Scientists have discovered that dark matter, the universe's most mysterious "stuff," obeys gravity on vast cosmological scales. This could help to dismiss the possibility of a fifth fundamental force of nature — but even if not, it certainly puts restraints on that potential force's strength.
It's long been known that "everyday matter" is made up of atoms, which are, in turn, composed of protons, neutrons and electrons. We also know that these particles fall in line with the known fundamental forces of nature: electromagnetism, gravity, the strong nuclear force and the weak nuclear force. However, what has been less clear is whether dark matter obeys these same four forces. Indeed, one of the reasons dark matter is so puzzling is that it doesn't seem to act in conjunction with light, or electromagnetic radiation. And if it does, it does so much more weakly than ordinary matter does. This makes dark matter effectively invisible, meaning the only way scientists can infer its presence is by observing its gravitational effects and then watching how that acts as a middleman and impacts light and ordinary matter.
