0:00:00.611,0:00:04.212 I have the answer to a question that we've all asked. 0:00:04.212,0:00:05.329 The question is, 0:00:05.329,0:00:07.613 Why is it that the letter X 0:00:07.613,0:00:09.611 represents the unknown? 0:00:09.611,0:00:12.578 Now I know we learned that in math class, 0:00:12.578,0:00:14.329 but now it's everywhere in the culture -- 0:00:14.329,0:00:17.130 The X prize, the X-Files, 0:00:17.130,0:00:21.053 Project X, TEDx. 0:00:21.053,0:00:23.048 Where'd that come from? 0:00:23.048,0:00:24.266 About six years ago 0:00:24.266,0:00:26.982 I decided that I would learn Arabic, 0:00:26.982,0:00:30.934 which turns out to be a supremely logical language. 0:00:30.934,0:00:33.251 To write a word or a phrase 0:00:33.251,0:00:34.932 or a sentence in Arabic 0:00:34.932,0:00:37.165 is like crafting an equation, 0:00:37.165,0:00:39.531 because every part is extremely precise 0:00:39.531,0:00:42.383 and carries a lot of information. 0:00:42.383,0:00:43.733 That's one of the reasons 0:00:43.733,0:00:45.248 so much of what we've come to think of 0:00:45.248,0:00:49.067 as Western science and mathematics and engineering 0:00:49.067,0:00:52.389 was really worked out in the first few centuries of the Common Era 0:00:52.389,0:00:55.705 by the Persians and the Arabs and the Turks. 0:00:55.705,0:00:58.022 This includes the little system in Arabic 0:00:58.022,0:00:59.738 called al-jebra. 0:00:59.738,0:01:02.906 And al-jebr roughly translates to 0:01:02.906,0:01:06.605 "the system for reconciling disparate parts." 0:01:06.605,0:01:10.655 Al-jebr finally came into English as algebra. 0:01:10.655,0:01:12.822 One example among many. 0:01:12.822,0:01:16.788 The Arabic texts containing this mathematical wisdom 0:01:16.788,0:01:18.571 finally made their way to Europe -- 0:01:18.571,0:01:19.857 which is to say Spain -- 0:01:19.857,0:01:22.322 in the 11th and 12th centuries. 0:01:22.322,0:01:23.472 And when they arrived 0:01:23.472,0:01:25.355 there was tremendous interest 0:01:25.355,0:01:27.089 in translating this wisdom 0:01:27.089,0:01:28.738 into a European language. 0:01:28.738,0:01:30.756 But there were problems. 0:01:30.756,0:01:32.473 One problem 0:01:32.473,0:01:35.106 is there are some sounds in Arabic 0:01:35.106,0:01:38.105 that just don't make it through a European voice box 0:01:38.105,0:01:40.372 without lots of practice. 0:01:40.372,0:01:42.106 Trust me on that one. 0:01:42.106,0:01:44.323 Also, those very sounds 0:01:44.323,0:01:46.237 tend not to be represented 0:01:46.237,0:01:49.825 by the characters that are available in European languages. 0:01:49.825,0:01:51.639 Here's one of the culprits. 0:01:51.639,0:01:53.523 This is the letter sheen, 0:01:53.523,0:01:57.122 and it makes the sound we think of as SH -- "sh." 0:01:57.122,0:01:59.724 It's also the very first letter 0:01:59.724,0:02:02.156 of the word shayun, 0:02:02.156,0:02:03.950 which means "something" 0:02:03.950,0:02:05.798 just like the the English word "something" -- 0:02:05.798,0:02:09.084 some undefined, unknown thing. 0:02:09.084,0:02:10.249 Now in Arabic, 0:02:10.249,0:02:11.450 we can make this definite 0:02:11.450,0:02:13.598 by adding the definite article "al." 0:02:13.598,0:02:16.200 So this is al-shayun -- 0:02:16.200,0:02:17.850 the unknown thing. 0:02:17.850,0:02:21.153 And this is a word that appears throughout early mathematics, 0:02:21.153,0:02:28.353 such as this 10th-century derivation of roots. 0:02:28.353,0:02:30.863 The problem for the Medieval Spanish scholars 0:02:30.863,0:02:33.431 who were tasked with translating this material 0:02:33.431,0:02:37.913 is that the letter sheen and the word shayun 0:02:37.913,0:02:39.863 can't be rendered into Spanish 0:02:39.863,0:02:42.449 because Spanish doesn't have that SH, 0:02:42.449,0:02:43.746 that "sh" sound. 0:02:43.746,0:02:45.328 So by convention, 0:02:45.328,0:02:46.994 they created a rule in which 0:02:46.994,0:02:51.212 they borrowed the CK sound, "ck" sound, 0:02:51.212,0:02:52.960 from the classical Greek 0:02:52.960,0:02:55.641 in the form of the letter Kai. 0:02:55.641,0:02:58.360 Later when this material was translated 0:02:58.360,0:03:00.708 into a common European language, 0:03:00.708,0:03:02.758 which is to say Latin, 0:03:02.758,0:03:04.791 they simply replaced the Greek Kai 0:03:04.791,0:03:07.141 with the Latin X. 0:03:07.141,0:03:08.410 And once that happened, 0:03:08.410,0:03:10.875 once this material was in Latin, 0:03:10.875,0:03:14.458 it formed the basis for mathematics textbooks 0:03:14.458,0:03:16.541 for almost 600 years. 0:03:16.541,0:03:18.559 But now we have the answer to our question. 0:03:18.559,0:03:21.340 Why is it that X is the unknown? 0:03:21.340,0:03:23.163 X is the unknown 0:03:23.163,0:03:26.945 because you can't say "sh" in Spanish. 0:03:26.945,0:03:29.329 (Laughter) 0:03:29.329,0:03:31.646 And I thought that was worth sharing. 0:03:31.646,0:03:34.763 (Applause)