Porn for math nerds

This recent xkcd should have you all reaching for your calculators.

I had to look up the population density in my area…it’s 18. Not 18 thousand, just 18. When I plug that number into the formula, I got a value of 4,500 meters, almost 3 miles. The parents of our students will find that a reassuring statistic, I hope.

Of course, the formula lacks a temporal component — that mean distance is going to vary with a circadian rhythm, I would think, with peaks in the evening and early morning hours. Rather than a static number, it should be a function that measures a kind of hourly flux, with all the sexy time people hovering in close around dusk and receding during the day.

Hmmm. If XF included masturbation, that number would be much higher…

1. says

Oh, wait…if XF includes masturbation, Xd would be much smaller. It might even out.

Need more data.

2. says

But I only do the calculations for the sake of math, nothing else.

3. LtStorm says

Also relevant to PZ’s interests (if he hasn’t seen it yet somehow);

http://xkcd.com/520/

(Also, as a chemist, I warn the biologists that we’re the ones that can synthesize poisons to kill anything that shows even vague signs of life.)

4. millsapian87 says

Average frequency of sex = 80 times/year? I wish!

…of course, I *have* been married for 20 years.

5. AnthonyK says

I’m not so interested in “Whether” as I am in “Where”. Also, how do I make that distance effectively, and practically, zero – for two people? Damn, maths can be so useless.

6. Parse says

The key question with regards to the population density, is how big of an area do you need to get that value of 18? For example, I’m looking at Morris’s stats on Wikipedia, and finding a density of 1183 people per square mile. So, taking into that account, I’m getting a value of 563.4 meters, or about .35 miles. So that’s better by a about a factor of 10, but still it’s a fair ways off. I recommend using a telescope.

7. Louis says

PZ,

Hmmm. If XF included masturbation, that number would be much higher…

and

Oh, wait…if XF includes masturbation, Xd would be much smaller.

Are you trying to tell us that Minnesotans are wankers? And specifically wankers with a hair trigger problem?

Surely a dedicated and important professor like yourself would be better placed to ignore these of the cuff* trivialities and focus on sea creatures instead. Long, throbbing four foot long sea creatures with dripping…..sorry where was I? Oh yes. Of course all those many Minnesotans will be mortally offended by your insinuations. Won’t someone please think of the Minnesotan children?

Enquiring minds want to know….something apparently.

Louis

*Or perhaps: wrist.

P.S. Glen, you only do the calculations for the sake of maths? I only read Playboy for the articles…. ;-)

8. rob says

i just did the calculation and now i am blind in one eye!

9. says

I wonder how this pi got in, and what that 2 is all about. I also doubt this square root. Oh well.

10. Steve says

Everyone folllow the actual link to xkcd, and hold your mouse over the comic.

11. stogoe says

Dur. I just found out myself and posted in the top topic, and now I feels all dumb to not see the post just below this. *pout*

12. says

Just like polls, we can beat this equation. Let’s get to work.

13. Tark says

@1 PZ …

Relax, you’re doing it wrong. Get all the data you need, its healthy.

Tax Religion. Ahead wank factor seven Mr. Sulu …
Tark

14. says

“Oh, wait…if XF includes masturbation, Xd would be much smaller. It might even out.”
Well, perhaps it would just be added in an average, or something.

15. varlo says

At 79 I am far less interested in any such distances except those six inches or less, but I am also having problems with that frequency number.

16. Hmmm. If XF included masturbation, that number would be much higher…

17. 30 Min?!

There’s a bunch of people in that statistical sample lyyyyyyyyyyyyyyyyyyin’ their ass off.

18. says

Oh, wait…if XF includes masturbation, Xd would be much smaller. It might even out.
Need more data.

Adding more events under the definition of sex can only reduce the radius, even if they are very short.

19. Thomas says

Oh, poor PZ! The figures are much better here in Paris’ XIe arrondisement:

Pd = 41 536 / km2
Xf = 130 / year
Xd = 32,5 min

which gives r = 43,7 m. I got Xf and Xd from national averages, wonder if they’re different for the city. Still, it’s pretty cozy here.

