explain xkcd - User contributions [en]

3071: Decay Chain

2025-04-03T14:42:28Z

108.162.242.27: /* 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 suggests that as iPhones get heavier (as model iterations get higher) they, like heavier chemical elements, become unstable and susceptible to decay. In science, some atoms decay into other atoms, releasing some energy in the process. This process is generally dictated by the ratio and configuration of the positively charged protons in an atomic nucleus, which dictate its chemical identity, with the neutrons, which need to act to keep the protons in as stable a clump as possible. Particular isotopes, increasingly so for the heavier atoms, are known to be subject to one or other 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 works the same, which is obviously absurd as iPhones are not radioactive{{citation needed}} and thus aren't subject to atomic decay.

The difference between iPhones undergoing {{w|alpha decay}} (vertically downwards, in the diagram) is the change in model number from a higher one to one 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 unstable protons (together with a couple of neutrons) leave the nucleus in the form of a helium ion. The {{w|mass number}} of such atoms 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'''

The process of beta minus decay (in elements, the effective conversion of a neutron into a proton and a free electron) raises the atomic number by one by transforming an excess neutral particle to a positive one, by emiting the small negatively charged {{w|beta particle}} (leaving the mass practically the same). 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 sideways and upwards step. The decay step from the iPhone 13 Pro to the iPhone 14 Plus, which is missing a symbol, is clearly one of the beta minus decay steps.

(After alpha or beta decay, atoms may then emit {{w|gamma radiation}} 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 outwith the natural decay chain of any such isotope, and can also result from nuclear fusion.)

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 each time (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}} being prompted to register the decay particles ejected from a decaying radioisotope. Presumably, 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.

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]]

3070: Orogeny

2025-04-01T13:32:25Z

108.162.242.27: /* Explanation */

{{comic
| number = 3070
| date = March 31, 2025
| title = Orogeny
| image = orogeny_2x.png
| imagesize = 740x303px
| noexpand = true
| titletext = Most properties can only boast INDOOR heated floors.
}}

==Explanation==
{{incomplete|Created by a OUTDOOR HEATED FLOOR - Needs someone who knows geology to add stuff. Do NOT delete this tag too soon.}}
This comic is about an {{w|orogeny}}, the creation of mountain ranges at convergent plate boundaries.

The mountain range that [[Cueball]] and [[Ponytail]] are looking at was formed a billion years ago, but the mountains themselves have been eroded away and replaced. This could reference the {{w|Ship of Theseus|Theseus’ Ship}} thought experiment. Cueball analogizes this to a fully-renovated home, and Ponytail continues the analogy by (jokingly) pretending to use this as a business opportunity, offering it for sale to Cueball. She makes the sales pitch that this is good old good solid {{w|Intrusive rock|plutonic bedrock}}, freshly uplifted , i.e. from below the surface from the collision of the tectonic plates. Cueball plays along by saying he'd prefer 'new construction', in this case a volcanic seamount, which Ponytail rejects on the basis of them being quite literally 'too hot' (i.e. covered in lava or soon to be so).

The title text talks about how magma is technically a heated floor. While most houses only have indoor heated floors, the volcanic seamounts can heat the ground outside when they erupt.

Orogeny was also mentioned in [[1082: Geology]].

This comic is reminiscent of the [[:Category:Home Inspections|Home Inspections]] series but, given that there is not yet a home to assess, it is not strictly part of that category. There was also the recent [[3051: Hardwood]], about defining underlying geology as part of a house, which might hint at Randall working all around a wider theme.

Despite being released on April 1st, it is not an April Fools comic{{citation needed}}. This may imply that the April Fools comic will be released later, as in [[2916: Machine]], or there may not be an April Fools comic at all this year.

==Transcript==
:[Cueball and Ponytail are seen from afar standing together on hill and looking out at a mountain range with mountains going all the way to the horizon, wit more than 20 peaks. The hills they are standing on is grassy and strewn with rocks.]
:Cueball: I hear these mountains are a billion years old.
:Ponytail: Well, sort of.

:[Close up of Cueball and Ponytail on a white background. Ponytail holds her hand palm up out towards Cueball.]
:Ponytail: An ancient collision created the mountain belt, but the actual rock layers have been continually uplifted and eroded away.

