I have the answer to a question that we've all asked.
The question is,
Why is it that the letter X
represents 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 ago
I decided that I would learn Arabic,
which turns out to be a supremely logical language.
To write a word or a phrase
or a sentence in Arabic
is like crafting an equation,
because every part is extremely precise
and carries a lot of information.
That's one of the reasons
so much of what we've come to think of
as Western science and mathematics and engineering
was really worked out in the first few centuries of the Common Era
by the Persians and the Arabs and the Turks.
This includes the little system in Arabic
called 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 wisdom
finally made their way to Europe --
which is to say Spain --
in the 11th and 12th centuries.
And when they arrived
there was tremendous interest
in translating this wisdom
into a European language.
But there were problems.
One problem
is there are some sounds in Arabic
that just don't make it through a European voice box
without lots of practice.
Trust me on that one.
Also, those very sounds
tend not to be represented
by 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 letter
of the word shayun,
which means "something"
just like the the English word "something" --
some undefined, unknown thing.
Now in Arabic,
we can make this definite
by adding the definite article "al."
So this is al-shayun --
the unknown thing.
And this is a word that appears throughout early mathematics,
such as this 10th-century derivation of roots.
The problem for the Medieval Spanish scholars
who were tasked with translating this material
is that the letter sheen and the word shayun
can't be rendered into Spanish
because Spanish doesn't have that SH,
that "sh" sound.
So by convention,
they created a rule in which
they borrowed the CK sound, "ck" sound,
from the classical Greek
in the form of the letter Kai.
Later when this material was translated
into a common European language,
which is to say Latin,
they simply replaced the Greek Kai
with the Latin X.
And once that happened,
once this material was in Latin,
it formed the basis for mathematics textbooks
for almost 600 years.
But now we have the answer to our question.
Why is it that X is the unknown?
X is the unknown
because you can't say "sh" in Spanish.
(Laughter)
And I thought that was worth sharing.
(Applause)