Both dark matter and dark energy have yet to be directly observed, and scientists know very little about them. However, research definitely points to their existence. Without dark energy, the expansion of the universe would be slowing due to gravity (and in fact, this is what people believed up until the end of the 1990s). But the universe's expansion is speeding up-and scientists think that the unknown properties of dark energy are the key to explaining this process.
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Key Facts In This Video
The known universe consists of about 70% dark energy, 25% dark matter, and 5% visible matter. 00:08
Dark energy seems to be intrinsic to empty space, which has more energy than everything else in the universe combined. 03:45
One theory of dark energy postulates that it comes from virtual particles in empty space that form and disappear constantly. 04:47