A clever experiment to test a popular theory of dark energy has found no evidence of new forces placing strong constrictions on related theories. Dark energy is the unknown force that is causing the universe to expand at an accelerating rate.
Some physicists advocate dark energy as a ‘fifth’ force that acts on matter after the four already recognized forces of gravitational, electromagnetic, and the strong and weak nuclear forces. Though, researchers think this fifth force may be ‘screened’ or ‘hidden’ for large objects like planets or weights on Earth, making it hard to detect.
Researchers at Imperial College London and the University of Nottingham have now tested the possibility of this fifth force acting on single atoms and detected absolutely no evidence of it in their most recent experiment. This discovery could rule out prevalent theories of dark energy that alter the theory of gravity and leaves lesser places to search for the elusive fifth force.
Finding The Fifth Force
The experiment, reported in Physical Review Letters, performed at Imperial College London and analyzed by theorists at the University of Nottingham.
Professor Ed 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.”
The experiment put to test concepts of dark energy that suggest that the fifth force is comparatively weaker when there is more matter around the opposite of how gravity behaves. This would imply that it is strong in a vacuum-like space but weak in the presence of lots of matter. Consequently, experiments using two large weights would mean the force becomes too weak to measure.
Experiment With A Single Atom
The researchers, in its place, tested a larger weight with an incredibly small weight, a single atom where the force should have been observed if it exists.
The team used an atom interferometer to test whether there were any extra forces that could be the fifth force acting on an atom. They placed a marble-sized sphere of metal in a vacuum chamber and atoms were permitted to free-fall inside the chamber. The theory that was being tested states that if there exists a fifth force acting between the sphere and atom, the atom’s path will slightly deviate as it passes by the sphere, triggering a change in the path of the falling atom. But no such force was detected.
Professor Ed Hinds, from the Department of Physics at Imperial, described, “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.”