A team of physicists from the University of California, Berkeley, has developed an unprecedentedly precise instrument designed to hunt for dark energy, the elusive force accelerating the Universe’s expansion.
Their experiment – results from which were published today in the prestigious journal Nature – targets a hypothesised particle known as the chameleon, which could be the key to understanding this mysterious cosmic force.
First identified in 1998, dark energy constitutes about 70 per cent of the Universe’s total matter and energy. Despite numerous theories, its true nature remains an enigma.
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Among the leading hypotheses is the existence of a fifth force, distinct from the four known fundamental forces of nature – gravity, electromagnetism, and the strong and weak nuclear forces.
This force would be mediated by a particle dubbed the chameleon due to its ability to hide in plain sight.
The UC Berkeley experiment, led by Prof Holger Müller, utilises an advanced atom interferometer combined with an optical lattice.
If that sounds technical, it’s because it is. Essentially, this setup allows for precise gravity measurements by holding free-falling atoms in place for a duration of time.
The longer you can get the atoms to hang there, the better your odds of finding (or not finding) traces of a chameleon become.
“Atom interferometry is the art and science of using the quantum properties of a particle, that is, the fact that it’s both a particle and a wave. We split the wave up so that the particle is taking two paths at the same time and then interfere them at the end,” Müller said
“The waves can either be in phase and add up, or the waves can be out of phase and cancel each other out. The trick is that whether they are in or out of phase depends very sensitively on some quantities that you might want to measure, such as acceleration, gravity, rotation or fundamental constants.”
While previous experiments could only immobilise atoms for milliseconds at a time, the new apparatus can maintain them for much longer – seconds to tens of seconds. This marks a significant improvement that enhances the most precise measurements by a factor of five.
In one recent paper published in the journal Nature Physics, Müller and his colleagues extended the hold time to a whopping 70 seconds.
To uncover whether the chameleon particle is indeed the mastermind behind dark energy, scientists need to find holes in the results predicted by the accepted theory of gravity – something no one has managed to do since Isaac Newton established his theories 400 years ago.
In their recent tests, Müller and his team found no deviations from Newtonian gravity, suggesting that if chameleons exist, their effects are extremely subtle.
Still, the researchers remain optimistic. The improvements in their instrument’s precision mean future experiments could provide the evidence needed to confirm or refute the presence of chameleons or other hypothetical particles contributing to dark energy.
About the expert
Holger Müller successfully applied for his first patent when he was 14. Later, he did his undergraduate thesis with Jürgen Mlynek at the University of Konstanz, Germany. He graduated from Humboldt-University, Berlin, with Achim Peters as his advisor. Müller received a fellowship from the Alexander von Humboldt Foundation and joined the group of Steven Chu at Stanford as a postdoc. In July 2008, he joined the physics faculty at U.C. Berkeley where he now presides as a professor of physics. He is now the principal investigator of his research group, the Müller group.
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Dr. Thomas Hughes is a UK-based scientist and science communicator who makes complex topics accessible to readers. His articles explore breakthroughs in various scientific disciplines, from space exploration to cutting-edge research.
