Beneath the Black Hills of North Dakota, scientists at the Sanford Underground Research Facility are using a device called a Large Underground Xenon (LUX) detector to hunt for particles of dark matter, the mysterious substance that's believed to account for most of the matter in the universe. Inside the massive device, which contains a third of a ton of liquid xenon inside a titanium vessel, an array of sensitive light detectors wait for the moment when a dark matter particle will collide with a xenon atom and emit a tiny flash of light.
In hopes of capturing the faint signal, LUX has been placed under a mile-thick layer of rock, which will help shield it from cosmic rays and other radiation that might interfere with the signal.
So far, LUX hasn't yet detected dark matter. But with a new set of calibration techniques that improve the detector's sensitivity, researchers hope to soon, finally, spot dark matter. "It is vital that we continue to push the capacity of our detector," says Brown University physics professor Rick Gaitskell in a press release.
If scientists do finally identify dark matter particles, it'll be the culmination of a search that dates back to the 1930s. That's when a Swiss astronomer named Fritz Zwicky determined the speed at which a distant cluster of galaxies revolved was an indication that they contained much more mass than observable light from them suggested.
Since then, scientists have been searching for dark matter and trying to figure out what exactly it is. In recent years researchers have relied on tools ranging from Europe's atom-smashing Large Hadron Collider to NASA's orbiting Chandra X-ray Observatory.
Assuming that researchers eventually come to grips with the nature of dark matter, another question may arise: Is there a way for humans to make use of it? Is this research just to help us understand the universe, or are there applicable technologies we could develop?
Liu's concept is based upon the not-yet-verified assumption that dark matter is made up of neutralinos, particles without any electrical charge. Neutralinos also happen to be antiparticles, which means that when they collide under the right circumstances, they annihilate each other and convert all of their mass to energy.
If that turns out to be true, a pound of dark matter could produce nearly 5 billion times the energy as the equivalent amount of dynamite. Yes, billion with a "b." That means a dark matter reactor would have plenty of oomph to propel a rocket ship through the cosmos, and a big enough core could accelerate the craft at close to the speed of light, according to Liu's paper.
Reaching the Stars
As a New Scientist article details, Liu's dark matter engine would be very different from a conventional rocket. Essentially, it would be a box with a door that would open in the direction of the rocket's movement to scoop up dark matter. When dark matter goes into the box, the door closes, and the box shrinks to compress the dark matter and increase the rate of annihilation. Once the particles are turned to energy, the door opens again, and the energy propels the craft. The cycle would be repeated throughout the space voyage.
One advantage of the dark matter engine would be that a spaceship wouldn't need to carry much fuel, because it could gather more along the way from the abundant dark matter in parts of the universe. And the faster that the rocket travels, the more rapidly it will scoop up dark matter and accelerate.
A 100-ton (90.7-metric ton) rocket ship theoretically could approach the speed of light within a few days. That, in turn, would shave the time needed to travel to Proxima Centauri, the nearest star to our solar system, from tens of thousands of years to perhaps five.
And beyond that, of course, there are the technologies and inventions that are unknown and seem impossible — until we realize they're possible.