explain xkcd - User contributions [en]

3071: Decay Chain

2025-04-04T02:31:13Z

172.68.55.113: /* Explanation */

{{comic
| number = 3071
| date = April 2, 2025
| title = Decay Chain
| image = decay_chain_2x.png
| imagesize = 312x595px
| noexpand = true
| titletext = If you have an old phone in a drawer, and you listen very carefully, you can occasionally hear the occasional tap of an emitted SIM card hitting the side of the drawer as the phone transmutes to a lower-end model.
}}

==Explanation==
{{incomplete|Created by an iPhone 6 that used to be an iPhone 13 - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
This comic is a play on nuclear {{w|decay chains}}, the series of radioactive disintegrations that the nuclei of unstable atoms undergo. Example diagrams of such nuclear decay chains can be seen {{w|Decay_chain#Thorium_series|here}}. This comic suggests that as iPhones model iterations get higher, they, similarly to heavier chemical elements, become unstable and susceptible to decay into lesser models. Some isotopes of atoms decay into other isotopes, releasing particles in the process. This process is generally dictated by the number of the positively charged protons in an atomic nucleus, which dictate its chemical identity, and the neutrons, which keep the protons in as stable a clump as possible. Particular isotopes, increasingly so for heavier atoms, are known to be subject to one or more modes of {{w|nuclear decay}} in order to attain a more stable and simpler form, including by several such steps. This comic humorously explores how an iPhone would decay if decaying worked similarly, which is absurd as iPhones are large objects that do not suddenly and drastically cahnge form.{{Citation needed}} (Although, almost all matter on Earth, including iPhones, contain ''some'' atoms that are radioactive and exhibit nuclear decay, mixed with a non-radioactive majority.)

The difference between iPhones undergoing {{w|alpha decay|alpha (''α'') decay}} (vertically downwards, in the diagram) is the change in model number from a higher one to a model two steps lower, except for the step involving the iPhone X which apparently exists instead of a "9" model. This is equivalent to the change in {{w|atomic number}} when two protons together with two neutrons leave the nucleus in the form of a helium ion (He2+), known as an alpha particle. The atomic number of such atoms reduces by two and the {{w|mass number}} reduces by four (that held by the departing He2+), though no evidence is given as to how the respective masses of the phones ''actually'' changes in this analogy. The specific reason for the decay chain stopping at iPhone '''7''' is unknown, although a possible reason for this is because lithium, which is often used in phone batteries, has the stable isotope lithium-7.

"Stable" may refer to the usability of the device in terms of whether or not the device still receives security updates, but the iPhone 6s also received the [https://support.apple.com/en-us/100100 latest security patch] as of the time this comic was published. In 2024, Apple lost [https://www.bbc.com/news/technology-67911517 a lawsuit] regarding one of their business practices of intentional obsolescence.

The process of beta minus (''β''-) decay (in elements, the effective conversion of a neutron into a proton and a free electron) raises the atomic number by one by transforming a neutral particle to a positive one via emission of a small negatively charged {{w|beta particle}} (an electron), leaving the mass only slightly decreased. In the terms of iPhones, this is represented by the removal of a brand-name modifier (usually denoting additional features included within the same model range) in order to perform a version-upgrade but now being closer to that new range's most basic release of model. This is represented by a rightward-and-upward step. The decay step from the iPhone 13 Pro to the iPhone 14 Plus, which is missing a symbol, is clearly one of the ''β''- decay steps.

(After alpha or beta decay, atoms may then emit {{w|gamma radiation}} (high-energy photons) as they rearrange their atomic state without changing their composition, but this process does not change the element in any meaningful way. It also will occur when neutron capture and/or atomic fission has occured, which is generally considered outside the natural decay chain of any such isotope, and can also result from nuclear fusion. Beta decay also requires emission of an antineutrino, but that particle interacts so weakly with matter that it's undetectable except by extremely sensitive experimental equipment.)

