10:13
TED2008

Stephen Hawking: Questioning the universe

Filmed:

In keeping with the theme of TED2008, professor Stephen Hawking asks some Big Questions about our universe -- How did the universe begin? How did life begin? Are we alone? -- and discusses how we might go about answering them.

- Theoretical physicist
Stephen Hawking's scientific investigations have shed light on the origins of the cosmos, the nature of time and the ultimate fate of the universe. His bestselling books for a general audience have given an appreciation of physics to millions. Full bio

There is nothing bigger or older than the universe.
00:14
The questions I would like to talk about are:
00:18
one, where did we come from?
00:22
How did the universe come into being?
00:29
Are we alone in the universe?
00:32
Is there alien life out there?
00:36
What is the future of the human race?
00:39
Up until the 1920s,
00:43
everyone thought the universe was essentially static
00:45
and unchanging in time.
00:49
Then it was discovered that the universe was expanding.
00:51
Distant galaxies were moving away from us.
00:56
This meant they must have been closer together in the past.
00:59
If we extrapolate back,
01:06
we find we must have all been on top of each other
01:08
about 15 billion years ago.
01:12
This was the Big Bang, the beginning of the universe.
01:14
But was there anything before the Big Bang?
01:20
If not, what created the universe?
01:23
Why did the universe emerge from the Big Bang the way it did?
01:27
We used to think that the theory of the universe
01:32
could be divided into two parts.
01:37
First, there were the laws
01:39
like Maxwell's equations and general relativity
01:42
that determined the evolution of the universe,
01:45
given its state over all of space at one time.
01:49
And second, there was no question
01:52
of the initial state of the universe.
01:55
We have made good progress on the first part,
01:58
and now have the knowledge of the laws of evolution
02:03
in all but the most extreme conditions.
02:06
But until recently, we have had little idea
02:09
about the initial conditions for the universe.
02:12
However, this division into laws of evolution and initial conditions
02:16
depends on time and space being separate and distinct.
02:21
Under extreme conditions, general relativity and quantum theory
02:27
allow time to behave like another dimension of space.
02:31
This removes the distinction between time and space,
02:39
and means the laws of evolution can also determine the initial state.
02:43
The universe can spontaneously create itself out of nothing.
02:51
Moreover, we can calculate a probability that the universe
02:55
was created in different states.
03:03
These predictions are in excellent agreement
03:05
with observations by the WMAP satellite
03:08
of the cosmic microwave background,
03:12
which is an imprint of the very early universe.
03:14
We think we have solved the mystery of creation.
03:18
Maybe we should patent the universe
03:24
and charge everyone royalties for their existence.
03:26
I now turn to the second big question:
03:33
are we alone, or is there other life in the universe?
03:36
We believe that life arose spontaneously on the Earth,
03:44
so it must be possible for life to appear on other suitable planets,
03:47
of which there seem to be a large number in the galaxy.
03:52
But we don't know how life first appeared.
03:56
We have two pieces of observational evidence
04:04
on the probability of life appearing.
04:07
The first is that we have fossils of algae
04:12
from 3.5 billion years ago.
04:15
The Earth was formed 4.6 billion years ago
04:19
and was probably too hot for about the first half billion years.
04:23
So life appeared on Earth
04:33
within half a billion years of it being possible,
04:35
which is short compared to the 10-billion-year lifetime
04:39
of a planet of Earth type.
04:42
This suggests that a probability of life appearing is reasonably high.
04:45
If it was very low, one would have expected it
04:50
to take most of the ten billion years available.
04:54
On the other hand, we don't seem to have been visited by aliens.
04:58
I am discounting the reports of UFOs.
05:04
Why would they appear only to cranks and weirdoes?
05:07
If there is a government conspiracy to suppress the reports
05:14
and keep for itself the scientific knowledge the aliens bring,
05:18
it seems to have been a singularly ineffective policy so far.
05:23
Furthermore, despite an extensive search by the SETI project,
05:27
we haven't heard any alien television quiz shows.
05:37
This probably indicates that there are no alien civilizations
05:41
at our stage of development
05:46
within a radius of a few hundred light years.
05:48
Issuing an insurance policy
05:53
against abduction by aliens seems a pretty safe bet.
05:55
This brings me to the last of the big questions:
06:02
the future of the human race.
06:05
If we are the only intelligent beings in the galaxy,
06:08
we should make sure we survive and continue.
06:12
But we are entering an increasingly dangerous period of our history.
06:19
Our population and our use of the finite resources of planet Earth
06:23
are growing exponentially, along with our technical ability
06:33
to change the environment for good or ill.
06:37
But our genetic code
06:44
still carries the selfish and aggressive instincts
06:46
that were of survival advantage in the past.
06:49
It will be difficult enough to avoid disaster
06:52
in the next hundred years,
07:00
let alone the next thousand or million.
07:01
Our only chance of long-term survival
07:08
is not to remain lurking on planet Earth,
07:11
but to spread out into space.
07:15
The answers to these big questions
07:17
show that we have made remarkable progress in the last hundred years.
07:22
But if we want to continue beyond the next hundred years,
07:27
our future is in space.
07:32
That is why I am in favor of manned --
07:34
or should I say, personed -- space flight.
07:39
All of my life I have sought to understand the universe
07:42
and find answers to these questions.
07:52
I have been very lucky
07:54
that my disability has not been a serious handicap.
07:57
Indeed, it has probably given me more time than most people
08:01
to pursue the quest for knowledge.
08:06
The ultimate goal is a complete theory of the universe,
08:08
and we are making good progress.
08:16
Thank you for listening.
08:18
Chris Anderson: Professor, if you had to guess either way,
08:26
do you now believe that it is more likely than not
08:29
that we are alone in the Milky Way,
08:33
as a civilization of our level of intelligence or higher?
08:36
This answer took seven minutes, and really gave me an insight
08:57
into the incredible act of generosity this whole talk was for TED.
09:03
Stephen Hawking: I think it quite likely that we are the only civilization
09:18
within several hundred light years;
09:23
otherwise we would have heard radio waves.
09:26
The alternative is that civilizations don't last very long,
09:29
but destroy themselves.
09:37
CA: Professor Hawking, thank you for that answer.
09:38
We will take it as a salutary warning, I think,
09:44
for the rest of our conference this week.
09:46
Professor, we really thank you for the extraordinary effort you made
09:50
to share your questions with us today.
09:54
Thank you very much indeed.
09:57
(Applause)
09:58

