1
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Time.

2
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Time does not exist.

3
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I have 15 minutes to convince you of it.

4
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Take two watches.

5
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Hopefully better than these old-fashioned
pocket watches of my grandfather.

6
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A bit more precise, okay?

7
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Make sure that they show the same time.

8
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They show the same time, the same as here,

9
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around 2:45.

10
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Now, try raising one of them
and lowering the other.

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Keep them like that for a while:

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one, two, three.

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Then bring them back together

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and see what they show.

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If the watches are a little more
precise than these,

16
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they no longer show the same time.

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The watch held higher reads faster,

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and the watch held lower reads slower.

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This is a fact.

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Obviously, with watches like these,
it's not very easy to see that.

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They're not precise enough.

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However, today there exist
extremely precise watches.

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That's one of them.

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It's the Boulder atomic clock in Colorado,

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one of those that are used to fix
the official time in the United States.

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We have similar ones
in Italy, in Florence, lots.

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There are also smaller versions,
more commercial versions,

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that are good enough
to observe this effect with.

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They are in small boxes.

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If you take one and put it low down,

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and put another high up,

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when you bring them back together again,
they no longer show the same time.

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Time goes faster higher up,

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and slower lower down.

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It's a fact.

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For instance,

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imagine you have a twin brother,

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you are the same age,
you grew up together.

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Imagine that your brother
goes to live in the mountains,

40
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and you go to live by the sea.

41
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If much later you meet up again,

42
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your brother will be older,
and you will be younger than he.

43
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It's not just watches that are influenced

44
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by the strength
of the gravitational field,

45
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but all phenomena connected with time.

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Aging, the speed of our thoughts,
a flower coming into bloom.

47
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Everything.

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A swinging pendulum.

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Time goes faster higher up,
and slower lower down.

50
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You see, when at the beginning of the 90s,

51
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the first satellites for GPS
were sent into orbit,

52
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for the sat nav devices
we have in our cars

53
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to tell us where we are,

54
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physicists told engineers,

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"Be careful, up there,
on the satellites, time goes faster."

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To work, the device needs to receive
messages from a satellite.

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On satellites, there's a clock.

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The clock goes faster than
what we would expect down here,

59
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so they'd need to take that into account.

60
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The engineers said, "Oh, okay."

61
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However, the entire project was, and is,
a project of the American military.

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GPS is operated by the US military.

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So, heading up the project
were American generals.

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The American generals were army generals.

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When told time goes slower,
faster, etc., their response was:

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"Time goes slower? Faster?
I don't believe it."

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So, the first satellites were sent up
with a double system

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that could work taking or not taking
into account this effect.

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The version that didn't take
this effect into account didn't work.

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The GPS would not work

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if it didn't take into account
the fact that up there time went faster.

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So, even the American generals
could not be other than convinced

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that time went faster up there.

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What does this mean?

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It means time is not
what we imagine it to be.

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We cannot think of a unique time
that flows the same everywhere.

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Somehow, we need to think

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that higher up, lower down,
more to the right, more to the left,

79
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for who moves more slowly,
for who moves faster,

80
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time goes at different speeds.

81
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We need to change how we see the world,

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from a single clock beating the time,

83
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to many clocks, each with its own time.

84
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The world is a choir of these clocks
that go at different speeds.

85
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Strange and difficult.

86
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But if you think about it,

87
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it's not the first time we've changed
how we see the world, is it?

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Is the Earth flat or round?

89
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This room, is it stationary
or is it moving?

90
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Stationary.

91
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No, we know it's moving,
travelling very fast around the sun.

92
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(Hesitation)

93
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A swallow comes from another swallow,

94
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its mother was a swallow,
its grandmother, and so on,

95
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swallow, swallow, swallow.

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I was born from a human being,
who was born from another human being,

97
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from another human being.

98
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So it's impossible I and a swallow
share the same ancestors.

99
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Not the case.

100
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We and the swallows
have the same, common ancestors.

101
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So, what's this all about?

102
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We tend to develop simple,
natural ideas about the world

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that are wrong.

104
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Not because they are
not adaptable to our lives.

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They are adaptable to our lives,
indeed that's the case;

106
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they refer to, are good on, our scale.

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They are no longer good
when we look at life,

108
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not on a scale of 10, 100 or 1,000 years,
but on a scale of millions of years,

109
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or when we think about
what happens very far away,

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with very fast, very small,
or very big objects.

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There's an example I really like
and think useful in understanding time,

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that about high and low, right?

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Things fall from high to low.

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That is high, and this is low.

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It's one of the basic structures
of the world as we see it.

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We organize our world
in terms of high and low, right?

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So in the universe, there's high and low.

