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1
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If you wish to make
an apple pie from scratch...
2
00:02:50,791 --> 00:02:54,887
...you must first invent the universe.
3
00:02:55,096 --> 00:02:56,688
Thank you very much.
4
00:02:57,865 --> 00:03:00,299
Suppose I cut a piece...
5
00:03:01,168 --> 00:03:03,102
...out of this apple pie.
6
00:03:15,783 --> 00:03:18,251
Crumbly, but good.
7
00:03:21,589 --> 00:03:26,526
And now suppose we cut
this piece in half, or more or less.
8
00:03:28,129 --> 00:03:30,996
And then cut this piece in half...
9
00:03:31,599 --> 00:03:33,760
...and keep going.
10
00:03:33,968 --> 00:03:38,632
How many cuts before we get
down to an individual atom?
11
00:03:38,839 --> 00:03:43,538
The answer is about
90 successive cuts.
12
00:03:44,645 --> 00:03:47,978
Of course, this knife isn't
sharp enough...
13
00:03:48,182 --> 00:03:50,650
...the pie is too crumbly...
14
00:03:50,851 --> 00:03:54,252
...and an atom is too small
to see in any case.
15
00:03:54,455 --> 00:03:57,891
But there is a way to do it.
16
00:04:00,528 --> 00:04:04,760
It was here at
Cambridge University in England...
17
00:04:04,965 --> 00:04:08,264
...that the nature of the atom was
first understood...
18
00:04:08,469 --> 00:04:12,838
...in part by shooting pieces
of atoms at atoms...
19
00:04:13,040 --> 00:04:16,203
...and seeing how they bounce off.
20
00:04:16,410 --> 00:04:19,937
A typical atom is surrounded...
21
00:04:20,147 --> 00:04:23,913
...by a kind of cloud of electrons.
22
00:04:24,118 --> 00:04:28,054
The electrons are electrically
charged, as the name suggests...
23
00:04:28,255 --> 00:04:31,622
...and they determine the chemical
properties of the atom.
24
00:04:31,826 --> 00:04:35,887
For example, the glitter of gold...
25
00:04:38,866 --> 00:04:40,800
...or the transparency of the solid...
26
00:04:41,001 --> 00:04:44,027
...that's made from the atoms
silicon and oxygen.
27
00:04:45,306 --> 00:04:47,536
But deep inside the atom...
28
00:04:47,741 --> 00:04:51,802
...hidden far beneath
the outer electron cloud...
29
00:04:52,012 --> 00:04:56,039
...is the nucleus, composed chiefly
of protons and neutrons.
30
00:04:56,250 --> 00:04:58,616
Atoms are very small.
31
00:04:58,819 --> 00:05:03,381
100 million of them, end to end,
would be about so big.
32
00:05:03,591 --> 00:05:08,494
And the nucleus is 100,000 times
smaller still.
33
00:05:08,996 --> 00:05:12,727
Nevertheless, most of the mass
in an atom is in the nucleus.
34
00:05:12,933 --> 00:05:15,993
The electrons are by comparison...
35
00:05:16,203 --> 00:05:19,172
...just bits of moving fluff.
36
00:05:19,373 --> 00:05:22,536
Atoms are mainly empty space.
37
00:05:22,743 --> 00:05:26,804
Matter is composed chiefly
of nothing.
38
00:05:29,717 --> 00:05:32,845
When we consider cutting this
apple pie, but...
39
00:05:33,053 --> 00:05:36,489
...down beyond a single atom...
40
00:05:36,757 --> 00:05:41,592
...we confront an infinity
of the very small.
41
00:05:41,795 --> 00:05:44,764
And when we look up
at the night sky...
42
00:05:44,965 --> 00:05:48,958
...we confront an infinity
of the very large.
43
00:05:49,170 --> 00:05:53,869
These infinities are among the most
awesome of human ideas.
44
00:05:54,074 --> 00:05:58,511
They represent an unending regress
which goes on...
45
00:05:58,913 --> 00:06:03,043
...not just very far, but forever.
46
00:06:03,250 --> 00:06:07,118
Have you ever stood between two
parallel mirrors...
47
00:06:07,321 --> 00:06:08,720
...in a barbershop, say...
48
00:06:08,923 --> 00:06:12,415
...and seen a very large
number of you?
49
00:06:12,626 --> 00:06:15,561
Or you could use...
50
00:06:16,797 --> 00:06:19,265
...two flat mirrors...
51
00:06:19,700 --> 00:06:22,100
...and a candle flame...
52
00:06:22,303 --> 00:06:25,602
...you would see a large number
of images...
53
00:06:25,806 --> 00:06:29,606
...each the reflection
of another image.
54
00:06:31,512 --> 00:06:34,743
You can't really see an infinity
of images...
55
00:06:34,949 --> 00:06:38,282
...because the mirrors aren't
perfectly flat and aligned.
56
00:06:38,485 --> 00:06:41,886
And there's a candle or
a candle flame in the way...
57
00:06:42,089 --> 00:06:44,819
...and light doesn't travel
infinitely fast.
58
00:06:45,025 --> 00:06:47,459
When we talk of real infinities...
59
00:06:47,661 --> 00:06:51,529
...we're talking about a quantity
larger than any number.
60
00:06:51,732 --> 00:06:56,192
No matter what number you have in
mind, infinity is larger.
61
00:06:59,907 --> 00:07:04,207
There's a nice way
to write large numbers.
62
00:07:04,411 --> 00:07:05,810
You can...
63
00:07:06,880 --> 00:07:09,314
...write the number 1000...
64
00:07:09,516 --> 00:07:12,110
...as 10 to the power three...
65
00:07:12,319 --> 00:07:16,255
...meaning, a one
followed by three zeros.
66
00:07:16,457 --> 00:07:21,394
Or a million is written as
10 to the power six...
67
00:07:21,729 --> 00:07:26,496
...meaning, a one
followed by six zeros.
68
00:07:27,234 --> 00:07:31,364
There's no largest number. If anybody
gives you a candidate...
69
00:07:31,572 --> 00:07:33,563
...you can always add the
number one to it.
70
00:07:33,774 --> 00:07:36,709
But there certainly are
very big numbers.
71
00:07:36,910 --> 00:07:41,609
The American mathematician Edward
Kasner once asked his nephew...
72
00:07:41,815 --> 00:07:45,216
...to invent a name for
an extremely large number:
73
00:07:45,919 --> 00:07:49,013
10 to the power 100...
74
00:07:49,223 --> 00:07:54,160
...which I can't write out all the
zeros because there isn't room.
75
00:07:54,361 --> 00:07:59,128
The boy called it a googol.
76
00:08:00,834 --> 00:08:05,635
If you think a googol is large,
consider a googolplex.
77
00:08:06,340 --> 00:08:08,900
It's 10 to the power of a googol.
78
00:08:09,109 --> 00:08:12,567
That is, a one followed, not by
100 zeros...
79
00:08:12,780 --> 00:08:15,943
...but by a googol zeros.
80
00:08:17,017 --> 00:08:18,780
Now, by comparison...
81
00:08:18,986 --> 00:08:21,648
...with these enormous numbers...
82
00:08:21,855 --> 00:08:25,052
...the total number of atoms
in that apple pie...
83
00:08:25,259 --> 00:08:28,228
...is only about 10 to the 26th.
84
00:08:28,429 --> 00:08:31,296
Tiny compared to a googol and...
85
00:08:31,498 --> 00:08:35,059
...of course, much, much less
than a googolplex.
86
00:08:35,269 --> 00:08:36,861
The number
of elementary particles...
87
00:08:37,071 --> 00:08:39,039
...protons, neutrons and electrons...
88
00:08:39,239 --> 00:08:40,934
...in the accessible universe...
89
00:08:41,141 --> 00:08:43,439
...is of the order of 10 to the 80th.
90
00:08:43,644 --> 00:08:45,669
A one followed by 80 zeros.
91
00:08:45,879 --> 00:08:47,938
Still much, much less than a googol...
92
00:08:48,148 --> 00:08:51,743
...and vastly less than a googolplex.
93
00:08:51,952 --> 00:08:56,719
And yet, these numbers, the googol
and the googolplex...
94
00:08:56,924 --> 00:09:01,657
...do not approach, they come
nowhere near infinity.
95
00:09:01,862 --> 00:09:06,697
In fact, a googolplex is precisely
as far from infinity...
96
00:09:06,900 --> 00:09:09,767
...as is the number one.
97
00:09:09,970 --> 00:09:13,201
We started to write out
a googolplex...
98
00:09:13,407 --> 00:09:15,204
...but it wasn't easy.
99
00:09:17,044 --> 00:09:19,672
SAGAN:
It's a very big number.
100
00:09:39,032 --> 00:09:43,332
Writing out a googolplex is a
spectacularly futile exercise.
101
00:09:43,937 --> 00:09:47,964
A piece of paper large enough to
contain the zeros in a googolplex...
102
00:09:48,175 --> 00:09:52,373
...couldn't be stuffed into
the known universe.
