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| via chandra.harvard.edu |
Most of the Universe is dark. The protons, neutrons and electrons that make up the stars, planets and us represent only a small fraction of the mass and energy of the Universe. The rest is dark and mysterious.
The two largest pieces of the Universe, dark matter and dark energy, are the two that we know the least about, yet nothing less than the ultimate fate of the Universe will be determined by them. Dark matter tends to pull the Universe together, and dark energy tends to drive it apart. A full understanding of this cosmic struggle will require every possible scientific tool.
