what proof do we have that dark matter exists
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M$2 Answers
The first observation that I heard about was about 3 years ago. In a massive collision of two galactic clusters, the normal matter was swept up by the collision, leaving dark matter behind. Basically, there is a region adjacent to the glowing gas and dust left from the collision where there is gravitational lensing, but no other evidence of the presence of normal matter. This is taken as strong evidence for the existence of dark matter.
There have been a couple of other similar observations since. Link goes to a news article about the original work.
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M$
While the existence of dark matter could explain this difference, there is no proof that dark matter exists. There are multiple other possible explanations for the differences.
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M$