103
00:09:58,085 --> 00:09:59,052
Fortunately...
104
00:10:00,587 --> 00:10:02,054
...there's a...
105
00:10:03,357 --> 00:10:05,689
...much simpler
and more concise way...
106
00:10:05,893 --> 00:10:07,986
...to write a googolplex.
107
00:10:16,236 --> 00:10:17,635
Like this.
108
00:10:17,838 --> 00:10:19,829
And infinity...
109
00:10:23,010 --> 00:10:25,444
...can be represented like this.
110
00:10:26,013 --> 00:10:29,915
This is the Cavendish Laboratory
at Cambridge University...
111
00:10:30,117 --> 00:10:34,076
...where the constituents of the atom
were first discovered.
112
00:10:34,288 --> 00:10:38,247
The realm of the very small.
113
00:10:39,526 --> 00:10:43,553
From the time of Democritus,
in the fifth century B.C...
114
00:10:43,764 --> 00:10:47,495
...people have speculated
about the existence of atoms.
115
00:10:47,701 --> 00:10:51,068
For the last few hundred years,
there have been persuasive...
116
00:10:51,271 --> 00:10:54,832
...but indirect arguments that all
matter is made of atoms.
117
00:10:55,075 --> 00:10:59,671
But only in our time, have we actually
been able to see them.
118
00:10:59,880 --> 00:11:04,476
Here the red blobs are the random
throbbing motions...
119
00:11:04,952 --> 00:11:06,442
...of uranium atoms...
120
00:11:06,653 --> 00:11:09,645
...magnified 100 million times.
121
00:11:10,924 --> 00:11:15,452
How Democritus of Abdera
would've enjoyed this movie.
122
00:11:20,467 --> 00:11:25,234
We pretty much take atoms for granted.
123
00:11:26,039 --> 00:11:29,031
And yet, there are so
many different kinds...
124
00:11:29,243 --> 00:11:33,646
...lovely and useful at
the same time.
125
00:11:33,847 --> 00:11:34,973
Look.
126
00:12:02,276 --> 00:12:06,303
There are some 92 chemically
distinct kinds of atoms...
127
00:12:06,780 --> 00:12:08,611
...naturally found on Earth.
128
00:12:08,815 --> 00:12:12,581
They're called the chemical elements.
129
00:12:28,135 --> 00:12:30,660
Virtually everything
we see and know...
130
00:12:30,871 --> 00:12:33,271
...all the beauty
of the natural world...
131
00:12:33,473 --> 00:12:36,965
...is made of these
few kinds of atoms...
132
00:12:37,177 --> 00:12:41,546
...arranged in harmonious
chemical patterns.
133
00:12:57,965 --> 00:13:01,662
Here we've represented
all 92 of them.
134
00:13:01,868 --> 00:13:06,202
At room temperature, many of
them are solids.
135
00:13:06,406 --> 00:13:08,101
A few are gases.
136
00:13:08,442 --> 00:13:09,773
And two of them...
137
00:13:11,078 --> 00:13:14,104
...bromine and mercury,
are liquids.
138
00:13:15,782 --> 00:13:19,548
They're arranged in order
of complexity.
139
00:13:19,753 --> 00:13:23,587
Hydrogen, the simplest element,
is element number 1.
140
00:13:23,790 --> 00:13:26,953
And uranium, the most complex...
141
00:13:27,394 --> 00:13:29,794
...is element 92.
142
00:13:33,133 --> 00:13:35,966
Some elements are very familiar.
143
00:13:36,637 --> 00:13:37,865
For example...
144
00:13:38,071 --> 00:13:42,167
...silicon, oxygen, magnesium,
aluminum, iron...
145
00:13:42,376 --> 00:13:43,900
...those that make up the Earth.
146
00:13:44,177 --> 00:13:48,671
Or hydrogen, carbon, nitrogen,
oxygen, phosphorus, sulfur...
147
00:13:48,882 --> 00:13:51,373
...the elements that are
essential for life.
148
00:13:51,585 --> 00:13:55,544
Other elements are
spectacularly unfamiliar.
149
00:13:55,756 --> 00:13:58,725
For example, hafnium.
150
00:13:59,326 --> 00:14:00,725
Erbium.
151
00:14:00,927 --> 00:14:02,827
Dysprosium.
152
00:14:03,430 --> 00:14:05,728
Praseodymium.
153
00:14:05,932 --> 00:14:08,833
Elements we don't bump
into in everyday life.
154
00:14:09,636 --> 00:14:14,573
By and large, the more familiar an
element is, the more abundant it is.
155
00:14:14,875 --> 00:14:17,207
There's a great deal of iron
on the Earth.
156
00:14:17,411 --> 00:14:21,006
Not all that much yttrium.
157
00:14:21,214 --> 00:14:22,442
The fact...
158
00:14:22,649 --> 00:14:26,244
...that atoms are composed of only
three kinds of elementary particles...
159
00:14:26,453 --> 00:14:28,921
...protons, neutrons and electrons...
160
00:14:29,122 --> 00:14:31,522
...is a comparatively recent finding.
161
00:14:31,725 --> 00:14:34,193
The neutron was not discovered
until 1932.
162
00:14:34,394 --> 00:14:38,854
And it, like the electron and
the proton, were discovered here...
163
00:14:39,066 --> 00:14:41,034
...at Cambridge University.
164
00:14:41,234 --> 00:14:45,330
Modern physics and chemistry
have reduced the complexity...
165
00:14:45,539 --> 00:14:50,101
...of the sensible world
to an astonishing simplicity.
166
00:14:50,310 --> 00:14:54,542
Three units, put together
in different patterns...
167
00:14:54,748 --> 00:14:58,684
...make, essentially, everything.
168
00:15:04,124 --> 00:15:07,616
A neutron is electrically neutral...
169
00:15:07,828 --> 00:15:10,319
...as its name suggests.
170
00:15:10,897 --> 00:15:14,731
A proton has a positive
electrical charge...
171
00:15:15,302 --> 00:15:19,568
...and an electron an equal,
negative electrical charge.
172
00:15:19,773 --> 00:15:22,298
Since every atom is
electrically neutral...
173
00:15:22,509 --> 00:15:24,739
...the number of protons
in the nucleus...
174
00:15:25,011 --> 00:15:29,072
...must equal the number of electrons
far away in the electron cloud.
175
00:15:29,282 --> 00:15:33,343
The protons and neutrons, together,
make up the nucleus of the atom.
176
00:15:34,421 --> 00:15:39,358
Now, the chemistry of an atom,
the nature of a chemical element...
177
00:15:39,559 --> 00:15:41,789
...depends only on the number
of electrons...
178
00:15:41,995 --> 00:15:45,590
...which equals the number of protons,
which is called the atomic number.
179
00:15:45,799 --> 00:15:48,097
Chemistry is just numbers.
180
00:15:48,301 --> 00:15:51,395
An idea which would have
appealed to Pythagoras.
181
00:15:51,605 --> 00:15:53,004
If you're an atom...
182
00:15:53,206 --> 00:15:56,403
...and you have just one proton...
183
00:15:56,610 --> 00:15:58,077
...you're hydrogen.
184
00:15:58,278 --> 00:16:00,473
Two protons, helium.
185
00:16:00,680 --> 00:16:02,511
Three, lithium.
186
00:16:02,716 --> 00:16:05,480
Four, beryllium.
Five protons, boron.
187
00:16:05,685 --> 00:16:10,247
Six, carbon, and seven, nitrogen.
Eight, oxygen, and so on.
188
00:16:10,457 --> 00:16:13,187
All the way to 92 protons...
189
00:16:13,393 --> 00:16:16,385
...in which case your name is uranium.
190
00:16:16,997 --> 00:16:20,125
Protons have positive
electrical charges...
191
00:16:20,333 --> 00:16:23,530
...but like charges repel each other.
192
00:16:23,737 --> 00:16:26,137
So why does the nucleus hold together?
193
00:16:26,339 --> 00:16:29,570
Why don't the electrical
repulsion of the protons...
194
00:16:29,776 --> 00:16:31,710
...make the nucleus fly to pieces?
195
00:16:32,312 --> 00:16:34,837
Because there's another
force in nature.
196
00:16:35,048 --> 00:16:37,608
Not electricity, not gravity...
197
00:16:37,818 --> 00:16:39,251
...the nuclear force.
198
00:16:39,452 --> 00:16:42,353
We can think of it as short-range...
199
00:16:42,556 --> 00:16:44,956
...hooks which start working...
200
00:16:45,158 --> 00:16:48,685
...when protons or neutrons
are brought very close together.
201
00:16:48,895 --> 00:16:51,386
The nuclear force can overcome...
202
00:16:52,132 --> 00:16:54,692
...the electrical repulsion of the
protons.
203
00:16:54,901 --> 00:16:57,961
Since the neutrons exert
nuclear forces...
204
00:16:58,471 --> 00:17:00,132
...but not electrical forces...
205
00:17:00,340 --> 00:17:04,834
...they are a kind of glue which holds
the atomic nucleus together.
