One of the criticisms of MiHsC (quantised inertia) is that "it relies on Unruh radiation which has not been seen". The fact that MiHsC predicts a whole range of important anomalies is some evidence for its use of Unruh radiation, but it is not direct evidence. In this blog entry I'd like to show you why I'm fairly confident that Unruh radiation has also been directly detected, based on papers by Beversluis et al. (2002) and Smolyaninov (2008).
Unruh radiation is usually difficult to see, to put it mildly, because its wavelength is L=8c^2/a, where a is acceleration and c is the speed of light, so for a typical acceleration of 9.8 m/s^2 the wavelength is eight light years. You'd have to wait eight years for the wave to pass by and be confirmed. It would make for a nice quiet sinecure, but there is a quicker way to see them. The formula shows that to produce Unruh waves near the more familiar EM spectrum you need to increase the acceleration, hugely!
This was done unwittingly by Beverluis et al, 2002. They shone a 780 nm laser at a gold nanotip, a very sharp pin if you like, so that the 'plasmons' (quantised waves of free electrons) formed had to travel over the very sharp tip (radius of curvature, r=10^-6 m) at a very fast speed (v) and were therefore accelerated by
a = v^2/r = c^2/10^-6 = 9x10^22 m/s^2.
They noticed an anomalous photoluminescence from the nanotip with a wavelength of about 900 nm (see the Figure below, from Beversluis et al., 2002, which shows the intensity of the radiation emitted on the y-axis, as a function of wavelength, on the x-axis. See the peak at 900 nm). Beversluis et al. proposed a complex 3-stage process to explain it but also stated that each step was implausible.
Enter Smolyaninov (2008) who claimed that their suggested 3-step process for explaining this 900 nm radiation was indeed implausible, and showed how the conversion of 780 nm laser light to 900 nm photoluminescence could be due to Unruh radiation instead. It works as follows: the 780 nm laser light impacts the gold surface and creates 'plasmons' (quantised waves of free electrons) which zoom around the sharp bend at the tip (this is well known). The plasmons' acceleration generates Unruh waves of wavelength L = 8c^2/a = 8000 nm. The newly-incoming laser photons excite the gold molecules and normally they'd then drop back to the ground energy state and emit the same frequency photon (Rayleigh scattering), but the ground state is now higher because of the Unruh excitation so the molecules don't lose as much energy as they gained, and the light they emit now has a lower energy (a longer wavelength). In more typical, non-Unruh, cases this is called Raman scattering and is usually undetectable, but for rough surfaces it can be enhanced (a well-known process called Surface Enhanced Raman Scattering, discovered first by Martin Fleischman in 1973, well before he co-discovered cold fusion / LENR). So the emitted light has a lower energy and frequency as follows:
f(emitted) = f(laser) - f(Unruh)
Replacing frequencies with wavelengths, L, given f = c/L
c/L(emitted) = c/L(laser) - c/L(Unruh)
L(emitted) = 1/(1/L(laser)-1/L(Unruh)) = 864 nm.
This predicts the emission of light of wavelength 864 nm (or above, from the less curved parts of the nanotip), which agrees with the observed anomalous photoluminescence seen by Beversluis et al. of around 800 nm and above (see figure) and so this is good evidence that Unruh radiation has been indirectly seen, since other explanations have been implausible, so far.
This interests me not only because it provides more direct evidence for Unruh radiation, but also that it implies that Unruh waves, seen only in the reference frame of the accelerated object, can cause directly testable effects in the laboratory frame, and this makes me wonder about sonoluminescence (which MiHsC predicts) and LENR (which it doesn't yet, but might if high accelerations are involved).
One way to confirm that this experiment shows Unruh radiation would be to vary the curve of the nanotip and see if the emitted wavelength varies as expected (for example, a spherical nanotip, of uniform curvature, with a cylindrical stem should show a narrower Unruh-peak). Another more direct test of MiHsC (quantised inertia) itself would be to try to interfere with these shorter Unruh waves by shielding them, to see if the plasmons' inertia (trajectory) is affected.
Beversluis, M.R., A. Bouhelier, L. Novotny, 2003. Continuum generation from single gold nanostructures through near-field mediated intraband transitions. Phys. Rev.B., 68, 115433.
Smolyaninov, I.I., 2008. Photoluminescence from a gold nanotip in an accelerated reference frame. Preprint