Vacuum has friction after all

Well as far as we can see this really does depend on your definition of a vacuum. Quantum mechanics seem to be able to change our understanding and perhaps this does allow us to see things from a different perspective – Deskarati

A ball spinning in a vacuum should never slow down, since no outside forces are acting on it. At least that’s what Newton would have said. But what if the vacuum itself creates a type of friction that puts the brakes on spinning objects? The effect, which might soon be detectable, could act on interstellar dust grains.

In quantum mechanics, the uncertainty principle says we can never be sure that an apparent vacuum is truly empty. Instead, space is fizzing with photons that are constantly popping into and out of existence before they can be measured directly. Even though they appear only fleetingly, these “virtual” photons exert the same electromagnetic forces on the objects they encounter as normal photons do.

Now, Alejandro Manjavacas and F. Javier García de Abajo of the Institute of Optics at the Spanish National Research Council in Madrid say these forces should slow down spinning objects. Just as a head-on collision packs a bigger punch than a tap between two cars one behind the other, a virtual photon hitting an object in the direction opposite to its spin collides with greater force than if it hits in the same direction.

So over time, a spinning object will gradually slow down, even if equal numbers of virtual photons bombard it from all sides. The rotational energy it loses is then emitted as real, detectable photons (Physical Review A, DOI: 10.1103/PhysRevA.82.063827).

The strength of the effect depends on the object’s make-up and size. Objects whose electronic properties prevent them from easily absorbing electromagnetic waves, such as gold, may decelerate little or not at all. But small, low-density particles, which have less rotational momentum, slow down dramatically.

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2 Responses to Vacuum has friction after all

  1. Pingback: Vacuum energy « Eikonal Blog

  2. alfy says:

    I am just a simple country boy, but isn’t there a confusion here between a vacuum and interstellar space? We can create very high vacuua here on earth, but a spinning ball would eventually slow down and stop due to the friction against any supporting surface. The earth’s gravity is still in operation. Out in space the gravitational effects would be very small, but very possibly not totally negligable.

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