An experiment to test a popular theory that dark energy –the unknown force that is causing the universe to expand at an accelerating rate– is a ‘fifth’ force that acts on matter has found no evidence of its existence. “The discovery of dark energy has greatly changed how we think about the laws of nature,” said Edward Witten, one of the world’s leading theoretical physicist at the Institute for Advanced Study in Princeton, N.J. who has been compared to Newton and Einstein.
Some physicists propose dark energy is a ‘fifth’ force beyond the four already known – gravitational, electromagnetic, and the strong and weak nuclear forces. However, researchers think this fifth force may be ‘screened’ or ‘hidden’ for large objects like planets or weights on Earth, making it difficult to detect.
“Dark energy is incredibly strange, but actually it makes sense to me that it went unnoticed,” said Noble Prize winning physicist Adam Riess, who was not part of the study, in an interview with The Atlantic. “I have absolutely no clue what dark energy is. Dark energy appears strong enough to push the entire universe – yet its source is unknown, its location is unknown and its physics are highly speculative.”
Now, researchers at Imperial College London and the University of Nottingham have tested the possibility that this fifth force is acting on single atoms, and found no evidence for it in their most recent experiment. 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.
The experiment, performed at Imperial College London and analyzed by theorists at the University of Nottingham, is reported today in Physical Review Letters.
“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 Ed Copeland, with the Center for Astronomy & Particle Physics at the University of Nottingham.
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. This would mean it is strong in a vacuum like space, but is weak when there is lots of matter around. 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.
The team 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 placed in a vacuum chamber and atoms were allowed to free-fall inside the chamber.
The theory is, 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, causing a change in the path of the falling atom. However, no such force was found.
In a March 2, 2019 post, Dark Energy –“New Exotic Matter or ET Force Field?” The Galaxy described a new, controversial theory suggesting that this dark energy might be getting stronger and denser, leading to a future in which atoms are torn asunder and time ends.
“Long, long ago, when the universe was only about 100,000 years old — a buzzing, expanding mass of particles and radiation — a strange new energy field switched on,” writes Dennis Overbye for New York Times Science. “That energy suffused space with a kind of cosmic antigravity, delivering a not-so-gentle boost to the expansion of the universe.”
Then, after another 100,000 years or so, the new field simply switched off, leaving no trace other than a speeded-up universe says a team of astronomers from Johns Hopkins University led by Adam Riess, a Bloomberg Distinguished Professor and Nobel laureate who is an expert in the Hubble constant. In a bold and speculative leap into the past, the team has posited the existence of this field to explain a baffling astronomical puzzle: the universe seems to be expanding faster than it should be.
“A growing mystery about the universe, known as the ‘Hubble Tension,’ is that it appears to be expanding much faster now than predicted even with our latest understanding of its initial conditions and contents,” says Riess. Their research is the first to provide a possible explanation—that the early universe received an infusion of dark energy soon after the Big Bang giving it a boost—which better matches all observations. This theory shows how this ‘tension’ may actually be revealing a new feature of the universe. It also makes predictions which can be tested so that more measurements should tell us if it is correct.”
An ET Force Field?
One idea for the mechanism of an accelerating cosmic expansion is called quintessence, a relative of the Higgs field that permeates the cosmos. Perhaps some clever life 5 billion years ago figured out how to activate that field, speculates astrophysicist Caleb Scharf in Nautil.us. How? “Beats me,” he says, “but it’s a thought-provoking idea, and it echoes some of the thinking of cosmologist Freeman Dyson’s famous 1979 paper Time Without End,” where he looked at life’s ability in the far, far future to act on an astrophysical scale in an open universe that need not evolve into a state of permanent quiescence. Where life and communication can continue for ever.
“Perhaps hyper-advanced life isn’t just external. Perhaps it’s already all around. It is embedded in what we perceive to be physics itself, from the root behavior of particles and fields to the phenomena of complexity and emergence,” says Scharf, a research scientist at Columbia University and director of the Columbia Astrobiology Center. “What we think might be the effects of mysterious forces such as dark energy and dark matter in the Universe, could actually be the influence of alien intelligence – or maybe even aliens themselves.”
The Daily Galaxy, Jake Burba, via Imperial College London
Dark Energy Spectroscopic Instrument (DESI) “first light” image of the Whirlpool Galaxy, also known as Messier 51 is shown at the top of the page. This image was obtained the first night of observing with the DESI Commissioning Instrument on the Mayall Telescope at the Kitt Peak National Observatory in Tucson, Arizona; an r-band filter was used to capture the red light from the galaxy.