Physicists Discover an Unexpected Force Acting on Nanoparticles in a Vacuum

Nanoparticles can be pushed by pure nothingness.

Researchers have discovered a new and unexpected force that acts on nanoparticles in a vacuum, allowing them to be pushed around by pure 'nothingness'.

Of course, quantum physics is beginning to make it clear that 'nothingness', as we like to think of it, doesn't actually exist - even vacuums are filled with tiny electromagnetic fluctuations. This new research is further proof that we're only beginning to understand the strange forces that are at work at the smallest level of the material world, by showing how nothingness can drive lateral motion.

So how can a vacuum carry force? One of the first things we learn in classical physics is that in a perfect vacuum - a place entirely devoid of matter - friction can't exist, because empty space can't exert a force on objects travelling through it.

But, in recent years, quantum physicists have shown that vacuums are actually filled by tiny electromagnetic fluctuations that can interfere with the activity of photons - particles of light - and produce a measurable force on objects.

This is called the Casimir effect, and it was first predicted by physicists back in 1948. Now, the new study has shown that this effect is even more powerful than they imagined.

Why does that matter? This Casimir effect might only be measurable on the quantum scale, but as we start engineering smaller and smaller technology, it's becoming clear that these quantum effects can greatly influence the overall products.

"These studies are important because we are developing nanotechnologies where we're getting into distances and sizes that are so small that these types of forces can dominate everything else," said lead researcher Alejandro Manjavacas from the University of New Mexico in the US.

"We know these Casimir forces exist, so, what we're trying to do is figure out the overall impact they have [on] very small particles."

To figure out how else Casimir forces could impact nanoparticles, the team looked at what happened with nanoparticles rotating near a flat surface in a vacuum.

What they found was that the Casimir effect could actually push those nanoparticles laterally - even if they weren't touching the surface.

That's a little strange, but imagine it like this - you have a tiny sphere rotating over a surface that's constantly being bombarded with photons. While the photons slow down the rotation of the sphere, they also cause the sphere to move in a lateral direction.

In the classical physics world, friction would be needed between the sphere and the surface to achieve this lateral motion, but the quantum world doesn't follow the same results, and so it can be pushed across a surface even when it's not touching it.

"The nanoparticle experiences a lateral force as if it were in contact with the surface, even though is actually separated from it," said Manjavacas.

"It's a strange reaction but one that may prove to have significant impact for engineers."

All of this might sound a little obscure, but it could play an important role in figuring out how to develop smaller and smaller technology, as well as devices such as quantum computers.

Intriguingly, the researchers show that they could control the direction of the force by changing the distance between the particle and the surface, which could one day come in handy for engineers and researchers who are constantly looking for better ways to manipulate matter on the nano-scale.

The findings now need to be replicated and verified by other teams. But the fact that we now have evidence of an intriguing new force that could be used to direct nanoparticles within 'nothingness' is pretty exciting - and suggests we're one step closer to understanding the weird forces at work in the quantum world.

The research has been published in Physical Review Letters.