Dark matter sounds like some physicist's tall tale: There's this invisible matter, see, and it has this powerful gravitational effect on galaxies. That's why we know it exists. In fact, it outweighs ordinary matter by about five to one. Problem is, dark matter doesn't reflect or absorb light, so we can't see it. Oh, and it rarely interacts with conventional atoms, so we can't feel it, either. However, we know it makes up a huge part of the universe, so we keep looking for it.
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