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The quest to prove out the theory of dark energy remains elusive as researchers found no evidence that the so-called fifth force acts on an unknown matter.
Researchers at Imperial College London and the University of Nottingham set out to test the theory that this fifth force, which some scientists think is causing the universe to expand at a quick pace, acts on matter beyond gravity, electromagnetics and the strong and weak nuclear forces. But the researchers found no evidence that the fifth force is being hidden by planets making it hard to spot.
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Fifth force doesn't cause the atom to deviate in the experiment
In an experiment published in Physical Review Letters, scientists led by Professor Ed Copeland, from the Centre for Astronomy & Particle Physics at the University of Nottingham, tested the theories of dark energy that contend the fifth force is weaker if more matter is around. That is the opposite of gravity.
The scientists tested the theory by paring a larger weight with a small weight, placing it in a vacuum chamber and then using an atom interferometer to ascertain whether there were any extra forces that may be the fifth force. The researchers placed a small sphere of metal in the vacuum chamber. The atom was allowed to fall inside the chamber and if the theory was true the atom would change slightly when it passed the sphere, changing the path of the free-falling atom. But the scientists weren't able to find the force.
"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," said Copeland in a press release announcing the results of the experiment. "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."
Scientists agree universe is expanding, but they don't know the cause
The universe is expanding at a pace that is quickening but scientists haven't been able to find the answer as to what is causing it. They do seem to agree its a form of energy that acts opposite of gravity. The researchers' experiment doesn't mean the fifth force doesn't exist. More research is needed to ascertain what is behind the so-called fifth force.