And now scientists are getting a little closer to understanding how it behaves. The big question is whether this dark energy is a constant force, which scientists have long thought, or whether the force is weakening, a surprising wrinkle tentatively proposed last year.

New data involving millions of galaxies and luminous galactic cores is providing fresh evidence that the enigmatic and invisible cosmic force called dark energy - responsible for the universe's accelerated expansion - has weakened over time rather than remaining constant,

A new map of cosmic expansion suggests that dark energy evolves over time, hinting that the universe doesn’t work the way we thought it did