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Particle Census

|< < Prev #3247 (May 18, 2026)

Title text: Remember, your answers to the physics census are confidential; we will not be issuing Pauli exclusion principle citations.

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Explanation

This comic references the Heisenberg uncertainty principle of quantum mechanics. Put simply, it states that there's a limit to how precisely we can know both the position and momentum of a particle — the more precisely we know one, the less we know the other. Megan says they're taking a census of the positions of all particles in the universe, so they'll be known precisely; therefore, all their momenta will be unknowable. And by the time we use the census results, we won't know where any of the particles are, we'll just know where they were at the instant their positions were recorded by the census.

In the United States, the Constitution mandates that a population census of people living in all the states be taken every ten years. This is primarily for the purpose of apportioning representatives to Congress, but it has come to be used for many other demographic purposes. There's no legal requirement for a decennial physics census; if physicists want to do this, it's their own decision. However, it's not really possible to measure the positions of all particles in the universe, as there are a lot of particles in the universe, and many are quite far away.^{[citation needed]} And unless the particles happen to be at absolute zero, they will be moving, potentially quite fast. So it would be a needlessly difficult census.

In the third panel, someone speaks up and is worried about what they will do with the particles in the potential “disruption”. Randomly taking someone’s particles and relocating them would be considered unpleasant,^{[citation needed]} even if you tell them where the particles are going.

The title text refers to the Pauli exclusion principle, which states that no two fermions — types of particles that include all ordinary matter — can occupy the same quantum state. As the results of the census are confidential, physics officials will not use it to determine whether to issue citations for particles that violate the exclusion principle. This confuses physical laws, which describe how the universe works and by their nature cannot be violated, with societal laws, which declare what is allowed or required by the government.

Trivia

When this comic was uploaded the normal sized image was incorrectly 2x size. It still shows up at 2x size on unixkcd.

Additionally, "indeterminate" is spelt "indeterminite" in the second panel text.

Transcript

[First Panel. Megan is standing at a lectern, presumably talking to an audience.]

Megan: Remember, Tuesday is the decennial particle census.

Megan: Physicists will be recording the location of all particles in the universe.

[Second Panel. Zooms out to show the stage Megan is on]

Megan: Of course, this will cause their momenta to become indeterminite, so please plan for some disruption.

[Third Panel. An audience member pipes up from off-panel.]

Audience member: Wait, disruption? Where will my particles go?

Megan: No one can say, but you'll know exactly where they were.

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