1531: The BDLPSWDKS Effect

Explain xkcd: It's 'cause you're dumb.
(Redirected from 1531)
Jump to: navigation, search
This well-known effect has of course been replicated in countless experiments.
Title text: This well-known effect has of course been replicated in countless experiments.


The BDLPSWDKS Effect in the title is an acronym for Bernoulli-Doppler-Leidenfrost-Peltzman-Sapir-Whorf-Dunning-Kruger-Stroop Effect, as explained by Ponytail in the comic. She stands in front of a slide that shows Cueball being subjected to this effect.

The effect mentioned appears to be a mashup of seven scientific principles (with nine scientists' names included) from physics and social sciences, with elements from each principle appearing in the resulting description of the effect:

  • Bernoulli's principle in fluid dynamics (also mentioned in 803: Airfoil) states that an increase in the speed of a fluid with certain properties occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.
    • This is referenced by the firetruck lifting off and hurtling.
  • The Doppler effect in physics refers to the change in a wave's frequency for an observer moving relative to its source. Sound from the oncoming firetruck increases in pitch.
    • This is referenced by Cueball reacting faster if the shouting is in a non-tonal language than a tonal language. In tonal languages, changes in pitch change the meaning, thus tonal languages may suffer more from Doppler distortion than non-tonal ones. Additionally, the choice of firetruck was likely influenced by this effect, as a firetruck and its siren are often invoked as an example of it.
    • This may also be referenced by the fact that Cueball reacts faster when red is shouted as the Doppler effect makes light shift up the spectrum : red may still be visible after the shift but green may be out of the visible range.
  • The Leidenfrost effect, in physics, refers to how liquid will produce an insulating vapor layer when in near contact with an extremely hot surface, causing it to hover over said surface.
    • This is referenced by the firetruck lifting off on a layer of superheated gas.
  • The Peltzman effect, in behavioral economics, refers to how regulations intended to increase safety are ineffective or counterproductive because people, feeling safer, will engage in riskier behaviours.
    • This is referenced by the fire truck, which is intended to improve public safety by putting out fires, speeding and thus creating a hazardous situation and reducing the safety of the pedestrian. The firefighter may also be more inclined to drive recklessly due to the feeling of safety they have in a modern firetruck.
  • The Sapir–Whorf hypothesis, in linguistics, states that a person's world view and cognitive processes are affected by the structure of the language the person speaks.
    • This is referenced by languages with a word for "firefighter" giving a quicker reaction. If Cueball speaks (or is currently thinking in) a language without a word for "firefighter", he might be slower to recognize the role and authority of the driver warning him, and thus slower to react to the danger.
  • The Dunning–Kruger effect, in social psychology, refers to unskilled people mistakenly perceiving themselves as more skilled than they really are, while skilled people underestimate their own abilities.
    • This is referenced by the tonal language being a language Cueball thinks he is fluent in but isn't.
  • The Stroop effect, in psychology, refers to the phenomenon in which it is easier to name the color of the ink in which a word is written when the word refers to the same color as the ink than when the word refers to a different color.
    • This is referenced by Cueball diving out faster if the driver screams "red!" than if the driver screams "green!", as a traditional American firetruck is red, and therefore it may create a moment of confusion for Cueball if the driver shouts "green!". It may also reference the common usage of "red" as indicating fire or danger, while "green" indicates safety.

This comic is probably a comment on the "replication crisis" in social psychology which has been in the news recently. For example, studies finding that merely thinking about intelligent people (e.g., writing down the attributes of a professor) will actually improve performance on math tests were once widely believed, and this "intelligence priming" effect is even included in textbooks. However, recent attempts to reproduce these effects have mostly failed and this failure to replicate is true of many social priming effects as well as other experiments in social psychology. Randall is also mocking the complicated, or even convoluted, setups often used in these experiments.

Usually, for an effect to be considered real, the scientific method requires the effect to be replicated by different experimenters in different times and places. It is hard to imagine several scientists in different parts of the world creating the setup to replicate this effect; however the title text mentions, sarcastically, that it has been done countless times.

Many other xkcd strips have commented on the ease with which surprising and novel, but false, results can be published in the scientific literature, such as 1478: P-Values and 882: Significant.


