2
00:00:09,690 --> 00:00:14,402
If the best insulating windows would be
ones that had nothing in between

3
00:00:14,402 --> 00:00:19,235
the two panes of glass, just a vacuum,
think about the Earth and the Sun.

4
00:00:19,235 --> 00:00:24,020
Which are separated from each other by 93
million miles of vacuum.

5
00:00:24,020 --> 00:00:26,350
It's kind of amazing, actually, that
the lump

6
00:00:26,350 --> 00:00:29,320
of atoms here that is the Earth, the
kinetic energy

7
00:00:29,320 --> 00:00:32,090
of those atoms, has anything to do with
the

8
00:00:32,090 --> 00:00:34,690
energy of the atoms in the sun, or
anything

9
00:00:34,690 --> 00:00:38,270
else in space.
It turns out that the way

10
00:00:38,270 --> 00:00:42,060
energy can be transferred through a vacuum
is by means of light.

11
00:00:44,020 --> 00:00:52,080
Light is composed of two properties of
space time.

12
00:00:52,080 --> 00:00:55,660
One of them is the electric field and the
other is the magnetic field.

13
00:00:55,660 --> 00:01:00,420
The electric field is manifested in
that if you take something

14
00:01:00,420 --> 00:01:06,930
that has a positive charge like a
proton, an H plus atom like what

15
00:01:06,930 --> 00:01:12,500
changes the acidity of water, that
has a positive charge and

16
00:01:12,500 --> 00:01:16,720
then an electron is a particle that has a
negative charge and you sort

17
00:01:16,720 --> 00:01:20,580
of set those things close to each other,
they will feel each other's presence.

18
00:01:20,580 --> 00:01:23,500
They will want to come together
even

19
00:01:23,500 --> 00:01:26,250
though there's nothing in between them
but vacuum.  

21
00:01:26,250 --> 00:01:29,910
The electric field is what these things
are feeling

22
00:01:29,910 --> 00:01:32,980
and that is sort of a property of the
vacuum.

23
00:01:32,980 --> 00:01:34,069
A property of space.

24
00:01:35,220 --> 00:01:39,420
Another property is the magnetic field

25
00:01:39,420 --> 00:01:42,860
I've drawn two magnets with north
and south

26
00:01:42,860 --> 00:01:46,680
poles and so the south pole of one magnet

27
00:01:46,680 --> 00:01:49,420
will be attracted to the north pole of
another.

28
00:01:49,420 --> 00:01:51,380
And there are some differences here.  

30
00:01:51,380 --> 00:01:58,100
One is that in the magnetic field there's
no such thing as a magnetic monopole.

31
00:01:58,100 --> 00:02:02,080
Something that only has a north or a south
charge.

32
00:02:02,080 --> 00:02:05,070
Electrical fields, you do have electric
monopoles such as

33
00:02:05,070 --> 00:02:08,600
the electron or the proton.  But in the magnetic

34
00:02:08,600 --> 00:02:10,230
field you just sort of have things where

35
00:02:10,230 --> 00:02:13,040
the charges are separated from each other
like this.

36
00:02:13,040 --> 00:02:15,620
The other difference
is that the magnetic

37
00:02:15,620 --> 00:02:16,870
field can reach farther.

38
00:02:16,870 --> 00:02:19,220
If you have 2 magnets and they're pretty
strong you can

39
00:02:19,220 --> 00:02:22,160
hold them pretty far apart and you'll feel
them pulling together.

40
00:02:22,160 --> 00:02:24,250
Whereas if you take a car

41
00:02:24,250 --> 00:02:26,790
battery and a jumper cable, do not try
this

42
00:02:26,790 --> 00:02:31,110
at home, but if you did put the one part
of the jumper cable to the plus and

43
00:02:31,110 --> 00:02:33,150
the other part of the same wire took it

44
00:02:33,150 --> 00:02:35,600
close to the minus, if you actually touch
it

45
00:02:35,600 --> 00:02:38,020
it would be an explosion, but before you
touch it

46
00:02:38,020 --> 00:02:41,260
you don't feel much attraction cause it
doesn't

47
00:02:41,260 --> 00:02:46,980
make it as far in space as the
magnetic field does.

