For almost a century, Albert Einstein’s Theory of General Relativity has reigned as the explanation for how gravity works. Einstein’s equations showed that gravity is a property of matter, and that matter “warps” the space-time around it. Yet there are both problems with General Relativity and questions about its effects.
Relativity applies to the universe on large scales, but not on the smallest scales, where quantum gravity takes over. Relativity also breaks down in the presence of the strongest gravitational fields, like those at the center of a black hole.
All the experiments to date have confirmed General Relativity’s effects on large scales, but scientists still aren’t certain whether gravity has remained constant since the Big Bang, whether it acts the same in all regions of the universe, and whether it retains its grip on the very largest scales.
It’s possible that gravity weakens on the largest scales – across billions of light-years – and thereby allowing the universe to expand at a faster rate as it grows larger.