This excellent answer to the question What is the physics of the “spinning dust” contribution to Cosmic Microwave Background measurements? includes the figure below which helps show what it was the triggered the existence-hypothesizing of cosmic spinning dust.

enter image description here

The question Why doesn't the equipartition theorem disallow spinning dust? is my way of starting to wonder if spinning dust is real, or if it really happens.

One thing that would make me more comfortable than an argument gedankenexperiment involving a modified Crookes radiometer with the gas removed would be some kind of experiment showing that simply being exposed to some very low pressure hydrogen, or photons, can make dust spin at anything close to 20 GHz!

These days optical trapping of particles in very high vacuum is readily accessible for example, so I think if someone wanted to try to make GHz-spinning-dust they could certainly have a go.

Question: Has this been tried? Has "GHz-spinning dust" ever been demonstrated in the laboratory?


This poster suggests an answer of yes and no. Essentially the poster reports a demonstration of some of the proposed mechanisms, but the rotation speeds produced are in the $kHz$ not $GHz$ range because the dust partcles are bigger, the vacuum less good and so on.

To quote the summary:

  • First laboratory measurements of rotation of the analogs of interstellar dust grains induced by radiative torques have been made
  • The measurements were made on irregularly shaped SiC particles particles of ~ 0.17 to 8.2 $\mu m$ effective radii levitated in an electrodynamic balance and illuminated with laser light at a wavelength of 5320 Å, at pressures of $10^{-3}$ to $10^{-5}$ torr.
  • The rotation rates with radiation intensities of ~ $4-30 Wcm^{-2}$ were observed in the range of 1,000-22,000 rot/sec.
  • The grain rotation rates were observed to follow the expected functional relationships, being directly proportional to the incident radiation intensities and inversely proportional to the drag represented by the ambient pressure.
  • $\begingroup$ Bingo! This is exactly the kind of thing I was looking for, thank you. $\endgroup$
    – uhoh
    Dec 18 '18 at 1:19
  • $\begingroup$ ...and I should have accepted earlier! $\endgroup$
    – uhoh
    Nov 25 '20 at 0:56

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