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Explained: What is dark energy, and have scientists finally detected it?

With advanced technologies and newer experiments, scientists have found certain clues about it and, last week, an international team of researchers made the first putative direct detection of dark energy.

While dark matter attracts and holds galaxies together, dark energy repels and causes the expansion of our universe.

Dark energy, the mysterious form of energy that makes up about 68% of the universe, has intrigued physicists and astronomers for decades. Dark energy has been noted as “the most profound mystery in all of science”. With advanced technologies and newer experiments, scientists have found certain clues about it and, last week, an international team of researchers made the first putative direct detection of dark energy.

They noticed certain unexpected results in an underground experiment and write that dark energy may be responsible for it. The XENON1T experiment is the world’s most sensitive dark matter experiment and was operated deep underground at the INFN Laboratori Nazionali del Gran Sasso in Italy.

The finding also suggests that experiments like XENON1T, which are designed to detect dark matter, could also be used to detect dark energy.

Dark energy Vs Dark matter

Everything we see – the planets, moons, massive galaxies, you, me, this website – makes up less than 5% of the universe. About 27% is dark matter and 68% is dark energy. While dark matter attracts and holds galaxies together, dark energy repels and causes the expansion of our universe.

“Despite both components being invisible, we know a lot more about dark matter, since its existence was suggested as early as the 1920s, while dark energy wasn’t discovered until 1998,” said Sunny Vagnozzi from Cambridge’s Kavli Institute for Cosmology, the first author of the paper published last week in Physical Review D in a release. “Large-scale experiments like XENON1T have been designed to directly detect dark matter, by searching for signs of dark matter ‘hitting’ ordinary matter, but dark energy is even more elusive.”

How did they make the detection?

Last year, the XENON1T experiment reported an unexpected signal. “These sorts of excesses are often flukes, but once in a while they can also lead to fundamental discoveries,” said co-author Luca Visinelli, from Frascati National Laboratories in Italy in the release.

“Basically there’s some background noise and the electrons in XENON1T will on average move a bit on their own even with no dark matter or dark energy around simply by virtue of “kicks” due to this background,”explained Dr. Vagnozzi in an email to indianexpress.com. “We saw that at energies around ~2 keV there are way more events than one expects simply due to noise and this could be due to dark energy”

“It was really surprising that this excess could in principle have been caused by dark energy rather than dark matter,” Vagnozzi said in the release. “When things click together like that, it’s really special.”

But some astronomers have their doubts too. “If it’s true, it’s a stunning discovery,” University of California, Berkeley astronomer Alexei Filippenko, who was not involved in the study, told inverse.com. “But a lot remains to be done to verify whether it’s true.”

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What if the signal was caused by some other force?

The team constructed a physical model, which used a screening mechanism known as chameleon screening, to show that dark energy particles produced in the Sun’s strong magnetic fields could explain the signal seen in XENON1T.

There are four fundamental forces in our universe, and speculative theories have proposed a fifth force – something that can’t be explained by the four forces. To hide or screen this fifth force, many models for dark energy use special mechanisms.

Dr Vagnozzi explains how the chameleon screening works: “Imagine two people carrying something, one heavy object and other one a light object. The person with the light object will most likely make it further. Similarly, here the fifth force carried by this heavy chameleon in a dense environment doesn’t make it far.”

When can we get direct detection of dark energy?

Dr. Vagnozzi says he has been thinking about new ways to search for dark energy. The team is hopeful that upcoming upgrades to the XENON1T experiment and similar experiments such as LUX-Zeplin – a next generation dark matter experiment located at the Sanford Underground Research Facility, and PandaX-xT – another project at China Jinping Underground Laboratory could help directly detect dark energy within the next decade.

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