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Physics Fever: Dark Matter Hunt

China's scientific ambitions and discoveries are changing the way we see the physical world

02·21·2015

From finding binary black holes in galaxies light years away to patiently pouring over four million bits of data over two kilometers underground to find evidence of dark matter, China’s entrance into the world of physics has taken the world by storm.

Just last year Chinese scientists measured the speed at which quantum particles interact with one another. The greatest minds in physics pondered the question for decades; the eminent Albert Einstein called the idea impossible because it would need to break the speed limit of the universe, the speed of light, dubbing it “spukhafte Fernwirkung”, or “spooky action at a distance”. Juan Yin and his team at the University of Science and Technology in Shanghai decided to measure this “spooky action” by shooting photons from a fish farm on Qinghai Lake over 15 kilometers and measuring the state for 12 hours. The results were astounding. This “spooky action” didn’t just break the speed limit of the universe, it obliterated it, occurring at least 10,000 times the speed of light, three trillion meters per second.

The study of physics is a wide field, from astrophysics and gravitation to fluid dynamics and quantum mechanics. China has only recently become a major player in the now popular world of physics, but modern developments point to China becoming the world’s premier source of scientific exploration in the field. China has the money, the brain power, and a pressing need to prove itself, and while landing on the moon and manually docking at a space station are all well and good, the heart of scientific discovery lies in the necessity to understand the physical world.

But, while one might happily wax philosophical on Juan Yin’s team’s discovery being about the art of reading a sunbeam, there are advantages beyond the academic in physics discoveries. The world runs on physics, be it airplanes or quantum computers, and the Middle Kingdom’s foray into the realm of discovery is one of boundless possibilities. And, while building a several billion dollar, 80-kilometer tube to smash protons together isn’t going to solve China’s smog problem anytime soon, doing this puts China in a unique position to change the world in ways unimaginable in the recent past.

In 1986, China published just four pieces with Physical Review Letters, a benchmark publication for achievement and discovery in the physical sciences. Ten years later, that number reached 28, and in 2006 China published 202, putting it on par with countries like Spain. Today, some of the most advantageous experiments in the various fields are done in China and are producing results that are critically changing the way we view the world around us. China shows no signs of slowing down and the investments the country makes in grand physics experiments and discoveries today will put the next generation on the path to making China the planet’s greatest science superpower.

Dark Matter Hunt

Today, we can estimate the age of the cosmos, the number of galaxies, and even the number of atoms in the universe (1078 to 1082), but among the myriad things we don’t know—not counting the things we don’t know that we don’t know—one of the most elusive is dark matter. Nearly two and a half kilometers underground in Sichuan Province, in the deepest laboratory of its type in the world, scientist are hunting for the most mysterious particles in the universe with the Particle and Astrophysical Xenon Detector. It’s called PandaX for short.

It is the first large scale experiment in China in the hunt for dark matter, and it is a promising experiment, indeed. But, it’s not the technology or the theories or even the device itself that gives the experiment such potential, but rather the choice of laboratory, Jinping Mountain. In a northern bend in the Yalong River, an 18-kilometer tunnel leads to the China Jinping Deep Underground Laboratory, built under a mountain of marble. The low-radiation in the rock above prevents cosmic rays and particles called muons from causing trouble with the search for dark matter, which, even under optimal circumstances, is unbelievably difficult to detect. There are labs attempting to detect dark matter in Korea, Japan, Canada, England, France, Germany, and the United States, but none have succeeded in producing stable, satisfactory results.

Currently, PandaX is just starting out but aims to be the most sensitive dark matter detector in the world in the next four years. The “detector” is what is termed a Time Projection Chamber, or TPC, using liquid xenon, currently running at 125 kilograms of xenon and later planning to move on to over a tonne. To little fanfare and to keep funds flowing in, the PandaX experiment released their first results late in 2014. Their results? Nothing.

The team of approximately 40 scientists—including four Chinese universities and two US universities—published their findings in Science China: Physics, Mechanics and Astronomy, having recorded four million events. Only about ten thousand of those left energy signatures having to do with dark matter, with 46 hitting the isolated, inner xenon target. Those proved to be background radiation.

Frustratingly, even though it cannot be reliably detected, dark matter, put simply, exists. It makes up a great deal of our universe and can be seen in the velocity of spiral galaxies like our own Milky Way and the disparities in known luminous mass (stars) and gravitational mass. The discovery of dark matter would change the Standard Model of physics as we know it, and, despite being one of China’s greatest discoveries in physics, it would have wide-ranging effects on how we understand things like extra dimensions and supersymmetry.

The lack of results means that China has simply joined the ranks of nations looking for dark matter, and it’s important to remember that no results are still results. Indeed, China’s PandaX project may end in abject, expensive failure, but, as China barrels into a new world of modern scientific endeavor, finding these bashful particles is only a matter of time.

 

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