2301: Turtle Sandwich Standard Model

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Turtle Sandwich Standard Model
It's possible the bread and shell can be split into a top and bottom flavor, and some models additionally suggest Strange Bread and Charm Shells.
Title text: It's possible the bread and shell can be split into a top and bottom flavor, and some models additionally suggest Strange Bread and Charm Shells.


This comic references particle physics. The Standard Model of physics explains the base particles and fields that make up the universe. The elementary fermions of the standard model can be laid out in a 3×4 grid, with three "generations" of matter, each containing a quark with charge +⅔, a quark with charge -⅓, a lepton with charge -1, and a neutrino with charge 0. The first generation contains the familiar up and down quarks, which make protons and neutrons, the electron, and the electron neutrino. Each succeeding generation of matter is more massive than the one before, and only the first generation of particles occurs naturally on Earth; the others have only been created and identified in particle accelerator experiments (although they also arguably exist in various extreme places around the universe; for example, the strange quark is suspected to be a component of the denser parts of neutron stars).

Quarks were initially proposed by Murray Gell-Mann to simplify the "particle zoo" that physicists were discovering. He found that the twenty-five or so mesons and hadrons that were known at that time could be organized into what he called the "eightfold way" by just three properties: spin, charge, and what he called "strangeness". He proposed that three quarks (and their corresponding antiquarks) governed these properties. His chart had an empty space for what he called the omega baryon, and when a particle of the properties he predicted (including its mass) was discovered, his model received a lot of support. The quark model was eventually extended to include six quarks, and as with the eightfold way, one of the lines of evidence in favor of what became known as the Standard Model is that it predicted the existence and masses of several particles, which have since been confirmed; the top quark's mass was predicted in 1973, and experimentally verified in 1995, for example, and on the gauge boson side of the chart, the Higgs boson was discovered in 2012.

In this comic strip, sandwiches (lettuce, cheese, tomato, and possibly other fillings, surrounded by bread) and turtles (an aquatic reptile which wears an armored shell) are likewise proposed to not be "elementary" entities, but in fact combinations of 4 elementary parts, namely bread, fillings, reptile, and shell. The narrator's lab is looking for the hypothesized "bread-shelled turtle" and "shell-coated sandwich". In fiction, turtles' shells are often depicted as articles of clothing which they can remove at will, but in the real world, the shell is a part of the turtle's skeleton, so unless the narrator's lab is willing to commit extremely invasive surgery, they will never find a bread-shelled turtle, although they could much more easily take the shell of a dead turtle and put some sandwich fillings inside.

The failure to detect the bread-shelled turtle could be taken as evidence that the turtle-sandwich standard model is flawed -- perhaps turtles and sandwiches are elementary entities, or perhaps the elementary entities that make them are much smaller than is proposed here. There is also the small matter that there are things besides sandwiches and turtles in the universe[citation needed]. Alternatively, it could be taken as evidence that the bread-shelled turtle has an extremely high energy, and so does not exist under typical conditions of our universe. This might be analogous to magnetic monopoles; we would know one if and when we saw one (and many experiments have sought them out), and we believe we know how they would behave, but no such particle has ever been verifiably detected or created.

In the same vein, the lack of observation could be due to the instability of the arrangements. Turtleshell-turtle assemblies can last for more than 100 years, while bread-filling assemblies are indefinitely stable under sufficiently low energies. The two other arrangements may simply be formed rarely, and have a relatively short half-life.

The title text introduces more particle physics jargon, proposing that the "top and bottom" parts of the bread and/or shell have distinct "flavors", and that there may be "strange" and "charm" variants as well (a reference to the higher-generation quarks -- strange and charm in the second generation, and top and bottom in the third).

Unlike the turtle-sandwich standard model, there are no particles predicted by our Standard Model that have not yet been detected; however, there are several gaps between the pure Standard Model and what we observe in reality, most notably the existence of gravity and the apparent asymmetry between the amounts of matter and antimatter in the universe. For this reason, the Standard Model is generally considered to be somehow incomplete.


