PHYSICS
Michael Irving
4 hours ago
2 PICTURES
![](https://image.dost-dongnai.gov.vn/english/atomic-experiment-2dark-energy-.jpg)
UK
researchers have conducted experiments to test a dark energy hypothesis and
found no trace of the mysterious force (Credit: Juric.P/Depositphotos)
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Dark energy was "discovered" in
1998, when physicists realized that the expansion of the universe wasn't slowing
down, as they expected. Instead, it seemed to be doing the exact opposite.
Further observations over the years have backed up the theory, and now it's a
widely accepted explanation that explains a lot of weirdness in the standard
model of cosmology.
But what is dark energy, exactly?
Nobody really knows, but it appears to be a fifth fundamental force, with the
known four being gravity, electromagnetism and the strong and weak nuclear
forces. Whatever dark energy is, it seems to act almost like the opposite of
gravity, strongly pushing matter away from all other matter instead of pulling
it together.
One branch of theories suggests
that dark energy gets weaker the more matter is around it, meaning it's at its
strongest out in the vacuum of space. That could also explain why some previous
tests to detect it came up empty – they were using large weights, which would
have reduced the effect of the force.
So a team from the University of
Nottingham and Imperial College London devised new experiments to test this
theory. They set out to investigate the interactions between a large and a small
weight. In this case, the "large" weight was a metal ball the size of a marble,
while the small weight was a single atom.
The researchers placed the ball
in a vacuum chamber, then dropped atoms around it. The idea was that if there
was a fifth force acting between the two weights, and it behaved the way this
theory suggested, then the path of the atom should bend slightly as it passed
the marble.
After running these tests, the
team found no trace of any such force. That effectively rules out this
particular theory, which would also have required modifications to the theory of
gravity. Similarly, another recent study ruled out "chameleon"
particles from the Sun as carriers of the force.
But a null result isn't
confirmation that dark energy itself doesn't exist – it just means it could be
hiding elsewhere, and we've now narrowed the search.
"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," says Ed Copeland, lead author of the
study.
The new experiments could also
add to a pile of increasing evidence that the dark energy theory itself is
wrong. Other alternative explanations include "Tardis"
regions of spacetime that are bigger on the inside, a "dark
fluid" with negative mass, or that by just accounting for the changing
structure of the cosmos, the need
for dark energy as a stand-in vanishes. Some even call into question
the validity of the original discovery that the expansion of the universe is
accelerating.
With so many questions
surrounding this mysterious force, no doubt many more studies will be conducted
to try to unravel the enigma.
The research was published in the
journal Physical
Review Letters.
Source: New Atlas URL:
https://newatlas.com/dark-energy-experiment-no-result/61143/Imperial
College London