206
00:17:06,379 --> 00:17:10,907
A lump of two protons
and two neutrons...
207
00:17:11,117 --> 00:17:13,017
...is the nucleus of a helium atom...
208
00:17:13,220 --> 00:17:15,688
...and is very stable.
209
00:17:15,889 --> 00:17:20,383
Three helium nuclei, stuck together by
nuclear forces...
210
00:17:20,594 --> 00:17:22,425
...makes carbon.
211
00:17:22,629 --> 00:17:26,030
Four helium nuclei makes oxygen.
212
00:17:26,233 --> 00:17:29,100
There's no difference between
four helium nuclei...
213
00:17:29,336 --> 00:17:31,896
...stuck together by nuclear forces
and the oxygen nucleus.
214
00:17:32,105 --> 00:17:33,595
They're the same thing.
215
00:17:33,974 --> 00:17:37,273
Five helium nuclei makes neon.
216
00:17:37,477 --> 00:17:39,877
Six makes magnesium.
217
00:17:40,080 --> 00:17:43,743
Seven makes silicon.
218
00:17:43,950 --> 00:17:46,510
Eight makes sulfur, and so on.
219
00:17:46,720 --> 00:17:49,120
Increasing the atomic
numbers by two...
220
00:17:49,322 --> 00:17:52,189
...and always making
some familiar element.
221
00:17:52,392 --> 00:17:53,324
Every time...
222
00:17:54,294 --> 00:17:56,319
...we add or subtract one proton...
223
00:17:56,529 --> 00:17:59,225
...and enough neutrons
to keep the nucleus together...
224
00:17:59,432 --> 00:18:01,900
...we make a new chemical element.
225
00:18:02,102 --> 00:18:04,866
Consider mercury:
226
00:18:05,071 --> 00:18:08,837
If we subtract one proton
from mercury...
227
00:18:09,042 --> 00:18:13,240
...and three neutrons,
we convert it into gold.
228
00:18:13,446 --> 00:18:17,542
The dream of the ancient alchemists.
229
00:18:18,551 --> 00:18:22,419
Beyond element 92, beyond uranium...
230
00:18:22,622 --> 00:18:25,090
...there are other elements.
231
00:18:25,292 --> 00:18:27,453
They don't occur naturally
on the Earth.
232
00:18:27,661 --> 00:18:30,095
They're synthesized by
human beings and...
233
00:18:30,297 --> 00:18:32,925
...fall to pieces pretty rapidly.
234
00:18:33,133 --> 00:18:36,762
One of them, element 94,
is called plutonium...
235
00:18:36,970 --> 00:18:40,701
...and is one of the most
toxic substances known.
236
00:18:40,907 --> 00:18:45,344
Where do the naturally occurring
chemical elements come from?
237
00:18:45,545 --> 00:18:49,982
Perhaps a separate creation
for each element?
238
00:18:50,183 --> 00:18:53,050
But all the elements are made of the
same elementary particles.
239
00:18:53,253 --> 00:18:56,245
The universe, all of it,
everywhere...
240
00:18:56,456 --> 00:18:59,857
...is 99.9% hydrogen and helium.
241
00:19:00,093 --> 00:19:01,958
The two simplest elements.
242
00:19:02,162 --> 00:19:03,356
In fact, helium...
243
00:19:03,797 --> 00:19:07,699
...was detected on the sun before it
was ever found on the Earth.
244
00:19:07,901 --> 00:19:11,701
Might the other chemical elements
have somehow...
245
00:19:11,905 --> 00:19:15,864
...evolved from hydrogen
and helium?
246
00:19:16,076 --> 00:19:18,442
To avoid the electrical repulsion...
247
00:19:19,145 --> 00:19:23,605
...protons and neutrons must be brought
very close together so the hooks...
248
00:19:23,817 --> 00:19:25,580
...which represent nuclear forces...
249
00:19:25,785 --> 00:19:27,150
...are engaged.
250
00:19:27,354 --> 00:19:30,482
This happens only at very high
temperatures, where particles...
251
00:19:30,690 --> 00:19:35,354
...move so fast that there's no
time for electrical repulsion to act.
252
00:19:35,628 --> 00:19:40,565
Temperatures of tens of
millions of degrees.
253
00:19:40,834 --> 00:19:44,235
Such high temperatures are
common in nature.
254
00:19:44,437 --> 00:19:45,734
Where?
255
00:19:45,939 --> 00:19:48,874
In the insides of the stars.
256
00:20:04,290 --> 00:20:08,056
Atoms are made in the
insides of stars.
257
00:20:08,261 --> 00:20:12,698
In most of the stars we see, hydrogen
nuclei are being jammed together...
258
00:20:12,899 --> 00:20:14,457
...to form helium nuclei.
259
00:20:14,868 --> 00:20:19,396
Every time a nucleus of helium is made,
a photon of light is generated.
260
00:20:20,373 --> 00:20:23,831
This is why the stars shine.
261
00:20:31,351 --> 00:20:35,344
Stars are born in great
clouds of gas and dust.
262
00:20:35,555 --> 00:20:39,286
Like the Orion Nebula,
1500 light-years away...
263
00:20:39,492 --> 00:20:43,485
...parts of which
are collapsing under gravity.
264
00:20:51,137 --> 00:20:55,540
Collisions among the atoms heat
the cloud until, in its interior...
265
00:20:55,742 --> 00:20:58,404
...hydrogen begins to fuse
into helium...
266
00:20:58,611 --> 00:21:01,409
...and the stars turn on.
267
00:21:07,520 --> 00:21:10,216
Stars are born in batches.
268
00:21:10,423 --> 00:21:12,823
Later, they wander out
of their nursery...
269
00:21:13,026 --> 00:21:15,654
...to pursue their destiny
in the Milky Way.
270
00:21:15,862 --> 00:21:18,695
Adolescent stars, like the Pleiades...
271
00:21:18,898 --> 00:21:21,662
...are still surrounded
by gas and dust.
272
00:21:21,868 --> 00:21:26,328
Eventually, they journey
far from home.
273
00:21:30,143 --> 00:21:35,080
Somewhere there are stars formed from
the same cloud complex as the sun...
274
00:21:35,448 --> 00:21:37,609
...5 billion years ago.
275
00:21:37,817 --> 00:21:40,377
But we do not know which
stars they are.
276
00:21:40,587 --> 00:21:42,487
The siblings of the sun...
277
00:21:42,822 --> 00:21:47,555
...may, for all we know, be on the
other side of the galaxy.
278
00:21:49,162 --> 00:21:54,099
Perhaps they also warm nearby
planets as the sun does.
279
00:21:56,703 --> 00:21:59,604
Perhaps they too have presided...
280
00:21:59,806 --> 00:22:03,708
...over the evolution
of life and intelligence.
281
00:22:25,265 --> 00:22:29,998
The sun is the nearest star,
a glowing sphere of gas...
282
00:22:30,503 --> 00:22:34,530
...shining because of its heat,
like a red-hot poker.
283
00:22:38,878 --> 00:22:43,815
The surface we see in ordinary visible
light is at 6000 degrees centigrade.
284
00:22:44,050 --> 00:22:45,847
But in its hidden interior...
285
00:22:46,586 --> 00:22:50,044
...in the nuclear furnace where
sunlight is ultimately generated...
286
00:22:50,256 --> 00:22:53,851
...its temperature is
20 million degrees.
287
00:23:02,235 --> 00:23:03,224
In x-rays...
288
00:23:03,436 --> 00:23:07,167
...we see a part of the sun
that is ordinarily invisible...
289
00:23:07,373 --> 00:23:10,001
...its million-degree halo of gas...
290
00:23:10,210 --> 00:23:12,303
...the solar corona.
291
00:23:12,745 --> 00:23:15,839
In ordinary visible light, these
cooler, darker regions...
292
00:23:16,049 --> 00:23:17,949
...are the sunspots.
293
00:23:20,687 --> 00:23:25,147
They are associated with
great surges of flaming gas...
294
00:23:25,358 --> 00:23:29,727
...tongues of fire which would engulf
the Earth if it were this close.
295
00:23:30,063 --> 00:23:33,829
These prominences are guided
into paths determined...
296
00:23:34,033 --> 00:23:36,263
...by the sun's magnetic field.
297
00:23:48,915 --> 00:23:51,145
The dark regions of the x-ray sun...
298
00:23:51,351 --> 00:23:54,047
...are holes in the solar corona...
299
00:23:54,254 --> 00:23:58,247
...through which stream the protons
and electrons of the solar wind...
300
00:23:58,458 --> 00:24:02,656
...on their way past the planets
to interstellar space.
301
00:24:05,164 --> 00:24:09,863
All this churning power is driven
by the sun's interior...
302
00:24:10,069 --> 00:24:13,971
...which is converting 400 million
tons of hydrogen into helium...
303
00:24:14,173 --> 00:24:15,697
...every second.
304
00:24:15,908 --> 00:24:19,503
The sun is a great fusion reactor...
305
00:24:19,746 --> 00:24:22,214
...into which a million Earths
would fit.
