TED Talks-Terry Moore: Why is "x" the unknown?

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Transcript:


I have the answer to a question that we've all asked.The question is,Why is it that the letter Xrepresents the unknown?Now I know we learned that in math class,but now it's everywhere in the culture --The X prize, the X-Files,Project X, TEDx.Where'd that come from?

About six years agoI decided that I would learn Arabic,which turns out to be a supremely logical language.To write a word or a phraseor a sentence in Arabicis like crafting an equation,because every part is extremely preciseand carries a lot of information.That's one of the reasonsso much of what we've come to think ofas Western science and mathematics and engineeringwas really worked out in the first few centuries of the Common Eraby the Persians and the Arabs and the Turks.

This includes the little system in Arabiccalled al-jebra.And al-jebr roughly translates to"the system for reconciling disparate parts."Al-jebr finally came into English as algebra.One example among many.

The Arabic texts containing this mathematical wisdomfinally made their way to Europe --which is to say Spain --in the 11th and 12th centuries.And when they arrivedthere was tremendous interestin translating this wisdominto a European language.

But there were problems.One problemis there are some sounds in Arabicthat just don't make it through a European voice boxwithout lots of practice.Trust me on that one.Also, those very soundstend not to be representedby the characters that are available in European languages.

Here's one of the culprits.This is the letter SHeen,and it makes the sound we think of as SH -- "sh."It's also the very first letterof the word shalan,which means "something"just like the the English word "something" --some undefined, unknown thing.

Now in Arabic,we can make this definiteby adding the definite article "al."So this is al-shalan --the unknown thing.And this is a word that appears throughout early mathematics,such as this 10th century derivation of proofs.

The problem for the Medieval Spanish scholarswho were tasked with translating this materialis that the letter SHeen and the word shalancan't be rendered into Spanishbecause Spanish doesn't have that SH,that "sh" sound.So by convention,they created a rule in whichthey borrowed the CK sound, "ck" sound,from the classical Greekin the form of the letter Kai.

Later when this material was translatedinto a common European language,which is to say Latin,they simply replaced the Greek Kaiwith the Latin X.And once that happened,once this material was in Latin,it formed the basis for mathematics textbooksfor almost 600 years.

But now we have the answer to our question.Why is it that X is the unknown?X is the unknownbecause you can't say "sh" in Spanish.(Laughter)And I thought that was worth sharing.

(Applause)