explain xkcd - User contributions [en]

2671: Rotation

2022-09-12T23:16:45Z

Ziggy: /* Explanation */ add to explanation of title text

{{comic
| number = 2671
| date = September 12, 2022
| title = Rotation
| image = rotation.png
| titletext = It's okay, we can just feed the one-pixel image into an AI upscaler and recover the original image, or at least one that's just as cool.
}}

==Explanation==
{{incomplete|Created by an AI upscaler - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

Another of Randall's [[:Category:Tips|Tips]], this tip claims that rotating a phone and taking a screenshot too many times will cause an image to disappear into nothingness, and warns the user against doing so. This is funny because while camera phone users are unlikely to do this, they are usually less aware of the optimal resolution for their intended purposes than they could be. A phone's "auto-rotation" feature will automatically rotate an image to the fit the current phone's orientation based on {{w|accelerometer}}s.

[[Image:World lines and world sheet.svg|thumb|200px|{{w|String theory}} describes the {{w|worldline}}s of point-like particles as {{w|worldsheet}}s of "closed strings," forming a topological foam.]]

For a fuller explanation of the concepts involved, including {{w|Planck units}}, often associated with the topological {{w|quantum foam}} of {{w|string theory}}, please see [https://www.youtube.com/watch?v=pUF5esTscZI this CGP Grey video.] For an explanation of topological string theory, see [[2658: Coffee Cup Holes]].

The title text refers to producing photographically likely higher resolution images from lower resolutions, an active area of current research. Because reducing the resolution of an image is a lossy process, however, the result obtained through such processes will not be able to perfectly recreate the original. When scaled all the way down to 1 pixel, everything except a small amount of data about the image's overall color is lost, making reconstructing the original image impossible, though the algorithm might produce a made up image of "equal coolness" to the original.

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

[A phone in portrait orientation shows an image. It is then rotated, showing the image smaller with bars in landscape orientation, then the next phone is in portrait showing the entire screen of the previous rotated sideways, shrinking it every time. The labels show the decreasing size of the original image as it goes through successive rotations.]

"9 rotations: original image is smaller than a pixel."

"25 rotations: original image is smaller than an atom."

"101 rotations: original image is smaller than the Planck length, at which the concept of distance may break down."

Bottom caption: "Phone tip: don't rotate and screenshot an image too many times or it will become lost in the quantum foam of the universe."

{{comic discussion}}
[[Category:Tips]]
[[Category:Smartphones]]

2556: Turing Complete

2022-09-10T17:57:45Z

Ziggy: /* Transcript */ Fix mismatch in transcribed caption

{{comic
| number = 2556
| date = December 17, 2021
| title = Turing Complete
| image = turing_complete.png
| titletext = Thanks to the ForcedEntry exploit, your company's entire tech stack can now be hosted out of a PDF you texted to someone.
}}

==Explanation==
{{incomplete|Created by a NATION-STATE THAT CAN RUN DOOM, CRYSIS, GRAND THEFT AUTO AND YOUR COMPANY'S CORPORATE ETHICS - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

A {{w|Turing machine}} is a theoretical computer that has an infinite tape of symbols. It can read and change the symbols on the tape as it moves up and down this tape according to a set of instructions (program).

This very simple machine can be shown to do every computational task that what we think of as a "computer" can do, given the right program and enough time. Something that is {{w|Turing complete}} is able to act as a Turing machine, though generally physical examples are limited to having a finite tape,{{citation needed}} and this means it is also able to do basically every computational task.

Many pieces of hardware and software are supposed to be Turing complete (even Excel, as previously pointed out in [[2453: Excel Lambda]]). Some other things turn out to be Turing complete, even if they weren't designed for it (for instance, the tabletop game [https://arstechnica.com/science/2019/06/its-possible-to-build-a-turing-machine-within-magic-the-gathering/ Magic: The Gathering] or, at least within xkcd meta-reality, [[505: A Bunch of Rocks|rocks in a desert]]). Whatever [[Ponytail]] has been referring to is not shown, but it seems to be an anecdote about how something seemingly too simple and/or specialised to exhibit such a computational equivalence has been discovered to actually be that capable. Ponytail may refer to the recent articles about the background of the NSO zero click exploit for iPhones, e.g. [https://securityboulevard.com/2021/12/nso-zero-click-exploit-turing-complete-cpu-in-image-file/ this].

