563: Fermirotica

Explain xkcd: It's 'cause you're dumb.
Jump to: navigation, search
I love how Google handles dimensional analysis. Stats are ballpark and vary wildly based on time of day and whether your mom is in town.
Title text: I love how Google handles dimensional analysis. Stats are ballpark and vary wildly based on time of day and whether your mom is in town.


Fermi problems are a type of estimation problem involving several quantities that are not to be measured but that can be estimated to within an order of magnitude to be inserted into equations relating the quantities to produce an estimate for a target quantity accurate to within an order of magnitude, based upon the assumption that overestimations and underestimations of the magnitude of the input quantities will compensate for each other in the resulting estimated quantity. Erotica is material meant to cause sexual arousal in a person. "Fermirotica", then, is erotica made from the solving of a Fermi problem.

In the comic, Cueball is solving the Fermi problem of finding the average distance from the observer wherein a couple can be found copulating. (The example parameters given in the comic yield 139 metres.) The implication of the equation is that we are surrounded by sex in our everyday lives and that this is arousing to Cueball.

Nevertheless, we rarely encounter couples during the act itself.[citation needed] In this way, the comic may also be referencing the Fermi paradox in that the calculation suggests that the observer is highly likely to be surrounded by copulation but, paradoxically, never observes it. This is similar to the Fermi paradox which suggests that extraterrestrial life (i.e. space aliens) should be commonplace in our universe yet humanity has yet to discover the presence of extraterrestrial life. Of course, the lack of empirical evidence of couples having sex can easily be explained by the fact that most couples only have intercourse in privacy. By the same token, the original problem may be explained thusly: Alien species might conceal themselves from our observations, e.g. in order to avoid interfering in the development of civilizations. This answer to the Fermi Paradox is commonly called zoo hypothesis.

The second panel has Cueball sexually aroused by imagining the intercourse that has been determined to be statistically nearby. This manner of arousal is termed statistical voyeurism by an off-frame speaker who is evidently upset by it. Possible reasons for being upset are that he considers it an inappropriate use of statistics, or finds voyeurism inappropriate in general, or because it accurately predicts an actual copulation he is aware of and would rather keep private (e.g. the off-frame speaker is actually about to have sex).

The title text refers to the Google calculator and praises its capabilities of dimensional analysis, and more specifically unit conversion. Randall assumes that most readers will enter the equation with the example parameters into the Google search engine. The built-in calculator will output the result in the correct SI unit metre, although the population density was given as people per square mile. The second part of the title text states that the examples are nothing more than an educated guess, and that the equation is simplified. In reality, more parameters must be taken into account, e.g. the time of day, since most people will have sex in the evening or night. The insulting[citation needed] suggestion that the probability of sex rises when the reader's (supposedly promiscuous) mother is in town represents a Yo Mama joke.

Note that this comic was released on April 1st without being an April Fools' Day comic. But Randall made another April Fool on his reader, see the trivia section.


[A formula is shown with the variables explained above:]
Pd Regional population density (e.g. 18,600/mi²)
Xf Average person's frequency of sex (e.g. 80/year)
Xd Average duration of sex (e.g. 30 minutes)
On average, someone within distance r of you is having sex.
[Cueball standing in front of an easel.]
Cueball: Mmm, That probable couple 150 meters away is so hot. Oh yeah, theoretically work it, baby.
From out of frame: Hey! No statistical voyeurism!


comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!


Explanation marked as incorrect. I would do some editing, but I do not have the time or explanation-writing skill to do so effectively.


1. The explanation's listed April Fools' joke seems to have no proof; it has no mention in the comic.

2. The title text seems to just be a complaint against Google's methods for statistics (i.e. "I love" is sarcasm). All it says is that Google just wildly guesses, based on unrelated, random events, and calls it statistics. Zweisteine (talk) 04:26, 12 January 2014 (UTC)

I doubt that the title text was complaining or sarcastic at all. If I recall correctly, the ability to plug calculations with units into Google was pretty new in 2009, and especially useful, given as he switched his time units from minutes to years. 17:04, 12 January 2014 (UTC)

Except that it specifically states that Google guesses (stats are ballpark) and change based un unrelated occurrences (time of day and your mother's presence). That sounds like either sarcasm, or him actually loving how google doesn't (or didn't at the time) do a very good job with stats. Zweisteine (talk) 23:08, 17 January 2014 (UTC)

