This is a video recording of a talk given by Dr. Robert A. Knop on May 2, 2009.


Modern cosmology tells us that the majority of the Universe is made up of stuff whose nature is largely unknown to us. Two thirds of it is Dark Energy; most of the rest is Dark Matter, the subject of this talk. Dark Matter interacts with normal matter through gravity, but otherwise it interacts hardly at all. Yet, we have very high confidence that this mysterious Dark Matter really does exist. Because it doesn't interact with light, we haven't seen it glowing, nor have we observed it absorbing background light as we've seen with dust clouds. All of the evidence we have for Dark Matter comes from its gravitational interaction with other matter, and with light. Yet, this evidence is extremely compelling. In this talk, I will attempt to convince you that there is no reasonable doubt that Dark Matter exists.

This talk was presented in the virtual world Second Life. It's part of a series of popular talks called Dr. Knop Talks Astronomy. Dr. Knop was on one of the teams that discovered the accelerating expansion of the universe.

Produced in association with the Meta Institute for Computational Astrophysics (MICA). For more information, see

Video recorded and edited by PookyMedia Films, see

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