explain xkcd:Museum

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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 is incomplete: This page was created at an INDETERMINITE TIME. Don't remove this notice too soon. If you can fix this issue, edit the page!

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. 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 them, 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. Furthermore, some of those particles will be in the equipment used to measure, and the people doing the measuring, which will further complicate matters.

In the third panel, someone speaks up and is worried about what will happen to particles during 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.

If all particles' locations were determined (as exactly as possible) it would have to be done using very high energy particles (which would, themselves, have to have their locations determined), leaving all the measured particles moving very fast (less than the speed of light, of course, but close to it), destroying everything (and everyone). So the concern voiced is very fair, but unnecessary, as it would not be possible to perform the task that Megan claims will happen.

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.

Transcript

[Megan is standing behind a lectern, addressing an unseen audience.]

Megan: Remember, Tuesday is the decennial particle census.

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

[Zoom out to show Megan is on a podium behind the lectern. She holds one hand, palm up, out towards the still unseen audience]

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

[The same scene with Megan's hands held down. A voice comes from off-panel at the left through a star burst at the edge of the panel.]

Audience member [off-panel]: Wait, disruption? Where will my particles go?

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

Trivia

• When this comic was uploaded the normal sized image was incorrectly 2x size. It kept showing up at 2x size on unixkcd for awhile.
• "Indeterminate" is spelt "indeterminite" in the second panel text.

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Discussion

Maybe it's more of statistics than exhibitions. --While False (speak|museum) 21:17, 3 October 2022 (UTC)

pixels-assembly-3.png

how is it 0 bytes?? i see that it is shown as 0 bytes on the wiki, but the file itself, when downloaded is 5kb! how???108.162.221.209 16:41, 4 October 2022 (UTC)Bumpf

If the question is how it can be written like that here, the answer is that I used the numbers of the wiki. —While False (speak|museum) 19:18, 4 October 2022 (UTC)

Sorry, should have made it more clear. Do you know why it is shown as 0 bytes on the file page? 172.70.134.103 12:37, 7 October 2022 (UTC)Bumpf

There's always the possibility that this is actually the Null image under the .png file format. Every other .png is defined by the delta required to display the desired graphic when starting from the baseline of this 'ur'-image, but if you ever wanted to display that graphic the undocumented format specifications allow you to omit all unnecessary bytes (including the magic header bytes) and it will happily produce its hardcoded "it's a PNG!" preprocessing template, which happens to be this image. Obviously, the PNG spec (and, ultimately, the original ancestor of the detailed source code tree for every subsequent implementation) was written before Randall ever got anywhere near to drawing this image so the chances are slim that he just happened to luck upon the exact image that happens to have a 100% compression rate because it just happened to consist of something Randall wanted to draw, and in the manner of Randall's artistry. But it's a non-zero likelihood that an arbitrary artist might draw exactly the same image as a purely arbitrary "index null" page's collection of pixels and so... This might not be the Best Of All Worlds, but there has to be some highly fortunate occurance to balance out all the unfortunate ones, statistically, and this is ours!

(Or maybe there's a minor bug/data-error in the way the wiki database serves the front-end webserver, but I can't ask you to believe something as trivially random as that!)) 172.70.90.245 15:03, 7 October 2022 (UTC)
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