Summary

Admittedly, dark matter is called "dark" because it does not interact with light and therefore "we don't yet know precisely what dark matter actually is," Randall reports. However, it is known that dark matter does not carry an electric charge; moves at only a fraction of the speed of light and interacts very weakly with ordinary matter and with itself.

Scientists do not know the mass of dark matter, even if it is made of an elementary particle; neither do they know whether dark matter has any non-gravitational interactions; nor do they know how it was created in the early universe. Although " most physicists would bet that dark matter is composed of a new elementary particle devoid of the usual interactions of standard model particles, according to Randall.

Randall digresses for a moment to consider the nature...