306
00:24:22,415 --> 00:24:25,543
Luckily for us, it's safely placed...
307
00:24:25,752 --> 00:24:29,279
...150 million kilometers away.
308
00:24:45,805 --> 00:24:49,707
It is the destiny of stars
to collapse.
309
00:24:50,810 --> 00:24:54,211
Of the thousands of stars you see
when you look up at the night sky...
310
00:24:54,414 --> 00:24:59,044
...every one of them is living in
an interval between two collapses.
311
00:24:59,252 --> 00:25:00,742
An initial collapse of...
312
00:25:00,953 --> 00:25:04,445
...a dark interstellar gas cloud
to form the star...
313
00:25:04,657 --> 00:25:07,125
...and a final collapse
of the luminous star...
314
00:25:07,327 --> 00:25:09,090
...on the way to its ultimate fate.
315
00:25:09,562 --> 00:25:14,499
Gravity makes stars contract unless
some other force intervenes.
316
00:25:14,901 --> 00:25:17,802
The sun is an immense ball
of radiating hydrogen.
317
00:25:18,004 --> 00:25:22,304
The hot gas in its interior tries
to make the sun expand.
318
00:25:22,508 --> 00:25:25,909
The gravity tries to make
the sun contract.
319
00:25:26,145 --> 00:25:29,376
The present state of the sun is
the balance of these two forces...
320
00:25:29,582 --> 00:25:34,144
...an equilibrium between
gravity and nuclear fire.
321
00:25:34,821 --> 00:25:37,483
In this long middle age
between collapses...
322
00:25:37,690 --> 00:25:40,386
...the stars steadily shine.
323
00:25:40,593 --> 00:25:44,427
But when the nuclear fuel is exhausted,
the interior cools...
324
00:25:44,630 --> 00:25:47,428
...the pressure no longer supports
its outer layers...
325
00:25:47,633 --> 00:25:49,794
...and the initial collapse resumes.
326
00:25:50,603 --> 00:25:52,901
There are three ways that stars die.
327
00:25:53,106 --> 00:25:55,540
Their fates are predestined.
328
00:25:55,742 --> 00:25:57,676
Everything depends on their
initial mass.
329
00:25:57,877 --> 00:26:00,471
A typical star with a mass
like the sun...
330
00:26:00,680 --> 00:26:03,274
...will one day
continue its collapse...
331
00:26:03,483 --> 00:26:06,384
...until its density becomes very high.
332
00:26:06,586 --> 00:26:08,315
And then the contraction is stopped...
333
00:26:08,521 --> 00:26:10,386
...by the mutual repulsion of...
334
00:26:10,590 --> 00:26:13,855
...the overcrowded electrons
in its interior.
335
00:26:14,060 --> 00:26:16,824
A collapsing star twice as
massive as the sun...
336
00:26:17,029 --> 00:26:19,554
...isn't stopped by the
electron pressure.
337
00:26:19,766 --> 00:26:22,132
It goes on falling in on itself...
338
00:26:22,335 --> 00:26:25,031
...until nuclear forces
come into play...
339
00:26:25,238 --> 00:26:28,332
...and they hold up the
weight of the star.
340
00:26:28,541 --> 00:26:31,704
But a collapsing star three times as
massive as the sun isn't...
341
00:26:31,911 --> 00:26:33,970
...stopped even by nuclear forces.
342
00:26:34,180 --> 00:26:39,117
There's no force known that can
withstand this enormous compression.
343
00:26:39,352 --> 00:26:42,412
And such a star has
an astonishing destiny.
344
00:26:42,622 --> 00:26:44,351
It continues to collapse...
345
00:26:44,624 --> 00:26:47,354
...until it vanishes utterly.
346
00:26:48,594 --> 00:26:53,054
Each star is described by the force
that holds it up against gravity.
347
00:26:53,266 --> 00:26:56,702
A star that's supported by
the gas pressure...
348
00:26:56,903 --> 00:27:00,600
...is a normal, run-of-the-mill star
like the sun.
349
00:27:00,807 --> 00:27:04,504
A collapsed star that's held up
by electron forces...
350
00:27:04,710 --> 00:27:06,337
...is called a white dwarf.
351
00:27:06,546 --> 00:27:10,380
It's a sun shrunk to
the size of the Earth.
352
00:27:10,583 --> 00:27:13,950
A collapsed star supported
by nuclear forces...
353
00:27:14,153 --> 00:27:16,018
...is called a neutron star.
354
00:27:16,222 --> 00:27:19,749
It's a sun shrunk to
the size of a city.
355
00:27:19,959 --> 00:27:22,894
And a star so massive that
in its final collapse...
356
00:27:23,095 --> 00:27:24,790
...it disappears altogether...
357
00:27:24,997 --> 00:27:26,658
...is called a black hole.
358
00:27:26,866 --> 00:27:29,858
It's a sun with no size at all.
359
00:27:30,536 --> 00:27:33,232
But on their ways to their
separate fates...
360
00:27:33,439 --> 00:27:38,103
...all stars experience
a premonition of death.
361
00:27:38,311 --> 00:27:40,779
Before the final
gravitational collapse...
362
00:27:40,980 --> 00:27:45,815
...the star shudders and
briefly swells into some...
363
00:27:46,285 --> 00:27:48,719
...grotesque parody of itself.
364
00:27:48,921 --> 00:27:53,290
With its last gasp,
it becomes a red giant.
365
00:27:57,029 --> 00:27:59,520
Some 5 billion years from now...
366
00:27:59,732 --> 00:28:04,135
...there will be a last,
perfect day on Earth.
367
00:28:07,139 --> 00:28:10,666
Then, the sun will slowly change...
368
00:28:10,877 --> 00:28:13,903
...and the Earth will die.
369
00:28:17,049 --> 00:28:19,950
There is only so much
hydrogen fuel in the sun.
370
00:28:20,152 --> 00:28:22,552
When it's almost all
converted to helium...
371
00:28:22,755 --> 00:28:26,418
...the solar interior will continue
its original collapse.
372
00:28:26,626 --> 00:28:31,086
Higher temperatures in its core will
make the outside of the sun expand...
373
00:28:31,330 --> 00:28:34,788
...and the Earth will
become slowly warmer.
374
00:28:35,034 --> 00:28:38,299
Eventually, life will be
extinguished...
375
00:28:38,671 --> 00:28:41,606
...the oceans will evaporate
and boil...
376
00:28:41,807 --> 00:28:45,834
...and our atmosphere will
gush away to space.
377
00:28:48,648 --> 00:28:52,448
The sun will become a bloated
red giant star...
378
00:28:52,652 --> 00:28:54,176
...filling the sky...
379
00:28:54,420 --> 00:28:58,584
...enveloping and devouring
the planets Mercury and Venus.
380
00:28:58,791 --> 00:29:01,851
And probably the Earth as well.
381
00:29:02,061 --> 00:29:06,998
The inner solar system will
reside inside the sun.
382
00:29:10,236 --> 00:29:13,103
But perhaps by then, our
descendants...
383
00:29:13,306 --> 00:29:15,866
...will have ventured somewhere else.
384
00:29:19,979 --> 00:29:24,382
In its final agonies, the sun
will slowly pulsate.
385
00:29:24,584 --> 00:29:27,485
By then, its core will have
become so hot...
386
00:29:27,687 --> 00:29:31,123
...that it temporarily converts
helium into carbon.
387
00:29:31,324 --> 00:29:35,226
The ash from today's nuclear fusion
will become the fuel...
388
00:29:35,528 --> 00:29:40,397
...to power the sun near the end of
its life in its red giant stage.
389
00:29:42,201 --> 00:29:45,034
Then the sun will lose
great shells...
390
00:29:45,571 --> 00:29:47,766
...of its outer atmosphere to space...
391
00:29:47,974 --> 00:29:51,375
...filling the solar system
with eerily glowing gas.
392
00:29:51,577 --> 00:29:54,637
The ghost of a star, outward bound.
393
00:29:54,847 --> 00:29:58,339
Perhaps half the mass of the sun
will be lost in this way.
394
00:30:00,286 --> 00:30:03,585
Viewed from elsewhere, our system
will then resemble...
395
00:30:03,789 --> 00:30:05,916
...the Ring Nebula in Lyra...
396
00:30:06,125 --> 00:30:10,755
...the atmosphere of the sun
expanding outward like a soap bubble.
397
00:30:11,631 --> 00:30:14,862
And at the very center will be
a white dwarf.
398
00:30:15,101 --> 00:30:17,569
The hot exposed core of the sun...
399
00:30:17,770 --> 00:30:21,331
...its nuclear fuel now
exhausted, slowly cooling...
400
00:30:21,574 --> 00:30:25,010
...to become a cold, dead star.
401
00:30:28,014 --> 00:30:30,642
Such is the life of an ordinary star.
402
00:30:30,850 --> 00:30:34,047
Born in a gas cloud,
maturing as a yellow sun...
403
00:30:34,253 --> 00:30:36,084
...decaying as a red giant...
404
00:30:36,288 --> 00:30:41,225
...and dying as a white dwarf
enveloped in its shroud of gas.