The title text suggests that the "alpha particle" of the iPhone is a {{w|SIM card}}, and that alpha-decaying phones will emit one of these with each decay (despite few phones having more than two, and most working ones only having one, but perhaps that's part of the mystery of telephonic {{w|Nuclear transmutation|transmutation}}). The sound of an old phone, sitting in a drawer, ejecting the unnecessary SIM is likened to the slow click of a {{w|Geiger counter}} registering the decay particles ejected from a decaying radioisotope. Radioactive decay is a random and spontaneous process; without the sound, one would never otherwise know if the phone even ''had'' decayed without {{w|Schrödinger's cat|opening the drawer}} to find out.

A similar comparison between smartphones and stars happened in [[1422: My Phone is Dying]].

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

[A flowchart with arrows leading from a circle with the words "iPhone 16 Pro Max", to circles with other iPhone names, eventually leading to a circle with the words "iPhone 7"]

:[Caption below the panel:]
:Physicists believe that an iPhone 16 Pro Max will, if left alone long enough, eventually decay into an iPhone 7, the heaviest stable model.

{{comic discussion}}

[[Category:Smartphones]]
[[Category:Physics]]

Talk:3062: Off By One

2025-03-15T16:35:26Z

172.68.55.113:

But what about floats? [[User:GreyFox|GreyFox]] ([[User talk:GreyFox|talk]]) 20:01, 12 March 2025 (UTC)

Is this dithering? [[User:Hcs|Hcs]] ([[User talk:Hcs|talk]]) 21:19, 12 March 2025 (UTC)

: Could be. --[[User:PRR|PRR]] ([[User talk:PRR|talk]]) 22:19, 12 March 2025 (UTC)

This language has a huge off by one error: the docs don't explicitly say if the random range is inclusive. EDIT: the comic description above now includes this, thx --[[User:Snaxmcgee|Snaxmcgee]] ([[User talk:Snaxmcgee|talk]]) 22:22, 12 March 2025 (UTC)

But if it's adjusted both on store and on read, then there is a chance (of about 1 in 22) that the value after read will be exactly the same as the value before store. This does not eliminate pre-existing off-by-one errors, and in fact, introduces new ones if the adjustment on read is off by one from the adjustment on store, when there was no off-by-one error in the original code. And what's worse - with a single store-read cycle, the value can never be off by 40 to 50. It can be off by up to 10, or by between 80 to 100, in either direction. --[[User:NeatNit|NeatNit]] ([[User talk:NeatNit|talk]]) 22:42, 12 March 2025 (UTC)
:I was ''just'' adjusting the explanation to imply this sort of thing (without having read your comment, just yet). Given the assumption that n=n±(40+rand(11)) at every stage (I'm assuming 'inclusive', Snaxmcgee!), two steps of 'intentional adjustment' might result in: -100 (x1), -99 (x2), -98 (x3), -97 (x4), -96 (x5), -95 (x6), -94 (x7), -93 (x8), -92 (x9), -91 (x10), -90 (x11), -89..-80 (x10..x1), -10 (x2), -9 (x4), -8 (x6), -7 (x8), -6 (x10), -5 (x12), -4 (x14), -3 (x16), -2 (x18), -1 (x20), ±0 (x22), +1..+10 (x20..x2), +80..+90..+100 (x1..x11..x1).
:This gives a chance of being entirely correct as 22/484 (4.5454...%) and ''each'' off-by-one as ''very'' slightly less (though ±1, in total is almost twice as likely!).
:Adding further steps (skipping odd step-cummulations, at least at first, until you get to nine of them and everything entirely stops being discontinuous) just spreads out an increased number of highs right next to zero deflection... [[Special:Contributions/172.70.86.129|172.70.86.129]] 23:38, 12 March 2025 (UTC)

