TED2018
Stephen Webb: Where are all the aliens?
Filmed:
Readability: 5
5,111,570 views
The universe is incredibly old, astoundingly vast and populated by trillions of planets -- so where are all the aliens? Astronomer Stephen Webb has an explanation: we're alone in the universe. In a mind-expanding talk, he spells out the remarkable barriers a planet would need to clear in order to host an extraterrestrial civilization -- and makes a case for the beauty of our potential cosmic loneliness. "The silence of the universe is shouting, 'We're the creatures who got lucky,'" Webb says.
Stephen Webb - Writer, scientist
Stephen Webb is a science fiction fan who's passionately interested in what the future might hold for our species. Full bio
Stephen Webb is a science fiction fan who's passionately interested in what the future might hold for our species. Full bio
Double-click the English transcript below to play the video.
00:13
I saw a UFO once.
0
1200
2176
00:15
I was eight or nine,
1
3400
1896
00:17
playing in the street with a friend
who was a couple of years older,
who was a couple of years older,
2
5320
3336
00:20
and we saw a featureless silver disc
hovering over the houses.
hovering over the houses.
3
8680
4656
00:25
We watched it for a few seconds,
4
13360
1776
00:27
and then it shot away incredibly quickly.
5
15160
3256
00:30
Even as a kid,
6
18440
1216
00:31
I got angry it was ignoring
the laws of physics.
the laws of physics.
7
19680
2840
00:35
We ran inside to tell the grown-ups,
8
23160
2256
00:37
and they were skeptical --
9
25440
1576
00:39
you'd be skeptical too, right?
10
27040
2080
00:42
I got my own back a few years later:
11
30120
1736
00:43
one of those grown-ups told me,
12
31880
1496
00:45
"Last night I saw a flying saucer.
13
33400
1816
00:47
I was coming out of the pub
after a few drinks."
after a few drinks."
14
35240
2576
00:49
I stopped him there.
I said, "I can explain that sighting."
I said, "I can explain that sighting."
15
37840
2816
00:52
(Laughter)
16
40680
1016
00:53
Psychologists have shown
we can't trust our brains
we can't trust our brains
17
41720
2896
00:56
to tell the truth.
18
44640
1216
00:57
It's easy to fool ourselves.
19
45880
1816
00:59
I saw something,
20
47720
1616
01:01
but what's more likely --
21
49360
1376
01:02
that I saw an alien spacecraft,
22
50760
2016
01:04
or that my brain misinterpreted
the data my eyes were giving it?
the data my eyes were giving it?
23
52800
3920
01:10
Ever since though I've wondered:
24
58200
1576
01:11
Why don't we see
flying saucers flitting around?
flying saucers flitting around?
25
59800
3016
01:14
At the very least,
26
62840
1216
01:16
why don't we see life
out there in the cosmos?
out there in the cosmos?
27
64080
2856
01:18
It's a puzzle,
28
66960
1216
01:20
and I've discussed it
with dozens of experts
with dozens of experts
29
68200
2456
01:22
from different disciplines
over the past three decades.
over the past three decades.
30
70680
3136
01:25
And there's no consensus.
31
73840
1856
01:27
Frank Drake began searching
for alien signals back in 1960 --
for alien signals back in 1960 --
32
75720
4336
01:32
so far, nothing.
33
80080
1896
01:34
And with each passing year,
34
82000
1416
01:35
this nonobservation,
35
83440
1536
01:37
this lack of evidence
for any alien activity gets more puzzling
for any alien activity gets more puzzling
36
85000
5656
01:42
because we should see them, shouldn't we?
37
90680
3000
01:47
The universe is 13.8 billion years old,
38
95120
3776
01:50
give or take.
39
98920
1256
01:52
If we represent the age
of the universe by one year,
of the universe by one year,
40
100200
3496
01:55
then our species came into being
about 12 minutes before midnight,
about 12 minutes before midnight,
41
103720
4576
02:00
31st December.
42
108320
1240
02:02
Western civilization
has existed for a few seconds.
has existed for a few seconds.
43
110120
3656
02:05
Extraterrestrial civilizations
could have started in the summer months.
could have started in the summer months.
44
113800
3720
02:10
Imagine a summer civilization
45
118600
2736
02:13
developing a level of technology
more advanced than ours,
more advanced than ours,
46
121360
4256
02:17
but tech based on accepted physics though,
47
125640
2136
02:19
I'm not talking wormholes
or warp drives -- whatever --
or warp drives -- whatever --
48
127800
3936
02:23
just an extrapolation
of the sort of tech that TED celebrates.
of the sort of tech that TED celebrates.