I agree with Zweisteine - it is obvious a sarcastic comment, because the results from Google is so random that it will change during the day - and of course there is the your mom joke. Is there a category for these comics? (Like with the velociraptor comics etc.) Kynde (talk) 11:20, 21 January 2014 (UTC)

The two sentences of the title text are unrelated. The first is not sarcasm, but is straightforward praise of Google's "dimensional analysis". Searching on "sqrt( 2 / (pi * (18600 / mile^2) * (80 / year) * 30 minutes) )" yields an answer of "139.379395 meters" with Google correctly doing all of the unit conversion for you. Wow, that really is cool! It should be noted when Google gained this capability, if we can find a source for that. The second sentence is a straightforward discussion of the limitations of the model, as the probability of having sex is not uniformly distributed throughout the day. The mom part is a joke because it applies to a specific individual, not simultaneously to the general population around you (unless it is "Moms Visit Campus Day"). There is no April Fool's joke here. Where does the 18,600 persons / square mile population density come from? Is it for a specific metropolitan area? Finally, what Randall is calling "dimensional analysis" is more commonly referred to as unit conversion. For physicists, at least, dimensional analysis refers to a more subtle and powerful tool where equations for phenomena can often be deduced (to within a scaling factor) purely by analyzing the units involved. Wikipedia's articles on "Dimensional analysis", "Units conversion by factor-label", "Drake equation", and "Fermi paradox" should all be linked. -- 12:26, 21 January 2014 (UTC)

Ah! I agree that the ... and (b) whether "your mom" was in town (she is exceptionally slutty) "your mom" joke is a better interpretation than my earlier thought that people have sex less often when their out-of-town mom is visiting them. Good job! - 02:28, 22 January 2014 (UTC)

April's fool seems to refer to the date of the comic being April 1st 2009. -- Eric957 (talk) (please sign your comments with ~~~~)

Understood, but there is no meta-"joke within a joke" or joke on the reader which would serve as a kind of April Fool's joke. This is just a regular comic which happened to be published on 1 April. -- 18:38, 21 January 2014 (UTC)

I think this represents a "Fermi Estimation" - it may give a number to a problem by taking "best guesses" for something that is not easily calculated exactly. See also http://whatif.xkcd.com/84/ Tier666 (talk) 17:58, 14 July 2014 (UTC)

I agree; I think it has little if anything to do with the Fermi Paradox. -- 03:21, 26 November 2016 (UTC)
Also agree! Pretty positive this has to do with “Fermi Problems” (aka “Fermi estimates”).
Uh, I got 10cm. Interpret that however you'd like. 05:52, 31 December 2015 (UTC)
I take it as you were off by an order of magnitude at least in one of your parameters or you made a mistake in the calculation. The only way you can get that without X_f and X_d being inconsistent is if you put the population density high enough that people are literally overlapping. -- 03:21, 26 November 2016 (UTC)
Yeah, make sure to convert your years or minutes so they are both in the same units of time. I came up with 4 meters on my first calculation, realized there was a mistake, corrected the units and got 7.1 kilometers. Now, if your units are correct and you got 10cm, then you might want to move to a quieter neighborhood. 01:24, 29 December 2016 (UTC)

This equation is not perfect (besides several environment factors, thus "on average"), because the times when people have sex are not independent: Usually two people have sex at the same time. 23:56, 20 November 2018 (UTC)

Wait, that's what the 2 is for. I should learn the circle equations... 00:01, 21 November 2018 (UTC)

Pretty sure this is about Fermi estimation more than the Paradox? Also disappointed to see no callout of the Fermi+Erotica pun. 10:10, 20 May 2023 (UTC)

Is the two supposed to represent the idea that there are two people having sex? If so, then it should almost certainly not be two - different numbers of people are involved in different sex acts, and the average number of people involved in an act of having sex (so to speak) is very unlikely to be exactly two. The overall average number will vary depending on how one defines sex. If, for example, you included group sex in your definition of sex, but excluded masturbation, then the average number of people involved in a single act of having sex would have to be greater than two, possibly significantly so. 21:06, 6 May 2024 (UTC)