Extra dimensional dark matter
If dark matter doesn’t exist in another world entirely, it might live in a fourth spatial dimension unseen by humans and our experiments. Such a dimension would be too small for us to observe a particle’s movements within it. Instead, we would see multiple particles with the same charge but different masses, an idea proposed by Theodor Kaluza and Oskar Klein in the 1920s. One of these particles could be the dark matter particle, a much more recent concept known as Kaluza-Klein dark matter. These particles wouldn’t shine or reflect any light, explaining why dark matter can’t be seen by anyone in our three dimensions.

Confirming that dark matter exists in another dimension could also be seen as support for string theory, which requires extra dimensions to work.

“You can go out there and map out the extra-dimensional world just like 500 years ago people mapped out the continents,” Feng says.