This theory could help create the world's first light-powered, ultra-tiny tractor beam.
For as long as fictional spaceships have been roaming the skies of our collective imagination, they've been stopping every now and then to drag objects, people, or space aliens up into their monsterous underbellies using tractor beams. Over the years, various scientists have proposed different methods for making these beams a reality - using heat to manipulate air pressure, for example, or doing the same with magnetic charges - with varying degrees of success. Now a physicist has proposed a novel way to handle the problem: light.
The physicist in question is Mordechai Segev of the Technion-Israel Institute of Technology, who put forward his theory in the journal Optics Express. In his article, Segev postulates that scientists may be able to use the peculiar phenomenon of negative radiation pressure to move objects using refracted light.
Negative radiation pressure occurs when light hits a material that has a negative refraction index, which means that light refracts off of it on the same side as it hits the object rather than anywhere else. Materials that possess such an index are known as "metamaterials," and have been used in the past to create semi-effective invisibility cloaks. In cases like the cloak, the metamaterial's negative refraction index effectively re-routes the light that enters it, rendering the object beneath it semi-invisible (well, in theory, at least).
What does this phenomenon have to do with tractor beams, then? Segev's theory goes like this: When light enters a metamaterial, the material's negative refraction index sends its photons barrelling back out in one direction; however, the overall shape of the light waves will be refracted in exactly the opposite direction. According to Segev, when these two groups diverge, we should find a miniscule area of negative radiation pressure between them. If physicists were able to control this negative zone, they might be able to move it - and any particles trapped within - around.
"But wait!" I hear you cry. "All the metamaterials we have are made of metal, and would therefore just absorb the electromagnetic particles essential to this operation, rendering it null and void!" You're right, science fan, that's a problem. Luckily, Segev plans to solve it by implementing quartz and other "birefringent" (something with multiple refraction indices) non-metal materials.
The end result of all this hypothesizing will be a seriously tiny (we're talking micrometers thick) layers of these materials could be manipulated to generate even tinier negative radiation zones between them. Boom! World's first light-powered tractor beam.
As Segev notes, this technology, if it works, will probably be at its most useful in sterile environments where people need to move around tiny objects without undue disturbance. He cites lung surgery, where stable air pressure and gas content are a necessity, as a specific example.
Sadly, we'll have no way of knowing if a negative pressure zone of the kind created by divergent light has the power to hold molecules in its thrall until Segev and his lab complete their tests of his hypothesis. So while this isn't a tractor beam yet - and certainly not one suitable for space-based activities - it is a genuinely interesting step towards practical tractor beam technology. Will further investigation of this theory lead to possible applications outside of the tiny, or will it fall flat in practice?