A type of matter which is found near other matter. It cannot be observed directly (it is "dark"), but can be noticed as a result of the pull of gravity from the dark matter. Astrophysicists believe that more than half of the Universe could be in the form of dark matter.
Come, you lost Atoms, to your Centre draw,
And be the Eternal Mirror that you saw:
Rays that have wander'd into Darkness wide,
Return and back into your Sun subside.
From Farid al-Din Attar's
The Conference of the Birds