405
00:30:50,269 --> 00:30:53,363
Suppose, as we traveled through
interstellar space...
406
00:30:53,572 --> 00:30:55,403
...in our ship of the imagination...
407
00:30:55,608 --> 00:30:59,977
...we could sample the cold,
thin gas between the stars.
408
00:31:00,179 --> 00:31:03,171
We would find a great
preponderance of hydrogen...
409
00:31:03,382 --> 00:31:05,942
...an element as old as the universe.
410
00:31:06,152 --> 00:31:08,848
We would find carbon,
oxygen, silicon.
411
00:31:09,055 --> 00:31:12,149
The most abundant atoms in the
cosmos, apart from hydrogen...
412
00:31:12,358 --> 00:31:15,794
...are those most easily made
in the stars.
413
00:31:15,995 --> 00:31:19,396
But we would also find
a small proportion of rare elements.
414
00:31:19,598 --> 00:31:22,396
Praseodymium, say, or gold.
415
00:31:22,601 --> 00:31:24,762
They're not made in red giants.
416
00:31:24,970 --> 00:31:29,600
Such elements are manufactured in
one of the most dramatic gestures...
417
00:31:29,842 --> 00:31:32,333
...of which a star is capable.
418
00:31:33,479 --> 00:31:36,744
A star more than about one and
a half times the mass of the sun...
419
00:31:37,149 --> 00:31:38,776
...cannot become a white dwarf.
420
00:31:38,984 --> 00:31:41,953
It will end its life by
blowing itself up...
421
00:31:42,154 --> 00:31:46,614
...in a titanic stellar explosion
called a supernova.
422
00:31:48,160 --> 00:31:51,823
There has been no supernova explosion
in our province of the galaxy...
423
00:31:52,198 --> 00:31:53,927
...since the telescope's invention...
424
00:31:54,133 --> 00:31:57,034
...and our sun will not
become a supernova.
425
00:31:57,236 --> 00:31:58,863
But in our imagination...
426
00:31:59,405 --> 00:32:02,704
...we can fulfill the dream of many
earthbound astronomers...
427
00:32:03,142 --> 00:32:07,875
...and safely witness, close-up,
a supernova explosion.
428
00:32:12,251 --> 00:32:16,153
Most of stellar evolution takes
millions or billions of years.
429
00:32:16,388 --> 00:32:19,915
But the interior collapse that
triggers a supernova explosion...
430
00:32:20,159 --> 00:32:21,592
...takes only seconds.
431
00:32:21,961 --> 00:32:25,954
The star becomes brighter than
all the other stars in the galaxy...
432
00:32:26,165 --> 00:32:27,564
...put together.
433
00:33:03,269 --> 00:33:05,533
If a nearby star became
a supernova...
434
00:33:05,738 --> 00:33:10,471
...it would be calamity enough for
the inhabitants of this alien system.
435
00:33:10,676 --> 00:33:13,076
But if their own sun went supernova...
436
00:33:13,279 --> 00:33:16,612
...it would be
an unprecedented catastrophe.
437
00:33:16,816 --> 00:33:19,250
Worlds would be charred and vaporized.
438
00:33:19,451 --> 00:33:23,911
Life, even on the outer planets,
would be extinguished.
439
00:33:24,123 --> 00:33:28,321
In our ship of the imagination, we
are now backing away from the star.
440
00:33:28,527 --> 00:33:30,188
But the explosion fragments...
441
00:33:30,396 --> 00:33:33,888
...traveling almost at the speed
of light, are overtaking us.
442
00:33:34,099 --> 00:33:38,695
Individual atomic nuclei, accelerated
to high speeds in the explosion...
443
00:33:38,904 --> 00:33:40,838
...become cosmic rays.
444
00:33:41,040 --> 00:33:45,306
This is another way that stars return
the atoms they've synthesized...
445
00:33:45,511 --> 00:33:47,376
...back into space.
446
00:33:48,147 --> 00:33:50,206
The shock wave
of expanding gases...
447
00:33:50,416 --> 00:33:52,941
...heats and compresses
the interstellar gas...
448
00:33:53,152 --> 00:33:56,144
...triggering a later generation
of stars to form.
449
00:33:56,355 --> 00:33:57,686
In this sense also...
450
00:33:57,890 --> 00:34:02,293
...stars are phoenixes
rising from their own ashes.
451
00:34:07,132 --> 00:34:10,966
The cosmos was originally
all hydrogen and helium.
452
00:34:11,203 --> 00:34:14,570
Heavier elements were made
in red giants and in supernovas...
453
00:34:14,773 --> 00:34:16,764
...and then blown off to space...
454
00:34:16,976 --> 00:34:19,706
...where they were available
for subsequent generations...
455
00:34:19,912 --> 00:34:21,539
...of stars and planets.
456
00:34:21,747 --> 00:34:25,513
Our sun is probably a
third-generation star.
457
00:34:25,718 --> 00:34:27,345
Except for hydrogen and helium...
458
00:34:27,553 --> 00:34:32,490
...every atom in the sun and the Earth
was synthesized in other stars.
459
00:34:32,758 --> 00:34:37,286
The silicon in the rocks, the oxygen
in the air, the carbon in our DNA...
460
00:34:37,496 --> 00:34:41,262
...the gold in our banks, the
uranium in our arsenals...
461
00:34:41,467 --> 00:34:45,062
...were all made thousands
of light-years away...
462
00:34:45,271 --> 00:34:47,136
...and billions of years ago.
463
00:34:47,339 --> 00:34:51,673
Our planet, our society
and we ourselves...
464
00:34:51,877 --> 00:34:55,142
...are built of star stuff.
465
00:35:00,152 --> 00:35:03,121
We're in a lava tube.
466
00:35:03,889 --> 00:35:08,223
A cave carved through the Earth...
467
00:35:08,427 --> 00:35:10,987
...by a river of molten rock.
468
00:35:11,997 --> 00:35:14,056
To do a little experiment...
469
00:35:15,067 --> 00:35:18,468
...we've brought a Geiger counter...
470
00:35:21,507 --> 00:35:25,102
...and a piece of uranium ore.
471
00:35:25,844 --> 00:35:30,781
The Geiger counter is sensitive to
high-energy charged particles...
472
00:35:31,150 --> 00:35:34,813
...protons, helium nuclei, gamma rays.
473
00:35:35,087 --> 00:35:38,488
If we bring it close
to the uranium ore...
474
00:35:38,691 --> 00:35:43,253
...the count rate, the number of
clicks, increases dramatically.
475
00:35:45,931 --> 00:35:48,229
We also have a lead canister here.
476
00:35:48,801 --> 00:35:51,361
And if I drop the uranium ore...
477
00:35:51,904 --> 00:35:56,603
...into the canister, which absorbs
the radiation, and cover it up...
478
00:35:58,978 --> 00:36:02,175
...I then find the count-rate
goes down substantially...
479
00:36:02,381 --> 00:36:04,076
...but it doesn't go down to zero.
480
00:36:05,284 --> 00:36:08,378
What's the source of the
remaining counts?
481
00:36:09,488 --> 00:36:13,948
Some of them come from radioactivity
in the walls of the cave.
482
00:36:14,159 --> 00:36:16,354
But there's more to it than that.
483
00:36:16,562 --> 00:36:19,998
Some of the counts are due to
high-energy charged particles...
484
00:36:20,199 --> 00:36:24,260
...which are penetrating the
roof of the cave.
485
00:36:24,470 --> 00:36:27,598
We are listening to cosmic rays.
486
00:36:28,774 --> 00:36:33,234
Every second they are penetrating
my body...
487
00:36:33,445 --> 00:36:34,707
...and yours.
488
00:36:34,913 --> 00:36:38,178
They don't do much damage. Cosmic
rays have bombarded the Earth...
489
00:36:38,417 --> 00:36:41,011
...for the entire history of
life on our planet.
490
00:36:41,220 --> 00:36:43,814
But they do cause some mutations...
491
00:36:44,023 --> 00:36:46,856
...and they do affect life
on the Earth.
492
00:36:48,994 --> 00:36:51,986
The cosmic rays, mainly protons...
493
00:36:52,197 --> 00:36:57,134
...are penetrating through the meters
of rock in the cave above me.
494
00:36:57,336 --> 00:37:00,032
To do this, they have to
be very energetic and in fact...
495
00:37:00,406 --> 00:37:03,466
...they are traveling almost
at the speed of light.
496
00:37:04,276 --> 00:37:05,675
Think of it.
497
00:37:06,145 --> 00:37:08,613
A star blows up...
498
00:37:08,947 --> 00:37:11,438
...thousands of light-years
away in space...
499
00:37:11,650 --> 00:37:14,448
...and produces cosmic rays which...
500
00:37:14,653 --> 00:37:17,918
...spiral through the Milky Way
galaxy for...
501
00:37:18,123 --> 00:37:21,149
...millions of years until,
quite by accident...
502
00:37:21,360 --> 00:37:24,124
...some of them strike the Earth...