{{w|Mario}} is the lead character in a long running series of video games including {{w|Donkey Kong}}, {{w|Super Mario Bros}} and {{w|Mario Kart}}. Running video games, [https://hackaday.com/tag/does-it-run-doom/ such as Doom], is one common way of demonstrating the ability to run arbitrary programs on devices that were not intended as general purpose computers. With complex processors being installed in more and more devices, it's plausible that someone could get a dishwasher to play Mario.

However, another reason to make a device run arbitrary code is to {{w|Arbitrary code execution|breach security.}} If the owner of a system assumes that it can only do one specific thing, like operate a dishwasher, they may not take precautions against hacking. But if the system is actually Turing-complete, a hacker could potentially make it do something else, like become part of a {{w|botnet}}. Therefore, "this is actually Turing-complete" could be the prelude to a complicated hacking attempt. Sophisticated hacking attacks are often the work of hackers that have the support of a government, or {{w|nation-state}}.

The {{w|FORCEDENTRY|ForcedEntry}} exploit is a way that was developed to allow {{w|PDF}} files to force malware onto various devices. PDF files are normally used to present documents. The exploit uses a PDF's ability to do logic operations on pixels to implement [https://googleprojectzero.blogspot.com/2021/12/a-deep-dive-into-nso-zero-click.html a simple virtual CPU] within one of the PDF renderer's decompression functions. Constructing a CPU in this way is similar to how a hardware CPU is made of individual logic gates. ForcedEntry was publicized a few days before this comic came out.

In the title-text it is suggested that this mechanism can be used for what might be more legal and practical purposes, although this might be up to some interpretation depending upon who has the right (and permission) to do what.

A {{w|Solution stack|tech stack}} is one shorthand way of describing the way an integrated grouping of communicating software packages provides everything from the deepest data handling (even as low-level as an operating system itself) to the user interface. All of these will normally be on a computer (or possibly many of them, whether locally or distributed worldwide) and if a sufficiently functional surrogate system is capable of emulating this (computing what the original computer(s) would do) then it can be considered to effectively ''be'' the same stack of technology and duplicate or replace the originals.

==Transcript==
:[Ponytail has raised her hand, palm up, as she addresses Cueball.]
:Ponytail: ...Now, it turns out this is actually Turing-Complete...

:[Caption below the panel:]
:This phrase either means someone spent six months getting a dishwasher to play Mario or you're under attack by a nation-state.

{{comic discussion}}

[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]
[[Category:Programming]]
[[Category:Video games]]

2670: Interruption

2022-09-10T04:23:02Z

Ziggy:

{{comic
| number = 2670
| date = September 9, 2022
| title = Interruption
| image = interruption.png
| titletext = It's been extra bad ever since my GPS got stuck on Phoebe Judge mode.
}}

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

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

[First panel, Cueball and Ponytail hosting a talk show]

Cueball: ...And that's when you knew she had betrayed you?"

Ponytail: Yeah, she picked up the money and walked out."

[Second panel, zoomed in on Ponytail]

Ponytail: To this day, I don't know if she planned it all.

Ponytail: But there was one moment that makes me think, maybe she did.

[Third panel, a silhouette in a doorway]

Ponytail: Just before she disappeared, she paused at the door, looked back at me, and said,

Silhouette: Hey - if I ever see you again,

[Fourth panel, zoomed in version of third panel]

Silhouette: Turn left at the next light

[Caption below the panels:]

It's so disorienting when a podcaster has a voice that's similar to my navigation app.

{{comic discussion}}