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This is Science Friday.

I'm Flor Lichtman.

Today in the podcast, new dark energy research begs the question,

just how much do we understand about how the universe works?

I mean, I think it's the most ambitious effort of humanity, really, is to try to understand

the big everything.

One of the mysteries of the universe is why does it expand at the rate it does?

Back in 1998, two teams of researchers observed that not only was the universe expanding,

but the rate of expansion was increasing. That observation was the basis for a concept

now known as dark energy. And in the years that followed,

cosmologists have been trying to get a better handle on how dark energy works and where it

comes from. This week, researchers on a project called DESE, the dark energy spectroscopic instrument,

released results based on their first three years of data.

And when you line up their results with those from other measurements, it hints that possibly

dark energy, whatever it is, has changed over the lifetime of the universe. The so-called

cosmological constant is not a constant.

Joining me now to try to explain are my guests.

Andre Cuchot is a postdoctoral research fellow at the Lawrence Berkeley National Laboratory,

and he's part of the DESE Project.

And Adam Reese, Bloomberg Distinguished Professor at Johns Hopkins University,

and the Space Telescope Science Institute,

...