1
00:00:00,611 --> 00:00:04,212
I have the answer to a question that we've all asked.

2
00:00:04,212 --> 00:00:05,329
The question is,

3
00:00:05,329 --> 00:00:07,613
Why is it that the letter X

4
00:00:07,613 --> 00:00:09,611
represents the unknown?

5
00:00:09,611 --> 00:00:12,578
Now I know we learned that in math class,

6
00:00:12,578 --> 00:00:14,329
but now it's everywhere in the culture --

7
00:00:14,329 --> 00:00:17,130
The X prize, the X-Files,

8
00:00:17,130 --> 00:00:21,053
Project X, TEDx.

9
00:00:21,053 --> 00:00:23,048
Where'd that come from?

10
00:00:23,048 --> 00:00:24,266
About six years ago

11
00:00:24,266 --> 00:00:26,982
I decided that I would learn Arabic,

12
00:00:26,982 --> 00:00:30,934
which turns out to be a supremely logical language.

13
00:00:30,934 --> 00:00:33,251
To write a word or a phrase

14
00:00:33,251 --> 00:00:34,932
or a sentence in Arabic

15
00:00:34,932 --> 00:00:37,165
is like crafting an equation,

16
00:00:37,165 --> 00:00:39,531
because every part is extremely precise

17
00:00:39,531 --> 00:00:42,383
and carries a lot of information.

18
00:00:42,383 --> 00:00:43,733
That's one of the reasons

19
00:00:43,733 --> 00:00:45,248
so much of what we've come to think of

20
00:00:45,248 --> 00:00:49,067
as Western science and mathematics and engineering

21
00:00:49,067 --> 00:00:52,389
was really worked out in the first few centuries of the Common Era

22
00:00:52,389 --> 00:00:55,705
by the Persians and the Arabs and the Turks.

23
00:00:55,705 --> 00:00:58,022
This includes the little system in Arabic

24
00:00:58,022 --> 00:00:59,738
called al-jebra.

25
00:00:59,738 --> 00:01:02,906
And al-jebr roughly translates to

26
00:01:02,906 --> 00:01:06,605
"the system for reconciling disparate parts."

27
00:01:06,605 --> 00:01:10,655
Al-jebr finally came into English as algebra.

28
00:01:10,655 --> 00:01:12,822
One example among many.

29
00:01:12,822 --> 00:01:16,788
The Arabic texts containing this mathematical wisdom

30
00:01:16,788 --> 00:01:18,571
finally made their way to Europe --

31
00:01:18,571 --> 00:01:19,857
which is to say Spain --

32
00:01:19,857 --> 00:01:22,322
in the 11th and 12th centuries.

33
00:01:22,322 --> 00:01:23,472
And when they arrived

34
00:01:23,472 --> 00:01:25,355
there was tremendous interest

35
00:01:25,355 --> 00:01:27,089
in translating this wisdom

36
00:01:27,089 --> 00:01:28,738
into a European language.

37
00:01:28,738 --> 00:01:30,756
But there were problems.

38
00:01:30,756 --> 00:01:32,473
One problem

39
00:01:32,473 --> 00:01:35,106
is there are some sounds in Arabic

40
00:01:35,106 --> 00:01:38,105
that just don't make it through a European voice box

41
00:01:38,105 --> 00:01:40,372
without lots of practice.

42
00:01:40,372 --> 00:01:42,106
Trust me on that one.

43
00:01:42,106 --> 00:01:44,323
Also, those very sounds

44
00:01:44,323 --> 00:01:46,237
tend not to be represented

45
00:01:46,237 --> 00:01:49,825
by the characters that are available in European languages.

46
00:01:49,825 --> 00:01:51,639
Here's one of the culprits.

47
00:01:51,639 --> 00:01:53,523
This is the letter sheen,

48
00:01:53,523 --> 00:01:57,122
and it makes the sound we think of as SH -- "sh."

49
00:01:57,122 --> 00:01:59,724
It's also the very first letter

50
00:01:59,724 --> 00:02:02,156
of the word shayun,

51
00:02:02,156 --> 00:02:03,950
which means "something"

52
00:02:03,950 --> 00:02:05,798
just like the the English word "something" --

53
00:02:05,798 --> 00:02:09,084
some undefined, unknown thing.

54
00:02:09,084 --> 00:02:10,249
Now in Arabic,

55
00:02:10,249 --> 00:02:11,450
we can make this definite

56
00:02:11,450 --> 00:02:13,598
by adding the definite article "al."

57
00:02:13,598 --> 00:02:16,200
So this is al-shayun --

58
00:02:16,200 --> 00:02:17,850
the unknown thing.

59
00:02:17,850 --> 00:02:21,153
And this is a word that appears throughout early mathematics,

60
00:02:21,153 --> 00:02:28,353
such as this 10th-century derivation of roots.

61
00:02:28,353 --> 00:02:30,863
The problem for the Medieval Spanish scholars

62
00:02:30,863 --> 00:02:33,431
who were tasked with translating this material

63
00:02:33,431 --> 00:02:37,913
is that the letter sheen and the word shayun

64
00:02:37,913 --> 00:02:39,863
can't be rendered into Spanish

65
00:02:39,863 --> 00:02:42,449
because Spanish doesn't have that SH,

66
00:02:42,449 --> 00:02:43,746
that "sh" sound.

67
00:02:43,746 --> 00:02:45,328
So by convention,

68
00:02:45,328 --> 00:02:46,994
they created a rule in which

69
00:02:46,994 --> 00:02:51,212
they borrowed the CK sound, "ck" sound,

70
00:02:51,212 --> 00:02:52,960
from the classical Greek

71
00:02:52,960 --> 00:02:55,641
in the form of the letter Kai.

72
00:02:55,641 --> 00:02:58,360
Later when this material was translated

73
00:02:58,360 --> 00:03:00,708
into a common European language,

74
00:03:00,708 --> 00:03:02,758
which is to say Latin,

75
00:03:02,758 --> 00:03:04,791
they simply replaced the Greek Kai

76
00:03:04,791 --> 00:03:07,141
with the Latin X.

77
00:03:07,141 --> 00:03:08,410
And once that happened,

78
00:03:08,410 --> 00:03:10,875
once this material was in Latin,

79
00:03:10,875 --> 00:03:14,458
it formed the basis for mathematics textbooks

80
00:03:14,458 --> 00:03:16,541
for almost 600 years.

81
00:03:16,541 --> 00:03:18,559
But now we have the answer to our question.

82
00:03:18,559 --> 00:03:21,340
Why is it that X is the unknown?

83
00:03:21,340 --> 00:03:23,163
X is the unknown

84
00:03:23,163 --> 00:03:26,945
because you can't say "sh" in Spanish.

85
00:03:26,945 --> 00:03:29,329
(Laughter)

86
00:03:29,329 --> 00:03:31,646
And I thought that was worth sharing.

87
00:03:31,646 --> 00:03:34,763
(Applause)