What Albert Einstein called his "biggest mistake" is helping scientists to explain the universe.
In 1917, Einstein's novel equations of space-time had geometric terms on the left and energy on the right. A constant on the left kept the universe steady, suiting observations at the time.
When it became clear that the universe wasn't actually static, but was expanding instead, Einstein dubbed the constant the "the biggest mistake of my life".
Another scientist Erwin Schrodinger toyed with Einstein's equations, moving the constant from the left to the right.
The simple move transformed the constant from part of the geometry of space-time to a source of energy for the universe.
Now historian Alex Harvey of New York University has re-analysed papers from the physicists, published in 1918.
At that time Einstein said that the properties of this new energy term were either nothing or demand a "non-observable negative density in interstellar spaces".
"That turns out to be dark energy," New Scientist quoted Harvey as saying.
Dark energy only emerged again in 1998 to explain the universe's accelerating expansion. (ANI)