20. Becca Stareyes says

10ch, would you like a derivation? I’m pretty sure the 2 comes from the fact you need two people for sex*, and the square root and pi come from converting an average area to an average distance.

* Thus the equation discounts threesomes and orgies as statistically insignificant.

21. frog says

Xf and Xc are way too high, even as a Fermian approximation. The “average” person includes children, lonely people, quadraplegics, celibates and guys in their 50s who lost interest in sex decades ago. Xc includes early ejaculators, fakers who just want to go to sleep, and anorgasmic women who’d rather he’d just get done and leave them alone.

I’m figuring he pulled these numbers from among young physicists — the Feynmann’s of this generation. You don’t have to pretty — just interested.

22. Kevin Anthoney says

Oh, wait…if XF includes masturbation, Xd would be much smaller. It might even out.

Also, has xkcd factored in the assumption that sex is for couples? That might be what the 2 is for. We’d need to replace that with an average participants per sex act.

23. SamB says

I dislike this equation immensely – the examples given aren’t standard units, and the figures change dramatically depending on whether you are using minutes or seconds.

If anyone could clarify this, it’d be great.

24. @www.10ch.org (#11)

I wonder how this pi got in, and what that 2 is all about. I also doubt this square root. Oh well.

Population density(people per mile^2) x sex frequency (sex acts per unit time per 2 people) x sex duration (unit time) = sex acts per mile^2 (=Pd*Xf/2*Xd)
If you draw a circle of radius r around yourself, it’ll have an area of A=πr^2. So the expected number of sex events in your area is the sex acts per area time the area or (PdXfXdπr^2)/2 If you set that to 1 and solve for r you get the xkcd equation.

~apologies to any faster typist who answered this question before me.

25. Thomas says

To those wondering about the 30 min: the figures I found for France included coitus and preliminary sexual acts in the time. Because you are trying to find the distance to two persons having sex, I think that’s the time period you are interested in. Unless Americans are that much faster than French persons, it’s probably about right.

26. Benjamin Geiger says

I’m pretty sure the 2 and pi come from it being a radius.

And I’d assume 30 minutes is the combination of all sexual activities, not just copulation. I may not be a super-stud able to pound away for hours, but I can certainly do other things for hours that make her feel just as good.

(But nobody ever lets me prove it. :-( )

27. says

No no!!! Don’t you know that masturbation will cause a person to become crippled and blind in one eye, as well as causing many other physical health problems?

Random question (since this is a science blog, after all) – is there actually any scientific basis to the idea that excessive masturbation can make one go blind, or is it just an old wives’ tale? I’ve always wondered.

28. spudbeach says

Umm — sorry to rain on everybody’s parade here, but that formula can’t be right — UNITS!!!!!

The comic has inverse square miles, inverse years and minutes — there has to be some conversion factors, or you are totally messed up.

Other than unit conversions, it makes some sense. Essentially, it postulates that the number of people having sex within a certain radius is a Poisson random variable, and hence the spacing between events is an exponential random variable. Once that is accepted, then the calculation of the mean spacing is reasonable.

Is it just the physicists that care that the units have to work?

29. Benjamin Geiger says

Walton:

The reasoning I’ve heard (which may not be 100% accurate, take this with a grain of salt) is that blind people (or insane people) were most likely to be caught in the act. Not sure where the hairy palms thing comes from, though. Maybe from observation of monkeys?

30. Walton, are you worried?

No of course it is a wives tale.

Stepping on cracks will however cause your mother’s back to break.

31. says

I wonder how this pi got in, and what that 2 is all about. I also doubt this square root. Oh well.

Those should be there. Without them, you’d have the average area you’d need to spread a circle to find someone having sex (which is pi r squared).

Except I think he’s assumed that the product of averages is the average of a products (that X_FX_d is the proportion of time the average person spends having sex) which isn’t quite right

32. says

The mornings, huh?

Well, your kids are all grown up, I guess. It’s going to be a long time before I can have sex in the mornings.

33. says

I’m terrible at math. I plugged a bunch of numbers, many of which were probably incorrect, into the equation. It seems that people are having sex within 1.222222222 meters of me. Having looked around and concluded that I don’t live in Kowloon City, I am assuming this number is wrong.

