A Fifth Fundamental Force Could Really Exist, But We Haven’t Found It Yet

The universe is governed by four fundamental forces: gravity, electromagnetism, and the strong and weak nuclear forces. These forces drive the motion and behavior of everything we see around us. At least that’s what we think. But over the past several years there’s been increasing evidence of a fifth fundamental force. New research hasn’t discovered this fifth force, but it does show that we still don’t fully understand these cosmic forces.

The fundamental forces are a part of the standard model of particle physics. This model describes all the various quantum particles we observe, such as electrons, protons, antimatter, and such. Quarks, neutrinos and the Higgs boson are all part of the model.

The term “force” in the model is a bit of a misnomer. In the standard model, each force is the result of a type of carrier boson. Photons are the carrier boson for electromagnetism. Gluons are the carrier bosons for the strong, and bosons known as W and Z are for the weak. Gravity isn’t technically part of the standard model, but it’s assumed that quantum gravity has a boson known as the graviton. We still don’t fully understand quantum gravity, but one idea is that gravity can be united with the standard model to produce a grand unified theory (GUT).

Every particle we’ve ever discovered is a part of the standard model. The behavior of these particles matches the model extremely accurately. We have looked for particles beyond the standard model, but so far we have never found any. The standard model is a triumph of scientific understanding. It is the pinnacle of quantum physics.

But we’ve started to learn it has some serious problems.

To begin with, we now know the standard model can’t combine with gravity in the way that we thought. In the standard model, the fundamental forces “unify” at higher energy levels. Electromagnetism and the weak combine into the electroweak, and the electroweak unifies with the strong to become the electronuclear force. At extremely high energies the electronuclear and gravitational forces should unify. Experiments in particle physics have shown that the unification energies don’t match up.

More problematic is the issue of dark matter. Dark matter was first proposed to explain why stars and gas on the outer edge of a galaxy move faster than predicted by gravity. Either our theory of gravity is somehow wrong, or there must be some invisible (dark) mass in galaxies. Over the past fifty years, the evidence for dark matter has gotten really strong. We’ve observed how dark matter clusters galaxies together, how it is distributed within particular galaxies, and how it behaves. We know it doesn’t interact strongly with regular matter or itself, and it makes up the majority of mass in most galaxies.

But there is no particle in the standard model that could make up dark matter. It’s possible that dark matter could be made of something such as small black holes, but astronomical data doesn’t really support that idea. Dark matter is most likely made of some yet undiscovered particle, one the standard model doesn’t predict.

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