:[In a frame-less panel Cueball atkes his hand to his chin looking down, while Ponytail now gestures away from Cueball with her palm held out.]
:Cueball: So it's an old mountain range, but it's been fully renovated?
:Ponytail: Yessir, torn down to the roots. This is good solid plutonic bedrock, freshly uplifted. Great value.
:Ponytail: You in the market?

:[They are now just standing normally talking to each other.]
:Cueball: I dunno, I was looking for new construction. You got any emerging volcanic seamounts?
:Ponytail: Nah, that market is a little too hot right now.

{{comic discussion}}

[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]
[[Category:Geology]]

399: Travelling Salesman Problem

2015-08-10T08:02:23Z

108.162.242.27: noted the cities

{{comic
| number = 399
| date = March 21, 2008
| title = Travelling Salesman Problem
| image = travelling_salesman_problem.png
| titletext = What's the complexity class of the best linear programming cutting-plane techniques? I couldn't find it anywhere. Man, the Garfield guy doesn't have these problems...
}}

==Explanation==
The {{w|Travelling salesman problem|travelling salesman problem}} is a classic problem in computer science. An intuitive way of stating this problem is that given a list of cities and their pairwise distances, the task is to find the shortest possible route that visits each city exactly once and then returns to the origin city. A naive solution solves the problem in {{w|Factorial|O(n!) time}} (where n is the size of the list), simply by checking all possible routes, and selecting the shortest one. A more efficient {{w|Dynamic programming|dynamic programming}} approach yields a solution in O(n22n) time. These times are given using {{w|Big O notation}}, which is commonly used in computer science to show the efficiency or complexity of a solution or algorithm.

The joke is that the salesman selling online (say on {{w|eBay}}, {{w|Amazon Marketplace}}, or other virtual marketplace) does not have to worry about this problem since he does not need to travel, to which the travelling salesman angrily responds "shut the hell up".

The title text wonders about the time complexity of the {{w|Cutting-plane method|cutting-plane method}}, which is sometimes used to solve optimization problems.
The last sentence suggests the down side for Randall of writing comics about computer science; he sometimes encounters problems to which he cannot find the answer, whereas authors of simpler comics such as {{w|Garfield}} do not have this problem. This is also likely a reference to [[78: Garfield]], which parodies Garfield's simplicity.

This is so far the only comic featuring the Brown Hat character.

Also see earlier strip [[287: NP-Complete]].

==Transcript==
:[There is a linked black web, with a path in red; it is a U.S. map with (from left to right) Seattle, San Francisco, Los Angeles, Phoenix, Denver, Minneapolis, Dallas, San Antonio, Houston, Chicago (cut off), Detroit, Atlanta, Miami, Washington D.C. Philadelphia, New York and Boston highlighted.]
:Brute-force solution:O(n!)
:[The web continues in this one. A man with a hat and a case is drawing it.]
:Dynamic programming algorithms: O(n22n)
:[Another man, with a hat too, is at a computer, looking back over the chair.]
:Selling on eBay: O(1)
:eBay salesman: Still working on your route?
:Drawing salesman: Shut the hell up.

{{comic discussion}}
[[Category:Comics with color]]
[[Category:Math]]

Talk:1561: Water Phase Diagram

2015-08-07T21:20:50Z

108.162.242.27: Minor suggestion - Miles Davis on bottom.

What's up with that square under "water vapor"? Is it just a glitch, or is it some hidden message like in https://xkcd.com/1005/? [[User:Nick818|Nick818]] ([[User talk:Nick818|talk]])

I think it is a hidden message, it almost looks like a tiny graph.

It looks like a tiny version of the same graph, but flipped upright so that pressure increases as you go up. (Doing this in the main strip would ruin the "Under Pressure" joke. --[[User:Druid816|Druid816]] ([[User talk:Druid816|talk]]) 05:19, 7 August 2015 (UTC)

I'd say it's the phase diagram Randall used as a template, see [https://en.wikipedia.org/wiki/Phase_diagram#Crystal_phase_diagrams Wikipedia] --[[Special:Contributions/108.162.229.232|108.162.229.232]] 05:28, 7 August 2015 (UTC)

