**Three mathematicians have a different explanation for the accelerating expansion of the universe that does without theories of "dark energy." Einstein's original equations for General Relativity actually predict cosmic acceleration due to an "instability," they argue in paper published recently in Proceedings of the Royal Society A.**

**About 20 years ago, astronomers made a startling discovery: Not only is the universe expanding—as had been known for decades—but the expansion is speeding up. To explain this, cosmologists have invoked a mysterious force called "dark energy" that serves to push space apart.**

**Shortly after Albert Einstein wrote his equations for General Relativity, which describe gravity, he included an "antigravity" factor called the "cosmological constant" to balance gravitational attraction and produce a static universe. But Einstein later called the cosmological constant his greatest mistake.**

**When modern cosmologists began to tackle cosmic acceleration and dark energy, they dusted off Einstein's cosmological constant as interchangeable with dark energy, given the new knowledge about cosmic acceleration.**

**That explanation didn't satisfy mathematicians Blake Temple and Zeke Vogler at the University https://phys.org/news/2017-12-dark-energy-mathematicians-alternative-explanation.htmlof California, Davis, and Joel Smoller at the University of Michigan, Ann Arbor.**

**"We set out to find the best explanation we could come up with for the anomalous acceleration of the galaxies within Einstein's original theory without dark energy," Temple said.**

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