[A two-by-two grid, with a piece of bread next to the top left cell; a turtle shell next to the bottom left cell; lettuce, cheese, and tomato above the top left cell; and an turtle head enclosed in a circle above the top right cell.]
[Top left cell: an image of a sandwich.]


[Top right cell: an image of a shell-less turtle sandwiched between two slices of bread.]


[Bottom left cell: an image of a turtle shell housing lettuce, cheese, and tomato - the contents of a sandwich.]


[Bottom right cell: an image of a turtle.]


[Caption below the panel]

Our lab is working to detect the two missing pieces of the turtle-sandwich standard model.


  • Comic 474 also puns on the flavors of quarks.
  • The phrase "Turtle Sandwich Standard Model" fits the same trochaic tetrameter stress pattern as Teenage Mutant Ninja Turtles and other Wikipedia articles enumerated in 1412: Teenage Mutant Ninja Turtles.
  • The comic may be a nod to turtles similarly used as metaphors in philosophy (cf. Achilles and the Tortoise) or religion and cosmology (cf. the World Turtle).
  • As of 5:23am UTC on 4 May 2020 a glitch caused the comic image to display at 4682 pixels wide when viewed on non-Retina/HiDPI screens.

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This is the first time I have had a chance to see the comic early enough to make a meaningful contribution to the explanation, but this time I have no idea whatsoever what the comic is about! Moosenonny10 (talk) 20:32, 1 May 2020 (UTC)

Looks like it is referencing the standard model of elementary particles. The title text mentions four of the quarks(top,bottom,charm,strange) 20:38, 1 May 2020 (UTC)

Disagree with DgbrtBOT that this is primarily to do with genetics. I agree that it's about the standard model. Up, down, charmed and strange. It may 'because I'm dumb', but even I'm not that dumb.

I agree that this is not about genetics. The usual Mendelian diagram has the same traits in both dimensions. Maybe he didn't make the particle physics connection because that has more than 4 boxes. Barmar (talk) 21:52, 1 May 2020 (UTC)
Agree with Barmar: This is not at all about genetics, but only about the particles standard model. Hence the name given by Randal, hence the dimensions not fitting Mendel, hence the lab reference and hence the biological absurd combinations. It does not fit genetics at all, but it perfectly fits a basic assumption of the standard particle modell: That every combination does exist. Labs all over the world have spend decades trying find/prove the existance of a particle predicted by lining up the dimensions of the particles standard model just as shown here and most seeming just as absurd. 00:06, 2 May 2020 (UTC)

I added a bit about the physics part of it, but it can definitely use more information! ChunyangD (talk) 20:52, 1 May 2020 (UTC)

Randall missed an obvious physics/turtle joke "turtles all the way down" reference here Glenn Strycker 4:56pm CDT 1 May 2020

It was the first thing I thought, Randall can be sure his readers fill in such details... 21:08, 2 May 2020 (UTC)

If this really is about genetics, which I question, it seems likely that most people who haven't studied genetics would find the use of genetics jargon to be less than helpful in an explanation.Darthpoppins (talk) 22:46, 1 May 2020 (UTC)

In my opinion, the ExplainXKCD community has been successfully trolled by the contributor of the explanation of this comic, and with humorous effect. The troll consists of an explanation couched entirely in terms used primarily by biologists but generally difficult for others to understand, contrary to this community's practice of trying to simplify. Genotypes, phenotypes, Punnett Squares, heterozygous, homozygous, ontogeny. That being said, the contributor is certainly correct that the comic is about genetics, in that the depicted two-by-two square is immediately suggestive of the visual tool used for predicting the results of cross-breeding experiments. And the comic is certainly also about particle physics, in that the comic title refers to a "Standard Model" and then the title text alludes to particle names used in the standard model of particle physics. So the comic's joke is about the unexpected juxtaposition of genetics with particle physics, and also is about turtle sandwiches which, as drawn, are intrinsically funny anyway. Yes, @Glen, all the way down. JohnB 00:25, 2 May 2020 (UTC)