::Obligatory quote:
There are two hard things in computer science: cache invalidation, naming things, and off-by-one errors.
::See here for a full story of this quote: https://twitter.com/codinghorror/status/506010907021828096
::--[[Special:Contributions/162.158.129.64|162.158.129.64]] 08:28, 13 March 2025 (UTC)
:::And 3 hard things in distributed computing: 3. Delivering messages exactly one time, 2. Making sure things happen in the correct order, and 3. Delivering messages exactly one time [[User:Jamcdonald|Jamcdonald]] ([[User talk:Jamcdonald|talk]])
::::Presumably 1 is not losing data? --[[User:NeatNit|NeatNit]] ([[User talk:NeatNit|talk]]) 10:19, 13 March 2025 (UTC)
::::: We may never know, Message 1 was never delivered [[User:Jamcdonald|Jamcdonald]] ([[User talk:Jamcdonald|talk]])
In the comic, Cueball clearly says the adjustment amounts is ‘’between’’ 40 and 50, yet this explanation says the adjustment is from 40 to 50, ironically making an off-by-1 error on both ends of the range. Neither integers 40 nor 50 are “between 40 and 50”. [[Special:Contributions/172.71.154.39|172.71.154.39]] 10:43, 13 March 2025 (UTC)
:English language is imprecise with its use of "between", but it's usually taken as inclusive. Most people, when asked, "Pick a number between 1 and 10," will assume that 1 and 10 are both valid choices. Even in computing, you have things like Excel's RANDBETWEEN function to generate random integers between two bounds, which is inclusive. {{unsigned ip|104.23.187.72|13:28, 13 March 2025}}
::Interestingly, in German such ranges are defined as including the borders, in Dutch they're defined as excluding the borders. (hence the Dutch t/m ("tot en met" - "up to, and including") [[Special:Contributions/104.23.170.81|104.23.170.81]] 15:28, 13 March 2025 (UTC)
::Yes, see {{wiktionary|between#Usage notes}} as one overview. Between as in "within the bounds defined by" is different from "amongst those things of which these items are the defining outer examples". Especially, but not exclusively, when that's just two distinct items which have ''no'' valid intermediate states betwixt the two to choose from ("you have to choose between me and my sister" isn't usually satisfactoraily answerable by choosing a different sibling, or perhaps parent, of the two). [[Special:Contributions/172.69.195.54|172.69.195.54]] 15:24, 13 March 2025 (UTC)

It's easy to make an off-by-one error without using a computer at all. Ask a friend how many fenceposts are needed for a 100-foot fence if the rails are ten feet long. [[Special:Contributions/172.71.30.199|172.71.30.199]] 12:58, 13 March 2025 (UTC)
:And how wide are the posts..? ;) [[Special:Contributions/141.101.98.6|141.101.98.6]] 15:27, 13 March 2025 (UTC)
::If I ever answer this question 100, it's obviously because in my mind each post (or more accurately, the distance between the grooves cut into the post) is a foot wide, which is slightly larger than usual but not totally unreasonable size, and not because I fell for the trick.--[[User:Snaxmcgee|Snaxmcgee]] ([[User talk:Snaxmcgee|talk]]) 16:47, 13 March 2025 (UTC)

I don't understand - what's all this got to do with water balloons? [[Special:Contributions/172.70.86.129|172.70.86.129]] 15:37, 13 March 2025 (UTC)
:(ISWYDT...) [[Special:Contributions/173.70.195.206|171.68.193.204]] 16:47, 14 February 2026 (UTC)
::What did they do. Waterballoons were the previous comic? What did they do? [[Special:Contributions/172.70.230.159|172.70.230.159]] 22:41, 13 March 2025 (UTC)
:::They were off by one [day] [[Special:Contributions/172.68.55.113|172.68.55.113]] 16:35, 15 March 2025 (UTC)

Let's make programming languages do this! There should be an implementations section! :D :D [[Special:Contributions/172.70.230.159|172.70.230.159]] 22:41, 13 March 2025 (UTC)

