Murmura: Whispering Gallery
Optics, Waves & Sound arc, page 113 of 193. Back to The Pixelated Physics Universe
Who they are
Murmura whispers into the wall, and her voice runs all the way round to the far side.
Murmura is a character of the Optics, Waves & Sound arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
Lord Rayleigh explained the whispering gallery of St Paul's Cathedral in 1910; optical whispering-gallery resonators reach Q > 10¹¹.
$$ \begin{gathered} 2\pi R \approx m\lambda \qquad (m \text{ large}) \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| $R$ | radius of the curved wall | m |
| $\lambda$ | wavelength | m |
| $m$ | number of wavelengths around the circumference | 1 |
| $Q$ | quality factor of an optical resonator | 1 |
Honest caveat: It is not an echo: the sound hugs the wall.
Sources
- Rayleigh (1910) The Problem of the Whispering Gallery, Phil. Mag. 20, 1001
- Savchenkov, Matsko, Ilchenko & Maleki (2007) Optical resonators with ten million finesse, Opt. Express 15, 6768
- Vahala (2003) Optical microcavities, Nature 424, 839
Crossovers
Murmura meets Ringward (Q Factor Resonance). Murmura's whisper clings to the curved wall and travels round it. Optical whispering-gallery resonators do the same with light and can reach very high Q, which is Ringward's measure of how long they ring.
Murmura meets Sabina (Echo Has a Clock). Sabina's echo dies at a rate set by the room's absorption: her reverberation time. Murmura keeps a whisper alive by skimming it along the wall. One room is designed to quiet sound, the other carries it.
Wear the lore
Concept keywords: Whispering Gallery, Murmura, Optics, Waves & Sound, physics lore, Pixelated Physics