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Math Cracks a Knuckle¹-Cracking Mystery

Knuckles² cracking. You may not mind the sound. You may despise it. Or you could study it.

指节开裂。你可能没有注意到它的声音。 你可能会鄙视它。 再或者你可以研究它。

Couple years back, Vinny Suja was taking a biomechanics class at the French Polytechnic³ School, outside Paris. And he was on the hunt for the perfect class project.

几年前，Vinny Suja在巴黎郊外的法国理工学院攻读生物力学课程。他正在寻找完美的课程项目来进行科研。

"Even though they suggested many projects, I couldn't find one which was both practical and that I could complete within the framework of this class. So in frustration⁴, I was cracking my knuckles one day and that's when I realized—'Huh, that's interesting.'"

“尽管他们提出了许多项目，但我找不到一个既实用又能在本课程框架内完成的项目，所以在挫折中，有一天我开始指责我自己，当时我意识到 - '呃， 那很有意思。'”

And so a project was born: the physics of knuckle cracking. It's actually a subject of intense scientific investigation⁵. Back in 1971, scientists figured they knew how it worked: the cracking sound was caused by bubbles popping within the fluid surrounding the knuckles.

所以一个项目终于诞生了：指节开裂的物理学。它实际上是一项深入科学调查的课题。早在1971年，科学家们就发现他们知道它是如何工作的原理：裂纹的声音是由指关节周围流体内的气泡爆裂引起的。

Or so they thought—because in 2015 shots were fired, in the form of MRI visualization⁶ of the knuckles post-cracking.

或者他们认为 - 因为在2015年拍摄的照片，以关节后裂纹的MRI可视化形式而不被采用。

In fact, the bubbles were still there. The whole process happens too fast for imaging technology to visualize⁷ in real time—you’d need to shoot at 1,200 frames per second, 10 times faster than the best x-ray and MRI machines on the market. "And that's when we realized that a model could help people better understand the origin of this sound."

事实上，泡沫仍然存在。 整个过程发生得太快，影像技术无法实时显示 - 您需要以每秒1200帧的速度进行拍摄，比市场上最好的X光机和MRI机器快10倍。 “那就是，当我们注意到一个模型，可以帮助人们更好地理解这种声音的起源。”

So, using mathematical models, Suja and his colleague Abdul Barakat found that just a partial collapse⁸ of the bubbles could cause cracking sounds of the same degree, which might explain why the 2015 researchers still saw bubbles after the crack. The details are in the journal Scientific Reports

因此，Suja和他的同事Abdul Barakat使用数学模型发现，气泡部分塌陷，可能会导致同样程度的开裂声音，这也许可以解释为什么2015年的研究人员仍然在裂纹后看到气泡。详情见《科学报告》杂志。

Further modeling of bubble behavior, both pre- and post-pop, will be needed, they say, before they’re confident that they've truly cracked the case.

他们认为，在他们确信自己，确实已经研究清楚项目之前，需要对泡沫行为进行进一步的模拟实验，包括关节声音前后泡沫行为研究实验。