Howard Georgi, a physicist at Harvard University, has recently published a paper on “unparticle physics,” which suggests the existence of “unparticle stuff” that cannot be accounted for by the standard model.

Unparticles can fit in a theory that has the property of continuous scale-invariance. A fractal is an example of discrete scale-invariance because it looks the same if multiplied by a fixed number.

“There could be a scale-invariant world separate from our own that is hidden from us at low energies because its interactions with us are so weak,” he said.