I vaguely remember this maybe being asked s few years ago, but I can’t be sure. Something about gases in the blood leaking out into the joints here and there?
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Dissolved gasses in the blood do play a part, and it basically works the same way that soda becomes flat. If the pressure in one area is lower than the pressure of the dissolved gas in another (such as when you pull on a joint), the gas comes out of solution.
However, joint popping often has more to do with synovial fluid, which is the stuff that lubricates your joints.
You know when you open the cap of a carbonated beverage, bubbles appear out of nowhere? That’s because you drastically reduced the pressure in the bottle by opening it. What was a stable solution of carbon dioxide in water is suddenly not stable because the conditions changed, and the water is now super saturated with carbon dioxide.
In the joints case, its nitrogen and synovial fluid, but it’s the same thing. You’re dropping the pressure drastically by manipulating the joint *just* right, making bubbles pop out.
Another similar phenomenon is when you’re boiling water. You know the noisy period before it starts to actually boil? The bottom of the pan has passed the boiling point of water, so any water there will boil. The rest of the water is still nowhere near the boiling point, so as soon as the bubbles of water vapour leave the bottom, they’re cooled down instantly, turning them into liquid again. This almost instantly collapses the bubble, effectively causing a small violent implosion accompanied by a *crack*. Thousands of little cracks turn into a rumble on your stove, and is essentially the same as what goes on in your knuckle too.
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