Chinese scientists' success crosses threshold that has opened way for grabbing tech.

Despite their influence on science fiction and even the occasional conspiracy theory, tractor beams, in reality, have not yet lived up to fantastical expectations. While it seems we are still far from capturing a spaceship that can do the Kessel Run in twelve parsecs, Earthlings have managed to use this light vacuum device to move about nano- and atomic-sized things – until now.

Perhaps disregarded through its use in cow-napping tales or the eye-rolling likelihood of a hero being captured in an invisible forcefield, tractor beams do, in fact, exist and are often employed in devices called optical tweezers.

This interesting technology is used to move microscopic objects like atoms and nanoparticles, which is primarily used in biology, nanotechnology, and medicine.

While these tractor beams work on microscopic objects, they are not even remotely powerful enough to pull larger macroscopic objects. Now, a team of Chinese researchers has taken the tractor beam to a whole new level.

"In previous studies, the light-pulling force was too small to pull a macroscopical object," said Lei Wang, lead author of the study from Qingdao University of Science and Technology. "With our new approach, the light pulling force has a much larger amplitude. In fact, it is more than three orders of magnitudes larger than the light pressure used to drive a solar sail, which uses the momentum of photons to exert a small pushing force."

While only able to function under very specific laboratory conditions, hence a demonstration and not a practical development, this opens the way for new avenues of research.

Earthbound tractor beam

With the physics of Earth, everyone and everything feels the same force exerting its pressure, more specifically, gravity. Due to the laws of nature, among many other physics factors, the ability to push and pull with light is an almost outlandish thing to even consider.

So how did these researchers accomplish this?

First of all, it works on carefully engineered test materials such as the macroscopic graphene silicon dioxide composite objects that the team built for the experiment. And secondly, it works in a rarefied gaseous environment, which has a much lower pressure than Earth's atmosphere.

Basically, lighter than air and lighter than gravity is the answer.

While this ultimately limits its effectiveness on the planet, not every world has as much atmospheric pressure as the Pale Blue Dot.

"Our technique provides a non-contact and long-distance pulling approach, which may be useful for various scientific experiments," said Wang. "The rarefied gas environment we used to demonstrate the technique is similar to what is found on Mars. Therefore, it might have the potential for one day manipulating vehicles or aircraft on Mars."

High-tech straw

Here on Earth, vacuums are kind of a misnomer. While called as such, a vacuum cleaner does not actually create a vacuum. This can apply to everything that creates a suction force, much like straws (you aren't actually sucking air through the straw, you are displacing pressure, meaning the liquid is being pushed into your mouth).

So how would you go about creating a pushing or pulling force without contact, using tiny subatomic particles of light, on an object that, by comparison, weighs a planet's worth of force?

The device actually works on the principle of gas heating.

A laser heats the composite objects, leaving one side hotter than the other. As gas molecules on the opposite side receive more energy, it then pulls the objects. In combination with the lower pressure in the rarefied gas environment, the object can then move.

In another example, the researchers built a torsional – or turning – pendulum device made from their graphene-SiO2 composite structure to demonstrate the laser-pulling phenomenon. Through this demonstration, it was made visible to the naked eye.

"We found that the pulling force was more than three orders of magnitudes larger than the light pressure," added Wang. "In addition, the laser pulling is repeatable, and the force can be tuned by changing the laser power."

Not alone in its research; others have made attempts over the years with mixed results. NASA was interested in pursuing the idea of using tractor beams to gather samples with the Curiosity rover, which has been exploring Mars for a decade.

One of Curiosity's instruments is called the ChemCam; simply put, it is a laser that vaporizes rock or regolith and, through the use of a micro imager, measures its constituents spectroscopically. But NASA wondered if a tractor beam could draw tiny particles from the vaporized sample into the rover for a more complete study.

While the research was eventually set aside, this is not a new idea to the scientific community, with a NASA presentation as late as 2010 positing the use of tractor beams to collect particles from comet trails, ice plumes on Enceladus, and even clouds in Earth's atmosphere or extraterrestrial atmospheres.

Nevertheless, the recent work carried out by the Chinese researchers produced interesting results and marked a first for possible practical tractor beams, albeit decades or even centuries away.

"Our work demonstrates that flexible light manipulation of a macroscopical object is feasible when the interactions between the light, object and medium are carefully controlled," said Wang. "It also shows the complexity of laser-matter interactions and that many phenomena are far from being understood on both macro and micro scales."

The critical part is that this study moves tractor beams from the microscopic to the macroscopic, a significant threshold that is difficult to cross.

"This work expands the scope of optical pulling from microscale to macroscale, which has great potential in macroscale optical manipulations," the authors write in their conclusion.

While spacecraft may use tractor beams one day, it's unlikely they'll look anything like they do in science fiction. So, until then, we can continue to enjoy them in our favorite movies, shows, and stories, and while they are often seen as a tool for conflict, in reality, they could turn out to be a most valuable scientific tool instead.