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Okay? A universal direction,
which is higher or lower.

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This isn't entirely true.

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What's high here is low in Sydney.

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What's more, if we leave the Earth,
there's not really high and low.

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Astronauts, we saw the pictures,
they move in any direction.

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The notion of high and low
doesn't exist out there in the universe;

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it's a notion appropriate only here to us.

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It's convenient and useful
to organize phenomena around us,

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but it becomes useless and meaningless
the moment we leave our planet

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and go to the moon, as our astronauts did.

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In all these cases, we find our simple way
of looking at the world is wrong,

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and things are a little more complicated.

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The nice thing is that
in all these cases, including time -

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I'm coming back to time -

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Nowadays, it's easy to think
that the Earth is round,

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and that outside of it
there's no high or low.

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We've seen the pictures taken
by the astronauts of Apollo 11

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on their way to the moon.

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The Earth is round.

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But we knew that before.

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Some of us already knew
that the Earth was round, right?

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Aristotle knew, Anaximander knew
that the Earth was round and flew.

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The Earth is moving.

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Now we've seen it from beyond it,

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but Galileo and Copernicus deduced it
without needing to see it.

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Darwin didn't see
species change; he deduced it.

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How did they deduce these things?

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Simply by starting
with what we know about the world,

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observing, and putting
together known facts,

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and noticing that the known facts
can be better understood

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if we change our conception
of the structure of,

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our way of looking at, the world.

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In this way, all these people came
to understand something new,

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something crucial.

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The fact that time goes
slower lower down and faster higher up,

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that we nowadays observe:

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we just need to buy
those very precise clocks,

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and anyone can see it's the case.

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It was understood before it was observed,

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by Einstein,

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almost 100 years ago,
97 years ago, in 1915,

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who was simply trying to clarify the ideas
of the physics of the world of his day.

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On one hand, Einstein had Newton's theory,
the great theories of mechanics;

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on the other, he had electromagnetism.

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Endeavouring to combine these two things

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in order to have
a coherent picture of the world,

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he realized that time doesn't go
at the same rate for everyone,

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that there are many different times,
that time goes at different rates.

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This was 100 years ago.

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The same thing is happening today.

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Because, today, we are again
in the same situation.

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Today, we have the great inheritance
of Einstein's very beautiful theories,

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which, for a century,
we have discovered work perfectly.

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We have confirmed them,

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we've seen there are black holes, etc.

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Alongside it, throughout the 20th century,
quantum mechanics was advancing.

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This morning we heard Marco telling us
about the world of particle physics,

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all in terms of quantum mechanics,
an outstanding theory of motion,

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but which doesn't work well
with Einstein's theories,

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with general relativity.

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So science tried once again
with endeavors

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to use what we know
to try to gain greater insight.

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In 1963, two brilliant America scientists,

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Joe Wheeler, the man
in the black and while photo,

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and Bryce DeWitt, the man
in the color photo,

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simply took Einstein's
general relativity equation,

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Einstein's theories,

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and quantum mechanics,

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and put them together
and wrote an equation

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that Wheeler called "DeWitt's Equation,"
and Dewitt "Wheeler's Equation,"

188
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and everyone else, a bit fed up,
"Wheeler-DeWitt's Equation."

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It's that one there,
but I won't go into details.

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An equation that to start with
was very confusing.

191
00:10:01,143 --> 00:10:04,066
It was studied a lot,
and today we continue to study it.

192
00:10:04,066 --> 00:10:06,124
Today, the theory has been developed,

193
00:10:06,138 --> 00:10:08,138
and we can write it more precisely,

194
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and we can better understand
its significance.

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That's what I work at.

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This equation has a characteristic
that was stunning at the time,

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and left everyone open-mouthed.

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00:10:19,305 --> 00:10:22,891
This equation was created putting together
all that we know about the world

199
00:10:22,891 --> 00:10:24,527
from one end to the other.

200
00:10:25,022 --> 00:10:27,929
It has the characteristic as follows.

201
00:10:28,758 --> 00:10:32,529
All equations, if you remember
something of school physics,

202
00:10:32,529 --> 00:10:36,163
all the important fundamental
equations of physics

203
00:10:36,163 --> 00:10:39,887
from Galileo to Newton,
Maxwell, Einstein, and so on,

204
00:10:39,887 --> 00:10:42,487
they say how things change with time -

205
00:10:42,487 --> 00:10:44,206
back to time again -

206
00:10:44,206 --> 00:10:48,430
and so they all have "t," time, in them,
whether it's velocity or acceleration,

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00:10:48,430 --> 00:10:51,609
changes in time, there's always
time in the equations.

