Dynamical Casimir photon creation by a moving massive mirror
In plain words
A mirror shaken fast enough should turn vacuum fluctuations into real photon pairs, the dynamical Casimir effect. It has been seen with electrical circuits that act like a moving mirror, but never with a real massive object.
Precise statement
A mechanical mirror or membrane forming one wall of an electromagnetic cavity, oscillating at frequency $\Omega$ with amplitude $a$; photon pairs are created at the cavity mode $\omega = \Omega/2$ at a rate set by $(a \Omega / c)^{2}$ and the cavity quality factor. Mechanical resonators reach Omega/2pi of order $1\mathrm{e}9 \text{ to } 1\mathrm{e}10\,\mathrm{s}^{-1}$ only with tiny amplitudes. An answer is detection of photon pairs from a mechanically moving body with rate and two-mode squeezing matching theory, separated from thermal and parametric backgrounds.
What would settle it
A cryogenic measurement of photon pair emission from a GHz mechanical resonator coupled to a high-Q cavity, with correlations distinguishing it from thermal emission.
Status in the literature
The effect was observed with a SQUID-modulated superconducting transmission line acting as an effective mirror (Wilson et al., Nature 2011); no massive-mirror observation is known.