Light from nothing

By | February 17, 2013

‘Virtual particles’ can have real physical effects.

A vacuum might seem like empty space, but scientists have discovered a new way to seemingly get something from that nothingness, such as light. And the finding could ultimately help scientists build incredibly powerful quantum computers or shed light on the earliest moments in the universe’s history.

Quantum physics explains that there are limits to how precisely one can know the properties of the most basic units of matter–for instance, one can never absolutely know a particle’s position and momentum at the same time. One bizarre consequence of this uncertainty is that a vacuum is never completely empty, but instead buzzes with so-called “virtual particles” that constantly wink into and out of existence.

These virtual particles often appear in pairs that near-instantaneously cancel themselves out. Still, before they vanish, they can have very real effects on their surroundings. For instance, photons–packets of light–can pop in and out of a vacuum. When two mirrors are placed facing each other in a vacuum, more virtual photons can exist around the outside of the mirrors than between them, generating a seemingly mysterious force that pushes the mirrors together.

This phenomenon, predicted in 1948 by the Dutch physicist Hendrick Casimir and known as the Casimir effect, was first seen with mirrors held still. Researchers also predicted a dynamical Casimir effect that can result when mirrors are moved, or objects otherwise undergo change. Now quantum (a) physicist … at Aalto University in Finland and his colleagues reveal that by varying the speed at which light can travel, they can make light appear from nothing.

The speed of light in a vacuum is constant, according to Einstein’s theory of relativity, but its speed passing through any given material depends on a property of that substance known as its index of refraction. By varying a material’s index of refraction, researchers can influence the speed at which both real and virtual photons travel within it. … one can think of this system as being much like a mirror, and if its thickness changes fast enough, virtual photons reflecting off it can receive enough energy from the bounce to turn into real photons. “Imagine you stay in a very dark room and suddenly the index of refraction of light [of the room] changes, … The room will start to glow.” …

The researchers detected photons that matched predictions from the dynamical Casimir effect. For instance, such photons should display the strange property of quantum entanglement–that is, by measuring the details of one, scientists could in principle know exactly what its counterpart is like, no matter where it is in the universe, a phenomenon Einstein referred to as “spooky action at a distance.”  …

Read more: nature.com

Reality is much stranger than we give it credit for.

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