I am preparing an outreach talk about CP violation. I can vaguely remember that there is a (famous?) nature paper about parity violating cows (direction of chewing rotation is not evenly distributed.) I think it could be quite entertaining to use this as a smooth introduction for parity violation (in more serious physics cases) and it would be even nicer, if I could reference this nature paper. Unfortunately, I cannot find it:/ Does anyone know this paper?

  • $\begingroup$ Frankly, the Jordan and Kronig paper (a copy is available here) does not offer any kind of evidence about the chirality of bovine chewing. From the paper itself: "The number of observations was, however, scarcely sufficient to make sure if the deviation from unity is real." $\endgroup$ – Emilio Pisanty Jul 12 '18 at 16:54
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    $\begingroup$ Related on Biology: Do cows chew in a preferential chirality? $\endgroup$ – Emilio Pisanty Jul 12 '18 at 17:14

I believe the paper you are looking for is the 1927 paper

Movements of the Lower Jaw of Cattle during Mastication. P. Jordan and R. de L. Kronig. Nature 120, 809 (1927),

This is paper also mentioned in the footnote to

The discovery and nondiscovery of parity nonconservation. A. Franklin. Stud. Hist. Philos. Sci. 10, 201 (1979)

(which is how I found it).

Overview of the Paper

Here is a brief overview of the paper (note though that the paper is less then a page long):

  • Some things in biology display a definite sense of rotation: e.g. growth of creepers or snail shells. This paper looks at the chewing motion of cows.
  • They found in the northern part of Sjaelland, Denmark, 55% of cows chew with a right-circular motion.
  • So actually there conclusion is that there is no parity violation in cows (since the number of left and right-circular chewers is approximately equal). As correctly pointed out by Emilio in the comments they don't really make any conclusions about the parity conservation due to the size of their data set.

Other Thoughts

Given that this does not demonstrate parity violation - you could use it as an example of parity conservation and then use the e.g. snail shells as parity violation.

  • $\begingroup$ If that 55-to-45 ratio of right-circular to left-circular chewing is statistically significant, then that is indeed enough to conclude that "there is parity violation" in cows. (Thus, you could e.g. radio out a set of instructions for telling right from left to an alien that, for whatever reason, had just landed in Denmark and could observe the chewing movements of a statistically significant number of cows, but couldn't dissect them or do any other type of experiment on them.) However, the paper itself steps back from claiming that their results are statistically significant. $\endgroup$ – Emilio Pisanty Jul 12 '18 at 17:03
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    $\begingroup$ ... which means that the evidence on offer thus far is insufficient to tell whether "there is parity violation" in bovine mastication. And the existence (or lack thereof) of the effect is irrelevant to whether it can be used as an illustration in a public lecture (though ideally it should be mentioned as well). Depending on what you're talking about, it has advantages that the other examples don't, such as being an example of dynamical (as opposed to structural) homochirality. $\endgroup$ – Emilio Pisanty Jul 12 '18 at 17:04

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