Physicists Probe the Deep Earth for a Fifth Fundamental Force
In general, people tend to use the phrase “force of nature” loosely, as in “she’s a real force of nature.” But physicists are pickier—they reserve the phrase for just four separate, universal forces they call the “fundamental forces”: gravity, electro-magnetism, and the strong and weak nuclear forces, which hold the nucleus together and are involved with radioactive decay, respectively.
That doesn’t mean physicists rule out the possibility that other forces exist. Since the models they have for explaining everything are incomplete, there’s a fairly good chance that there’s something else out there, pulling matter apart or pushing it together in a different way than all the forces identified so far.
A team of physicists at the University of Massachusetts, Amherst is looking for one potential fifth force—one that might arise from the spin of electrons interacting with the spins of other subatomic particles. We experience the short-range effects of electron spin every time we snap two magnets together—a result of the fact that iron contains electrons that line up with Earth’s magnetic field—but scientists think that particles’ spin may cause them to interact over very long distances, too.
The problem is, even if this long-range force, called “spin-spin force,” does exist, it’s incredibly weak, and therefore extremely difficult to detect. Larry Hunter, chief scientist on the Amherst team, calculates that the long-range spin-spin force is about a million times weaker than the gravitational attraction between a neutron and an electron. Since gravity is the most obvious force in our lives, it seems like a strong one, but on the scale of individual sub-atomic particles, it’s almost completely insignificant (the electrostatic force between two electrons is a million trillion trillion trillion times stronger).