Mental Floss

Physicists Believe They've Discovered a Fifth Fundamental Force of the Universe

Dan Falk
iStock / iStock

Although physics may seem complicated to the uninitiated (or even to the trained professional, for that matter), it’s worth remembering that physics deals with only four known forces: gravity (which keeps us from floating off the Earth); electromagnetism (which binds electrons to atoms, and atoms to each other); and two forces that operate over very short distances—the strong nuclear force (which binds atomic nuclei together) and the weak nuclear force (which governs certain kinds of radioactive decay).

But if recent experimental work in particle physics pans out, we may have to get used to the idea of a fifth force. The research outlining the evidence for this fifth force was published last week in the journal Physical Review Letters.

If the discovery holds up, it will radically shake up what we know about the workings of the universe. “This would be quite a significant change in our understanding of how physics works, if it turns out to be true,” lead researcher Jonathan Feng, a physicist at the University of California, Irvine, tells mental_floss.

The research builds on earlier work by a team of Hungarian physicists who smashed a stream of protons into a thin film of lithium, creating an unstable isotope of beryllium, which then decayed. Searching through the data produced by those decaying beryllium atoms, they found evidence for what they said might be a new particle. Now Feng and his colleagues have taken a closer look at that data and concluded that, yes, it could be evidence of a new particle. More specifically, it could be a force-carrying particle—the kind of particle associated with a particular force. Perhaps the most familiar example is the photon, which carries the force of electromagnetism. (We're still looking for the force-carrying particle for gravity; this still-theoretical particle is called a graviton.)

For now, the result remains tentative—but the good news is that it should be relatively easy for other physicists to confirm or refute the result, Feng says. He points out that the Hungarian scientists used a room-sized experimental set-up, one that could in principle be replicated in many labs around the world.

The last of the known forces to be discovered were the nuclear forces, whose properties were only revealed through particle accelerator experiments in the 1970s. Electromagnetism has been understood since the work of James Clerk Maxwell in the 19th century, while gravity was (mostly) figured out by Isaac Newton in the 17th century, with some tweaks by Albert Einstein in the early 20th century. While gravity and electromagnetism are long-range forces, the two nuclear forces operate only over very short distances. If this fifth force exists, it, too, works only over short distances—typically around the size of an atomic nucleus, Feng says. And it would have to be extremely weak. “It’s weak, even compared to these nuclear forces—that’s why it’s been hidden for all these years,” Feng says.

If the research pans out, it could be particularly helpful in at least two lines of research. It could help physicists understand the nature of dark matter, a mysterious form of matter that accounts for more than one-quarter of the mass and energy in the universe but doesn’t interact with ordinary matter by any of the known forces except for gravity. It could also offer new hints in the on-going quest to unify the forces of nature into a single theoretical framework, Feng says.