[Ponytail stands next to a screen displaying a firetruck hurtling toward Cueball on what appears to be a layer of gas.]
Ponytail: The Bernoulli-Doppler-Leidenfrost-Peltzman-Sapir-Whorf-Dunning-Kruger-Stroop Effect states that if a speeding fire truck lifts off and hurtles towards you on a layer of superheated gas, you'll dive out of the way faster if the driver screams "red!" in a non-tonal language that has a word for "firefighter" than if they scream "green!" in a tonal language with no word for "firefighter" which you think you're fluent in but aren't.

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


Doesn't the reference to the "Doppler" effect refer to the fact that the Doppler effect may distort the meaning of words in a tonal language, thus making it harder to perceive the word being shouted out of the firetruck? A-jay (talk) 07:52, 29 May 2015 (UTC)

I thought this too - tonal languages will inevitably suffer more from Doppler distortion than non-tonal ones, so it's going to take the listener longer to react to it. Obviously, that's not the sole cause for the delay with the BDLPSWDKS effect, but it's surely a contributing factor. Bish (talk) 11:22, 29 May 2015 (UTC)

I think it is a bit more complex than effect mentioned having an individual referent. It becomes complex because the language level, for example, interacts with the physics level. (I think this is the joke, that such random effects from different fields can actually interrelate in some bizarre scenario) A tonal language would be much more susceptible loss of meaning due to blue shift from the doppler effect than a nontonal language. Shouting red is also probably a reference to the 'red-shift' in the doppler effect, which, depending on the speed of the truck may distort the sound the shout or make it unintelligible. At sufficient speed, this would also distort the actual color of the firetruck, which is a topic Randall discussed in one of the What-If's about traffic lights and should probably be linked here. --MareCrisium (talk) 08:15, 29 May 2015 (UTC)

I thought of the red being a redshift as well, but what the heck is "GREEN" then (rather than "BLUE")? Odysseus654 (talk) 09:05, 29 May 2015 (UTC)
I'm pretty sure this is a reference to an idea that appeared (I don't know whether it's true, but I assume it also appeared in other places) in my Intro Psych textbook – that humans respond, in theory, to green firetrucks better than they do to red ones. See, for example, [1]. See the end of the third paragraph. If that's not a contributing factor to the BDLPSWDKS effect, I don't know what is. COgnaut (talk) 01:03, 5 June 2015 (UTC)
Colors undergoing a red-shift move through the whole spectrum in sequence. Green is in the middle. Red-shifts happen when something is moving away from you, and blue-shifts happen when something is moving toward you, (although sometimes the more common term red-shift is used to describe both effects in casual context) but neither means that they thing turns red or blue. They mean that the color moves toward the red or blue side of the spectrum, from the (somewhat arbitrary) "middle" which is usually depicted as green. If the firetruck is coming toward the observer, they would be experiencing a blue-shift. If the fire truck is red, and moving very fast toward the observer, the apparent color would move toward the other end of the spectrum, but it may not be moving fast enough to get all the way to blue. Randall already did the calculations for a what if about the speeds necessary to change from red to green in an question about stoplights. --MareCrisium (talk) 00:06, 2 June 2015 (UTC)

I wonder if the reference to whether the language has a word for "firetruck" is a Sapir Whorf reference? If there's no word for firetruck, the listener (victim?) is likely to be more confused by the situation than a listener who can at least recognize what kind of vehicle is about to kill him/her (Curses! There's no sexless personal pronoun in this language!) So the reaction time of the first person is likely to be longer than that of the second person.

"They/them/etc." has been the accepted sexless personal pronoun for a long time (in the order of centuries), even in the singular. The only people who say you shouldn't use it for such a purpose are the same ones who say you shouldn't split an infinitive despite it having been acceptable for centuries, simply because it's impossible to split infinitives in Latin. -- 19:42, 29 May 2015 (UTC)
"...simply because it's impossible to -- in Latin -- split infinitives." 19:10, 2 June 2015 (UTC)larK
Quite false-I think it’s perfectly okay to occasionally split infinitives but never okay to use they/them in singular. 12:53, 12 April 2019 (UTC)
Then you should ask them why they find that correlation. “That Guy from the Netherlands” (talk) 13:54, 12 April 2019 (UTC)
No one is disputing a correlation in this conversation. However the made claim that only people who do not accept splitting infinitives object to they/them in singular has been conclusively rejected by a counterexample. While False (talk) 06:35, 26 April 2022 (UTC)