Nearly added the following information to the Explanation, but it's probably too specific an example:
:The language {{w|Perl}} can be asked (with an array <code>@array</code>) for either the number of elements (with something like <code>int(@array)</code>) ''or'' the index of the final element (typically by <code>$#array</code>) of lists that ''usually'' start at the index of zero. The method of looping through the array should then be carefully matched to the limit given (shift/pop it as many times as there are elements, as one of the various "do-while" or "while-do" types of loop available, or else run from index zero to the topmost index value that ''normallybought to be'' 'elements minus one', with one of the more "for(;;)"-style counting-loops).
And, of course, there are subtle differences between Perl versions, not nust limited to whetger it's <code>$array[$index]</code> or <code>@array[$index]</code>, and if <code>$[</code> or 'arybase' can be used to mix things up a bit. (Though I might just <code>map {...} @array</code> it, or do something potentially awful but valid like <code>{@array||last;print$".splice@array,rand@array,1;redo}</code> if it seemed like I should.) [[Special:Contributions/172.70.163.167|172.70.163.167]] 00:33, 14 March 2025 (UTC)

3055: Giants

2025-02-24T18:57:34Z

172.68.55.113: /* Explanation */

{{comic
| number = 3055
| date = February 24, 2025
| title = Giants
| image = giants_2x.png
| imagesize = 341x423px
| noexpand = true
| titletext = I can't get over the suspicion that all those viral pictures are photoshopped and 'Flemish' belongs in the lower right circle.
}}

==Explanation==
{{incomplete|Created by a BOT giant - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

{| class="wikitable"
|-
! Name !! Class !! Explanation
|-
| Red Giant || Space || A type of star
|-
| Blue Giant || Space || A type of star
|-
| Iron Giant || Space, Not Real || A comic book character: a robot from outer space.
|-
| Frost Giant || Not Real || Beings from Norse mythology.
|-
| Jolly Green Giant || Not Real || A mascot for a brand of canned vegetables.
|-
| Cardiff Giant || Geologic/Planetary, Not Real || An 1869 hoax
|-
| Atacama Giant || Geologic/Planetary || A prehistoric geoglyph
|-
| Salt Giant || Geologic/Planetary || A huge salt deposit below the Mediterranean sea
|-
| Gas Giant || Space, Geologic/Planetary || A gaseous planet like Jupiter or Saturn
|-
| Ice Giant || Space, Geologic/Planetary || An icy planet like Uranus or Neptune
|-
| The Man In The Moon || Space, Geologic/Planetary, Not Real || A face visible in a crescent moon's shadow, sometimes shown as a character in children's nursery rhymes

|}

The title text refers to the {{w|Flemish Giant rabbit}}, the largest breed of domestic rabbit (about the same size as a small dog like a terrier).

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

{{comic discussion}}

3054: Scream Cipher

2025-02-21T18:25:33Z

172.68.55.113: /* Explanation */

{{comic
| number = 3054
| date = February 21, 2025
| title = Scream Cipher
| image = scream_cipher_2x.png
| imagesize = 287x416px
| noexpand = true
| titletext = AAAAAA A ÃA̧AȂA̦ ǍÅÂÃĀÁȂ AAAAAAA!
}}

==Explanation==
{{incomplete|Created by a SCREAMING BOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
A {{w|substitution cipher}} is a simple form of encryption where each letter in the original text is replaced with a unique letter. In the comic's cipher, the replacement letters are all variants of the letter A with different {{w|diacritical marks}}.

It's named "Scream Cipher" (as a pun on stream ciphers, commonly used in computing) because the written form of a scream is a long string of As, possibly with some other characters at the end (and an excamation point for emphasis) e.g. "Aaaaaah!" or "Aaaaaaagh!". The name is not a reference to IBM's {{w|Scream_(cipher)|Scream cipher}} published in 2002.

In the comic, [[Cueball]] texts the cipher for "HELLO", and [[Megan]] responds with the cipher for "HI".

