2776: Crystal Ball

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Crystal Ball
They often use ball lenses to collect light at the ends of optical fibers, so when you look stuff up on the internet you're actually scrying through a crystal ball.
Title text: They often use ball lenses to collect light at the ends of optical fibers, so when you look stuff up on the internet you're actually scrying through a crystal ball.


Ambox notice.png This explanation may be incomplete or incorrect: Created by AN INSUFFICIENT UNDERSTANDING OF THE PHYSICS PRINCIPLES BEHIND REFRACTION AND WHY LIGHT MIGHT ONLY HAVE A ONE-WAY SPEED- Elaborate on the title-text. Do NOT delete this tag too soon.
If you can address this issue, please edit the page! Thanks.

In optics, spherical aberration is an image imperfection that occurs due to the increased refraction of light rays that occurs when rays strike a spherical lens near its edge, in comparison with those that strike nearer the center. The origin lies within the fact, that reflection/ refraction on a spherical surface is not perfectly focused on a single point, in contrast to paraboloid reflective surfaces, that have a single focus point. From the perspective of a viewer, this causes the image to appear blurry.

The comic makes the joke that, since a crystal ball is a sphere, anyone trying to use one for scrying or seeing the future would have to deal with this issue as well; the wizard is telling Cueball that he can only make out the parts of his future which are near the center, as the rest are distorted. Spherical aberration is specifically a property of refracted light, and since the crystal ball is presumably not showing an image originating from the other side of the ball (unless it is a hypersphere additionally extending itself though a time-like dimension), the image should not be distorted by both entering and leaving the sphere, perhaps only in the manner of a hemispherical lens (for which the internally formed holographic image-source perhaps could be properly anamorphically adjusted to exit in all directions a coherent manner). However, traditional scrying may have actually relied on spherical aberration, to allow unexpected shapes to emerge from subtleties such as surrounding flickering candles, that the seer may have used to amplify intuition and visions. The comic also incorrectly implies that spherical aberration only affects the edges of the image, possibly confusing it with field curvature. In reality, spherical aberration affects the full field of view.

The comic is also making use of the vague meaning of something being "hard to see". One would expect that this would mean that Cueball's future is vague or mysterious, as is often the case in many fantasy novels. But in this case, the wizard is telling Cueball that his future is literally hard to see due to the spherical aberration.

The title text observes a real-world action that could technically be described as "scrying through a crystal ball", that being the usage of the internet. Information over the internet is often transmitted via light sent through fiber-optic cables, which is sometimes collected using ball lenses.[1] Due to the similarity between ball lenses and crystal balls, Randall argues that this is technically scrying through a crystal ball because you're receiving information from elsewhere (searching for something) and receiving it by way of a crystal ball (through the ball lenses). This is flawed as any lenses at the end of a fiber optic cable are to assist a detector in decoding potentially billions of light flashes per second into computer signals as opposed to actually allowing a human to view the contents of the internet with their eyes.


[A wizard with with a pointed hat, long hair and a large beard is sitting on a chair at the left side of a table. He is holding a crystal ball with both hands while he is looking into it. The ball has a reflection on the side towards Cueball who is sitting on a chair at the opposite side of the table with his hands in his lap.]
Wizard: Your future is hard to see.
Wizard: I can make out some hazy details in the center, but the off-axis components are particularly unclear.
[Caption below the panel:]
Wizards never did figure out how to fix spherical aberration.

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I added an explanation of spherical aberration and the tendency of light to distort around spherical objects, as well as the idea of how fisheye lenses use this principle to do their thing. Darkwolf0218 (talk) 01:01, 16 May 2023 (UTC)

Thank you, the spherical aberration discussion is much better than before. Much better than the optics course I took where they consistently failed to notice that spherical aberration is because the lens is the wrong shape; it is an engineering problem not a physics problem. 16:32, 21 May 2023 (UTC)

I can't seem to find the citation toolbar while editing on mobile. So dropping this here for a reference to ball lenses on fiber optic cables. Template:Cite web https://www.edmundoptics.com/knowledge-center/application-notes/optics/understanding-ball-lenses/ Iggynelix (talk) 12:37, 16 May 2023 (UTC)

We very rarely use Cites on this site. Just add a link (in alternate-word form to flow with the sentence, ideally).
I've never really used toolbar stuff (simple enough to tap in {s, }s, [s and ]s, as well as any <s and >s needed for HTML, etc), and it's simple to (eventually, perhaps checking via Preview that it's not totally messed up on the first go or two) work out what others did to add references and copy the style of the right kinds of them.
So if you want to mention a link to ball lenses, just do something like this. (PS., use the full ~~~~ when signing Talk contributions, I fixed yours without using the {{unsigned}} 'reminder'..) 14:28, 16 May 2023 (UTC)

Why am I now ear-wormed by "Beware of the Beautiful Stranger" by Clive James and Pete Atkin? "That ball needs a re-gun" I said, shelling out The future you see there has all come about" https://genius.com/Pete-atkin-beware-of-the-beautiful-stranger-lyrics https://www.youtube.com/watch?v=MeOYHZQqWao 17:56, 16 May 2023 (UTC)

I’m going to edit the part on the title text to be more broad, as Google isn’t the exclusive way to receive any kind of information on the internet 19:35, 16 May 2023 (UTC)

While we can all applaud the connection of spherical aberration to crystal balls, unfortunately the off-axis part of joke misses the mark as spherical aberration is an aberration that is generally uniform across the frame. 19:52, 16 May 2023 (UTC)

Yes, the comic seems to be confusing spherical aberration with coma, which makes it hard to produce a good explanation. I think the current reference to fisheye lenses, and distorted shapes, is a red herring. Spherical aberration rather appears as a lack of sharpness. 03:34, 18 May 2023 (UTC)

I'm new to the whole xkcd's websites and comic strips and I desire to meet some other xkcd fans as well!ArchaRaid (talk) 23:29, 16 May 2023 (UTC)