503
00:37:24,329 --> 00:37:28,231
...penetrate this cave,
reach this Geiger counter...
504
00:37:28,500 --> 00:37:29,865
...and us.
505
00:37:30,235 --> 00:37:35,104
The evolution of life on Earth is
driven in part through mutations...
506
00:37:35,307 --> 00:37:38,401
...by the deaths of distant stars.
507
00:37:38,610 --> 00:37:41,408
We are, in a very deep sense...
508
00:37:41,647 --> 00:37:44,377
...tied to the cosmos.
509
00:37:47,052 --> 00:37:49,987
Our ancestors knew this well.
510
00:37:50,189 --> 00:37:52,851
The movements of the sun, the moon,
and the stars...
511
00:37:53,058 --> 00:37:57,654
...could be used by those skilled in
such arts to foretell the seasons.
512
00:37:57,863 --> 00:38:00,798
So the ancient astronomers
all over the world...
513
00:38:00,999 --> 00:38:03,092
...studied the night sky with care...
514
00:38:03,302 --> 00:38:07,363
...memorizing and recording the
position of every visible star.
515
00:38:07,573 --> 00:38:11,976
To them, the appearance of any new
star would have been significant.
516
00:38:12,177 --> 00:38:16,614
What would they have made of the
apparition of a supernova...
517
00:38:16,815 --> 00:38:20,307
...brighter than every other
star in the sky?
518
00:38:26,692 --> 00:38:31,356
On July 4th, in the year 1054...
519
00:38:31,563 --> 00:38:36,500
...Chinese astronomers recorded what
they called a guest star...
520
00:38:36,702 --> 00:38:38,795
...in the constellation of
Taurus the Bull.
521
00:38:39,004 --> 00:38:43,134
A star never before seen
burst into radiance...
522
00:38:43,342 --> 00:38:46,470
...became almost as bright
as the full moon.
523
00:38:46,678 --> 00:38:51,115
Halfway around the world, here in
the American Southwest...
524
00:38:51,316 --> 00:38:56,015
...there was then a high culture,
rich in astronomical tradition.
525
00:38:56,221 --> 00:39:00,453
They too must have seen this
brilliant new star.
526
00:39:00,659 --> 00:39:04,026
From carbon-14 dating...
527
00:39:04,263 --> 00:39:08,723
...of the remains of a charcoal fire,
we know that in this very spot...
528
00:39:08,934 --> 00:39:12,563
...there were people living
in the 11th century.
529
00:39:13,305 --> 00:39:18,242
The people were the Anasazi, the
antecedents of the Hopi of today.
530
00:39:18,744 --> 00:39:21,645
And one of them
seems to have drawn...
531
00:39:21,914 --> 00:39:25,247
...on this overhang, protected
from the weather...
532
00:39:25,450 --> 00:39:27,441
...a picture of the new star.
533
00:39:27,653 --> 00:39:32,090
Its position near the crescent moon
would have been just what we see here.
534
00:39:32,291 --> 00:39:35,192
And the handprint is, perhaps...
535
00:39:35,394 --> 00:39:38,124
...the artist's signature.
536
00:39:38,830 --> 00:39:43,290
This remarkable star is now
called the Crab Supernova.
537
00:39:43,502 --> 00:39:46,596
"Nova" from the Latin word for new
and "Crab" because...
538
00:39:46,805 --> 00:39:50,002
...that's what an astronomer centuries
later was reminded of...
539
00:39:50,209 --> 00:39:54,009
...when looking at this explosion or
remnant through the telescope.
540
00:39:54,213 --> 00:39:58,206
The Crab is a star that
blew itself up.
541
00:39:58,417 --> 00:40:01,181
The explosion was seen
for three months.
542
00:40:01,386 --> 00:40:05,254
It was easily visible
in broad daylight.
543
00:40:05,457 --> 00:40:08,324
And you could read by it at night.
544
00:40:10,462 --> 00:40:12,589
Imagine the night when that...
545
00:40:12,798 --> 00:40:15,426
...colossal stellar explosion...
546
00:40:15,634 --> 00:40:18,228
...first burst forth.
547
00:40:27,412 --> 00:40:28,811
A thousand years ago...
548
00:40:29,047 --> 00:40:32,574
...people gazed up in amazement
at the brilliant new star...
549
00:40:32,784 --> 00:40:35,218
...and wondered what it was.
550
00:40:39,258 --> 00:40:42,853
We are the first generation
privileged to know the answer.
551
00:40:43,061 --> 00:40:46,326
Through the telescope we have seen
what lies today...
552
00:40:46,531 --> 00:40:49,762
...at the spot in the sky noted
by the ancient astronomers.
553
00:40:49,968 --> 00:40:53,563
A great luminous cloud,
the remains of a star...
554
00:40:53,772 --> 00:40:58,709
...violently unraveling itself back
into interstellar space.
555
00:41:04,049 --> 00:41:07,382
Only the massive red giants
become supernovas.
556
00:41:07,586 --> 00:41:10,680
But every supernova was
once a red giant.
557
00:41:10,889 --> 00:41:12,151
In the history of the galaxy...
558
00:41:12,357 --> 00:41:16,453
...hundreds of millions of red
giants have become supernovas.
559
00:41:19,131 --> 00:41:22,794
The bit of the star that isn't blown
away collapses under gravity...
560
00:41:23,001 --> 00:41:26,266
...spinning ever faster like a
pirouetting ice skater...
561
00:41:26,471 --> 00:41:27,802
...bringing in her arms.
562
00:41:28,006 --> 00:41:31,407
The star becomes a single, massive
atomic nucleus...
563
00:41:31,610 --> 00:41:33,271
...a neutron star.
564
00:41:33,478 --> 00:41:36,709
The one in the Crab Nebula
is spinning 30 times a second.
565
00:41:36,915 --> 00:41:38,974
It emits a beamed pattern of light...
566
00:41:39,184 --> 00:41:43,018
...and seems to us to be blinking on
and off with astonishing regularity.
567
00:41:43,221 --> 00:41:46,952
Such neutron stars are
called pulsars.
568
00:41:48,593 --> 00:41:50,618
Neutron star matter...
569
00:41:50,829 --> 00:41:54,731
...weighs about a mountain
per teaspoonful.
570
00:41:54,933 --> 00:41:58,369
So much that if I had a piece of it
here and let it go...
571
00:41:58,570 --> 00:42:00,936
...I could hardly
prevent it from falling.
572
00:42:01,139 --> 00:42:04,074
It would effortlessly pass through the
Earth like a...
573
00:42:04,276 --> 00:42:06,642
...a knife through warm butter.
574
00:42:06,845 --> 00:42:10,246
It would carve a hole for itself
completely through the Earth...
575
00:42:10,449 --> 00:42:14,476
...emerging out the other side
perhaps in China.
576
00:42:14,686 --> 00:42:18,315
The people there might be
walking along when a...
577
00:42:18,523 --> 00:42:23,324
...tiny lump of neutron star matter
comes booming out of the ground...
578
00:42:23,528 --> 00:42:25,155
...and then falls back again.
579
00:42:25,364 --> 00:42:26,797
The incident might...
580
00:42:27,032 --> 00:42:30,695
...make an agreeable break in the
routine of the day.
581
00:42:30,902 --> 00:42:34,303
The neutron star matter, pulled
back by the Earth's gravity...
582
00:42:34,506 --> 00:42:36,974
...would plunge again
through the Earth...
583
00:42:37,175 --> 00:42:41,578
...eventually punching hundreds of
thousands of holes...
584
00:42:41,780 --> 00:42:46,581
...before friction with the interior
of our planet stopped the motion.
585
00:42:46,785 --> 00:42:48,946
By the time it's at rest at
the center of the Earth...
586
00:42:49,187 --> 00:42:53,886
...the inside of our world would look
a little bit like Swiss cheese.
587
00:43:09,040 --> 00:43:13,739
There are places in the galaxy
where a neutron star and a red giant...
588
00:43:14,045 --> 00:43:17,981
...are locked in a mutual
gravitational embrace.
589
00:43:18,183 --> 00:43:20,549
Tendrils of red giant star stuff...
590
00:43:20,752 --> 00:43:23,585
...spiral into a disc
of accreting matter...
591
00:43:23,789 --> 00:43:27,190
...centered on the hot neutron star.
592
00:43:37,169 --> 00:43:40,297
Every star exists in
a state of tension...
593
00:43:40,505 --> 00:43:42,530
...between the force that
holds it up...
594
00:43:42,741 --> 00:43:45,209
...and gravity, the force that
would pull it down.
595
00:43:45,410 --> 00:43:49,744
If gravity were to prevail, a
stellar madness would ensue...
596
00:43:49,948 --> 00:43:54,044
...more bizarre than
anything in wonderland.
597
00:43:55,654 --> 00:43:58,555
Alice and her colleagues feel,
more or less...
598
00:43:58,757 --> 00:44:01,317
...at home in the gravitational
pull of the Earth...
599
00:44:01,526 --> 00:44:04,324
...called one g,
"g" for Earth gravity.
