3247: Particle Census

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.

|< < Prev Random Explanation

Explanation

This is one of 45 incomplete explanations: 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 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 (human or physical) 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. Proton and neutron 'particles' are in turn composed of three quarks (numbers of which which also form other so-called-particles/hadrons), which may easily multiply the the number of separately surveyable particles. 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 surveyed. If dark matter is to be included, we don't even know what it is, let alone have a method of detecting and recording its particles (if any). We don't know the size of the universe as a whole, and many physicists theorise it is infinite, in which case, 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 could tell them where the particles are going, which you can't in this instance.

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. Given that, the concern voiced is very fair, but unnecessary, as it would not be possible to perform the task that Megan claims will happen.

The apparent need to conduct a thorough particle census, and the (perhaps legitimate) worry about the disruption that is caused bears some resemblence to the impact of an audit (either regularly scheduled or possibly imposed to answer some questions about the target of the audit). While there may be legitimate business/regulatory need to uncover the exact nature of the audit's focus, those people who are still trying to work within the auditable environment may (even if they have nothing personal to hide from it) find the involvement of the auditing team to be disruptive and interfering with their expected workflow (such as key documents being unavailable, as they are being scrutinised by the auditors and unavailable to be suitably updated with work currently in progress, without sparking off further auditing actions in response). In some cases, an 'audit' can even be threatened as a response to some nominal non-compliance with (perhaps unreasonable) demands, the implication being that all normally filed documents are heavy-handedly gone through leaving the target of the audit with an actual mess, the object not necessarily to discover desired information but to cause trouble and inconvenience to those that don't provide satisfactory complience to prior 'requests'. In the comic's instance, it is seemingly more a regular chore than an ad hoc pressure technique, but at least some of those who are more subject to the audit than they are net beneficiaries of its outcome seem to know that they will be significantly inconvenienced by it.

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 data recorded by the census is 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.

  Add comment        Create topic (use sparingly)       Refresh 

Discussion

The 'standard' and '2x' sized images had unexpected sizes, so an imagesize parameter has been added to render the image consistently with other comics on this website. See the web archive for more details. --TheusafBOT (talk) 18:54, 18 May 2026 (UTC)

should've been bigger 😒 Caliban (talk) 22:01, 18 May 2026 (UTC)

GRAMMATICAL ERROR! Should there be a category for grammar mistakes (Example 1662: Jack and Jill, where there was a grammar mistake.)? YZ100 22:20, 18 May 2026 (UTC)

Indeterminite? Location (singular)? 197.185.221.9 04:20, 19 May 2026 (UTC)

'Indeterminite' isn't a grammatical error - it's a spilling error. 82.13.184.33 08:47, 19 May 2026 (UTC)

Oh, the irony. He means 'spelling error.' Was that intentional? SomebodyElse (talk) 11:06, 19 May 2026 (UTC)

It was very much indented. Though not as much as this one. 82.13.184.33 13:49, 19 May 2026 (UTC)

When I say grammatical errors, I also include spelling errors. YZ100 22:17, 19 May 2026 (UTC)

That's a category error. 82.13.184.33 07:21, 20 May 2026 (UTC)

Could there be an additional joke in the title text related to how things like cences and tax forms (in the US) sometimes remind people that their answers will not be use against them

legally? - Human Physics Padawan

In most civilized countries the census process is historically used to plan the sizing of public infrastructures (schools, hospitals, water and electricity infrastructures, waste disposal facilities, used water treatment, and all that sort of seemingly unimportant things). It does not surprise me that in the US it is primarily used as a political instrument, however. 2001:861:3F07:A020:CBE1:3BDB:88F9:709A 23:28, 18 May 2026 (UTC)

"sizing of public infrastructures (schools, hospitals, water and electricity infrastructures, waste disposal facilities, used water treatment, and all that sort of seemingly unimportant things). […] primarily used as a political instrument" – i agree with the sentiment (not just for the US) but/and that is pretty much a definition of what politics is (should be) by a list of examples. 2A00:20:6346:8265:F4E8:8C7:66E:1D5 08:21, 19 May 2026 (UTC)

Remember that at the time the Constitution was written, the federal government was not expected to be involved much in most of that stuff, they're state matters. Barmar (talk) 14:09, 19 May 2026 (UTC)

