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Annotated captions of Stephen Hawking asks big questions about the universe in English

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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)