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This number proves that nothing in the world is solid

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One branch of science, rheology, has invented a dimensionless number. It's called the Deborah Number, and it is meant to quantify the motto of the science: "Everything flows." Put another way, everything in the world has liquid properties. Even mountains.

Rheology was created in 1928, the collaboration of an engineer, a chemist, and a professor of classical languages. It is the study of how matter flows, and meant to straddle the divide between chemistry and physics. Rheology was chosen by the linguist in order to keep from alienating either scientific discipline.


Practically speaking, rheology studies the behavior of fluids of different viscosities, as well as the non-Newtonian fluids — like ketchup and snake venom — that flow freely only when put under certain mechanical stresses. But rheology's aim is far more ambitious than that. To define the scope of the science, its creators went down a path that doesn't always lead to the best results, and checked out the Bible.


In Judges, the prophet Deborah says, "The mountains flowed before the Lord." The scientists figured that the mountains flowed because even solid material, when put under stress, would change shape and "flow." The problem is, it flows only before the Lord because the Lord has time on his hands.

Allow enough time and solids can flow like liquids, and so we get the Deborah Number. It's a dimensionless number defined by the time of the "relaxation" of the substance divided by the time of observation. The higher the Deborah Number, the more solid the material, and the more time the Lord has to put in to watching it flow. Some Deborah Numbers should be pretty high, but everything has one.


[Via The Deborah Number]