Dark energy is the name given to an almost-entirely unknown force causing the universe to expand at an ever-accelerating rate. Some describe dark energy as a “fifth” force acting on matter. The is beyond the four already known: gravitational, electromagnetic, and the strong and weak nuclear forces.
This fifth force may be “screened” or “hidden” for large objects like planets or objects on Earth, making it difficult to detect.
The theory suggest dark energy may work in the opposite way of gravitational forces, meaning it became stronger when operating in the vast vacuum of space away from other objects.
Now, researchers tested the possibility dark energy is acting at the atomic level – and found no trace of it.
This result could rule-out popular dark energy theories that modify the theory of gravity, leaving fewer places to search for the fifth force.
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Professor Ed Copeland, of 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.”
The experiment, performed at Imperial College London, tested a dark energy theory proposing the fifth force is comparatively weaker when there is more matter – the opposite of how gravity behaves.
Therefore, experiments using two large weights would mean the force becomes too weak to measure.
The researchers instead tested a larger weight with an incredibly small weight – a single atom – where the force should have been observed if it exists.
Scientists used an atom interferometer to test whether there were any extra forces that could be the fifth force acting on an atom.
A marble-sized sphere of metal was inserted into a vacuum chamber and atoms were allowed to free-fall inside the chamber.
The researchers theorised if there is a fifth force acting between the sphere and atom, the atom’s path will deviate slightly as it passes by the sphere.
This would cause a change in the path of the falling atom. However, no such force was found.
Professor Ed Hinds, of Imperial College London, said: “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.”