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
TED2008

Stephen Hawking: Questioning the universe

Filmed:
12,876,555 views

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

Double-click the English transcript below to play the video.

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