Editing 273: Electromagnetic Spectrum

The wavelength starts at high values on the left and decreases in a {{w|logarithmic scale}} to the right. As a result of the inverse relationship between frequency and wavelength, the frequency scale starts at low values and increases logarithmically. Both scales are labeled with powers of ten and with {{w|metric prefix}}es. For frequencies above 100 {{w|tera-}}Hertz, it just says "other entertaining Greek prefixes like {{w|peta-}} and {{w|exa-}} and zappa-." The last prefix should be {{w|zetta-}} (denoting a factor of 10²¹), but is intentionally mislabelled, referencing musician {{w|Frank Zappa}}. The nonsense ''Q'' parameter does not change monotonically with either frequency or wavelength. On the scale, there is 17, an unlucky number in Italy. Next to it, Randall seems to offer an alternative, 117. After that, {{w|pi}}, a mathematical constant, is followed by another 17 and then by 42, the answer to Life, the Universe and Everything. Then, there is {{w|Golden Ratio|phi}}, another mathematical constant, followed by e to the pi minus pi, a joke referencing [[217: e to the pi Minus pi]]. To make this scale even more absurd, Randall adds -2, 540^50, 12 and 11² to the end of the scale.

* Slinky waves by a coil. These can be either longitudinal or transverse waves, depending on the manner in which the Slinky is driven. Notably, Randall has drawn the Slinky as tangled up; if you've ever played with a Slinky, you know how frustrating it is to untangle it.

* The human audio spectrum (from 20 Hz to 20 kHz). The "high-pitched noise in empty rooms" refers to {{w|tinnitus}}. This was later referenced to in [[1590: The Source]].

* "{{w|Wave (audience)|The Wave}}" in a stadium, a transverse wave phenomenon that travels through people.

;Power and Telephone

"{{w|CIA}} (Secret)" is a joke about all the wiretapping on phones and such.

;Radio and TV

"Shouting car dealership commercials" is a reference to the massive and often extreme advertising for car retailers. {{w|Ham radio}} is a private amateur radio used for communication. "Kosher radio" is playing with the ambiguousness of the word HAM. {{w|Kosher}} is a Jewish law for food, and it states, amongst others, that Jews are never allowed to eat meat from the unclean pigs - so no ham! Some frequencies of famous FM broadcast stations. "99.3 The Fox" is a modern rock station in {{w|Vancouver}}, {{w|British Columbia}}. "101.5 The Badger" is a classic rock station in {{w|Madison, Wisconsin}} (home of the University of Wisconsin, whose mascot is a badger). "106.3 The Frightened Squirrel" is not a real station, but makes a play off of the animal names commonly used as nicknames for either radio stations, programs, or hosts. The rays controlling {{w|Steve Ballmer}} are nonsense, but may reference real {{w|Balmer series}}, a set of transitions in the hydrogen atom that produce photons in the optical and ultraviolet light range. AM {{w|Amplitude modulation}}, VHF {{w|Very high frequency}}, and UHF {{w|Ultra high frequency}} are frequency ranges approved for commercial broadcasting companies. "Cell phone cancer rays" is playing with the belief of many people that mobile phones may cause cancer. Aliens belong to a range slightly higher than the frequencies used by human communications. So they can't hear us. Cell phones as a cause of cancer was later referred to in [[925: Cell Phones]].

;Microwaves

{{w|SETI}} is the "Search for ExtraTerrestrial Intelligence" project trying to find messages from aliens. Most genuine astronomical research in this area concentrates in the microwave and radio regimes. Since aliens work at different frequencies on this diagram, that might explain why there has of yet been no positive results from SETI. {{w|WIFI}} is the standard for wireless computer communications. FHF is probably "Fucking high frequency;" it is not an abbreviation for any broadcasting frequency ranges and lies above the (real) V(ery)HF and U(ltra)HF. {{w|Gravity wave}}s are a phenomenon in fluid dynamics, and distinct from {{w|Gravitational wave}}s. Neither is related to electromagnetic emission. Brain waves could be a reference to {{w|Neural oscillation}}. {{w|Sulawesi}} is an island in the Indian Ocean that belongs to Indonesia, whose shape has several wave like features.