This looks less like a Punnet Square than it does like one of those political alignment chart memes. Punnet squares use symbols next to each other to designate genotypes, not diagrams of the results. Not to mention that the individual labels along the sides are supposed to be alleles, not separate effing traits! That whole paragraph is completely wrong and should be removed. GreatWyrmGold (talk) 00:44, 2 May 2020 (UTC)

Isn't this about supersymmetry? The missing pieces are the bosonic partners of the known fermions (matter particles), and the fermionic partners of the known bosons (force particles).... Joel K

For a second, I thought it said "Turkey Sandwich Standard Model"AllTheWayDown (talk) 01:31, 2 May 2020 (UTC)

This is clearly a use of the box method for factoring a trinomial in standard form (ax^2 + bx + c) which the coefficient of the first term (say ax^2) is not simply 1 (a<>1). Actually, the moment I saw it I knew exactly what it was, simply because I have been helping my high school son with his algebra the past few weeks. I laughed out loud! I never heard of this method as a math undergrad because it was brand new at the time, but now it's evidently fairly standard.

You create a 2x2 box, and write the first term of the trinomial (ax^2) in the top right corner and the last term (c) in the lower left. Then you have to figure out what factoring of a x c gives you two middle terms that when added will yield the middle term, bx. Let's call those b1x and b2x (where b1 x b2 = a x c, and b1 + b2 = b). You put those terms, b1x and b2x in the two empty boxes (in either order). Then you pull out common factors along each row and column until they multiply correctly to get the table. The terms you have pulled out then are your two binomial factors of the trinomial.

Randall has factored a turtle sandwich where the first term (ax^2) is a sandwich and the last term (c) is a turtle. These are the known terms (check marks). The unknown terms, through working the box method, turn out work if the bread is the common factor along the top row and the turtle shell on the bottom row. The sandwich filling is the common factor in the first column, and the shell-less turtle is the common factor on the second column.

I believe the alt-text is a play on the fact that, if I'm not mistaken, there are more ways to factor a trinomial if you allow imaginary numbers, because that allows square roots of negative numbers. Analogously, dividing shells differently suggests subatomic particles—thus, various quark flavors like charm and strange. EternalLearner (talk) 01:52, 2 May 2020 (UTC)

Apropos of nothing, and just for the comic relief of the commenters, I searched for 'turtle' 'sandwich' 'standard' 'model' and came across | this bad boy. I couldn't resist sharing. Thanks for the knowledge. -- brad

Uhm,wut,mostly. Okay so the earth is on a turtle. What holds the turtle up? It's turtles, all the way down, I've heard but? "Turtle legs" is my answer. Why I'm here: didn't xkcd.com used to say it was updated Monday, w, f, ? 04:55, 2 May 2020 (UTC)

Obviously, the turtle doesn't need to be held up. It's a sea turtle, it swims. -- Hkmaly (talk) 23:13, 2 May 2020 (UTC)

Please refer to http://recipes-plus.com/recipe/turtle-sandwiches-kids-30062 for the top left sighting. Steven Nijhuis (talk) 05:35, 2 May 2020 (UTC)

LOL. This is the most random comments I have seen on one of these. This is 100% particle physics. Standard model of particle physics, up quarks, charmed quarks.. this is a commentary on how we know there is gravity, and we know there are electrons and we have a standard model which is still being filled in, in order to unify the theories.

--Adam Outler 06:03, 2 May 2020 (UTC)

I'm a bit confused by these comments. It seems like people are getting thrown off by the 2x2 table thinking that the comic must be related to where they've seen tables before (genetics / factoring quadratics / ...). This is wrong though, this comic is 100% particle physics. In particle theoretical (particle) physics, the way forward has often been unification (combining forces of nature mathematically). We know the Standard Model is wrong, so physicists have been searching for ways to theoretically extend the known theory for decades. One of the most popular ways of doing this is looking for a larger symmetry group that encompasses the known symmetry groups of the equations governing the Standard Model. And the first time that physicists got REALLY close to a working theory was extending to E(5). When doing this mathematical extension of the Standard Model, you automatically get new messenger particles that are predicted (leptoquarks) that would theoretically make a transition between leptons and quarks possible (much like the weak interaction allows for transitions between quarks). The whole thing tends to get represented as a matrix visually, much like the turtle sandwich joke. tl;dr: The joke makes perfect sense in theoretical particle physics. This type of diagram is common in extending the Standard Model (which is definitely incomplete) to a larger symmetry group like E(5). Tom B

