By Robert Nemiroff

A sonic boom is heard by an observer, for example, when a supersonic airplane passes by. A lesser known phenomenon dubbed a photonic boom is seen by an observer, for example, when an always-superluminal spot from a laser pointer sweeps by.

Both booms are perceived image pair-creation events. With sound, after the boom, the airplane is heard later from two diverging locations. Lord Rayleigh realized that one sound sequence from a supersonic source would be heard backwards. Ahrens and Spors (2008) indicated confirmation of this in the lab, and Randall Munroe summarized it on what-if.xkcd.

With light, a photonic boom is seen first when the radial component toward the observer of the superluminal sweeping laser spot drops to subluminal (Nemiroff 2015). Subsequently, two laser spots are seen at diverging locations. Were the laser pointer showing a video, one video of this pair would be seen playing normally -- the other time-reversed.

The initial flash of the perceived light-spot pair-creation event of the photonic boom directly corresponds to the initial bang of the perceived sound pair-creation event of the sonic boom.


This Brief Idea was linked to near the end of an article on LiveScience:

Robert Nemiroff · 26 Apr, 2016
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Robert Nemiroff



Published: 15 Apr, 2016

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