49
131760
4520
02:28
That civilization could program
self-replicating probes
self-replicating probes
50
136880
3576
02:32
to visit every planetary
system in the galaxy.
system in the galaxy.
51
140480
2640
02:35
If they launched the first probes
just after midnight one August day,
just after midnight one August day,
52
143840
4520
02:41
then before breakfast same day,
53
149200
2256
02:43
they could have colonized the galaxy.
54
151480
2120
02:46
Intergalactic colonization
isn't much more difficult,
isn't much more difficult,
55
154640
2576
02:49
it just takes longer.
56
157240
1240
02:51
A civilization from any one
of millions of galaxies
of millions of galaxies
57
159080
2936
02:54
could have colonized our galaxy.
58
162040
2360
02:56
Seems far-fetched?
59
164960
1736
02:58
Maybe it is,
60
166720
1216
02:59
but wouldn't aliens engage
in some recognizable activity --
in some recognizable activity --
61
167960
5096
03:05
put worldlets around a star
to capture free sunlight,
to capture free sunlight,
62
173080
4256
03:09
collaborate on a Wikipedia Galactica,
63
177360
3176
03:12
or just shout out
to the universe, "We're here"?
to the universe, "We're here"?
64
180560
2920
03:16
So where is everybody?
65
184920
1200
03:18
It's a puzzle because we do expect
these civilizations to exist, don't we?
these civilizations to exist, don't we?
66
186760
5416
03:24
After all, there could be
a trillion planets in the galaxy --
a trillion planets in the galaxy --
67
192200
3176
03:27
maybe more.
68
195400
1360
03:29
You don't need any special knowledge
to consider this question,
to consider this question,
69
197600
4376
03:34
and I've explored it
with lots of people over the years.
with lots of people over the years.
70
202000
3896
03:37
And I've found they often
frame their thinking
frame their thinking
71
205920
2976
03:40
in terms of the barriers
that would need to be cleared
that would need to be cleared
72
208920
3096
03:44
if a planet is to host
a communicative civilization.
a communicative civilization.
73
212040
4240
03:49
And they usually identify
four key barriers.
four key barriers.
74
217120
3816
03:52
Habitability --
75
220960
1376
03:54
that's the first barrier.
76
222360
1416
03:55
We need a terrestrial planet
in that just right "Goldilocks zone,"
in that just right "Goldilocks zone,"
77
223800
4616
04:00
where water flows as a liquid.
78
228440
2240
04:03
They're out there.
79
231400
1256
04:04
In 2016, astronomers confirmed
there's a planet in the habitable zone
there's a planet in the habitable zone
80
232680
4576
04:09
of the closest star,
81
237280
1456
04:10
Proxima Centauri --
82
238760
1776
04:12
so close that Breakthrough Starshot
project plans to send probes there.
project plans to send probes there.
83
240560
5056
04:17
We'd become a starfaring species.
84
245640
2880
04:21
But not all worlds are habitable.
85
249480
1616
04:23
Some will be too close to a star
and they'll fry,
and they'll fry,
86
251120
2336
04:25
some will be too far away
and they'll freeze.
and they'll freeze.
87
253480
2120
04:28
Abiogenesis --
88
256800
1216
04:30
the creation of life from nonlife --
89
258040
1775
04:31
that's the second barrier.
90
259839
1281
04:34
The basic building blocks of life
aren't unique to Earth:
aren't unique to Earth:
91
262000
3896
04:37
amino acids have been found in comets,
92
265920
2736
04:40
complex organic molecules
in interstellar dust clouds,
in interstellar dust clouds,
93
268680
3096
04:43
water in exoplanetary systems.
94
271800
2600
04:47
The ingredients are there,
95
275160
1256
04:48
we just don't know
how they combine to create life,
how they combine to create life,
96
276440
2656
04:51
and presumably there will be worlds
on which life doesn't start.
on which life doesn't start.
97
279120
3160
04:55
The development of technological
civilization is a third barrier.
civilization is a third barrier.
98
283840
3680
05:00
Some say we already share our planet
with alien intelligences.
with alien intelligences.
99
288600
4776
05:05
A 2011 study showed that elephants
can cooperate to solve problems.
can cooperate to solve problems.
100
293400
4800
05:10
A 2010 study showed
101
298840
1536
05:12
that an octopus in captivity
can recognize different humans.
can recognize different humans.