There's a whole class of psychology experiments (with both human and animal subjects) that uses reaction-time as a measure of degree of understanding in various situations. Is this effect named after a famous experimental psychologist? If so, Randall may have to issue an update to this cartoon... -- Ribbit (talk) (please sign your comments with ~~~~)

If you think English has no sexless personal pronoun you *clearly* haven't read comic 145. Ahem... --MareCrisium (talk) 08:49, 29 May 2015 (UTC)

Off topic, but I agree 'them' is a sufficient pronoun in this case, since you've already specified the singular 'listener'. Bish (talk) 11:22, 29 May 2015 (UTC)

Might the comic also involve the game Red Light, Green Light. In the firetruck version of the game, firetrucks don't stop for red lights. There's more to it than that, but you can google around for it because I don't want to post about that... 00:06, 3 June 2015 (UTC)

To the best of my knowledge, the Bernoulli effect is, in fact, responsible to the aerodynamic lift. While it is correct that most people trying to explain aerodynamic lift use an incorrect explanation, the incorrect part has nothing to do with Bernoulli, as implied by the explanation. Shachar (talk) 09:53, 29 May 2015 (UTC)

The Bernoulli effect describes how pressure distribution changes with speed, and needs to be understood if you want to fully grasp all the science behind it. That being said, there isn't an intuitive way to grasp how airspeed varies across a wing's surface which ultimately means that any accurate explanation dependent on the Bernoulli effect goes well beyond the scope of a layperson's understanding. It's better to note that wings are tilted to push the airflow downward and for every action their's an equal and opposite reaction.(User talk:Some Guytalk) -- 11:36, 29 May 2015 (UTC)

Um, I'll give you half points – it depends on what type of wing you're talking about. You can have a "high lift" type wing fly straight and level and still provide plenty of lift. But a low chord wing (eg "fighter jet style") more greatly depends on forward speed and angle of attack to stay up than the lift provided by the wings. Needless to say, airplanes make people think - and too often the more people think about them, the more confused they get. Jarod997 (talk) 13:10, 29 May 2015 (UTC)

There's a difference between saying this is how wings generate lift and this is the only factor in the equation. On top of which angle of attack is not defined by the zero lift angle. that being said, every scrap of airfoil data I've ever seen shows a proportional relationship between (angle of attack - zero lift angle of attack) and CL (and by extension lift). Is that everything a professional needs to know about aerodynamics? Far from it. Is it an adequate explanation for laypeople? As far as I'm concerned, yes.--Someguy173.245.54.156 20:57, 29 May 2015 (UTC)

"The Peltzman effect refers to how regulations intended to increase safety are ineffective or counterproductive. This is likely referenced by the observer responding to a dangerous situation more slowly if the language he is warned in has a word describing the object he's in danger from ("firefighter") than if the language didn't." The comic states that the person reacts more *quickly* if the language has a word for firefighter... (talk) (please sign your comments with ~~~~)

I think it's actually about how the firefighter has gotten himself into a dangerous situation due to the feeling of safety he has from being in a modern firetruck, since a major case of the Peltzman effect is that increased car safety leads us to drive at higher speeds. The innocent pedestrian is less safe because the firefighter is driving more recklessly. Not-my-username (talk) 16:10, 29 May 2015 (UTC)

He totally could've added the McGurk effect in there. Just saying. 15:37, 30 May 2015 (UTC)

Isn't part of the Doppler joke the fact that it is a fire truck, as emergency vehicle sirens are very often used as an example of the Doppler effect? 13:18, 30 May 2015 (UTC)

Is there a name for the law that states "red ones go faster"? I believe that too was referenced, but possibly not by name. 19:59, 1 June 2015 (UTC)

I'm not sure if this helps, but I'll leave it here. 20:01, 25 December 2015 (UTC)

Saw a nice post on this before I actually saw the comic, and came here to create a reference to it: http://languagelog.ldc.upenn.edu/nll/?p=19252 ... for extra commentary. Jadawin (talk) 21:44, 2 June 2015 (UTC)

And then I read that link's comments to the end, and saw a link here! Circularity achieved! Jadawin (talk) 21:48, 2 June 2015 (UTC)