The original justification for the census in the UK was as much, if not more, about figuring out how many people there were to exploit economically and militarily (as well as, weirdly, about helping the life insurance industry), as it was about allocating public goods. 82.13.184.33 14:20, 19 May 2026 (UTC)

"if physicists want to do this, it's their own decision." Not if the universe is deterministic. 82.13.184.33

Can someone find all the other comics where quantum principles are mentioned? I am fairly sure the Foxtrot one during Guest Week was one of those. SomebodyElse (talk) 11:06, 19 May 2026 (UTC)

Particle Man, Particle Man, Particle Man, Particle Man, Particle Man... 24.123.140.66 13:16, 19 May 2026 (UTC)

Triangle Man hates Particle Man. Probably because he can never work out exactly where he is. He's impossible to triangulate. 82.13.184.33 13:49, 19 May 2026 (UTC)

Pauli Exclusion principle does allow 2 fermions to have the same position if they have opposite spins.
Is the anonymity guarantee to ensure the privacy of particles that might be occupying the "wrong" space at the time of the census? Galeindfal (talk) 13:41, 19 May 2026 (UTC)

Is Megan really pointing towards the audience in panel 2? It looks to me like she's just pointing to the lectern, maybe her notes there. Barmar (talk) 14:03, 19 May 2026 (UTC)

It looks to me more like a palm up gesture. 82.13.184.33 16:30, 19 May 2026 (UTC)

The universe as a whole is generally assumed to be infinite,[actual citation needed] Yeah I'm still confused whether there's an actual astrophysical practice using, IDK some Calculus with "$\infty$", for example, or if it's just a horrible assumption that's just plain wrong. It's less that a citation is needed, as additional context is needed 174.16.177.185 (talk) 05:14, 20 May 2026 (UTC) (please sign your comments with ~~~~)

Toned down the infinite universe bit. 82.13.184.33 07:32, 20 May 2026 (UTC)

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... In the same way that the cardinality of the natural numbers equals that of the rationals, needing N particles to store info about 1 particle is not a logical problem if you have an infinte number of them. The main problem is the infinite time that it would take, and the fact that this probably cannot be done in such a way that, for all particles P, the particles that record the info of P all lie in P's observable universe. Note, however, that if we store the location of P into P's location(*), the spin of P in its spin, P's momentum in the momentum of P etc, we trivially retain all the information using exactly one particle per particle: a universe is trivially able to contain all the information it contains(**). Of course, this would still not be a very meaningful "census". (*) Of course, when you do quantum mechanics, "position" becomes more complicated than just a three dimensional real vector, but you can still fit the data about the position into the data about the position. (**) For example, we could leave every particle as it is. We could also rotate the entire universe by 90 degrees along some axis, or maybe even swap all particles in a predetermined way. These kinds of operations would not destroy any information (if we recorded somewhere which operation exactly we did). Tempestas (talk) 06:29, 20 May 2026 (UTC)

There's good and bad news about storing the particulate data upon particles. Good news is, only the position is (apparently) needed, so we might store P's position upon P's position (or upon Q, with Q's (original) position perhaps stored upon R's position, perhaps eventually some storer of position looping back to be stored/encoded as a new position for P, unless 'feathered out' as per the next storage opportunity), but we could equally store/encode it in some manner in P's spin/etc (and/or that of Q, R, and onwards, as necessary, there being properties (of perhaps lesser degres of freedom, individually,cbut receptive enough asca group) that are not being surveyed so can be used as 'data-sinks' for the data that is being surveyed, by some trivial one-to-one conversion process (possibly even checksumming or index-space/metadata wriggle-room to spare?). This might even include one or more (or a mixed combination) of momentums, motions and related, as a 'store-to property', so long as you're storing the information as absolutes rather than differences (given that you'd not be able to know what the original was that you had then systematically applied your data as an offset measurement). And as the data you're storing has no referencable copy, it doesn't matter that you have 'known' the absolute momentum-encoded-value, because it's only now encoded with the momentum that cannot even be back-derived without losing sight of the resulting position info which would be needed to unobscure the chain of interactions that led to the changes of state across and beyond the survey-event. (Also, one has obliterated the pre-survey momentums/etc by such an uncompromising reset-by-absolute-value applied to the non-positional qualifies.) So it might be possible. FCVO 'possible'... (Noting that any appeal to "but data can be compressed" forgets that there necessarily must be some configuration-states of data whose post-compression states (within the exact same 'state-space', not inventing further encodings outside of the original stream) are going to require more space than the pre-compression one, even if it's just adding one single meta-bit of "this data could not be (non-lossily) compressed" to the original raw data that had a consistency that resisted the process.)