600
00:44:04,729 --> 00:44:08,187
What would happen if we made the
gravity less, or more?
601
00:44:08,400 --> 00:44:10,459
At lower gravity, things get lighter.
602
00:44:10,669 --> 00:44:13,433
Near zero g, the slightest motion
sends our friends...
603
00:44:13,638 --> 00:44:15,629
...floating and tumbling in the air.
604
00:44:15,841 --> 00:44:18,639
Little blobs of liquid
tea are everywhere.
605
00:44:19,077 --> 00:44:20,601
Curious.
606
00:44:21,146 --> 00:44:23,614
If we now return the gravity
to one g...
607
00:44:24,149 --> 00:44:28,210
...it's raining tea, and our friends
fall back to Earth.
608
00:44:29,588 --> 00:44:33,080
I've been to a couple of
parties like that myself.
609
00:44:35,093 --> 00:44:38,551
At higher gravities, two or
three g's, say, things get...
610
00:44:38,763 --> 00:44:41,391
...really laid back.
611
00:44:41,600 --> 00:44:45,593
Everyone feels heavy and leaden.
612
00:44:48,273 --> 00:44:51,709
Except by special dispensation...
613
00:44:52,010 --> 00:44:53,773
...the Cheshire cat.
614
00:44:54,579 --> 00:44:57,571
As a kindness, we remove them.
615
00:44:57,782 --> 00:45:01,274
At thousands of g's,
trees become squashed.
616
00:45:01,486 --> 00:45:05,923
At 100,000 g's, rocks
become crushed by their own weight.
617
00:45:06,124 --> 00:45:09,753
At all these gravities, a beam of
light remains unaffected...
618
00:45:09,961 --> 00:45:11,929
...continuing up in a straight line.
619
00:45:12,130 --> 00:45:13,825
But at billions of g's...
620
00:45:14,032 --> 00:45:18,560
...a beam of light feels the gravity
and begins to bend back on itself.
621
00:45:18,770 --> 00:45:22,228
Curiouser and curiouser.
622
00:45:22,440 --> 00:45:26,501
Such a place, where the gravity is so
large that even light can't get out...
623
00:45:26,711 --> 00:45:29,202
...is called a black hole.
624
00:45:29,414 --> 00:45:32,679
It's a star in which light
itself is imprisoned.
625
00:45:32,884 --> 00:45:35,182
Black holes were
theoretical constructs...
626
00:45:35,387 --> 00:45:38,686
...speculated about since 1783.
627
00:45:38,890 --> 00:45:42,485
But in our time, we've
verified the invisible.
628
00:45:42,694 --> 00:45:46,323
This bright star has a
massive, unseen companion.
629
00:45:46,531 --> 00:45:51,366
Satellite observatories find the
companion to be an x-ray source...
630
00:45:51,570 --> 00:45:54,095
...called Cygnus X-1.
631
00:45:54,306 --> 00:45:56,866
These x-rays are like
the footprints...
632
00:45:57,075 --> 00:46:01,808
...of an invisible man
walking in the snow.
633
00:46:07,118 --> 00:46:10,178
The x-rays are thought to be
generated by friction...
634
00:46:10,388 --> 00:46:13,880
...in the accretion disc
surrounding the black hole.
635
00:46:14,092 --> 00:46:17,289
The matter in the disc
slowly disappears...
636
00:46:17,495 --> 00:46:19,463
...down the black hole.
637
00:46:21,967 --> 00:46:26,063
Massive black holes, produced by the
collapse of a billion suns...
638
00:46:26,271 --> 00:46:28,865
...may be sitting at the centers
of other galaxies...
639
00:46:29,074 --> 00:46:33,067
...curiously producing great
jets of radiation...
640
00:46:33,278 --> 00:46:35,371
...pouring out into space.
641
00:46:38,283 --> 00:46:41,980
At high enough density,
the star winks out...
642
00:46:42,187 --> 00:46:46,055
...and vanishes from our universe
leaving only its gravity behind.
643
00:46:46,257 --> 00:46:51,092
It slips through a self-generated
crack in the space-time continuum.
644
00:46:51,296 --> 00:46:55,596
A black hole is a place
where a star once was.
645
00:46:56,301 --> 00:46:59,168
Here we have a flat two-
dimensional surface...
646
00:46:59,371 --> 00:47:04,138
...with grid lines on it, something
like a piece of graph paper.
647
00:47:05,043 --> 00:47:07,204
Suppose we take a small mass...
648
00:47:07,412 --> 00:47:12,145
...drop it on the surface and
watch how the surface distorts...
649
00:47:12,350 --> 00:47:16,218
...or puckers into
the third physical dimension.
650
00:47:20,091 --> 00:47:24,528
Gravity can be understood as
a curvature of space.
651
00:47:26,264 --> 00:47:29,290
If our moving ball approaches a
stationary distortion...
652
00:47:29,501 --> 00:47:32,868
...it rolls around it like a
planet orbiting the sun.
653
00:47:33,071 --> 00:47:37,474
In this interpretation, due to
Einstein, gravity is only a pucker...
654
00:47:37,676 --> 00:47:41,237
...in the fabric of space which
moving objects encounter.
655
00:47:41,446 --> 00:47:46,383
Space is warped by mass into an
additional physical dimension.
656
00:47:48,887 --> 00:47:53,483
The larger the local mass, the
greater is the local gravity...
657
00:47:53,692 --> 00:47:57,150
...and the more intense is
the distortion...
658
00:47:57,362 --> 00:48:00,559
...or pucker, or warp of space.
659
00:48:00,765 --> 00:48:02,858
So, by this analogy...
660
00:48:03,068 --> 00:48:07,698
...a black hole is a kind of
bottomless pit.
661
00:48:07,906 --> 00:48:09,771
What would happen if you fell in?
662
00:48:09,974 --> 00:48:13,171
Assuming you could survive the
gravitational tides...
663
00:48:13,378 --> 00:48:18,042
...and the intense radiation flux,
it is just barely possible...
664
00:48:18,249 --> 00:48:21,343
...that by plunging into
a black hole...
665
00:48:21,553 --> 00:48:25,319
...you might emerge in another
part of space-time.
666
00:48:25,523 --> 00:48:27,218
Somewhere else in space...
667
00:48:27,425 --> 00:48:31,020
...some-when else in time.
668
00:48:31,229 --> 00:48:33,163
In this view, space is...
669
00:48:33,364 --> 00:48:36,356
...filled with a network
of wormholes...
670
00:48:36,568 --> 00:48:38,433
...something like the wormholes
in an apple.
671
00:48:38,636 --> 00:48:41,730
Although by no means is this
point demonstrated...
672
00:48:41,940 --> 00:48:45,137
...it is merely an exciting suggestion.
673
00:48:45,343 --> 00:48:46,742
If it is true...
674
00:48:46,945 --> 00:48:50,938
...then perhaps there exist
gravity tunnels...
675
00:48:51,149 --> 00:48:54,550
...a kind of interstellar or
intergalactic subway...
676
00:48:54,753 --> 00:48:56,482
...which would permit you
to get from...
677
00:48:56,688 --> 00:48:59,179
...here to there in much less than
the usual time.
678
00:48:59,390 --> 00:49:03,349
A kind of cosmic rapid transit system.
679
00:49:06,064 --> 00:49:08,464
We cannot generate black holes...
680
00:49:08,666 --> 00:49:11,396
...our technology is far
too feeble to...
681
00:49:11,603 --> 00:49:14,299
...move such massive amounts
of matter around.
682
00:49:14,506 --> 00:49:17,498
But perhaps someday, it will be
possible to voyage hundreds or...
683
00:49:17,709 --> 00:49:21,577
...thousands of light-years to
a black hole like Cygnus X-1.
684
00:49:21,780 --> 00:49:23,941
We would plunge down to emerge...
685
00:49:24,149 --> 00:49:27,209
...in some unimaginably
exotic time and place.
686
00:49:27,418 --> 00:49:32,082
Our common-sense notions of reality
severely challenged.
687
00:49:34,325 --> 00:49:36,987
Perhaps the cosmos is infested
with wormholes...
688
00:49:37,195 --> 00:49:39,527
...every one of them a
tunnel to somewhere.
689
00:49:39,731 --> 00:49:43,963
Perhaps other civilizations, with
vastly more advanced technologies...
690
00:49:44,169 --> 00:49:48,572
...are today riding the
gravity express.
691
00:49:50,875 --> 00:49:54,572
It's even possible that a
black hole is a gate...
692
00:49:54,779 --> 00:49:58,146
...to another, and
quite different, universe.
693
00:50:36,187 --> 00:50:38,678
The lives and deaths of the stars...
694
00:50:38,890 --> 00:50:42,291
...seem impossibly remote
from human experience...
695
00:50:42,493 --> 00:50:46,395
...and yet we're related in the most
intimate way to their life cycles.
696
00:50:46,598 --> 00:50:48,566
The very matter that makes us up...
697
00:50:48,766 --> 00:50:53,703
...was generated long ago and far away
in red giant stars.
