Main Page

Welcome to the explain xkcd wiki!
We have an explanation for all 3209 xkcd comics, and only 60 (1.9%) are incomplete. Help us finish them!

 Go to this explanation

Latest comic

Chemical Formula

|< < Prev #3200 (January 28, 2026)

Title text: Some of the atoms in the molecule are very weakly bound.

|< < Prev Random Explanation

Explanation

This supposed "chemical formula for the universe" merely lists the numbers of atoms of each element that are thought to exist in the observable universe. Usually, chemical formulae imply rather more of a discrete binding together of the atoms involved. They also represent a single molecule of the substance, rather than trying to cover the entire number of atoms in the whole quantity under consideration.

This may be poking some fun at the relative usefulness (or rather, uselessness) of chemical formulas for large organic molecules. While it is a useful concept for teaching people about chemistry and balancing equations, and it was useful in the early days of chemistry to try to categorize and learn about molecules via stoichiometry - it does not give much useful information, such as its structure. For example, even the simple formula C₁₁H₁₅NO₂ has 302 registered isomers.^{[actual citation needed]} Many of them are NOT good to eat.^{[citation needed]} For other purposes, formulae may group the components accordingly, such as CH₃CCl₃ (simplifies to C₂H₃Cl₃, as does an isomer) or [NH₄]₂CO₃ (not usually identified as CH₈O₃N₂, and not strictly an organic compound either).

As is common practice for real compounds that contain organic structures or substructures, the numbers of atoms of carbon and hydrogen are listed before all of the others; the others are listed in alphabetical order. There are estimated to be 10⁸⁰ atoms of hydrogen (H), by far the most common element in the universe. The next most common element, helium (He), is a long way to the right in the list, and out of view, but would be about a third as many as the hydrogens.

In reality, there is not a fixed number of atoms of each element across the lifetime of the universe. The matter originally created in the Big Bang was unbound protons and neutrons. In the first few minutes, some of these combined to form lightweight nuclei, but most remained as protons (i.e. the nuclei of hydrogen atoms). Other more complex atoms, up to atomic mass 56, formed later (and are still being formed) as a result of stellar nucleosynthesis. Still more massive nuclei have been and are being formed via supernova nucleosynthesis. Although the proportions of these atoms depend in a complex way on the fusion processes involved, and on the stabilities of those nuclei, the most massive atoms are generally both short-lived and less favored to form, so their elemental abundances in the universe are very small. As shown above, the number of americium (Am) atoms is much smaller than those of any other element in the visible part of the "formula". There are slightly fewer atoms of americium in the entire universe than the total number of atoms of hydrogen and oxygen in 1.0 L of liquid water.

The title text is probably referencing gravity, because, for the most part, these atoms would be "held together" only by gravity, and it is a very weak bond indeed.

The numbers of atoms are large, but they are not nameless. Using the long and short scales, these numbers can be described as:

Pos	Symb	Name	Quantity	Short Scale name	Long Scale name(s)	Ranked quantity*
1	C	Carbon	1076	Ten quattuorvigintillion	Ten thousand duodecillion Ten duodecilliard	4
2	H	Hydrogen	1080	One hundred quinvigintillion	One hundred tridecilllion	1
3	Ac	Actinium	1067	Ten unvigintillion	Ten undecillion	≈84
4	Ag	Silver	1069	One duovigintillion	One thousand undecillion One undecilliard	≈68
5	Al	Aluminium Aluminum	1075	One quattuorvigintillion	One thousand duodecillion One duodecilliard	14
6	Am	Americium	1026	One hundred septillion	One hundred quadrillion	≈84
7	Ar	Argon	1075	One quattuorvigintillion	One thousand duodecillion One duodecilliard	11
8	As	Arsenic	1070	Ten duovigintillion	Ten thousand undecillion Ten undecilliard	≈40
9	At	Astatine	1047	One hundred quattuordecillion	One hundred thousand septillion One hundred septilliard	≈84
10	Au	Gold	1069	One duovigintillion	One thousand undecillion One undecilliard	≈68
11	B	Boron	1071	One hundred duovigintillion	One hundred thousand undecillion One hundred undecilliard	≈61
12	Ba	Barium	1070	Ten duovigintillion	Ten thousand undecillion Ten undecilliard	≈33
13	Be	Beryllium	1071*	One hundred duovigintillion	One hundred thousand undecillion One hundred undecilliard	≈61
43*	He	Helium	1079*	Ten quinvigintillion	Ten tridecilllion	2
73*	O	Oxygen	1078*	One quinvigintillion	One tridecilllion	3

* - Information not provided by the comic; Source for ranked data, in particular, does not entirely agree with the quantities that are given in the comic.

