Editing 2293: RIP John Conway

{{comic
| number    = 2293
| date      = April 13, 2020
| title     = RIP John Conway
| image     = rip_john_conway.gif
| titletext = 1937-2020
}}

==Explanation==
{{w|John Horton Conway|John Conway}}, an English mathematician, passed away of [[:Category:COVID-19|COVID-19]] on April 11, 2020. ([http://conwaylife.com/wiki/Conway Alternative link]) Two days later, [[Randall]] created this [[:Category:Tribute|memorial comic]]. It is the 6th memorial comic, but it is the first released in almost 5 years, since [[1560: Bubblegum]].

One of Conway's most famous creations was the {{w|cellular automaton}} known as {{w|Conway's Game of Life}}. A cellular automaton is a machine composed of cells, each of which can be in a different state. Every generation, each cell in the automaton may transition to a new state depending on a set of rules. (Conway's work in mathematics was vast and various, but he is perhaps best known in the field for discovering the {{w|surreal numbers}}, which inspired [[Donald Knuth]] to write a novel which may have been referenced back in [[505: A Bunch of Rocks]].)

Conway's Game of Life was first popularized to the general public in the form of a game, Life Genesis, bundled into some distributions of Windows 3.1, an operating system from the early-90s that Randall most likely used in his preteen years.

Conway's Game of Life is a 2-state automaton (i.e., every cell can be "alive" or "dead") that is implemented on a two-dimensional grid of cells using the {{w|Moore neighborhood}} - this means that each cell can only be influenced by the eight cells directly surrounding it, both orthogonally and diagonally. The transition rules that Conway used are as follows:

* If an "alive" cell has no live neighbors, or only one live neighbor, it becomes "dead". (This simulates death by isolation).
* If an "alive" cell has four or more live neighbors, it becomes "dead". (This simulates death by overcrowding).
* If a "dead" cell has exactly three live neighbors, it becomes "alive". (This simulates birth).

Despite the simplicity of these three rules, Conway showed that patterns of amazing complexity can nonetheless develop out of simple cell arrangements. Some patterns do not evolve at all ("still lifes"), some enter a cyclic, repeating state ("oscillators"), and some reproduce their own pattern displaced by an offset, resulting in patterns that can move across the grid under their own power ("gliders" and "spaceships"). This last category is of particular interest, as it allows the Game of Life to transmit information from one location to another, allowing for rich, dynamic behavior and even for the creation of computational machines within the automaton itself.

This comic begins with the shape of a stick figure as the starting cell configuration of the Game of Life. The black cells are "alive" and the white cells are "dead". This configuration then evolves via Conway's rules, disintegrating into nothingness except for a five-cell pattern known as a "glider", which ascends up and to the right. This visually suggests an eternal "soul" breaking away as the corporeal body disintegrates. The glider is perhaps the most iconic pattern of the Game of Life, and is often used symbolically to represent the phenomenon of emergence. 

Here the topology of the grid on which the cells evolve is not known, the cellular automaton can be run on many topologies, for example you can choose to make cells reappear from the opposite side once they reach an edge (similarly to the behaviour of the well known Pacman). Here once the glider reaches the top right, we know for sure that the actual grid is bigger (since the glider leaves the frame while continuing its pattern), and we are only seeing part of the full grid.

The initial state presented in the comic does actually evolve in that manner, as can be verified by entering the pattern into a cellular automaton simulator such as [http://golly.sourceforge.net/ Golly] or web services such as [https://bitstorm.org/gameoflife/ this one] or [http://catagolue.hatsya.com/object/xkcd_48jsj8gzwe9e/b3s23 that one]. It seems that no one else have created this pattern before. At least, despite discussion in the comments, no one has found anything to show that this is not Randall's own discovery of this pattern. 

The title text simply states Conway's birth and death year: 1937-2020.

Conway's Game of Life was previously mentioned in [[696: Strip Games]]. Cellular automata was also referenced in [[505: A Bunch of Rocks]].

This comic is the 18th comic in a row (not counting the [[2288: Collector's Edition|April Fools' comic]]) in a [[:Category:COVID-19|series of comics]] related to the {{w|COVID-19 pandemic}}. Although this comic is, of course, mainly a tribute to John Conway, the fact that he died of COVID-19 in the middle of this long series of coronavirus-related comics by Randall is relevant.

==Table of generations==
{| class="wikitable"
!Generation
!Notes
|-
|[[File:Generation 0.jpg|thumb]]||Starting state (or "zeroth generation").
|-
|[[File:Generation 1.jpg|thumb]]||First generation. Note that this image is not aligned with the previous one: the position of all cells has shifted downward by one cell.  All further generations are aligned the same as this one.
|-
|[[File:Generation 2.jpg|thumb]]||Second generation.
|-
|[[File:Generation 3.jpg|thumb]]||Third generation.
|-
|[[File:Generation 4.jpg|thumb]]||Fourth generation.
|-
|[[File:Generation 5.jpg|thumb]]||Fifth generation.
|-
|[[File:Generation 6.jpg|thumb]]||Sixth generation. The first appearance of the {{w|Glider (Conway's Life)|glider}}, a well-known formation in Conway's Game of Life.
|-
|[[File:Generation 7.jpg|thumb]]||Seventh generation. The glider takes on its other shape.
|-
|[[File:Generation 8.jpg|thumb]]||Eighth generation. The glider returns to its first shape, pointing right instead of up.
|-
|[[File:Generation 9.jpg|thumb]]||Ninth generation. The glider's second shape again, pointing right instead of up.
|-
|[[File:Generation 10.jpg|thumb]]||Tenth generation. The glider is now in its original form, but one cell higher and one cell to the right.  It will continue to progress, cycling through these four states every four generations.  The remains of the chaos down below will take two more generations to disappear completely.
|}

==Transcript==
:[A pixelated image of a stick figure using 21 pixels, could be a pixel Cueball, which waves with one hand up while holding the other hand down. The head consist of 7 pixels, the top row of three having two pixels beneath the two outer pixels, thus having two empty pixels beneath the central pixel. The neck and torso is a typical cross made from six pixels. The two legs are two pixels each shifted left and right of the cross. The arm to the left that waves is two pixels one down and the next back up to the level of the cross central beam. The arm to the right has the first pixel similarly but the second pixel continues one further step down. After less than one second it turns out that the image is animated, with the pixels changing according to the rules of Conway's Game of Life. The figure splits into three groups, two of which dissipates in a similar way at the bottom of the panel. The other becomes a 'glider' and moves off to the top-right corner of the image and out of the frame. The animation then repeats.]

==Trivia==

* "XKCD RIP John Conway" has been cited on [http://conwaylife.com/wiki/Pure_glider_generator LifeWiki]
* "XKCD RIP John Conway" is now available on [http://catagolue.hatsya.com/object/xkcd_48jsj8gzwe9e/b3s23 Catagolue] <!-- Catagolue is down at the moment in some places -->

==Issues with some clients==

Some clients of the site crashed on this xkcd, most notably the Samsung Smart TV client.

{{comic discussion}}

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