Dark energy -- a constant companion?

The latest big -- one might say, cosmic -- news is that dark energy is not getting appreciably stronger over time. Some dark-energy theories had predicted a strengthening of the phenomenon.

This stability conclusion comes from comparing the sizes of distant (hence seen with old light) and nearby (hence seen with recent light) galaxy clusters. Old clusters evolved in a smaller, hence more gravitationally influenced universe. Cluster formation is influenced by both gravitational (attractive) and dark-energy (repulsive) influences. Maximum cluster sizes over time fit a model of dark energy whose strength has not varied by much over billions of years. Indeed, when combining observations made in different wavelengths, the latest findings say that dark energy hasn't varied by more than 10%.

Less than ten percent? That's verging on dark energy being the cosmological constant that Einstein introduced as an ad hoc adjustment to his theory of general relativity.

So now when I'm lying awake at night, I needn't worry that all the atoms in the universe will come apart in a Big Rip in a few billion years. THAT'S a load of my mind ;-)

Now if only we knew what dark energy IS ...