Dark energy, mysterious as it sounds, has become part of the furniture in cosmology. The evidence that this repulsive energy infuses space has stacked up since 1998. That was the year astronomers first discovered that the expansion of the universe has been speeding up over time, with dark energy acting as the accelerator. As space expands, new space arises, and with it more of this repulsive energy, causing space to expand even faster.

Two decades later, multiple independent measurements agree that dark energy comprises about 70% of the universe’s contents. It is so baked into our current understanding of the cosmos that it came as a surprise when a recent paper published in the journal Astronomy & Astrophysics questioned whether it’s there at all.

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