The only thing I can think of is "water + vapor + paper" with the letters being {unique, identical, second, first, identical}. No idea if that means anything. It's probably just a pencil drawing that Randall forgot to remove before publishing. [[Special:Contributions/108.162.216.70|108.162.216.70]] 06:45, 7 August 2015 (UTC)
:Seems to be the phase diagram from wikipedia. I put a contrast enhanced zoom [http://i.imgur.com/wJGVriV.png here] and it corresponds extremely well with the wikipedia version (including darker pixels where the blue is). -- [[Special:Contributions/141.101.105.234|141.101.105.234]] 13:36, 7 August 2015 (UTC)
::I think it might be a reference to the "Full text of the Wikipedia article on pareidolia" of the [http://www.explainxkcd.com/wiki/index.php/1551 Pluto comic]. --[[User:Lokar|Lokar]] ([[User talk:Lokar|talk]]) 15:26, 7 August 2015 (UTC)
Why no mention of the relation to the current whatif? [[Special:Contributions/141.101.91.91|141.101.91.91]] 07:01, 7 August 2015 (UTC)

Disagree that the title text is definitely in reference to any line in the song, just because it includes the word "collaborate[d]" [[Special:Contributions/108.162.228.17|108.162.228.17]] 07:49, 7 August 2015 (UTC)

Surely this comic would have been a perfect opportunity to mention {{w|Kurt Vonnegut}}'s fictional {{w|Ice-nine}}? Disappointed in you Randall! [[User:Cosmogoblin|Cosmogoblin]] ([[User talk:Cosmogoblin|talk]]) 09:42, 7 August 2015 (UTC)

I’m not happy with the title-text-explanation. In my eyes the joke is that Randall try to make us believe that Vanilla-icecream is ice IV – and they somehow managed in the 90s to let it exists at high temperatures (for us: normal room temp). --[[User:DaB.|DaB.]] ([[User talk:DaB.|talk]]) 11:31, 7 August 2015 (UTC)
: I have to disagree for one important reason: (Vanilla) Icecream was produced in high quantities since approx. the 1950's (or even earlier) and not just since the 90's, which is common sense, I think. Imho "Vanilla Ice was produced in small quantities for years" refers more to the fact, that many of Vanilla Ice's tracks consist of different samples of earlier produced songs (such as Under Pressure) or even complete covers (i.e. Play that funky Music). However, Randall might have missed another perfect opportunity for a different joke: Since "Vanilla" is used as expression for "normal" or "trivial" he could have placed it for Ice (I), the "normal" solid water. In that case the Under Pressure reference would have been a bit less obvious, though. [[User:Elektrizikekswerk|Elektrizikekswerk]] ([[User talk:Elektrizikekswerk|talk]]) 12:22, 7 August 2015 (UTC)

Purely as a tangent, ice cream was commonly available in the U.S. in the 1700's, and by the 1800's large silver flatware sets often included (along with other odd specialty pieces like asparagus tongs) sets of ice cream forks. Yes, ice cream was originally "properly" eaten with a fork. [[User:Miamiclay|Miamiclay]] ([[User talk:Miamiclay|talk]]) 20:40, 7 August 2015 (UTC)

I thought for sure the intersection of the three was called "Ice-T" [[Special:Contributions/173.245.48.184|173.245.48.184]] 13:40, 7 August 2015 (UTC)

I don't see any square, faded or otherwise, by label "water vapor". [[Special:Contributions/108.162.219.231|108.162.219.231]] 13:04, 7 August 2015 (UTC)

I have to very strongly disagree with the opinion expressed by [[Special:Contributions/108.162.216.173|108.162.216.173]] in [http://www.explainxkcd.com/wiki/index.php?title=1561:_Water_Phase_Diagram&diff=99284&oldid=99281 this edit], namely that 'pressure scale incresing down isn't so jokes are at bottom, it facilitates being "Under" Pressure - the joke doesn't work any other way.' Being at the bottom along the pressure axis doesn't mean that region is "under" pressure. It's "under" Vanilla Ice. The joke works because it is ''under pressure'', a very high amount of pressure, not because it is geometrically below pressure in any sense (it really isn't). My original text, that pressure increases downwards so the jokes are at the bottom, makes far more sense to me (well, naturally). It's the "reveal". If the jokes were at the top, they'd be read before the average reader had even grasped what the comic was about. But anyway, that's just my opinion; does anyone else have any thoughts? -- [[User:Peregrine|Peregrine]] ([[User talk:Peregrine|talk]]) 15:07, 7 August 2015 (UTC)

Sorry, got lost, but I wanted to suggest it's missing Miles Davis at the very bottom. "Birth of The Cool", ya know. [[Special:Contributions/108.162.242.27|108.162.242.27]] 21:20, 7 August 2015 (UTC)