102
300400
4280
05:17
2017 studies show that ravens
can plan for future events --
can plan for future events --
103
305360
3896
05:21
wonderful, clever creatures --
104
309280
2736
05:24
but they can't contemplate
the Breakthrough Starshot project,
the Breakthrough Starshot project,
105
312040
3216
05:27
and if we vanished today,
106
315280
2256
05:29
they wouldn't go on
to implement Breakthrough Starshot --
to implement Breakthrough Starshot --
107
317560
2856
05:32
why should they?
108
320440
1376
05:33
Evolution doesn't have
space travel as an end goal.
space travel as an end goal.
109
321840
2760
05:37
There will be worlds where life
doesn't give rise to advanced technology.
doesn't give rise to advanced technology.
110
325160
4560
05:43
Communication across space --
that's a fourth barrier.
that's a fourth barrier.
111
331040
2856
05:45
Maybe advanced civilizations
choose to explore inner space
choose to explore inner space
112
333920
3776
05:49
rather than outer space,
113
337720
2336
05:52
or engineer at small distances
rather than large.
rather than large.
114
340080
3520
05:56
Or maybe they just don't want
to risk an encounter
to risk an encounter
115
344600
2856
05:59
with a potentially more advanced
and hostile neighbor.
and hostile neighbor.
116
347480
4136
06:03
There'll be worlds where,
for whatever reason,
for whatever reason,
117
351640
2176
06:05
civilizations either stay silent
or don't spend long trying to communicate.
or don't spend long trying to communicate.
118
353840
4640
06:12
As for the height of the barriers,
119
360600
2096
06:14
your guess is as good as anyone's.
120
362720
2400
06:18
In my experience,
121
366080
1256
06:19
when people sit down and do the math,
122
367360
2056
06:21
they typically conclude there are
thousands of civilizations in the galaxy.
thousands of civilizations in the galaxy.
123
369440
4880
06:27
But then we're back to the puzzle:
Where is everybody?
Where is everybody?
124
375640
2720
06:32
By definition,
125
380055
1361
06:33
UFOs -- including the one I saw --
126
381440
2336
06:35
are unidentified.
127
383800
1296
06:37
We can't simply infer they're spacecraft.
128
385120
3736
06:40
You can still have some fun
playing with the idea aliens are here.
playing with the idea aliens are here.
129
388880
3480
06:45
Some say a summer civilization
did colonize the galaxy
did colonize the galaxy
130
393000
3856
06:48
and seeded Earth with life ...
131
396880
2000
06:51
others, that we're living
in a cosmic wilderness preserve --
in a cosmic wilderness preserve --
132
399800
2856
06:54
a zoo.
133
402680
1240
06:56
Yet others --
134
404480
1496
06:58
that we're living in a simulation.
135
406000
2176
07:00
Programmers just haven't
revealed the aliens yet.
revealed the aliens yet.
136
408200
2320
07:03
Most of my colleagues though
argue that E.T. is out there,
argue that E.T. is out there,
137
411680
4336
07:08
we just need to keep looking,
138
416040
1616
07:09
and this makes sense.
139
417680
1576
07:11
Space is vast.
140
419280
1776
07:13
Identifying a signal is hard,
141
421080
2816
07:15
and we haven't been looking that long.
142
423920
2600
07:19
Without doubt, we should
spend more on the search.
spend more on the search.
143
427160
3136
07:22
It's about understanding
our place in the universe.
our place in the universe.
144
430320
3336
07:25
It's too important a question to ignore.
145
433680
3320
07:29
But there's an obvious answer:
146
437840
2096
07:31
we're alone.
147
439960
1296
07:33
It's just us.
148
441280
1616
07:34
There could be a trillion
planets in the galaxy.
planets in the galaxy.
149
442920
3496
07:38
Is it plausible we're the only creatures
capable of contemplating this question?
capable of contemplating this question?
150
446440
4480
07:43
Well, yes, because in this context,
151
451840
2616
07:46
we don't know whether
a trillion is a big number.
a trillion is a big number.
152
454480
2360
07:50
In 2000, Peter Ward and Don Brownlee
proposed the Rare Earth idea.
proposed the Rare Earth idea.
153
458040
5296
07:55
Remember those four barriers
154
463360
1816
07:57
that people use to estimate
the number of civilizations?
the number of civilizations?
155
465200
3856
08:01
Ward and Brownlee said
there might be more.
there might be more.
156
469080
2120
08:03
Let's look at one possible barrier.
157
471840
1696
08:05
It's a recent suggestion by David Waltham,
158
473560
2656
08:08
a geophysicist.