The formula as it appears in the comic is truncated. The complete formula of the universe in this style (but arranged in decreasing order of abundance after carbon, which also happens to place hydrogen immediately after) would be C₁₀⁷⁷ H₁₀⁸⁰ He₁₀⁷⁹ O₁₀⁷⁸ Ne₁₀⁷⁶ N₁₀⁷⁶ Fe₁₀⁷⁶ S₁₀⁷⁶ Mg₁₀⁷⁵ Si₁₀⁷⁵ Ar₁₀⁷⁵ Ni₁₀⁷⁵ Ca₁₀⁷⁵ Al₁₀⁷⁵ Na₁₀⁷⁵ Cr₁₀⁷⁵ Ti₁₀⁷⁴ Mn₁₀⁷⁴ P₁₀⁷⁴ K₁₀⁷⁴ V₁₀⁷⁴ Cl₁₀⁷⁴ Co₁₀⁷⁴ F₁₀⁷³ Zn₁₀⁷³ Ge₁₀⁷³ As₁₀⁷² Br₁₀⁷² Li₁₀⁷² Sc₁₀⁷² Cu₁₀⁷² Ga₁₀⁷² Se₁₀⁷² Kr₁₀⁷² Rb₁₀⁷² Sr₁₀⁷² Zr₁₀⁷² Te₁₀⁷² Xe₁₀⁷² Ba₁₀⁷² Ce₁₀⁷² Pb₁₀⁷² B₁₀⁷¹ Be₁₀⁷¹ Y₁₀⁷¹ Nb₁₀⁷¹ Mo₁₀⁷¹ Ru₁₀⁷¹ Pd₁₀⁷¹ Cd₁₀⁷¹ Sn₁₀⁷¹ I₁₀⁷¹ La₁₀⁷¹ Pr₁₀⁷¹ Nd₁₀⁷² Sm₁₀⁷¹ Gd₁₀⁷¹ Dy₁₀⁷¹ Er₁₀⁷¹ Yb₁₀⁷¹ Os₁₀⁷¹ Ir₁₀⁷¹ Pt₁₀⁷¹ Hg₁₀⁷¹ Rh₁₀⁷⁰ Ag₁₀⁷⁰ In₁₀⁷⁰ Sb₁₀⁷⁰ Cs₁₀⁷⁰ Eu₁₀⁷⁰ Tb₁₀⁷⁰ Ho₁₀⁷⁰ Tm₁₀⁷⁰ Lu₁₀⁷⁰ Hf₁₀⁷⁰ Ta₁₀⁷⁰ W₁₀⁷⁰ Re₁₀⁷⁰ Au₁₀⁷⁰ Tl₁₀⁷⁰ Bi₁₀⁷⁰ Th₁₀⁷⁰ U₁₀⁷⁰ Tc₁₀⁰ Pm₁₀⁰ Po₁₀⁰ At₁₀⁰ Rn₁₀⁰ Fr₁₀⁰ Ra₁₀⁰ Ac₁₀⁰ Pa₁₀⁰ Np₁₀⁰ Pu₁₀⁰ Am₁₀⁰ Cm₁₀⁰ Bk₁₀⁰ Cf₁₀⁰ Es₁₀⁰ Fm₁₀⁰ Md₁₀⁰ No₁₀⁰ Lr₁₀⁰ Rf₁₀⁰ Db₁₀⁰ Sg₁₀⁰ Bh₁₀⁰ Hs₁₀⁰ Mt₁₀⁰ Ds₁₀⁰ Rg₁₀⁰ Cn₁₀⁰ Nh₁₀⁰ Fl₁₀⁰ Mc₁₀⁰ Lv₁₀⁰ Ts₁₀⁰ Og₁₀⁰ according to some broad stroke estimates of abundance.

Transcript

[A long panel with a chemical formula trailing off the right side]

C_10⁷⁶ H_10⁸⁰ Ac_10⁶⁷ Ag_10⁶⁹ Al_10⁷⁵ Am_10²⁶ Ar_10⁷⁵ As_10⁷⁰ At_10⁴⁷ Au_10⁶⁹ B_10⁷¹ Ba_10⁷⁰ Be

[Caption below the panel:] The approximate chemical formula for the universe

---

        View comic discussion

New here?

Last 7 days (Top 10)

Rank Score Pages Changes Username 1 22 18 22 TheusafBOT 2 16 13 16 Natg19 3 14 7 21 BunsenH 4 14 8 17 Elizium23 5 12 9 11 Qwertyuiopfromdefly 6 8 6 7 FaviFake 7 7 5 6 Elektrizikekswerk 8 7 7 7 Victoria 9 7 4 6 DollarStoreBa'al 10 6 2 7 Megan

Lots of people contribute to make this wiki a success. Many of the recent contributors above have just joined. You can do it too! Create your account here.

You can read a brief introduction about this wiki at explain xkcd. Feel free to create an account and contribute to the wiki! We need explanations for xkcd comics, characters, What If? articles, and everything in between. If it is referenced in an xkcd comic, it should be here.

• If you're new to wiki editing, see the explain xkcd:Editor FAQ for a specific guidance to this wiki and the more general help on how to edit wiki pages. There's also a handy wikicode cheatsheet.

• Discussion about the wiki itself happens at the Community portal.

• You can browse the comics from the list of all comics or by navigating the category tree at Category:Comics.

• The incomplete explanations are listed here. Feel free to help out by expanding them!

Rules

Don't be a jerk!

There are a lot of comics that don't have set-in-stone explanations; feel free to put multiple interpretations in the wiki page for each comic.

If you want to talk about a specific comic, use its discussion page.

Please only submit material directly related to xkcd and, of course, only submit material that can legally be posted and freely edited. Off-topic or other inappropriate content is subject to removal or modification at admin discretion, and users who repeatedly post such content will be blocked.

If you need assistance from an admin, post a message to the Admin requests board.