Science 3 min read

Experiment on Dark Energy Rules Out a Fifth Force

Physicists tested popular theory of dark energy on a single atom and found no evidence pointing to the alleged fundamental force -- fifth force.

Image courtesy of Pixabay

Image courtesy of Pixabay

In the Universe, there’s a hypothetical “dark sector” where our physics comes to a standstill. And “dark” here has less to do with the true hues of this sector than our understanding of it.

Astronomers know a mysterious force is there, they see its unmistakable effect on the fabric of space-time. Yet, it’s so far they can’t figure out how to directly detect it. Dark energy is the name they gave to this force that drives the expansion of the Universe at an ever-accelerating rate.

Some physicists suggested dark energy is one of nature’s fundamental forces, or the fifth force, affecting matter and reality just like gravity, electromagnetism, and strong and weak nuclear forces.

A recent experiment put to the test this fifth force theory, and the results rule it out.

Single-Atom Saps the Fifth Force Theory’s Strength

The experiment was performed at the Imperial College London labs, and scientists from the University of Nottingham analyzed the results.

The team tested the possibility that dark energy, as the fifth force, is acting on single atoms.

“The experiment tested theories of dark energy that propose the fifth force is comparatively weaker when there is more matter around – the opposite of how gravity behaves.”

Gravity increases proportionally to the amount of matter available. That makes sense. Bigger cosmic objects like stars tend to have stronger gravitational force than smaller objects like planets.

Some physicists think this fifth force may be screened for large objects like planets, would become stronger with less matter present. You’d expect the fifth force to be stronger around a single atom in the vacuum of space than, say, here in the open air surrounded by all the matter on Earth.

And that’s how this experiment was designed.

The researchers put a marble-sized sphere of metal into a vacuum chamber, allowing atoms to fall freely inside. They aimed an atom interferometer at the chamber to detect any extra forces that might show action on a single atom.

If there were a fifth force in the chamber, between the sphere and the atom, then the atom would slightly deviate from its ordinary path as it passes by the sphere.

The results showed no evidence of a fifth force or any new forces for that matter.

Co-author Professor Edmund Copeland, from the Centre for Astronomy & Particle Physics at the University of Nottingham, said:

“This experiment, connecting atomic physics and cosmology, has allowed us to rule out a wide class of models that have been proposed to explain the nature of dark energy, and will enable us to constrain many more dark energy models.”

This study doesn’t rule out dark energy but suggests that if it is something, then it is not a fundamental force of nature.

“This could rule out popular theories of dark energy that modify the theory of gravity, and leaves fewer places to search for the elusive fifth force.”

As simple as the experiment may sound, its results could be of greater significance for physics as a whole going forward.

Says Ed Hinds of the Department of Physics at Imperial

“It is very exciting to be able to discover something about the evolution of the universe using a table-top experiment in a London basement.”

Read More: What is the Fifth Force of Nature?

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Zayan Guedim

Trilingual poet, investigative journalist, and novelist. Zed loves tackling the big existential questions and all-things quantum.

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