What Einstein called his worst mistake, scientists are now depending on to help explain the universe.

In 1917, Albert Einstein inserted a term called the cosmological constant into his theory of general relativity to force the equations to predict a stationary universe in keeping with physicists' thinking at the time. When it became clear that the universe wasn't actually static, but was expanding instead, Einstein abandoned the constant, calling it the '"biggest blunder" of his life.

But lately scientists have revived Einstein's cosmological constant (denoted by the Greek capital letter lambda) to explain a mysterious force called dark energy that seems to be counteracting gravity — causing the universe to expand at an accelerating pace.

A new study confirms that the cosmological constant is the best fit for dark energy, and offers the most precise and accurate estimate yet of its value, researchers said. The finding comes from a measurement of the universe's geometry that suggests our universe is flat, rather than spherical or curved.

Geometry of the universe

Physicists Christian Marinoni and Adeline Buzzi of the Universite de Provence in France found a new way to test the dark energy model that is completely independent of previous studies. Their method relies on distant observations of pairs of galaxies to measure the curvature of space.

"The most exciting aspect of the work is that there is no external data that we plug in," Marinoni told SPACE.com, meaning that their findings aren't dependent on other calculations that could be flawed.

The researchers probed dark energy by studying the geometry of the universe. The shape of space depends on what's in it — that was one of the revelations of Einstein's general relativity, which showed that mass and energy (two sides of the same coin) bend space-time with their gravitational force.

Marinoni and Buzzi set out to calculate the contents of the universe — i.e. how much mass and energy, including dark energy, it holds — by measuring its shape.

There were three main options for the outcome.