For the past generation, we’ve recognized that our Universe is a particularly dark place. Sure, it’s filled with stars, galaxies, and a slew of light-emitting phenomena everywhere we look. But each and every one of the known processes that generate light is based on the particles of the Standard Model: the normal matter in our Universe. All the normal matter there is — protons, neutrons electrons, neutrinos, etc. — represents just 5% of what’s out there.
The other 95% is a dark mystery, but it can’t be any of the particles we know. According to our best measurements, 27% of the Universe is made of some type of dark matter, which doesn’t interact with light or normal matter in any known way. And the remaining 68% is dark energy, which appears to be a form of energy inherent to space itself. A new set of observations is challenging what we presently think about dark energy. If it holds up, everything we know will change.