Refined Hubble Constant Narrows Possible Explanations for Dark Energy

Their result is consistent with the simplest interpretation of dark energy: that it is mathematically equivalent to Albert Einstein's hypothesized cosmological constant, introduced a century ago to push on the fabric of space and prevent the universe from collapsing under the pull of gravity. (Einstein, however, removed the constant once the expansion of the universe was discovered by Edwin Hubble.)

"If you put in a box all the ways that dark energy might differ from the cosmological constant, that box would now be three times smaller," says Riess.