A team of physicists at the University of California, Berkeley has developed the most sophisticated instrument ever designed to search for dark energy, the mysterious force that is accelerating the expansion of the universe.
The results of their experiment were published today in a prestigious journal. Nature – targets a hypothetical particle known as the chameleon, which could hold the key to unlocking this mysterious cosmic force.
First identified in 1998, dark energy makes up about 70 percent of all matter and energy in the universe, and despite many theories, its true nature remains a mystery.
One leading hypothesis is that there is a fifth force that is distinct from the four fundamental forces known in nature (gravity, electromagnetism, and the strong and weak nuclear forces).
This power is thought to be mediated by particles known as chameleons due to their ability to hide in plain sight.
In an experiment at the University of California, Berkeley, Professor Holger Muller utilizes an advanced atom interferometer combined with an optical lattice.
If that sounds technical, it is. Essentially, this setup allows for precise gravity measurements by holding free-falling atoms in place for a set period of time.
The longer we can keep the atoms there, the greater our chances of finding (or not finding) a trace of the chameleon.
“Atom interferometry is the technology and science that exploits the quantum properties of particles – their properties as both particles and waves. We split the waves so that the particles take two paths at the same time, and then we interfere with them at the end,” Muller said.
“The waves are either in phase and add, or out of phase and cancel each other out. The key is that whether they are in phase or out of phase depends very sensitively on the quantities you want to measure, such as acceleration, gravity, rotation, or fundamental constants.”
Whereas previous experiments have only been able to move atoms for a few milliseconds at a time, the new device can keep them in motion for much longer periods – from seconds to tens of seconds – a major improvement that improves the most precise measurements by a factor of five.
In a recent paper published in the journal Natural Physics Muller and his colleagues extended the hold time to a whopping 70 seconds.
To reveal whether chameleon particles are indeed the dark energy mastermind, scientists would need to find holes in the outcomes predicted by the accepted theory of gravity — something no one has managed to do since Isaac Newton formulated it 400 years ago.
Muller and his team found no deviations from Newtonian gravity in their recent tests, suggesting that if chameleons exist, their effects are quite subtle.
Still, the researchers are optimistic: The improved precision of their instruments means future experiments may provide the evidence needed to confirm or disprove the existence of chameleons and other hypothesized particles that contribute to dark energy.
About the Experts
Holger Muller At the age of 14, he successfully filed his first patent. He then wrote his undergraduate thesis under the supervision of Jürgen Mullinek at the University of Konstanz in Germany. He graduated from the Humboldt University in Berlin with Achim Peters as his supervisor. Müller received a fellowship from the Alexander von Humboldt Foundation and joined Steven Chu’s group at Stanford University as a postdoctoral researcher. In July 2008, he joined the Physics Department at the University of California, Berkeley, where he is currently a Professor of Physics and Principal Investigator. He is currently the Principal Investigator of his research group, the Müller Group.
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Source: www.sciencefocus.com
