Scientists used to believe that the sound created when we crack our knuckles was caused by the collapse of the gas bubbles between our joints. Now we know that it is actually the reverse, where bubbles are actually formed between our joints. As Wired explains:
As the bones in the joint separate, negative pressure means gas (likely nitrogen) in the synovial fluid gathers together, resulting in the sudden formation of bubbles—the scientific term for that is tribonucleation. And with that comes the pop.
When you look at the video, you can see a light flash between the two bones. What makes the study interesting is that when the bubble collapses is not when the cracking sound is heard – but when it is formed. Scientists are now trying to figure out if this popping causes any long-term damage to the surrounding tissue. But in case your wondering if cracking your knuckles causes arthritis, don’t worry. Thanks to a scientist who methodically cracked only one hand’s knuckles for 60 years, it doesn’t.