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You can try it with your own uncooked spaghetti if you want; it almost always breaks into three when you snap it. I am asking for a good physical theory on why this is along with evidence to back it up. Or, a reference to a good study previously done on this would also be satisfactory. The math behind everything would be a great bonus if it exists.

My hypothesis is that a strand of dry spaghetti has two main pressure areas being put on it due to how brittle and how high the length to thickness ratio is, and that they snap at almost the same time due to the manufacturing process of the strand causing it to have a very consistent breaking point. Also that vibrations from a first break could influence the causing of another. I'm not sure how this could be tested, though.

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    $\begingroup$ Slow-motion video for disbelievers: youtube.com/watch?v=8GutricnMNc According to the intro text there, Feynman himself pondered this (awesome) question. $\endgroup$
    – user10851
    Commented Jul 20, 2013 at 5:58
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    $\begingroup$ I removed your request for discussion-provoking comments because questions here are meant to be answered, not spark discussions. (Physics Chat is the place for that, if you want it.) On another note, I have heard that someone has done a study to answer exactly this question, though I don't know the reference. $\endgroup$
    – David Z
    Commented Jul 20, 2013 at 5:58

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The breaking of dry spaghetti was discussed in a 2005 Phys. Rev. Lett. by French physicists Audoly and Neukirch. Bottom line is that elastic (flexural) waves propagating along the spaghetti cause local increases in curvature leading to multiple breaking points: abstract to article. In essence, your assumption "that vibrations from a first break could influence the causing of another" is correct.

This work earned both authors the 2006 Ig Nobel prize for physics.

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    $\begingroup$ What? Breaking of spaghetti in Physics Review LetterS? . $\endgroup$
    – Abhimanyu Pallavi Sudhir
    Commented Jul 20, 2013 at 6:22
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    $\begingroup$ @Dim10 - as you can see from the link to the Ig Nobel prize, APS was in hindsight probably a bit embarrassed: "While the subject may at first seem a bit frivolous for the pages of a prestigious journal such as Physical Review Letters ..." $\endgroup$
    – Johannes
    Commented Jul 20, 2013 at 6:26
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    $\begingroup$ @Mr.Fate: "Ig Nobel", not "Nobel". :-) $\endgroup$
    – ruakh
    Commented Jul 20, 2013 at 23:42
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    $\begingroup$ @ruakh - better than some other (non-physics) Nobel prizes out there. $\endgroup$
    – Deer Hunter
    Commented Jul 21, 2013 at 6:24
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    $\begingroup$ @DeerHunter: I'm just stating the fact, not passing judgment. :-) $\endgroup$
    – ruakh
    Commented Jul 21, 2013 at 6:30
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This video by Get Smarter Everyday is a quite informative one. He shoots the failure at a staggering 250000(quarter million) fps.

And your assumption is right about the first fracture triggering the rest.

PS:At some instances the spaghetti doesn't break into 3 pieces, but 4 or more!

https://www.youtube.com/watch?v=ADD7QlQoFFI

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    $\begingroup$ Could you recap the conclusion of the video a bit more, since currently this is not a complete answer and more of a comment. $\endgroup$
    – fibonatic
    Commented Dec 27, 2014 at 23:41

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