Odd idea about lemon juice turned sour for robber
Dunning-Kruger effect in Action: Dimwit grossly overestimAted his own intelligence
It happened in Pittsburg in 1995. The bank robber got away with his heist and was totally shocked when he was tracked down by the police the same evening.
They had the evidence, the officers explained, brandishing the bank’s video surveillance tapes. “But I wore the juice,” the befuddled robber was heard to mumble as he was led away in handcuffs. The “juice” he was talking about was lemon juice that he had rubbed on his face, convinced it would make his features invisible to the video cameras. Of course, it didn’t do that. What it did do, was make his scientific ignorance visible.
Apparently, our robber, obviously not the sharpest knife in the drawer, had read something about lemon juice being used as invisible ink and had totally misunderstood the concept. Indeed, anything written with lemon juice on paper is invisible until heat is applied, turning the writing brown. The chemistry here is quite complex and involves a number of reactions. Cellulose, the main component of paper, is a polymer composed of glucose molecules linked together in a long chain. Citric and ascorbic acids in the juice degrade some of the cellulose to glucose, which then caramelizes with heat.
Caramelization begins with simple carbohydrates, such as glucose, releasing water, the “hydrate” component of carbohydrates. This leaves behind a mix of simpler compounds that then link together to form brown polymers. At the same time, more dark compounds form via the “Maillard reaction” as some of the glucose reacts with amino acids in the juice.
The same reaction is also responsible for the brown colour of roasted coffee, seared steaks, bagels, toast and french fries.
To complicate things even further, ascorbic acid, or Vitamin C, also undergoes changes with heat to yield furfural, a compound that can go on to form coloured polymers. Furthermore, furfural can also engage with amino acids in the Maillard reaction.
Clearly, the reaction of lemon juice with heat presents some very complicated and interesting chemistry, but it suffices to say that heat will reveal the presence of any “invisible” marks on paper made with lemon juice. Obviously lemon juice does not render anything “invisible.”
The scriptwriters of National Treasure, an entertaining movie, also showed their chemical incompetence in a scene in which the heroes visualize some secret writing on the Declaration of Independence by spreading lemon juice on the document and blowing on it with supposedly hot breath. This is a total misinterpretation of the role of lemon juice in invisible writing.
The only possibility, in this case, is the document turning brown wherever the juice had been applied, obliterating any secret message. Never mind that breath is not hot enough to change the colour of lemon juice.
The somewhat dim-witted bank robber’s belief that he had come up with an ingenious scheme caught the attention of psychologist David Dunning at Cornell University. Dunning had been interested in the subject of how peoples’ assessment of their intellectual abilities compares with objective evidence of their mental prowess. Indeed, the doomed bank robber had believed himself to be more clever than he actually was.
To further explore this phenomenon, Dunning and his graduate student Justin Kruger designed a test based on simple general knowledge that they administered to undergraduate students who were then asked to estimate how well they did, and how they thought they would rank when compared with other students. Amazingly, the students who did the most poorly on the test were the ones who most significantly overestimated their success and believed they had performed better than others.
To see whether such overestimation of knowledge extended beyond the classroom, the Cornell scientists questioned gun hobbyists about safety. The ones who got the fewest questions right were the ones who overestimated their correct responses the most. Such lack of awareness of incompetence has since been referred to as the “DunningKruger effect,” first formulated in 1999. Many others throughout history have, however, recognized the problem of some peoples’ inability to recognize the true level of their knowledge, leading to an overestimation of their competence.
Confucius remarked that “Real knowledge is to know the extent of one’s ignorance,” and in As You Like It, Shakespeare noted “The fool doth think he is wise, but the wise man knows himself to be a fool.” Alexander Pope told us that “a little learning is a dangerous thing” and Charles Darwin opined that “Ignorance more frequently begets confidence than does knowledge.” Famed philosopher Bertrand Russell once said that “One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision.” Russell’s remarks ring true today more than ever with various bloggers with no relevant background pontificating in a simple-minded manner on complex issues such as cancer, genetic modification and diets.
The Dunning-Kruger effect is indeed in full bloom.