Could Einstein’s equations explain the universe’s expansion?

For almost three decades, dark energy has been the standard explanation for why the universe is expanding at an accelerating rate. Now, a team of mathematicians is challenging this widely accepted theory. The mathematicians at the University of California, Davis, argue that the answer may already lie within Einstein’s own equations and that an invisible form of energy may not be needed at all. The findings are published in the journal Proceedings of the Royal Society A. The researchers worked with the Einstein-Euler equations, which combine Einstein’s general relativity with the rules that govern how fluids move. They used these tools to test the leading framework for explaining the universe’s evolution since the Big Bang, known as the Lambda-cold dark matter model, and found a weak spot in its very foundation.Einstein’s equations may explainBlake Temple, the study’s corresponding author and a professor emeritus of mathematics at UC Davis, offered a simple comparison: a pencil balanced vertically on its tip. “All the forces are in balance when a pencil is standing on end, so it is a ‘solution’ of the equations. But it’s unstable. Any breath of air and it falls away,” Temple said in...