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| Particle Census |
 Title text: Remember, your answers to the physics census are confidential; we will not be issuing Pauli exclusion principle citations. |
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 that 'physicists' are 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 law of physics requiring a decennial physics census; if physicists want to do this, it's their own decision.
There are estimated to be approximately 1080 protons, neutrons, neutrinos and electrons in the observable universe, which would make even the task of simply enumerating them difficult. If photons are to be included in the census, that increases the number of particles to about 1089... with a further problem that detecting them would involve processes that generate more photons than are being counted. If dark matter is to be included, we don't even know what it is, let alone have a method of detecting and counting its particles (if any). The universe as a whole is generally assumed to be infinite,[actual citation needed] so covering all the particles in that would be an infinite task. If any meaningful and usable information about each particle is to be recorded, storing that information would require many particles for each particle in the universe, which would be a logical contradiction unless all of the extra particles were coming from some other space (such as an alternate universe).
Many particles, even within the observable universe, are at vast distances from Earth, where they will be difficult to detect. Some particles, particularly neutrinos, are extremely difficult to detect at all, because of their limited interaction with other forms of matter. Simultaneity is impossible, because of relativity, so it would be meaningless to try to catalog them at a specific time. 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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