Dark energy makes up about 70% of the universe, and it’s the mysterious force pushing the cosmos to expand faster and faster. For decades, scientists assumed it was constant — a fixed energy of empty space, as Einstein once proposed.

But new research from the Dark Energy Survey, the Dark Energy Spectroscopic Instrument, and other major experiments suggests something shocking: dark energy may be evolving over time.

A team at the University of Chicago analyzed multiple datasets and found that models where dark energy slowly decreases in strength actually fit the data better than the traditional constant model. In fact, they report that the standard model might be excluded at 99.6% confidence.

If this is true, it could mean dark energy is driven by a new, ultra-light particle — billions of billions of times lighter than an electron — acting almost like a cosmic axion field that only recently began to “roll” and change.

So what does this mean for the universe’s future? If dark energy weakens, cosmic acceleration could slow down, avoiding both the catastrophic Big Rip and the Big Crunch. Instead, the cosmos would expand forever, growing colder and darker — a scenario scientists call the Big Freeze.

This is the first real hint in 20 years that dark energy might not be constant. If confirmed by upcoming surveys like the Vera Rubin Observatory, it could rewrite our understanding of physics — and of the universe’s ultimate fate.