Physics theories can get pretty hairy, but don’t worry: If our universe isn’t the only one—if in fact there are an infinite number of universes out there—then in at least one of them you are a brilliant theoretical physicist that kinda gets this stuff.
The idea of a multiverse comes up in a number of different physics theories. For example, if space-time stretches to infinity, then at some point it starts repeating itself. As Clara Moskowitz writes for Space.com, "So if you look far enough, you would encounter another version of you, in fact, infinite versions of you." Another idea: parallel universes might be just beyond our own in another dimension.
All this may be comforting—endless possibilities—or uninspiring: What’s the point if these other selves are so far away or completely hidden? Well, a new theory posits that other universes may not be so separate from our own at all.
Quantum physicist Howard Wiseman and his colleagues just proposed a new "many interacting worlds" theory in the journal Physical Review X. Their theory helps explain that some of the very weird physics we can observe at the quantum level—"bizarre quantum effects such as particles that tunnel through solid barriers," they write—might be explained by another universe, or world, interacting with our own.
For New Scientist, Michael Slezak writes:
"One way to think about it is that they coexist in the same space as our universe, like ghost universes," Wiseman says. These other worlds are mostly invisible because they only interact with ours under very strict conditions, and only in very minute ways, he says, via a force acting between similar particles in different universes. But this interaction could be enough to explain quantum mechanics.
Another, earlier "many worlds" theory, proposed by Hugh Everett III in the 1950s, put forth the idea that worlds "branch out independently from one another," writes Alexandra Witze in Nature News. But the newer theory adds the interaction bit. Each individual world is governed by the tame, classical Newtonian physics. But when they interact, quantum weirdness springs up.
Wiseman and his colleagues calculated how multiple worlds interacting can explain several well-known phenomena, including the tunneling effect and something called the double-slit experiment that shows light can behave like a particle or a wave. But the theory is new, and many more calculations will be needed to try and test it out. Or figure out what it means for us. But the idea is intriguing.
“In our theory, all other worlds are as real as our world, and they’ve all been around since the beginning of time,” Wiseman told Motherboard. “The only mystery is what particular world we occupy.”