This just in: Based on the independent observation of thousands of galaxies by the European Southern Observatory’s Very Large Telescope array, astronomers have constructed 3-D maps that show that dark energy, the force which appears to be winning a cosmic tug of war with gravity and is responsible for the expanding universe, is really, really there.
We just don't know what it is. Alan Boyle at Cosmic Log:
Scientists say the resolution of the data isn't yet good enough to determine exactly what's behind dark energy, but they say a finer-scale survey could tell whether it's an exotic characteristic of the space-time continuum – or whether it's just that everything we know about gravity is wrong.
Baryonic matter, which interacts with electricity and magnetism, and what you and I see when we look up at the night sky, is just a fraction of what's out there. The rest is dark matter and dark energy, and together they make up about 96 percent of the mass-energy of the universe.
Since neither can be observed directly, their composition and dynamics must be inferred from the effect they have on the observable universe. Tests using the Large Hadron Collider, slated to go online this year, could produce fleeting evidence for dark matter.
Of interest to me is this question: What should we make of nothing?
Maybe it’s not just our powers of perception that aren’t up to the task but also our powers of conception. [As Carl Sagan famously said] extraordinary claims... require extraordinary evidence, but what if that evidence has to be literally beyond the ordinary? Astronomers now realize that dark matter probably involves matter that is nonbaryonic. And whatever it is that dark energy involves, we know it’s not 'normal,' either. In that case, maybe this next round of evidence will have to be not only beyond anything we know but also beyond anything we know how to know.