It has to do with tension
There are a lot of things you can do with an egg: scramble it, poach it, fry it, hard boil it, soft boil it, bake it, take it in the palm of your hand and squeeze it as hard as you can. That last option, if done right, is a surefire way to impress those who aren’t aware that the egg (usually) won’t break if it’s positioned properly. (An alternative option is to hold the egg between both your palms and squeeze inward, which probably won’t break the shell if you apply pressure in the right areas.) Why are eggshells so strong? A new research article, titled "Nature's technical ceramic: the avian eggshell' and published in Journal of the Royal Society Interface, gets at the heart of this seemingly unusual feature of the common egg.
Researchers tested the strength of a variety of different eggs, including ostrich, quail and chicken eggs—which are made of calcium carbonate—by compressing them between steel plates cushioned with rubber. When the eggs broke, they were able to weigh the egg’s “compressive strength.” For chicken eggs, that was 100 pounds, while for ostriches it was more than 1,000 pounds.
“We answered the paradox that was posed to me fifty years ago, and that makes me very happy,” Marc A. Meyers, a scientist at the University of California, San Diego, and an author of the study, told the Royal Society’s blog, adding that he would like to test penguin, eagle and dinosaur eggs in the future. “This paper revealed, for the first time, the mechanism by which the eggs break when subjected to axial compression. It is not the compression by my hands that breaks the egg, but the tension generated radially.”
While the results are certainly interesting, it’s a wonder why nobody thought to do this before. Now that you know all about the compressive strength of an eggshell—and having seen the video embedded in this post—you’re probably going to want to squeeze your own egg to see if it’s possible. And by all means, I say, give it a go. But before you do, let me just warn you that I have tried squeezing a chicken egg in the palm of my hand on two occasions. The first, I squeezed with all my might and couldn’t so much as dent the thing. The second time, testing my luck, I must have held the egg improperly, because it splattered all over me and my kitchen. It took days to eradicate all the little hidden bits of yolk that had crusted into cupboard crevices. After that incident, I haven’t squeezed an egg again.