▲Back to top

About the Speaker:

Stephen Hawking - Theoretical physicist
Stephen Hawking's scientific investigations have shed light on the origins of the cosmos, the nature of time and the ultimate fate of the universe. His bestselling books for a general audience have given an appreciation of physics to millions.

Why you should listen

Stephen Hawking is perhaps the world's most famous living physicist. A specialist in cosmology and quantum gravity and a devotee of black holes, his work has probed the origins of the cosmos, the nature of time and the universe's ultimate fate -- earning him accolades including induction into the Order of the British Empire. To the public, he's best known as an author of bestsellers such as The Universe in a Nutshell and A Brief History of Time, which have brought an appreciation of theoretical physics to millions.

Though the motor neuron disorder ALS has confined Hawking to a wheelchair, it hasn't stopped him from lecturing widely, making appearances on television shows such as Star Trek: The Next Generation and The Simpsons -- and planning a trip into orbit with Richard Branson's Virgin Galactic. (He recently experienced weightlessness aboard Zero Gravity Corporation's "Vomit Comet.") A true academic celebrity, he uses his public appearances to raise awareness about potential global disasters -- such as global warming -- and to speak out for the future of humanity: "Getting a portion of the human race permanently off the planet is imperative for our future as a species," he says.

Hawking serves as Lucasian Professor of Mathematics at the University of Cambridge, where he continues to contribute to both high-level physics and the popular understanding of our universe.

More profile about the speaker
Stephen Hawking | Speaker | TED.com