34. seattler says

I like having sexy times in the afternoon. Its a benefit of telecommuting.

35. Clemens says

@SamB
Well of course you have to provide all quantities in the right units AND also make sure X_D and X_F use the same unit for time. If you multiply “80/year” with 30 minutes, you get “80 * 30 * minutes / year” so now you also have to figure out how many minutes there are in a year.

Or you type it into the Google calculator. It will do the dimensional analysis for you

36. Siveambrai says

When I ran the numbers I came up with the answer that someone with a foot of me is having sex. Of course I’m sitting right next to the wall that is shared with a neighboring apartment. I guess I know what they’re doing right now. :)

According to math, I’m probably having sex right now!

38. Damien says

You have to use the number of minutes in a year to balance the number of minutes a year that people spend in sex. It should be in the upper part of the ratio.
Not sure about the 2, also.

39. frog says

Spudbeach: Is it just the physicists that care that the units have to work?

XKCD is written by a physicist.

40. SamB says

@Clemens

Thanks for the tip. Should’ve used google calculator sooner, but oh well.

I got 370.520382 meters, but it’s a massively rough figure. I used the pop. density of my town but I live in a quieter part of the town, next to a great big forest. The town center (lots of blocks of flats and council housing there) are a couple of miles away, and the distance would be lower. Right here, it would be higher.

But the important figure, i.e how many people are getting it on in the radius of 1 m^2, is currently (and also for a long time in both directions) 0 :(

41. frog says

RevBigDumbChimp: There’s a bunch of people in that statistical sample lyyyyyyyyyyyyyyyyyyin’ their ass off.

It’s a “Fermi calculation”. Fermi used to do pull-numbers-out-of-your-ass calculations about problems like this, to teach students that if you get the magnitudes right, you’re 9/10’s of the way to solving the problem.

No statistical sample involved, just reasonable numbers will get you a fairly good approximation if your equations are right. There goes the whole idea of proper sampling being the end-all of science…

42. says

XKCD is written by a physicist.

No it isn’t. Munroe was roboticist; now he’s a full-time cartoonist.

43. Damien says

44. Clemens says

@SamB
Well of course you have to provide all quantities in the right units AND also make sure X_D and X_F use the same unit for time. If you multiply “80/year” with 30 minutes, you get “80 * 30 * minutes / year” so now you also have to figure out how many minutes there are in a year.

Or you type it into the Google calculator. It will do the dimensional analysis for you

45. frog says

Walton: is there actually any scientific basis to the idea that excessive masturbation can make one go blind, or is it just an old wives’ tale?

If you have male friends, just note the percentage of them who are blind. That’s science.

46. Boomer says

@1 (PZ)

You would also have to change the numerator to a number like (2-Xm), where Xm is some sort of masturbation factor.

47. Damien says

48. says

Not sure about the 2, also.

ahh wait.. the 2 is assuming that if someone is having sex exactly one other person is having with them (so you don’t double count the pairing). So there we go; wanking doesn’t count, and group sex skews the estimate.

49. Sam the geophysicist says

80/year? I am zero for the last year. And I’m 22! who is throwing off these averages!?

50. It’s a “Fermi calculation”. Fermi used to do pull-numbers-out-of-your-ass calculations about problems like this, to teach students that if you get the magnitudes right, you’re 9/10’s of the way to solving the problem.

No statistical sample involved, just reasonable numbers will get you a fairly good approximation if your equations are right. There goes the whole idea of proper sampling being the end-all of science…

Yeah, I forget this is a science blog sometimes where the slightest misstep in language will screw up a joke.

I was more making a joke about people’s self opinions of themselves and less about the sample.

51. Confused says

Of course, the formula lacks a temporal component — that mean distance is going to vary with a circadian rhythm, I would think, with peaks in the evening and early morning hours. Rather than a static number, it should be a function that measures a kind of hourly flux, with all the sexy time people hovering in close around dusk and receding during the day.

The alt text for this comic includes the disclaimer:
“Stats are ballpark and vary wildly by time of day and whether your mom is in town.”