48
00:02:46,980 --> 00:02:50,860
The two fields are coupled together by
the

49
00:02:50,860 --> 00:02:54,820
fact that if you change the electric
field, 

50
00:02:54,820 --> 00:02:57,570
if you oscillate it, move it up and down,

51
00:02:57,570 --> 00:03:01,250
dial it up and down, it will induce a magnetic
field.

52
00:03:01,250 --> 00:03:02,900
And so this is how, for example, an

53
00:03:02,900 --> 00:03:06,660
electromagnet works or an electric

54
00:03:06,660 --> 00:03:10,610
motor uses this this (phenomenon).

55
00:03:10,610 --> 00:03:15,730
Or if you change the magnetic field that
can induce an electric field.

56
00:03:15,730 --> 00:03:17,910
And that's how, for example, a generator
works.

57
00:03:17,910 --> 00:03:20,950
So if you have some power from a waterfall
or something and

58
00:03:20,950 --> 00:03:25,995
you're twisting some magnets around you
can use that to generate electricity.

60
00:03:29,180 --> 00:03:36,530
Light is a coupled oscillation of the
electric and the magnetic fields.

61
00:03:36,530 --> 00:03:38,430
It's like the energy bounces back and
forth

62
00:03:38,430 --> 00:03:42,030
between the electric to magnetic and
back again.

63
00:03:42,030 --> 00:03:47,190
If you were to draw a graph of the
electric field as

64
00:03:47,190 --> 00:03:51,020
a function of time or distance, either way
since it's sort of a wave,

65
00:03:53,370 --> 00:03:57,580
this is a time where the electric field is
changing

66
00:03:57,580 --> 00:04:02,520
and as a result this induces a strong
magnetic field.

67
00:04:03,660 --> 00:04:06,080
Now here the magnetic field is collapsing
and

68
00:04:06,080 --> 00:04:10,290
changing and so that induces a strong
electric field

69
00:04:10,290 --> 00:04:12,190
and so the energy is sort of bouncing back

70
00:04:12,190 --> 00:04:15,130
and forth between the electric and the
magnetic fields.

71
00:04:16,700 --> 00:04:18,550
Now this thing sets

72
00:04:18,550 --> 00:04:24,430
up a wave that's very analogous to a water
wave on the surface of water.

73
00:04:24,430 --> 00:04:27,680
If this is the flat surface
of the

74
00:04:27,680 --> 00:04:33,030
water and you make the water actually do
like this, there's gravity

75
00:04:33,030 --> 00:04:36,750
tending to pull this water down and
tending to push that water up

76
00:04:36,750 --> 00:04:40,840
and make it sort of go back to a flat
surface.

77
00:04:40,840 --> 00:04:44,070
But if you do it just right there can be
motion

78
00:04:44,070 --> 00:04:50,100
of the water in the wave in a sort of
circular pattern like this that creates

79
00:04:50,100 --> 00:04:55,260
another wave a few seconds later that has
the same shape as the first wave.

80
00:04:55,260 --> 00:04:59,870
And the point is the only way this can
work is if the speed

81
00:04:59,870 --> 00:05:04,660
of the wave is right so that it can sort
of self-reproduce itself like this.

82
00:05:04,660 --> 00:05:09,870
Make something that looks like it did only
just moved over a little bit in space.

83
00:05:09,870 --> 00:05:12,120
So if you tried to make a water wave and

84
00:05:12,120 --> 00:05:15,000
make it go 100 miles an hour it would
break.

85
00:05:15,000 --> 00:05:15,920
It wouldn't work.

86
00:05:15,920 --> 00:05:19,750
It wouldn't self-replicate and so it
wouldn't be a wave.

87
00:05:19,750 --> 00:05:21,080
Well, light is the same way.

88
00:05:21,080 --> 00:05:24,220
It has to reproduce itself.

89
00:05:24,220 --> 00:05:25,580
It has to bounce the energy from the

90
00:05:25,580 --> 00:05:28,640
electric field, the magnetic field, and
back again

91
00:05:28,640 --> 00:05:33,950
so that it looks the same way after a
split second but just moved in space.

92
00:05:33,950 --> 00:05:34,902
And that's what

93
00:05:34,902 --> 00:05:37,282
sets up the speed of light, is this 

94
00:05:37,282 --> 00:05:39,876
requirement that it sort of ring like a
bell.

95
00:05:39,876 --> 00:05:43,125
So that it self reproduces
itself.