Unlocking the Dark Universe With a Mysterious Fifth Force

By Paul M. Sutter, Universe Today January 25, 2025

Collected at: https://scitechdaily.com/unlocking-the-dark-universe-with-a-mysterious-fifth-force/

Researchers hypothesize a fifth force of nature that could explain the intricate relationship between dark matter and dark energy, suggesting a revolutionary expansion of the Standard Model of physics.

Could a new, fifth force of nature help answer some of the biggest mysteries about dark matter and dark energy? Scientists are actively exploring the possibility.

The Standard Model of physics is widely regarded as one of the greatest achievements in modern science. It describes the universe’s four known forces — gravity, electromagnetism, and the strong and weak nuclear forces — as well as a diverse array of fundamental particles and their interactions. By many measures, it stands as one of the most successful scientific theories in history.

And it’s fantastically incomplete.

The Incompleteness of the Standard Model

The Standard Model accounts for less than 5% of all the matter and energy in the universe. About 25% is attributed to dark matter, an invisible and mysterious form of matter. The remaining 70% is dark energy, a perplexing force driving the accelerated expansion of the universe. Despite its successes, the Standard Model cannot explain these enigmatic components of the cosmos.

One of the first things astronomers noticed when they first discovered dark matter and dark energy was their apparent similarity. Why in the world are the two dark components of our universe roughly the same strength? I know, 25% and 70% don’t sound very similar, but when it comes to astronomy – and especially cosmology – they’re basically the exact same number.

Maybe it’s just a coincidence that they have about the same strength, and we’re overthinking it.

Theoretical Propositions for a New Force

Or maybe it’s something else. Clever physicists have proposed connections within the “dark sector” of the universe, where dark matter and dark energy talk to each other. This would allow them to follow each other’s evolution, ensuring that they have roughly equal contributions to the energy budget of the universe for long periods of time.

To make them talk to each other, you need a force. But this force can’t be any of the known ones, otherwise dark matter and/or dark energy must also interact with normal matter, and we would have seen more directly evidence of them already.

Hypotheses and the Search for Answers

So it has to be a new force, a fifth force of nature, completely different from electromagnetism, gravity, strong nuclear, and weak nuclear. While ideas like this remain only in the realm of hypothesis, some of the ideas already have names.

One name is quintessence, the fifth essence of the universe. Another is dark photons, a particle that travels the cosmos like a photon but is, as its name suggests, dark.

To test these ideas we have to turn to the cosmos for answers. If a fifth force exists, it must be very subtle. Stronger manifestations of the fifth force have already been ruled out by observations of galaxy clusters, the expansion of the universe, and even the behaviors of neutron stars. So we have our work cut out for us – it will take a truly massive amount of data to tease out some signal that differs from expectations.

Adapted from an article originally published on Universe Today