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Hyperacute Interdynamics

|< < Prev #3178 (December 8, 2025)

Title text: Our models fall apart where the three theories overlap; we're unable to predict what happens when a nanometer-sized squirrel eats a grapefruit with the mass of the sun.

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Explanation

Miss Lenhart is teaching a class, a recurring theme on xkcd. She describes the three pillars of physics. These three are normally mentioned General relativity concerning very large objects, Quantum mechanics concerning very small objects, and Thermodynamics.

But in the comic, Miss Lenhart replaces Thermodynamics with the fictional Hyperacute Interdynamics, which specifically covers objects 10-30cm (~4" - ~12") in size and 200-700g (0.44lb - 1.54lb) in mass. A student points out that the concept of Hyperacute Interdynamics is quite limited.

Miss Lenhart responds by stating that this is made up for by the fact that it is apparently very accurate and precise, and gives examples of how it is able to perfectly describe squirrels and grapefruit, two objects which both fit the necessary size and weight specifications. She also states that there are hopes to unify this system with the other two. A joke on how physicist hope to unify relativity with quantum mechanics, so far without success.

The title text takes the joke further, giving reason to Miss Lenhart's remark about unification. She comments that, under the current system, measurements which require elements from all three pillars are impossible. The example she gives is equally absurd as the concept of Hyperacute Interdynamics itself, stating that it is unknown when a nanometer-sized squirrel (covering Quantum Mechanics and Hyperacute Interdynamics) eats a grapefruit with the mass of the sun (once again covering Hyperacute Interdynamics as well as General Relativity). This scenario would never occur in real life, so it is unknown why scientists would be willing to pursue it.

There is an inaccuracy in the comic: the Eastern Gray Squirrel, which is the most prevalent squirrel in Massachusetts (where Randall lives), measures 16-20 inches (approx. 40-50 centimeters) on average when fully grown, meaning that a fully-grown squirrel would be too big for Hyperacute Interdynamics to apply.

Transcript

[Miss Lenhart is teaching a classroom holding a finger up in front of the class. Two students can be seen sitting at desks in front of her, a Cueball like boy is on the first row and Jill, taking notes, is in the second row.]

Miss Lenhart: Modern physics rests on three main pillars:

General relativity, which describes very massive objects,

[Close up of Miss Lenhart.]

Miss Lenhart: Quantum Mechanics, which describes very small objects,

[In a frame-less panel the view zooms back out, but shows only Miss Lenhart.]

Miss Lenhart: and Hyperacute Interdynamics, which describes objects 10-30cm in size and 200-700g in mass.

[The panel zooms back in to a close up of Miss Lenhart.]

Student (off-panel): That last one seems kind of limited.

Miss Lenhart: Yeah, but over it's domain it's really precise. Absolutely nails squirrels and grapefruit.

Miss Lenhart: Someday we hope to unify it with the other two.

---

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