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