698
00:50:54,806 --> 00:50:58,469
A blade of grass,
as Walt Whitman said...
699
00:50:58,676 --> 00:51:00,906
"...is the journey work of the stars."
700
00:51:01,112 --> 00:51:02,636
The formation of the solar system...
701
00:51:02,847 --> 00:51:05,975
...may have been triggered by a
nearby supernova explosion.
702
00:51:06,184 --> 00:51:07,674
After the sun turned on...
703
00:51:07,886 --> 00:51:10,719
...its ultraviolet light poured
into our atmosphere.
704
00:51:10,922 --> 00:51:12,913
Its warmth generated lightning.
705
00:51:13,124 --> 00:51:16,025
And these energy sources sparked
the origin of life.
706
00:51:17,061 --> 00:51:19,393
Plants harvest sunlight...
707
00:51:19,597 --> 00:51:22,498
...converting solar into
chemical energy.
708
00:51:23,301 --> 00:51:26,395
We and the other animals are
parasites on the plants.
709
00:51:26,604 --> 00:51:30,540
So we are, all of us, solar-powered.
710
00:51:30,942 --> 00:51:33,433
The evolution of life is
driven by mutations.
711
00:51:33,645 --> 00:51:37,775
They are caused partly by natural
radioactivity and cosmic rays.
712
00:51:37,982 --> 00:51:42,282
But they are both generated in the
spectacular deaths of massive stars...
713
00:51:42,487 --> 00:51:44,478
...thousands of light-years distant.
714
00:51:46,024 --> 00:51:49,653
Think of the sun's heat on your
upturned face...
715
00:51:49,861 --> 00:51:52,125
...on a cloudless summer's day.
716
00:51:52,330 --> 00:51:55,458
From 150 million kilometers away...
717
00:51:55,667 --> 00:51:58,135
...we recognize its power.
718
00:51:58,336 --> 00:52:02,170
What would we feel on its seething,
self-luminous surface...
719
00:52:02,373 --> 00:52:05,831
...or immersed in its heart
of nuclear fire?
720
00:52:06,044 --> 00:52:10,981
And yet, the sun is an ordinary,
even a mediocre star.
721
00:52:11,215 --> 00:52:15,049
Our ancestors worshiped the sun
and they were far from foolish.
722
00:52:15,253 --> 00:52:18,051
It makes good sense to revere
the sun and the stars.
723
00:52:18,256 --> 00:52:22,215
Because we are their children.
724
00:52:25,196 --> 00:52:29,292
We have witnessed the life
cycles of the stars.
725
00:52:29,500 --> 00:52:33,937
They are born, they mature
and then they die.
726
00:52:34,138 --> 00:52:36,402
As time goes on, there are
more white dwarfs...
727
00:52:36,607 --> 00:52:39,098
...more neutron stars,
more black holes.
728
00:52:39,310 --> 00:52:42,143
The remains of the stars accumulate...
729
00:52:42,347 --> 00:52:44,440
...as the eons pass.
730
00:52:44,649 --> 00:52:48,415
But interstellar space also becomes
enriched in heavy elements...
731
00:52:48,619 --> 00:52:52,578
...out of which form new generations
of stars and planets...
732
00:52:52,790 --> 00:52:54,849
...life and intelligence.
733
00:52:55,059 --> 00:52:59,257
The events in one star can influence
a world halfway across the galaxy...
734
00:52:59,464 --> 00:53:01,694
...and a billion years in the future.
735
00:53:09,107 --> 00:53:12,634
The vast interstellar clouds
of gas and dust...
736
00:53:12,844 --> 00:53:14,471
...are stellar nurseries.
737
00:53:14,679 --> 00:53:18,740
Here first begins the inexorable
gravitational collapse...
738
00:53:18,950 --> 00:53:22,010
...which dominates the
lives of the stars.
739
00:53:22,220 --> 00:53:26,623
Massive suns may evolve through the
red giant stage in only millions of years.
740
00:53:26,824 --> 00:53:31,090
Dying young, never leaving the
cloud in which they were born.
741
00:53:33,131 --> 00:53:37,693
Other suns, longer-lived, wander
out of the nursery.
742
00:53:37,902 --> 00:53:40,029
Our sun is such a star...
743
00:53:40,238 --> 00:53:43,298
...as are most
of the stars in the sky.
744
00:53:54,485 --> 00:53:59,047
Most stars are members of double
or multiple star systems...
745
00:53:59,257 --> 00:54:03,557
...and live to process their nuclear
fuel over billions of years.
746
00:54:03,761 --> 00:54:06,821
The galaxy is 10 billion years old.
747
00:54:07,031 --> 00:54:08,623
Old enough to have spawned...
748
00:54:08,833 --> 00:54:12,599
...only a few generations
of ordinary stars.
749
00:54:17,408 --> 00:54:20,741
The objects we encounter
in a voyage through the Milky Way...
750
00:54:20,945 --> 00:54:25,075
...are stages in the life cycle
of the stars.
751
00:54:25,283 --> 00:54:27,513
Some are bright and new...
752
00:54:27,718 --> 00:54:31,711
...and others are as ancient as
the galaxy itself.
753
00:54:43,568 --> 00:54:47,095
Surrounding the Milky Way
is a halo of matter...
754
00:54:47,305 --> 00:54:50,297
...which includes
the globular clusters...
755
00:54:50,508 --> 00:54:53,944
...each containing up to
a million elderly stars.
756
00:54:54,145 --> 00:54:58,514
At the centers of globular clusters
and at the core of the galaxy...
757
00:54:58,716 --> 00:55:03,380
...there may be massive black holes
ticking and purring...
758
00:55:03,588 --> 00:55:06,113
...the subject of future exploration.
759
00:55:24,008 --> 00:55:26,943
We on Earth marvel,
and rightly so...
760
00:55:27,145 --> 00:55:30,171
...at the daily return
of our single sun.
761
00:55:30,381 --> 00:55:34,147
But from a planet orbiting a star
in a distant globular cluster...
762
00:55:34,352 --> 00:55:37,185
...a still more glorious dawn awaits.
763
00:55:37,388 --> 00:55:40,653
Not a sunrise, but a galaxy-rise.
764
00:55:40,858 --> 00:55:44,589
A morning filled with
400 billion suns...
765
00:55:44,795 --> 00:55:47,059
...the rising of the Milky Way.
766
00:55:47,265 --> 00:55:51,167
An enormous spiral form
with collapsing gas clouds...
767
00:55:51,369 --> 00:55:55,100
...condensing planetary systems,
luminous supergiants...
768
00:55:55,306 --> 00:55:57,274
...stable middle-aged stars...
769
00:55:57,475 --> 00:56:01,844
...red giants, white dwarfs, planetary
nebulas, supernovas...
770
00:56:02,046 --> 00:56:06,483
...neutron stars, pulsars,
black holes and...
771
00:56:06,717 --> 00:56:09,686
...there is every reason to think,
other exotic objects...
772
00:56:09,921 --> 00:56:12,116
...that we have not yet discovered.
773
00:56:15,126 --> 00:56:18,994
From such a world, high above
the disc of the Milky Way...
774
00:56:19,197 --> 00:56:23,224
...it would be clear as it is
beginning to be clear on our world...
775
00:56:23,434 --> 00:56:26,494
...that we are made
by the atoms in the stars...
776
00:56:26,704 --> 00:56:30,765
...that our matter
and our form are determined...
777
00:56:30,975 --> 00:56:34,570
...by the cosmos
of which we are a part.
778
00:56:42,920 --> 00:56:47,186
I only have a moment, but I wanted you
to see a picture of Betelgeuse...
779
00:56:47,391 --> 00:56:49,325
...in the constellation Orion.
780
00:56:49,527 --> 00:56:52,621
The first image of the surface
of another star.
781
00:56:52,897 --> 00:56:55,559
But the most exciting recent
stellar discovery...
782
00:56:55,766 --> 00:56:57,597
...has been of a nearby supernova...
783
00:56:57,802 --> 00:56:59,997
...in a companion galaxy
to the Milky Way.
784
00:57:00,204 --> 00:57:04,504
We are here seeing chemical elements
in the process of synthesis...
785
00:57:04,709 --> 00:57:08,270
...and have had our first glimpse
of the supernova...
786
00:57:08,479 --> 00:57:11,642
...through a brand-new field:
neutrino astronomy.
787
00:57:11,849 --> 00:57:15,046
And we're now seeing, around
neighboring stars...
788
00:57:15,620 --> 00:57:19,317
...discs of gas and dust just
like those needed to explain...
789
00:57:19,523 --> 00:57:22,253
...the origin of the planets
in our solar system.
790
00:57:22,460 --> 00:57:25,190
Worlds may be forming here.
791
00:57:25,396 --> 00:57:28,661
It's like a snapshot of our
solar system's past.
792
00:57:29,100 --> 00:57:32,228
And there are so many such
discs being found these days...
793
00:57:32,436 --> 00:57:36,964
...that planets may be very common
among the stars of the Milky Way.
9999
00:00:0,500 --> 00:00:2,00
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