If I was less lazy I’d try and calculate a rough formula to turn a sine wave into an approximation of the copulation probability over time…

And as mentioned above, this looks like it’s mostly the formula for the area of a circle backwards, with an approximation of probability in there, explaining the presence of pi and square root.

52. Nicholas says

53. Free Lunch says

Uh, could someone explain Crossbows? Please.

54. says

is there actually any scientific basis to the idea that excessive masturbation can make one go blind, or is it just an old wives’ tale

There appears to be one way that masturbation can cause blindness, which is by causing anxiety in individuals so that when they masturbate they are afflicted by hysterical blindness. Documented cases exist.

One could ask if the masturbation is actually “the cause” in such events, but it is at least “causal,” if not the “primary cause.” To be sure, there would be no hysterical blindness due to masturbation if people didn’t first tell, well, kids usually, that whacking off causes blindness.

55. Damien says

“ahh wait.. the 2 is assuming that if someone is having sex exactly one other person is having with them (so you don’t double count the pairing). So there we go; wanking doesn’t count, and group sex skews the estimate.”

Makes sense. You assume that they neccessarily come in pairs… Makes sense.

56. says

O several people already explained the 2. sorry.

Is that multiplying the averages thing OK? It’s a long time since I did stats. Is it at least the best estimate if average frequency and average duration are the data you have? Seems like it should be, but I don’t feel like trying to prove it.

57. frog says

Chimp: Yeah, I forget this is a science blog sometimes where the slightest misstep in language will screw up a joke.

Achtung! Ve vil have no huma hea! Huma ees streectly verboten!

Die Fuhrer vil hea about dis!

58. co says

the 2 is assuming that if someone is having sex exactly one other person is having with them (so you don’t double count the pairing). So there we go; wanking doesn’t count, and group sex skews the estimate.

Proper estimates (weighted) for Xd and Xf will take that into account. After all, Munroe doesn’t say what metric is used for the “average”.

59. says

Achtung! Ve vil have no huma hea! Huma ees streectly verboten!

Die Fuhrer vil hea about dis!

Germans speak English with a rhotic accent; “huma” rather than “hoomor” made that completely unfunny.

60. Clemens says

Excuse my double post. That was weird. I got the usual error message, so I hit the back button, refreshed, and it still wasn’t there, so I sent it again. Now it’s here twice.

Whatever. In my part of Germany, I get r = 140m. oO

61. Akiko says

Sometimes I will be in line at the grocery or sitting in traffic and will think, “Everyone in my sight has had sex at least once with another human being.” In most cases that is just gross. I also think, “In 100 years everyone I can see will be dead and forgotten”. Fun with life.

62. says

Tench in eleven: I wonder how this pi got in…

Pie leads to sex; I thought everyone knew that.

Telecommuting, retirement, kids fledged, nightshift work, and a wobbly factor involving individual noisiness, distance from neighbors, soundproofing (vs. open windows on a Spring day), and bashfulness would influence the numbers too. So might the proportion of relatively randy young adults studying inflammatory subjects like biology.

‘Scuse me; I’m about to get distracted.

63. Darren S. A. George says

For the population density, you surely wouldn’t use the sate-wide, province-wide or national average, but the density of your immediate vicinity. You’d be better off taking the population of your city and dividing it by its area.

64. DuckPhup says

Another interesting statistic that should probably get factored-in is that the average penis is 6″ and the average vagina can accommodate about 8″. That means that there’s roughly 250 miles of unused pussy in just Florida.

65. Olie says

Theoretically, r = 250 m for University of Maryland at College Park.

I guarantee you, the dorms are much closer than 250m apart.

Though the closest dorms probably are about 250 meters away from the physics building, hrm.

66. lytefoot says

I dislike this equation immensely – the examples given aren’t standard units, and the figures change dramatically depending on whether you are using minutes or seconds.

If anyone could clarify this, it’d be great.

and all the other griping about dimensional analysis…

Come on! We’re all grown ups here, we can be expected to do dimensional analysis by ourselves. The formula should NOT contain the conversion factors, those are assumed in the inputs. One of the secrets of elegant physics is leaving conversion factors out of formulas.