But the bad news is: If the mere act of measuring precise position had not already rendered the whole system's non-positional (and thus un-censused) information unknowable (by standard Heisenburgian measurement exclusivity), the schema used to write/record the universe's (position-limited) state upon itself (not limited to position, perhaps even deliberately avoiding adjusting it that way!) will, as stated, exacerbate the 'random' redistribution of everything to somewhere else through the application of that data-encoding momentum/etc, and time taken until any further wish to read back in the census data renders the location of the location-encoded information (even barring further interaction having occured, with backtrackable changes to each interactee or not) problematic. (For this reason, you might desire to store both fact-of-particle and id-of-particle into the (presumed proxy-)particles state, the data-packing required for this left entirely as an exercise for the reader!)

I am, however, making the (in my mind, far more likely) assumption of the universe being finite-but-boundless. Or at least having a finite number of particles. (Whatever the nature of spacetime itself, which we at the very least tend to define a limit of t=0 for, and from that point (literally!) onwards must have a limit defined by however far spacetime and its contents must have expanded no farther than (if it isn't folded back upon itself, for no boundary but a limited non-cyclic size), and ...depending upon the future evolution of that spacetime... possibly a rebound down to a big-crunch at t=<loads> to seal the whole of blocktime into a finite 4(-or-more)-dimensional package of definite (if unknowable) size.) I'm open to the possibility of infinite numbers (at which point,the Hilbert Hotel could still afford to shuffle its infinite existing residents around enough to free up the rooms necessary to accomodate a further number of guests arriving in an infinite number of coaches, each containing an infinite number of people; and thus so might the whole infinite number of particles be able to be assigned a set of further particles to take an infinite amount of data (including the ordinal identity of each source-particle), with ease... but I feel it is more logically consistent (and it is stated as much in the Explanation, with a broad upper limit given to the number of particles, even if that's only in the Observable Universe) to presume finite lements for both survey and storage purposes, if one were to enumerate them.

(The easiest solution for implementing storage is of course the completely tautological one... The position(s) of particle P is 'stored' directly into the position(s) of particle P, with no kind of conversion at all and the mere existence of a particle being its own 'index' of identity. Technically, then can further also "know" the momentum, equally tautologically, at least until the point at which you wish to poll for either data element by 'reading' it (and/or it just becomes outdated information). The system where data is exchanged or otherwise transformed between dimensional sub-vectors (e.g. simply flipping or rotating the fact-data to produce the store-data) is similarly unproblematic regarding finding the data-space to replicate the original data in, but with significantly additional effort needed to implement.)

There's also the need for simultaneity, but I'm open to either a 'wavefront' of census-fulfillment spreading out across the universe from Physicist Central (essentially conveying ripples, with ten-year-long wavelengths, throughout the universe at least until they meet the ripples coming from around the other side of wrap-around spacetime) or some superluminal 'now' (by whatever handy but arbitrary inertial frame causes fewest problems) acting throughout the universe) as a kind of flash. Either way, the opportunity to poll a distant particle's information (assuming its information is stored 'locally' is going to be delayed by either the full light-distance between it (and hence its data-store location) or twice that (give or take the effects of frame-dragging or wormholes). The third synchronisation method is to 'have had' censused every particle (also then to have-had requested the data, already) such that the whole universe has been enacting the necessary censusing at the suitable point in the past such that the realisation of it is just now happening to our Physicist Central, in a 'reverse ripple' back from the mists of the early and (at least now) far flung parts of the universe, all these wavefronts of information to converge upon here-and-now (as a prior one did yen years ago, the next one is destined to do so in ten years hence, etc). I make no judgement about which option (or 'spooky action at a distance', I suppose, as the "lazy" idea) is the case here. I'm sure the surveyors have that covered, just like the various other implementation possibilities whose details I am left to only speculate about. 82.132.239.85 11:56, 20 May 2026 (UTC)
        Add comment