159
476240
1240
08:10
This is my very simplified version
160
478000
2456
08:12
of Dave's much more
sophisticated argument.
sophisticated argument.
161
480480
2600
08:16
We are able to be here now
162
484240
2016
08:18
because Earth's previous
inhabitants enjoyed
inhabitants enjoyed
163
486280
2656
08:20
four billion years of good weather --
164
488960
2176
08:23
ups and downs but more or less clement.
165
491160
2640
08:26
But long-term climate
stability is strange,
stability is strange,
166
494960
2496
08:29
if only because astronomical influences
167
497480
2416
08:31
can push a planet
towards freezing or frying.
towards freezing or frying.
168
499920
4056
08:36
There's a hint our moon has helped,
169
504000
2176
08:38
and that's interesting
170
506200
2176
08:40
because the prevailing theory is
171
508400
1656
08:42
that the moon came into being when Theia,
172
510080
2496
08:44
a body the size of Mars,
173
512600
1616
08:46
crashed into a newly formed Earth.
174
514240
2736
08:49
The outcome of that crash could have been
a quite different Earth-Moon system.
a quite different Earth-Moon system.
175
517000
4120
08:54
We ended up with a large moon
176
522120
2256
08:56
and that permitted Earth
to have both a stable axial tilt
to have both a stable axial tilt
177
524400
3856
09:00
and a slow rotation rate.
178
528280
3176
09:03
Both factors influence climate
179
531480
1656
09:05
and the suggestion is that they've helped
moderate climate change.
moderate climate change.
180
533160
3600
09:09
Great for us, right?
181
537440
1240
09:11
But Waltham showed that if the moon
were just a few miles bigger,
were just a few miles bigger,
182
539360
3736
09:15
things would be different.
183
543120
1616
09:16
Earth's spin axis
would now wander chaotically.
would now wander chaotically.
184
544760
3336
09:20
There'd be episodes
of rapid climate change --
of rapid climate change --
185
548120
2896
09:23
not good for complex life.
186
551040
2376
09:25
The moon is just the right size:
187
553440
2216
09:27
big but not too big.
188
555680
3056
09:30
A "Goldilocks" moon around
a "Goldilocks" planet --
a "Goldilocks" planet --
189
558760
2416
09:33
a barrier perhaps.
190
561200
1520
09:35
You can imagine more barriers.
191
563200
1816
09:37
For instance,
192
565040
1216
09:38
simple cells came into being
billions of years ago ...
billions of years ago ...
193
566280
3040
09:42
but perhaps the development
of complex life
of complex life
194
570480
3296
09:45
needed a series of unlikely events.
195
573800
2896
09:48
Once life on Earth
had access to multicellularity
had access to multicellularity
196
576720
2576
09:51
and sophisticated genetic structures,
197
579320
2056
09:53
and sex,
198
581400
1256
09:54
new opportunities opened up:
199
582680
1536
09:56
animals became possible.
200
584240
1360
09:58
But maybe it's the fate of many planets
201
586240
2816
10:01
for life to settle
at the level of simple cells.
at the level of simple cells.
202
589080
3840
10:06
Purely for the purposes of illustration,
203
594760
3096
10:09
let me suggest four more barriers
to add to the four
to add to the four
204
597880
3056
10:12
that people said blocked the path
to communicative civilization.
to communicative civilization.
205
600960
3920
10:17
Again, purely for the purposes
of illustration,
of illustration,
206
605760
3256
10:21
suppose there's a one-in-a-thousand chance
of making it across each of the barriers.
of making it across each of the barriers.
207
609040
4256
10:25
Of course there might be
different ways of navigating the barriers,
different ways of navigating the barriers,
208
613320
3136
10:28
and some chances will be better
than one in a thousand.
than one in a thousand.
209
616480
2776
10:31
Equally, there might be more barriers
210
619280
1856
10:33
and some chances
might be one in a million.
might be one in a million.
211
621160
2256
10:35
Let's just see
what happens in this picture.
what happens in this picture.
212
623440
2080
10:39
If the galaxy contains a trillion planets,
213
627120
2576
10:41
how many will host a civilization
capable of contemplating like us
capable of contemplating like us
214
629720
5496
10:47
projects such as Breakthrough Starshot?
215
635240
2200
10:50
Habitability --
216
638480
1256
10:51
right sort of planet
around the right sort of star --
around the right sort of star --
217
639760
2816
10:54
the trillion becomes a billion.