Anyway… come on! 80 times a year is less than twice a week! Between adults under 40 in LTRs and people who are just easy, it’s not hard to get the average up that high.

I do agree that the 2 should be replaced by some sort of Nav factor for the average number of participants in a typical act.

The products of averages work out if we assume the values of Xf and Xd are uncorrelated. One might claim that the two values seem likely to influence one another, but a linear relationship seems highly unlikely.

@#54: here

67. Bill Dauphin says

Siveambrai (@38):

Actually, the sex act next door only exists as a fog of probability, unless you poke your nosy self in and take a peek. Your neighbor’s name isn’t Schrödinger, is it?

PZ:

Oh, wait…if XF includes masturbation, Xd would be much smaller. It might even out.

I guess there’s no way for me to dispute this without implying TMI about my own sexy-time performance, eh? In any case, I’m pretty sure the duration function you’re alluding to is gender-specific, so there’s even more added terms in the equation!

68. rob says

this xkcd comic is an example of a Fermi Problem

the estimates that go in are usually order of magnitude (so really the 2 and pi aren’t strictly necessary)

anyhow, when you plug the numbers in you need to use consistent units (as spudbeach notes above).

so converting the values given in the comic
Pd=18,600/square mile = 0.0073 / square meter
Xf= 80/year = 2.5e-5 / second
Xd=30 min = 1800 seconds

when you plug the MKS unit values in, you get

r~45 meters.

69. frog says

MattHeath: Germans speak English with a rhotic accent; “huma” rather than “hoomor” made that completely unfunny.

I’ve never heard a German make the v/w error, the long i/short i error, or reference telling Hitler as a threat. Germans are also usually pro-humor — at least as equivalent to any other nationality.

However, that is a perfect Hogan’s Hero’s Nazi accent. You some kinda pansy Euro, that you don’t know that? It’s one of America’s great cultural treasures.

70. says

Tried to do the numbers for me, but my first search at Statistics Finland for “sex” gave the first three hits as “sector”, “personal services not enumerated elsewhere” and “the manufacture of rubber items not enumerated elsewhere”.

Couldn’t go on.

71. eNeMeE says

“I dislike this equation immensely – the examples given aren’t standard units, and the figures change dramatically depending on whether you are using minutes or seconds.

If anyone could clarify this, it’d be great.”

Go read the mouseover text at the actual xkcd site.

The joke is a)about the pulling numbers out of your ass (Fermi problem) and b)dimensional analysis.

72. says

@frog: Sorry, too many layers of irony now; I’m confused. You got I was pretending to think the joke was ruined right?

73. says

I did the numbers for Providence, RI.

We have:
Pd = 200000/18 or 11,111 sq/mi
If I plug that into the formula I get: r=1.54, I’m assuming that’s in meters. Damn there’s a lot of sex going on.

If we play with the frequencies, say set Xf to 50 and Xd to 20 the number comes out to r=2.3m

74. frog says

MattHeath:

My God will smite you for this offense to my (and It’s) Dignity.

Await thy Stubb’d Toe.

75. Marcus says

What about a factor for religious tendencies in the area. Those nice religious folks obviously only have sex in marriage, and for procreation. So they probably only bang it out 10 or 20 times in their entire life (from what they want us to believe). As opposed to atheists who will shag anything that has a pulse.

So heavily religious areas will knock the frequency down to around 1, and the duration probably back to around 60 seconds. Any more than that and you might enjoy it.

76. Bill Dauphin says

I’ve never heard a German make the v/w error

Really? I’m sure I must have. I can’t narrate a specific instance, but given that the correct German pronunciation of w exactly matches the correct English pronunciation of v, it would be shocking if they didn’t occasionally transpose those sounds. I wouldn’t call it an “error,” though; more like a predictable aspect of accent.

