When Hungarian theoretical particle physicists detected a radioactive decay anomaly in a series of experiments, they published a paper in 2015 suggesting those anomalies pointed to the existence of dark photons. These theoretical force carriers have never been detected, and might indicate unseen dark matter (so-called because it neither absorbs nor emits light, and so is impossible to detect directly) – which could help researchers understand why the universe is filled with dark matter. Or maybe, said a group of American physicists who reviewed the Hungarians’ research in 2016, this is actually the signature of a fifth fundamental force.
“If confirmed by further experiments, this discovery of a possible fifth force would completely change our understanding of the universe, with consequences for the unification of forces and dark matter,” said one of the new study’s authors, Jonathan Feng, a professor of physics and astronomy at University of California, Irvine.
Up to this point, scientists had previously identified four fundamental forces: gravitation, electromagnetism, the strong nuclear force and the weak nuclear force. Each force governs some aspect of how the particles interact with each other; the scope of their power ranges from the subatomic to the galactic (for a crash course on how each of the fundamental forces work, check out this video series). And while the four fundamental forces have helped researchers understand a great deal about the universe, there are some glaring gaps in the model.
For one thing, the four forces can explain neither the existence of dark matter, which makes up nearly 27 percent of the universe’s mass-energy density, nor dark energy, which makes up more than 68 percent. Scientists know dark matter and dark energy exist even though they can’t see them because they can monitor their effects on the universe. For example, given the effects of gravity, the universe should be slowing in its expansion – but it’s actually
Lorraine Boissoneault is a writer in Chicago who covers science, history, foreign affairs, and adventure. She's written for Weather.com, Salon, Forbes, JSTOR Daily and many others. Her first book, The Last Voyageurs, was published by Pegasus in April 2016.