Two mathematicians have, rather bravely, proposed a unified theory of dark matter and dark energy that alters Einstein's equations describing the fundamentals of gravity.

Shouhong Wang of Indiana University and Tian Ma of Sichuan University suggest that the law of energy and momentum conservation in spacetime is valid only when normal matter, dark matter and dark energy are all taken into account.
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For normal matter alone, energy and momentum are no longer conserved, they say.

The two aren't arguing with the concept of curved spacetime that Einstein used in his field equations. But, they suggest, the presence of dark matter and dark energy requires a new set of gravitational field equations that take into account a new type of energy caused by the non-uniform distribution of matter in the universe.

This new energy can be both positive and negative, and the total over spacetime is conserved, they say.