system
Given the following post, respond as if you're commenting on Reddit:
human
When were sonic booms first discovered?

Were they discovered as the technology allowed aircrafts to travel faster than the speed of sound, thus creating the phenomena? Or were they theorized before technological capabilities allowed them fly at such speeds?
gpt
The "sonic boom" is an example of a shock wave, an example of something close to a spatial discontinuity in nature, where the properties of the fluid (temperature, pressure, entropy, etc.) change across a very small region, with thickness on the order of only 100 nm (this is only the size of a few hundred atoms, or only about 2 times as far as a typical N2 or O2 molecule will travel before hitting another molecule in air at STP).

The phenomenon of a shock wave was certainly known long before humans developed heavier-than-air flight.   The equations describing the relationship between the properties on either side of a shock wave, the Rankine–Hugoniot relations, were published in the third quarter of the 19th century. Schlieren photography, often used to photograph shock waves (though not exclusively), was invented by August Toepler in 1864.  The research of shock waves was triggered by the development of high explosives, which generate shock waves, in the mid 1800s.  The first, nitroglycerin, was invented in 1847, but of course as nitroglycerin is difficult to work with, the use of high explosives became much more widespread with the invention of dynamite ca. 1867.