A Fifth Fundamental Force? | Vol. 3 / No. 42.2

Image: Jakob Breivik Grimstveit, CC BY-SA 2.0

Phys.org is reporting, as of yesterday, that physicists have confirmed the “possible discovery of fifth force of nature.” That’s some pretty big talk, but let’s back up for a second.

There are four fundamental forces of nature, the strong force (whose carriers are gluons and pions, and which not only binds quarks together into hadrons like protons by keeping them colour-neutral, but also keep positively-charged atomic nuclei together just so); the weak force (whose carriers are called W and Z bosons, and allows for atomic decay); gravity (whose carriers would be the basically unobservable gravitons and, uh, you know what gravity does so fine); and electromagnetism (whose carriers are photons, and which is responsible for tons of fun things like electricity). If you want to know more, I’ve linked each one to a respective explainer by Hank Green over at SciShow.

A fifth fundamental force would be a massive change to the way we understand physics, which is why we’ve got such wishy-washy language and why the nobel prize committee isn’t banging down the doors of the authors of this study.

So here’s what happened. There were some researchers last year at the Hungarian Academy of Sciences looking for “dark photons,” hypothetical particles that would serve as the force-carriers for the electromagnetic force in dark matter, and which would (again theoretically) be a kind of dark matter we could actually detect. But that’s not what they found, because what showed up seemed to be a new particle, but one with mass (a dark photon, like a regular old photon, wouldn’t have mass).

This year a team from the University of California, Irvine (UCI) looked over their data while trying to determine what the particle, which is about 30 times heavier than an electron (so still very, very light — an electron is 0.054386734 percent of the weight of a neutron), might be. The dark photon being ruled out, they’ve apparently also ruled out it being a “mass particle” (the kind of thing matter’s made up of) and so what’s left is the possibility that it may be a “force carrier” particle, like the photon, gluon, pion, W and Z bosons, and gravitons.

And that would require another force.

Right now they’re calling it the “protophobic X boson” because it only reacts (at extremely close range) with electrons and neutrons, and not with protons.

The good thing is that – if it’s real, you understand – it should be pretty easy to spot. It hasn’t been hiding because it’s like the Higgs boson, which requires massive amounts of energy to create, but rather because it’s so weakly interacting. So there are a number of labs around the world that should be able to go looking for this thing and find it. And then, well, then they have to make sense of the data in a way that either does or does not require another fundamental force of nature.

I guess we’ll see.

The paper, “Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays,” is in preprint over at arXiv.org.


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Richard Ford Burley is a human, writer, and doctoral candidate at Boston College, as well as an editor at Ledger, the first academic journal devoted to Bitcoin and other cryptocurrencies. In his spare time he writes about science, skepticism, feminism, and futurism here at This Week In Tomorrow.