The title text deciphers to "AAAAAA A SCARY MONSTER AAAAAA!"

In Unicode the cipher can be described as

{|class="wikitable"
! Input !! Substitution
|-
| U+0041 LATIN CAPITAL LETTER A || U+0041 LATIN CAPITAL LETTER A
|-
| U+0042 LATIN CAPITAL LETTER B || U+0226 LATIN CAPITAL LETTER A WITH DOT ABOVE
|-
| U+0043 LATIN CAPITAL LETTER C || U+0041 LATIN CAPITAL LETTER A, U+0327 COMBINING CEDILLA
|-
| U+0044 LATIN CAPITAL LETTER D || U+0041 LATIN CAPITAL LETTER A, U+0332 COMBINING LOW LINE
|-
| U+0045 LATIN CAPITAL LETTER E || U+00C1 LATIN CAPITAL LETTER A WITH ACUTE
|-
| U+0046 LATIN CAPITAL LETTER F || U+0041 LATIN CAPITAL LETTER A, U+032E COMBINING BREVE BELOW
|-
| U+0047 LATIN CAPITAL LETTER G || U+0041 LATIN CAPITAL LETTER A, U+030B COMBINING DOUBLE ACUTE ACCENT
|-
| U+0048 LATIN CAPITAL LETTER H || U+0041 LATIN CAPITAL LETTER A, U+0330 COMBINING TILDE BELOW
|-
| U+0049 LATIN CAPITAL LETTER I || U+1EA2 LATIN CAPITAL LETTER A WITH HOOK ABOVE
|-
| U+004A LATIN CAPITAL LETTER J || U+0041 LATIN CAPITAL LETTER A, U+0313 COMBINING COMMA ABOVE
|-
| U+004B LATIN CAPITAL LETTER K || U+1EA0 LATIN CAPITAL LETTER A WITH DOT BELOW
|-
| U+004C LATIN CAPITAL LETTER L || U+0102 LATIN CAPITAL LETTER A WITH BREVE
|-
| U+004D LATIN CAPITAL LETTER M || U+01CD LATIN CAPITAL LETTER A WITH CARON
|-
| U+004E LATIN CAPITAL LETTER N || U+00C2 LATIN CAPITAL LETTER A WITH CIRCUMFLEX
|-
| U+004F LATIN CAPITAL LETTER O || U+00C5 LATIN CAPITAL LETTER A WITH RING ABOVE
|-
| U+0050 LATIN CAPITAL LETTER P || U+0041 LATIN CAPITAL LETTER A, U+032F COMBINING INVERTED BREVE BELOW
|-
| U+0051 LATIN CAPITAL LETTER Q || U+0041 LATIN CAPITAL LETTER A, U+0324 COMBINING DIAERESIS BELOW
|-
| U+0052 LATIN CAPITAL LETTER R || U+0202 LATIN CAPITAL LETTER A WITH INVERTED BREVE
|-
| U+0053 LATIN CAPITAL LETTER S || U+00C3 LATIN CAPITAL LETTER A WITH TILDE
|-
| U+0054 LATIN CAPITAL LETTER T || U+0100 LATIN CAPITAL LETTER A WITH MACRON
|-
| U+0055 LATIN CAPITAL LETTER U || U+00C4 LATIN CAPITAL LETTER A WITH DIAERESIS
|-
| U+0056 LATIN CAPITAL LETTER V || U+00C0 LATIN CAPITAL LETTER A WITH GRAVE
|-
| U+0057 LATIN CAPITAL LETTER W || U+0200 LATIN CAPITAL LETTER A WITH DOUBLE GRAVE
|-
| U+0058 LATIN CAPITAL LETTER X || U+0041 LATIN CAPITAL LETTER A, U+033D COMBINING X ABOVE
|-
| U+0059 LATIN CAPITAL LETTER Y || U+0041 LATIN CAPITAL LETTER A, U+0326 COMBINING COMMA BELOW
|-
| U+005A LATIN CAPITAL LETTER Z || U+023A LATIN CAPITAL LETTER A WITH STROKE
|}

