Quantum friction — the vacuum as a shear medium
University. · 1 min czytania
Co proponuje
Slide two perfectly clean, perfectly smooth surfaces past each other in vacuum at absolute zero, with nothing touching, and there is still friction. Momentum crosses the empty gap. That is a mechanical channel into the vacuum that nobody has built a machine around, and it is the clearest case of the vacuum behaving as a medium rather than as a bookkeeping term — because a medium is a thing that can drag.
Dla kogo jestTribologistsNear-field thermal engineersPrecision-mechanics engineers
Why the library suggests it
John Pendry showed that a moving surface has a lopsided reflection coefficient along its direction of travel, so the two surfaces trade virtual photons asymmetrically and momentum crosses the gap; for a semi-metal at atomic separation sheared at a metre per second he estimates about three thousand newtons per square metre of true contact area, or roughly three newtons per square metre once you allow for how little of two pressed surfaces actually touches (Shearing the vacuum — quantum friction, 1997). Pendry's own remark is the one that matters here: the simplest case gives exactly the friction the vacuum would produce if it behaved as a viscous fluid. The companion survey of fluctuation-induced forces is The "friction" of vacuum, and other fluctuation-induced forces (1999).
The experiment or build
The measurement has never been made cleanly because contamination and real contact swamp it. Two routes are now open that were not in 1997. First, use the near-field radiative heat-transfer geometry, where a nanometre gap carries a flux almost five orders of magnitude above the black-body limit and the same fluctuational electrodynamics applies (Near-field radiative heat transfer in many-body systems, 2021). Second, use the patterned surfaces of the geometry card above to change the predicted drag by a known factor while leaving every contaminant unchanged. The settling measurement is the shear force per unit area against sliding velocity, at fixed separation, with the force changing by the predicted factor when only the surface pattern changes. A drag that tracks geometry is a drag that came from the field.
Na jakim jest etapie
What to watch — the theory is published and the magnitude is ordinary; the measurement has not been isolated from contact and contamination, and the pattern-dependence test names exactly what would isolate it.
Podejmij tę kartę
- Pomiar, który rozstrzyga
- The settling measurement is the shear force per unit area against sliding velocity, at fixed separation, with the force changing by the predicted factor when only the surface pattern changes.
- Ile kosztuje start
- University.
- Inżynier, którego kształtuje
- A genuinely open measurement with everyday-sized numbers in it, which is rare in this subject.
Na czym się opiera
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