The stuff you and me are made out of is called “normal” matter, despite the fact that it makes up less than 5% of all the matter and energy in the universe. Besides people, planets, stars, and random gas clouds, the cosmos is also composed of dark matter and dark energy.
We can’t see the dark matter directly (hence the name), but we know it’s out there based on its gravitational relationships with everything else. It makes stars orbit faster than they would otherwise inside galaxies, it makes galaxies zip around faster inside of clusters, and it shapes and sculpts the largest structures in the universe.
And as for dark energy, that’s just the name we give to the accelerated expansion of the universe, and that’s about all we know about it.
As far as we’ve been able to measure, dark matter only connects to normal matter through its gentle gravitational whispers and subtle tugs. But we don’t know for sure if dark matter also talks to normal through one of the other three fundamental forces (strong nuclear, weak nuclear, or electromagnetic) or if there are new, fifth forces of nature floating around.
One way to poke at this is to very carefully measure various atomic and nuclear properties and compare those properties to what we expect from known physics. If there’s a major discrepancy, it could be a sign that there’s more to the dark side of the universe.
The latest in these experiments was performed in Dusseldorf, Germany, and concerned a peculiar atomic creature known as HD+. This little fella is a proton paired with a deuteron (which is itself made of one proton and one neutron), with a single electron hanging out nearby.
The distance between the proton and the deuteron in HD+ can be calculated from our understanding of quantum physics and the nature of the forces, and the team in Dusseldorf measured this distance by carefully monitoring its rotation rate when hit by lasers.
The end result: exactly what we expected. Their measurements agreed with theoretical predictions, as they have for the past century, but this time to a level twenty times more precise that before.
If you want to live in a universe with fifth forces or extra, dark-based physics, it’s unlikely to be this one, as anything past the four known forces has to be incredibly weak in order to satisfy this stringent experimental results.