I used to think the l/r confusion you so often see in TV depictions of Asian characters was just mindless racism… until I lived in Korea, and discovered there was a perfectly organic basis for it in their language. In Korean (which, despite being a distinct language, shares much of its sound-set with other East Asian languages), there is no precise analog for either l or r, but there is a letter in hangul (yes, letter, not character; hangul is a phonetic alphabet) that makes either a not-quite-but-almost-l sound or a not-quite-but-almost-r sound, depending on the surrounding sounds. After learning that, the whole l/r thing seemed more like a fairly sophisticated understanding of the accent than like a racist caricature (though it can obviously become that, if oversimplified).

Disclaimer: I’m not a linguist (cunning or otherwise); hopefully if there’s one in the peanut gallery, any errors I’ve made here can be gently corrected.

77. Bill Dauphin says

What about a factor for religious tendencies in the area.

Not to mention some factor to account for local restrictions on the sale, possession, and use of “marital aids.”

Oy! This calc is getting more complex by the femtosecond!

78. Clemens says

Crossbow: In the first-person-shooter “HalfLife”, you play the particle physicist Dr. Freeman. An experiment in the BlackMesa research complex goes completely wrong and aliens from the dimension Xen (or so) overrun the complex. Although a physicist, you’re also a tough guy and shoot your way through claustrophobia-prone laboratories and one of your cooler weapons apart from the gluon-gun is a crossbow.

79. frog says

BD: Really? I’m sure I must have.

I’d expect more likely the reverse error — an overcorrection, since so many of the cognates between the language have that sound shift (but of course, not all).

In some East Asian languages, there’s no distinction between l/r sounds — the phoneme can often shift in phonetic value. In English, the phoneme k has both the King and Can values — which are distinguishable in Arabic, I understand. In those cases, the foreign speaker has difficulty learning the distinction.

Germans just use the grapheme W for the phoneme English-v; it’s not that sometimes you pronounce the phoneme W as an English-v, sometimes as an English-w, and sometimes in between. They have another phoneme V, which sounds like an English-f, but neither sounds like an English W anywhere in it’s spectrum, as far as I know.

80. Heather says

My son is legally blind. I don’t believe it’s excessive wanking that caused it, but rather being born 14 weeks early. We’re quite happy that he has any vision left at all. We’ve gotten the warnings about no contact sports, he should be careful not to get things in his eye (his one good eye, the other one is pretty useless), etc.

As of yet, the good doctor has not said anything about avoiding masturbation. Maybe he assumes that it’s not an issue yet. But said son is 10 years old, so I believe if it’s not yet an issue, it is a pending issue. Maybe we should have a talk about it.

Of course, since he’s already blind he may just figure what the heck, I’m ALREADY blind – so that’s like a license to wank all I want!

81. Free Lunch says

Lytefoot, the entry about Higgs bosons is informative but gave me no clue what it had to do with crossbows.

Thanks, Clemens for that background.

I’m glad that the denizens at the XKCD Crossbows discussion are as in the dark as I.

82. I’ve never heard a German make the v/w error

But have you ever heard a German make the b/m/w error?

*quickly exits before the first tomato can be thrown*

83. frog says

Clemens: you just made it unfunny for me.

84. Clemens says

frog: Yeah I know. If you gotta explain it, it’s not funny. But at least, you know are a bit more educated in… useful(?) trivia.

In XKCD, if you hover over the cartoon with your mouse, you get a pop-up text (in most browsers) which in this case says “I love how Google handles dimensional analysis. Stats are ballpark and vary wildly by time of day and whether your mom is in town.”

The dimensional analysis of Google calculator lets your do calculations without having to conver years vs. minutes etc. For example, if you type into Google:

1 rod * 1 fathom * 1 meter in bushels

you get 261.00009 bushels.

86. NewEnglandBob says

The ultimate insult:

His penis is so small, it makes Planck length look humongous.

Planck length = 1.616 252 times 10^{-35} meters
(about 0.000 000 000 000 000 000 000 000 000 000 000 016 2 meters)

87. Bill Dauphin says

frog:

I’d expect more likely the reverse error

Reverse? I didn’t mean to be specifying a direction. I only meant that when you pronounce w one way in Hamburg and a different way in Hartford, there’s a pretty good chance that at some point you’re going have some intracranial crosstalk and produce the Hamburg pronunciation in Hartford.