;Toasters

This is a pun on the microwave oven, which emits light at its namesake frequencies to cook food. It also takes a stab at people who claim that microwaved food is dangerous, by pointing out that toasters also heat food using electromagnetic radiation, of frequencies just higher than microwaves. (The actual spectrum of a toaster goes all the way into visible frequencies.)

;IR (infrared)

{{w|Infrared}} belongs to heat. The reference to {{w|Superman}} covers his heat vision power, which has been used many times within the canon. American comedian {{w|Jack Black}} starred in a proposed scifi/comedy television show in 1999 titled "{{w|Heat Vision and Jack}}", which covered the adventures of an astronaut and his talking motorcycle.

;Visible light

At the bottom, it is split into "visible light" and "visible dark." While dark is the opposite of light in many grammatical contexts, in the physical sense it only reflects the absence of visible photons. The human visible spectrum is shown by all colors, including {{w|octarine}}, the color of magic on the fictional {{w|Discworld}} (in the books by {{w|Terry Pratchett}}). On top, there are two {{w|absorption spectrum|absorption spectra}}, hydrogen and helium. These are the two most common elements in the Sun, and their presence in the Sun's outer envelope and Earth's atmosphere does block some small frequencies from the Sun. Next come two cases of {{w|Absorption (chemistry)|absorption}} in the chemical/technical meaning. {{w|Depends}} is a brand of underwear for adults experiencing urinary or faecal incontinence. The color is consequently yellow. {{w|Tampax}} is a brand of tampon. The color is, therefore, red.

;UV (ultraviolet)

{{w|Ultraviolet}} light cannot be seen by humans. No entries here.

;Miller Light

{{w|Miller Lite}} is a lager beer. "Light beer" typically has a lower alcohol content and calorie count, although it is also usually a light color for beer.

;Empty section

One section is reserved for "Main Death Star Laser". In ''{{w|Star Wars}}'' the Death Star was a space station with a green laser cannon powerful enough to destroy planets. (It is unclear why its spectrum is well outside of the visible range.)

;Censored under {{w|Patriot Act}}

No entry because it's censored; this is a humorous exaggeration of how much authority the government can supposedly exercise under said bill.

;X-rays

Potatoes absorb and reflect radiation waves the same way humans do, because their chemistry and water content is very similar to the human body. Look here: [http://www.usatoday.com/story/todayinthesky/2012/12/24/boeing-wifi-potatoes/1789109/ Boeing uses potatoes to improve Wi-Fi signals]. Mail-order x-ray glasses refers to {{w|X-Ray Specs (novelty)|a novelty item}} based on an optical effect, not actual x-rays. {{w|Google Glass}} did not exist at the time when this comic was created.

;Gamma/Cosmic rays

Blogorays are emitted by the {{w|Blogosphere}}; apparently only Randall can detect them. Sinister Google Projects: {{w|Google}}, despite having a motto "don't be evil", has such significant power that it is a frequent target of conspiracy theories.  

;Title Text

Randall likes to speculate what the world would look like if humans could see radio waves, gamma waves, etc. Such a thought experiment would be pretty abstract due to the total lack of a frame of reference (since everything outside the visible light spectrum is by definition invisible and thus beyond human optical perception), but for many people, that's also what makes it enticing. Randall immediately turns this profound train of thought around with a crude joke that he wants to know what the viewer's sister would look like in the nude, an activity for which x-rays would be useful.

:[Three parallel scales are across the bottom. The first is lambda (m), ranging from 100Mm to 100fm; second is f (Hz), which starts at 1 Hz and reaches 100 THz about 2/3 of the way along, after which the labels read "other entertaining greek prefixes like peta- exa- and zappa-;" last is Q (Gal²/Coloumb), whose labels are 17, 117, pi, 17, 42, phi, e^pi-pi, -2, 540^50, and 11². Above the scales and lined up accurately with the first two are the following:]

This comic used to be [https://web.archive.org/web/20220125023401/https://store.xkcd.com/products/signed-prints available as a signed print] in the xkcd store before it was [[Store|shut down]].