Ready for a mind-boggling idea?

The majority of the universe may not be made of the same type of matter as the Earth. We infer from gravitational effects the presence of this dark matter, a type of matter that we cannot see. There is strong evidence that it might not be made up of protons, neutrons, and electrons.

What is dark matter, then? We don't know. Perhaps it is composed of neutrinos, or even more exotic forms of matter, like neutralinos, one of the theoretical supersymmetric particles.