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Figure 1 | Phonon transmission across a vacuum. Fong et al.1 show that phonons — vibrations in an atomic lattice — can be transported between objects that are separated by a vacuum gap. To understand how this process occurs, consider an object at a fixed temperature T 1 . Thermal agitation of the object’s atoms produces phonons that propagate as acoustic waves and cause the object’s surface to exhibit time-varying undulations (the amplitudes of the undulations shown are exaggerated for clarity). A second object, at a fixed temperature T 2 < T 1 , is brought close to the first object, with a vacuum gap between the objects. The undulations of the first object’s surface exert a time-varying ‘Casimir’ force (caused by quantum fluctuations) on the second object’s surface, which gives rise to phonons in the second object. Because phonons are heat carriers, heat is transferred from the first object to the second one.

Physicists have managed to observe heat transferred across a vacuum by phonons. The effect joins conduction, convection and radiation as ways for heating to occur — but only across tiny distances. The heat is transferred by phonons — the energy-carrying particles of acoustic waves. The effect takes advantage of the Casimir effect, in which the quantum fluctuations in the space between two objects that are really, really close together result in physical effects not predicted by classical physics.

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Reference: Nature paper

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