system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do we know that 194 decibels is the loudest sound possible?
gpt
As we all know, sound is a series of pressure wave travelling in air: sound waves are caused by oscillations of pressure in the air.  The loudness of a sound possible on earth is limited by the size of this oscillation of air pressure.  This presents a natural limit to how loud a (sustained) sound can get - the pressure of the air cannot drop below a vacuum.  So the loudest (sustained) sound possible is therefore a pressure wave oscillating between vacuum and +2 atmospheres.  And this is equal to 194 decibels.  No sound on earth (at sea level) can exceed 194 decibels because of this.