I'm pretty sure the factoring comment is satirizing the people who think it is about genetics. Probably not Douglas Hofstadter (talk) 05:13, 10 May 2020 (UTC)

Outside of anything scientific, I think it's also referring to the memetic "Is a BLANK a sandwich?" debate (normally a hotdog or a calzone) 18:12, 2 May 2020 (UTC)

The big debate, surely, is orientation. If I prepare (say) some chicken-breast in some sort of marinade, and then half-toast some bread (half-way towards toasting, not one-sidedly; I put the slices in the toaster but manually eject them when it makes a click which equates to roughly half way to the dialled-in toasting degree, at least on my old toaster) then lightly butter(/non-dairy spread) them and use them to sandwich the chicken, but with a slice of cheese atop the chicken, then it tastes nice. If, during consumption or just moving the construct to a plate, I end up inverting it so it's bread/chicken/cheese/bread from top to bottom (happens when passed from hand to hand, I think, between picking up and alighting anew) it tastes... still nice, but different. Yes, the tongue is set only below the route the sandwich takes, but I'm not sure that accounts for it (experiments while inverting myself, with or without inverting the sandwich, are yet to be trialled without other factors going uncontrolled). However, it does mean that a sandwich cannot be assumed to have a reflective or rotational symmetry in the horizontal plane or any horizontal axis, which is the usual bar quoted against the smörgåsbord... 01:35, 3 May 2020 (UTC)
Yes, orientation plays a role in surprisingly bizzarre situations. Have you noticed that USB Type A plugs have 1/2 spin? You try to stick one in a socket - it doesn't fit. You turn it 180 degrees - it doesn't fit. You turn it further 180 degrees - now it fits! -- Malgond (talk) 14:45, 5 May 2020 (UTC)
Try inverting your tongue and see what effect that has. 06:36, 3 May 2020 (UTC)

Anyone else mistakenly see the tomato slice/cheese/lettuce as a Turtle Chocolate and a slice of Turtle Pie?

Seeing the turtle without a shell between the two slices of bread in the grid reminds me of the other old question regarding turtles: If a turtle has lost its shell, is it homeless or naked? RAGBRAIvet (talk) 05:03, 3 May 2020 (UTC)

A turtle without its shell is spineless. Rtanenbaum (talk) 20:46, 5 May 2020 (UTC)

I think the commentary is missing a main point. If you you hold a turtle in one hand and a sandwich in the other, you cannot help but notice the similar structure. In fact you can find two kinds of pictures of "Turtle Sandwich" on the internet. Sandwich made to look like a turtle. or a turtle made to look like a sandwich. So the question becomes, which of these is the "standard model". Which then opens us up to a pun on the "standard model" from quantum physics. Rtanenbaum (talk) 20:46, 5 May 2020 (UTC)

The linked page on the Standard Model doesn't say anything about either turtles or sandwiches, so I think some more explanation on that part is welcome. --IByte (talk) 10:54, 3 May 2020 (UTC)

Perhaps we can find some clues at 2251. (That's what this reminded me of, anyway.) —Scs (talk) 12:59, 3 May 2020 (UTC)

=== Size

Why is it big now? Is it just big for me? Anyone else seeing this? 04:52, 4 May 2020 (UTC)

I can see it too.
Saved in Wayback Machine:

https://web.archive.org/web/20200504044520/https://xkcd.com/ -- 04:56, 4 May 2020 (UTC)

The issue only affects the non-Retina/HiDPI version. On a high res screen, the 2x image is loaded with a width of 624px. On a normal res screen, the regular image is loaded with a width of 4682px. Stevage (talk) 10:42, 4 May 2020 (UTC)

Meanwhile, C++ programmers are waiting to see where to position MockTurtle on the diagram (with no apologies whatsoever to Lewis Carroll)Cellocgw (talk) 16:48, 4 May 2020 (UTC)