https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&feedformat=atom&user=Crazynerd2049explain xkcd - User contributions [en]2026-04-21T01:13:25ZUser contributionsMediaWiki 1.30.0https://www.explainxkcd.com/wiki/index.php?title=2991:_Beamsplitters&diff=3515062991: Beamsplitters2024-09-27T22:36:56Z<p>Crazynerd2049: Added transcript</p>
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<div>{{comic<br />
| number = 2991<br />
| date = September 27, 2024<br />
| title = Beamsplitters<br />
| image = beamsplitters_2x.png<br />
| imagesize = 479x385px<br />
| noexpand = true<br />
| titletext = Under quantum tax law, photons sent through a beamsplitter don't actually choose which path they took, or incur a tax burden, until their wavefunction collapses when the power is sold.<br />
}}<br />
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==Explanation==<br />
{{incomplete|Created by a SOLAR PANEL HIDDEN DEEP IN MEDIAWIKI'S HQ - Please change this comment when editing this page. Do NOT delete this tag too soon.}}<br />
A {{w|beamsplitter}} is a device, usually made from a pair of prisms or a half-silvered mirror, that splits a beam of light into two beams going in different directions. Beamsplitters are used in numerous scientific instruments such as microscopes and (here) telescopes. In a microscope, a beamsplitter may be used to direct the imaging beam to the user's eyes, or to a recording device such as a camera, or to both at once.<br />
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In this comic, a beamsplitter is being used in a large-scale telescope to "steal" part of the incident light beam and direct it to an electricity-generating solar panel. The power generated is then sold on the local grid. The situation may be taken as a darkly humorous comment on the state of funding for scientific research, at least in the USA, implying that surreptitious, and legally/ethically questionable, strategies are needed to fund scientists and their projects. The comic pushes the point by supposing that the practice had become so commonplace that the IAU got wind of it, and, presumably to minimize the fallout from legal actions and negative publicity, has acted to ban the practice. <br />
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Most optical instruments, even large telescopes, are unlikely to capture enough light during regular operations to make the "banned" strategy feasible. Moreover, the ban is ham-fisted, as it makes legitimate operation of telescopes profoundly more difficult. For the sake of the joke, both of these issues are ignored.<br />
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The title text humorously conflates financial tax laws, applicable to the sale of the "stolen" electricity, with the laws of quantum physics, governing the behavior of the photons that are generating the electricity.<br />
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==Transcript==<br />
{{incomplete transcript|Do NOT delete this tag too soon.}}<br />
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Cross section of a telescope with some parts of the image darkened to represent the path of light, with portions where the light would be more concentrated being darker<br />
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Labels with arrows as they appear left to right, top to bottom:<br />
"Incoming Light"<br />
"Primary Mirror"<br />
"Secondary Mirror"<br />
"Beamsplitter"<br />
"Sensor"<br />
"Secret Solar Panel"<br />
"Power Sold To Grid"<br />
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The comic is captioned "Astronomy News: The international astronomical union has finally banned beamsplitters, optical devices used by scientists to embezzle light from their instruments"<br />
{{comic discussion}}</div>Crazynerd2049