. One of the physical anomalies that supports it has to do with interference patterns. If you've taken physics and already know what this is and about the double slit experiment, you can skip the rest of this paragraph. When two waves(such as light or sound) come into contact, they either undergo constructive or destructive interference depending on which parts of the waves overlap. I'm sorry, but I don't think I could explain it properly without being able to draw it, but just note that this only happens as a result of the waves interfering with each other. Because of this, an interference pattern is observed in a double slit experiment.
Basically, 2 tiny parallel slits next to each other. The pattern seen on a screen behind the slits is a series of bars of light and darkness. The places where the waves undergo constructive interference yield light, and destructive yields dark. So naturally, when you shine light through only one slit, you just get one bar, because it's not interfering with anything. All you really need to know is that that pattern arises because of the two streams of light interacting with each other.
Ok, so here's the weird part that nobody can explain and one of the theories to explain it is the theory of a multiverse. An experiment can be done shining light through the double slits that is so weak where only one photon at a time is released.(photon's are the little packets of energy that light is made out of.) When they do this, they hit a special screen that can detect one photon at a time, and see where they land. When they do, they still produce the interference pattern!
What are they interfering with? Some theories include the photon splitting and probability waves, but one is the multiverse. This says that there are an infinite number of universes that are splitting constantly. If something has a 50% chance of happening, it is said that it will happen in half of the universes and not happen in the other half. They say that closely related(reently split) universes can react on the subatomic level, and the photons are interfering with those from other universes.