Of course, I wouldn’t expect a German to pronounce the English word vessel as “wessel” (anyway, that’s a movie-cliche Russian accent; just ask Ensign Chekhov!)… but I wouldn’t be surprised if she pronounced weasel as “veezil.”

As you point out, the German pronunciation of v actually sounds like English f, hence fahrvergnügen is pronounced “fahrfergnügen.” ;^)

BTW, is this…

.there’s no distinction between l/r sounds — the phoneme can often shift in phonetic value…

…linguisticalese for what I said:

…there is a letter in hangul … that makes either a not-quite-but-almost-l sound or a not-quite-but-almost-r sound, depending on the surrounding sounds…

Cool.

88. frog says

BD: Of course, I wouldn’t expect a German to pronounce the English word vessel as “wessel”.

That’s what I meant by direction — I’d expect that some beginning English learners German-speakers would say something like “wessel” for “vessel” — they first thing you would learn is that a lot of words in German that have the “V” sound are pronounced in English with a “W” sound. You’d overcorrect, particularly on borrow words (rather than genealogical cognates) that retain the German V sound.

It’s usually though much worse of a problem with people who are switching dialectics within the same language, I understand. The closeness of the dialects make over-correction endemic: “Between you and I”, for a grammatical example (modeling from X and me ‘verb’ –> X and I ‘verb’).

89. says

NewEnglandBob at #88:

The ultimate insult: His penis is so small, it makes Planck length look humongous.

But Bob, wouldn’t that be such a monumentary discovery to find something so small he would be an instant celebrity recognized everywhere and —

Oh.

90. Alex Deam says

Hold on… r can never be equal to zero. For that to happen, at least one of the three variables would have to be infinite, which is obviously not going to happen. Currently, the formula suggests the calculator (the person, not the thing with buttons) can’t have sex on average (which incorporates the idea that nerds and sex are mutually exclusive).

So we have to assume that this formula only applies from a distance about 90cm (approximately half a person’s height) away from the calculator’s body centre, assuming the obligatory “people = spheres” assumption that we physicists just love (another problem with the formula is it assumes all sex occurs on the same plane as the calculator, yet we live in 3 dimensions, not to mention the 4th is missing too as PZ pointed out above. I guess this formula would give wildly inaccurate results in a skyscraper-heavy place like New York, for instance).

The 90cm (ish) rule would allow a calculator having sex on average to be included in the result. Inside the 90cm, a new formula would have to be used: specifically how often you yourself have sex. (Kinda reminds me how outside of a massive sphere, gravity follows an inverse square law, but inside, gravity follows a linear relationship. Obviously both results are derivable from the same concept, so maybe something could be done to find an underlying concept for this xkcd formula?)

And yes, I did just type all that out above instead of going out and trying to decrease my r value (and no, not in a perverted voyeuristic sense). Maybe I just showed the original xkcd to be right after all: the calculator doesn’t have sex on average?

91. Sili says

I’m disappointed to learn that the Crossbow joke was just a videogame reference.

It seemed funnier when it just existed in a surreal vacuum.

Bugger.

92. says

Mrcus #77: As opposed to atheists who will shag anything that has a pulse.

Wait, it’s supposed to have a …

Uh-oh.

(I’m dyin’ of street trees here; going for the low-hanging fruit.)

93. Pierce R. Butler says

If Regional Population Density is calculated in miles, why is the voyeur solving the equation in metric units? Is it hotter that way?

… that mean distance is going to vary with a circadian rhythm…

Has the Esteemed Professor neglected his rollover homework?

94. says

No, Walton, me auld skin, masturbation is actually good for you. Men who shoot their load regularly (in whatever way) suffer less from prostate trouble in later life, so don’t be afraid to tug away to your heart’s content.

95. says

I did the math for Fairbanks, Alaska. The nearest is apparently within 5 km away. Given the location of my humble abode, that’s probably not a bad estimate of a search radius.

Statistics has allowed us to identify the radius in which you’d have to search to find a random person having sex. However, it’s my expert opinion as a wildlife scientist, based off of the oral reports and the collar data, that all you have to do to find someone having sex is to find out where the older Palins are staying.

