2776: Crystal Ball

2023-05-17T06:49:52Z

Greer: /* Explanation */

{{comic
| number = 2776
| date = May 15, 2023
| title = Crystal Ball
| image = crystal_ball_2x.png
| imagesize = 257x336px
| noexpand = true
| titletext = 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.
}}

==Explanation==
{{incomplete|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.}}

In optics, {{w|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. This causes the parts of an image reflected near the edges of a sphere (from the perspective of a viewer) to be distorted. As the viewer moves, the parts of the image which are distorted move as well. The origin lies within the fact, that reflection/ refraction on a spherical surface is not perfectly focussed on a single point, in contrast to paraboloid reflective surfaces, that have a single focus point.

This is the principle behind a {{w|Fisheye lens}}, which corrects for the distortion to provide an image that is circular in shape and tends to be convex (i.e, bulges outwards) towards the center of the image.

The comic makes the joke that, since a {{w|crystal ball}} is a sphere, anyone trying to use one for {{w|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 {{w|3-sphere|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).

The title text observes a real-world action that could [[1475: Technically|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 {{w|fiber-optic cables}}, which, according to the title text, is sometimes collected using ball lenses. 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 fibre 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 see the contents of the internet.

==Transcript==
:[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.

{{comic discussion}}

[[Category:Characters with hats]]
[[Category:Comics featuring Cueball]]
[[Category:Physics]]
[[Category:Internet]]

explain xkcd - User contributions [en]

2776: Crystal Ball