218
642600
2336
10:56
Stability --
219
644960
1336
10:58
a climate that stays benign for eons --
220
646320
3416
11:01
the billion becomes a million.
221
649760
1856
11:03
Life must start --
222
651640
1200
11:05
the million becomes a thousand.
223
653600
2216
11:07
Complex life forms must arise --
224
655840
2256
11:10
the thousand becomes one.
225
658120
2576
11:12
Sophisticated tool use must develop --
226
660720
1856
11:14
that's one planet in a thousand galaxies.
227
662600
2000
11:17
To understand the universe,
228
665480
1576
11:19
they'll have to develop the techniques
of science and mathematics --
of science and mathematics --
229
667080
3216
11:22
that's one planet in a million galaxies.
230
670320
2096
11:24
To reach the stars,
they'll have to be social creatures,
they'll have to be social creatures,
231
672440
2656
11:27
capable of discussing
abstract concepts with each other
abstract concepts with each other
232
675120
2816
11:29
using complex grammar --
233
677960
1896
11:31
one planet in a billion galaxies.
234
679880
3216
11:35
And they have to avoid disaster --
235
683120
1736
11:36
not just self-inflicted
but from the skies, too.
but from the skies, too.
236
684880
4056
11:40
That planet around Proxima Centauri,
237
688960
2936
11:43
last year it got blasted by a flare.
238
691920
2320
11:47
One planet in a trillion galaxies,
239
695200
1936
11:49
just as in the visible universe.
240
697160
2760
11:54
I think we're alone.
241
702480
1200
11:57
Those colleagues of mine
who agree we're alone
who agree we're alone
242
705240
2296
11:59
often see a barrier ahead --
243
707560
3136
12:02
bioterror,
244
710720
1256
12:04
global warming, war.
245
712000
1560
12:06
A universe that's silent
246
714320
3016
12:09
because technology itself
forms the barrier
forms the barrier
247
717360
3416
12:12
to the development
of a truly advanced civilization.
of a truly advanced civilization.
248
720800
3936
12:16
Depressing, right?
249
724760
1440
12:19
I'm arguing the exact opposite.
250
727240
1680
12:22
I grew up watching "Star Trek"
and "Forbidden Planet,"
and "Forbidden Planet,"
251
730560
2576
12:25
and I saw a UFO once,
252
733160
1776
12:26
so this idea of cosmic loneliness
I certainly find slightly wistful.
I certainly find slightly wistful.
253
734960
6080
12:34
But for me,
254
742240
2096
12:36
the silence of the universe is shouting,
255
744360
1936
12:38
"We're the creatures who got lucky."
256
746320
1720
12:40
All barriers are behind us.
257
748800
1856
12:42
We're the only species
that's cleared them --
that's cleared them --
258
750680
2416
12:45
the only species capable
of determining its own destiny.
of determining its own destiny.
259
753120
4416
12:49
And if we learn to appreciate
how special our planet is,
how special our planet is,
260
757560
3200
12:53
how important it is to look after our home
261
761840
2136
12:56
and to find others,
262
764000
1816
12:57
how incredibly fortunate we all are
simply to be aware of the universe,
simply to be aware of the universe,
263
765840
4816
13:02
humanity might survive for a while.
264
770680
2336
13:05
And all those amazing things
265
773040
1656
13:06
we dreamed aliens
might have done in the past,
might have done in the past,
266
774720
2856
13:09
that could be our future.
267
777600
1200
13:11
Thank you very much.
268
779640
1256
13:12
(Applause)
269
780920
3520
ABOUT THE SPEAKER
Stephen Webb - Writer, scientistStephen Webb is a science fiction fan who's passionately interested in what the future might hold for our species.
Why you should listen
An early preoccupation with science fiction ended up influencing most of Stephen Webb's professional activity. It instilled in him a deep love of science and the scientific endeavor, which in turn led him to complete a PhD in theoretical particle physics. Isaac Asimov's story "The Fun They Had," about computerized homeschooling, prompted him to consider how digital technology might deepen students' learning, which in turn led to posts in a variety of UK universities.
And it was in the pages of a science fiction magazine that he first encountered the Fermi paradox, which kindled a lifelong fascination with the problem of why we see no signs of extraterrestrial intelligence -- and led to his book Where Is Everybody, which explores the question in detail. Webb hopes to pass on his love of science through his outreach work, and he is the author of a number of popular science books. He is working on New Light Through Old Windows, an anthology of classic science fiction tales; each tale appears alongside a commentary detailing the latest scientific thinking relating to the story's theme.
Stephen Webb | Speaker | TED.com