96. Anonymous Coward says

For those of you who say that they’ve never heard a German exhibiting the stereotypical German accent, be assured that that is perfectly possible. The standard German pronunciation-to-orthography correspondence listings don’t apply to many ‘local’ German accents. And one of the most widespread accent groups, ranging from the Dutch border to beyond Berlin, actually pronounces the w, v and f more like you would expect and there is a real audible difference between the onset of Wahrheit, Vater and Faden. Anyway, Germany is a big country and I think that talking about The German Accent is pretty pointless.
Back to topic: the two X’s represent the proportion of the time you’re having sex. So as mentioned, adding more sex acts may decrease the other parameter, but the total has to increase.

97. Captain C says

Re: the East Asian l/r thing, I recall reading, some years ago, an article in a popular science magazine (though not necessarily Popular Science) where they described an experiment in which they brain-scanned various people talking, and found that while there were two distinct brain locations/patterns for “l” and “r” in Westerners, in East Asians it was closer to being one region/pattern.

98. Andrew says

Hasn’t anyone noticed that this formula is totally wrong!!???
the distance can’t possibly be inversely proportional to the
population density, it would have to be some kind of direct
proportionality!!!!!!!!!

99. Alex Deam says

Hasn’t anyone noticed that this formula is totally wrong!!???
the distance can’t possibly be inversely proportional to the
population density, it would have to be some kind of direct
proportionality!!!!!!!!!

No Andrew, calm down, it shouldn’t. The distance should be inversely proportional to the population density. The higher the population density (i.e. the more people), the less distance you have to look before you will find someone having sex on average. As one goes up, the other goes down. That’s what inversely proportional means.

100. says

The equation leaves out dimensional effects. For example, the pop density of Manhattan is around 70,000 per square mile. The formula suggests that the average couple having sex is about 233 feet away. That tells me that, walking the streets of New York, you would be, like, constantly hearing people having sex. Especially in the evenings. But the population of New York is distributed through a volume, not an area….

Oh, and for the masturbation fans out there… don’t forget to change the 2 to a 1 in the numerator….

BBB

101. Eleanor says

Also important to consider: frequency of sex varies a lot depending on location. For example, on college campuses, generally people are either having a lot of sex or no sex at all. I’m not sure whether that pulls the average up or down . . .

102. * Thus the equation discounts threesomes and orgies as statistically insignificant.

That tallies with my own experience, dammit.

103. Kat says

I’m on a college campus. This should at least double the odds someone is having sex somewhere near me…

104. says

>…the formula lacks a temporal component — that mean distance is going to vary with a circadian rhythm, I would think, with peaks in the evening and early morning hours.

But PZ, you have to remember that nothing requires the quantities in the formula to be constants. Each quantity could be called in from a separate formula of its own. You’d probably be looking at a sinusoidal function for Xf. On the other hand, at the times when Xf is lowest, Xd might be highest.

This will require further study, most likely involving bugs and telescopes and great dedication.

105. says

You have to watch the units, people. You have to watch the units.

Recall that π = about 3.1415927 only when both the diameter and circumference of the circle are measured in metres. If the circumference is given in feet and the diameter in inches (which I believe would not be at all unusual in the USA, where they persist in using stupid units up on which the rest of the world — except the British anti-science movement — was smart enough to give a long time ago), then π = about 0.2617994!

You need the population density to be measured in people per square metre, the frequency of sex to be measured in Hertz (shags per second!) and the duration of sex to be measured in seconds (ah, that’s OK for the Brits and the Yanks, then :) )

While these figures may be a bit odd (though not all units can be conveniently-sized; capacitance is naturally measured in Farads, which are stupidly big for most capacitors in real-life electronic circuits and pressure is naturally measured in Pascals, which are stupidly small for most pressures encountered acting equally in all directions in real-life fluids), that’s exactly what exponential notation is for. What’s more, if you normalise the exponent to be a multiple of three (which no doubt will piss off the pure-maths crowd; you know, the ones who insist to refer to j as i) then it will always correspond with a named prefix. In fact, that’s so useful that there is even a button for it on most calculators (labelled ENG.)