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[Top of the panel has 26 letters of the alphabet, each followed by a hyphen and the letter "A" with a unique diacritical mark for each:]
:{|
|A - A
|-
|B - Ȧ
|G - A̋
|L - Ă
|Q - A̤
|V - À
|-
|C - A̧
|H - A̰
|M - Ǎ
|R - Ȃ
|W - Ȁ
|-
|D - A̲
|I - Ả
|N - Â
|S - Ã
|X - A̽
|-
|E - Á
|J - A̓
|O - Å
|T - Ā
|Y - A̦
|-
|F - A̮
|K - Ạ
|P - A̯
|U - Ä
|Z - Ⱥ
|}

:[Cueball and Megan typing on their phones, Cueball with two hands and Megan with one hand.]
:Cueball's phone: A̰ÁĂĂÅ
:Megan's phone: A̰Ả

:[Caption below the panel:]
:In the ''Scream Cipher'', messages consist of all As, with different letters distinguished using diacritics.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Language]]
[[Category:Cryptography]]

3053: KM3NeT

2025-02-19T20:25:08Z

172.68.55.113: /* Explanation */

{{comic
| number = 3053
| date = February 19, 2025
| title = KM3NeT
| image = km3net_2x.png
| imagesize = 313x436px
| noexpand = true
| titletext = Unfortunately, KM3NeT led to the discovery of the Pauli anglerfish, which emits Cherenkov radiation to prey on neutrino researchers.
}}

==Explanation==
{{incomplete|Created by a CHERENKOV ANGLERFISH WITH C-SICKNESS - Please continue to expand the explanation, and explain the title text. Do NOT delete this tag too soon.}}
{{w|KM3NeT}} is a telescope under the {{w|Mediterranean Sea}}. As [[Ponytail]] explains, its goal is to detect {{w|neutrino}} interactions with the seawater. Neutrinos very rarely interact with solid matter, so a telescope looking for them needs a lot of matter, in this case seawater, to spot collisions in. This also uses {{w|Cherenkov radiation}}, as a neutrino interaction can release enough energy to exceed the speed of light in water, producing a blue flash the telescope detects.

When [[Cueball]] questions the rationale by pointing out the existence of {{w|Bioluminescence|bioluminescent}} fish, which might also produce blue light, Ponytail responds with a pun: Aquatic life can be called "undersea" life, and Cherenkov radiation is only produced by particles exceeding the {{w|speed of light}} in water, "c"; so fish are also "under-c" life, as they do not travel at the speed of light in water, which cannot produce Cherenkov radiation. Usually, "c" represents the speed of light in _vacuum_, so the pun is a stretch, but perhaps also irresistible, especially as discussing traveling faster than light can at first provide a postfuristic[definition?] thrill. "c" is considered a fundamental constant speed in physics that it is impossible to exceed.

The title text continuous Cueball's attempt to explain the detected radiation by the existence of aquatic life, hypothesizing the existence of an {{w|anglerfish}} (the Pauli anglerfish, presumably named after the theoretical physicist {{w|Wolfgang Pauli}}) which would be able to emit or emulate Cherenkov radiation.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:[Ponytail is presenting to Cueball and Megan on a drop down screen.]
:[On the screen is a side view of a deep-water telescope, attached to the bedrock, floating in the ocean. It looks like four series of circles stringed together from the ground.]
:Ponytail: The KM3NeT deep-water telescope detects the flashes of Cherenkov light from neutrino interactions.
:Cueball: How do you know you aren't just seeing bioluminescent fish?
:Ponytail: Cherenkov radiation is only emitted when things exceed the local speed of light, so it can't be produced by under-c life.

{{comic discussion}}

[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Telescopes]]
[[Category:Physics]]
[[Category:Animals]]
[[Category:Puns]]