208
00:10:51,609 --> 00:10:54,483
This equation here
doesn't have time in it,

209
00:10:54,483 --> 00:10:58,245
the variable "time" has been left out,
it's vanished, it's not there.

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It's as if trying to write
all we know about the world,

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00:11:02,313 --> 00:11:04,251
time is no longer there.

212
00:11:04,251 --> 00:11:05,701
What does this mean?

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00:11:06,471 --> 00:11:10,651
That is what I'll try to explain
in the remaining four minutes.

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00:11:10,651 --> 00:11:13,240
If you listen to me carefully,

215
00:11:13,240 --> 00:11:15,247
I hope I'll be able to make clear to you

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00:11:15,247 --> 00:11:18,571
what it means to write an equation
to describe the world without time.

217
00:11:19,021 --> 00:11:21,996
Let's go back to simpler physics.

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00:11:21,996 --> 00:11:25,204
The first thing that those
who enroll in physics study

219
00:11:25,204 --> 00:11:28,592
is how a pendulum moves, for example,
or something else that moves.

220
00:11:28,892 --> 00:11:32,577
We need to describe
how its position changes with time.

221
00:11:33,557 --> 00:11:37,577
So we need to measure the position
and the time with a clock, right?

222
00:11:38,077 --> 00:11:40,500
We look at the position
and what the clock reads,

223
00:11:40,500 --> 00:11:41,700
make a chart,

224
00:11:41,700 --> 00:11:47,132
and write an equation that describes
how the position changes with time.

225
00:11:48,723 --> 00:11:50,597
But, here, we are not observing time;

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00:11:50,597 --> 00:11:52,983
here, we are looking at
the hand's position, right?

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The hand is moving,

228
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and this is moving.

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We're just describing
how this position shifts

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when the hand's position shifts.

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And if you think about it,
it's what we always do.

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00:12:07,985 --> 00:12:10,934
We always describe something
as a function of something else.

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00:12:10,934 --> 00:12:13,834
Clocks are just things
among others that move,

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but that have the characteristic
of all moving together ...

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more or less all together.

236
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What does this mean?

237
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It means that we can do without time

238
00:12:23,191 --> 00:12:26,232
and just talk in terms of
how the pendulum moves

239
00:12:26,232 --> 00:12:28,295
as a function of the position of the hand.

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00:12:28,574 --> 00:12:31,987
Instead of saying,
"I woke up at 8 this morning,"

241
00:12:31,987 --> 00:12:35,087
I could say that I woke up
when the sun was in a given position,

242
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that I started talking
the moment the lights went off,

243
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and so on and so forth,

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00:12:39,726 --> 00:12:42,441
with no reference to time at all.

245
00:12:42,661 --> 00:12:44,974
Let's take "high" and "low," for example.

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I could say this is high, and this is low,

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or I could avoid mentioning
"high" or "low."

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I could say this is towards
that bright light there,

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and this is towards
the red circle underneath me.

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If I'm on Earth, I complicate life.

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But if I'm an astronaut in a capsule
and say to my friend,

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"Hey, Anderson, could you pass me
that clock up there?"

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he'll reply, "Where's up there?"

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But if I say "the one towards
the red mat" instead,

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he'll be, "Oh, the one
towards the red mat."

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So the notion of high or low
is meaningless when we leave the Earth.

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Well, the notion of time
becomes meaningless, disappears,

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as soon as I leave normal space

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and enter one where I have to use
quantum gravity, this equation here.

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And where is this space?

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Where things are extremely big
or extremely small:

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there where we're still without
clear ideas on the world.

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If we observe the extremely small,

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observe on an extremely small scale,

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space, space itself fluctuates, spikes,

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it's like a stormy sea,

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but what it is, is space-time
in the extremely small,

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as if time jumps.

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These two clocks, each weaving
its own path at a different speed,

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in the smallest of places, they go
forward and backward, they move, etc.

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On this extremely small scale,

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our notion of time is no longer good,
no longer useful, no longer works well.

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So we have to re-describe
the world in terms of those variables,

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one by one, without reference to time,

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as if we had a lot of clocks
that had lost their hands,

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and we could only see
how one moves in respect to the other.

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Imagine, to give you an idea,

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how we think about the world
as a combination of things that move,

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that change, that dance, all together,

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in time to a conductor of an orchestra

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who gives the beat:
1, 2, 1, 2 ... all together ... 1, 2.

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This picture no longer works
for the small.

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In the extremely small,
there's no unique beat for all,

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and the world is as if it were a dance
of every microelement with its neighbor,

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but not all together.

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What's the moral of this whole story?

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Time is a useful concept,

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it organizes our daily experiences,

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but it is not a fundamental concept.

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Just as "high" and "low"
are very useful concepts,

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but don't work anymore
when we leave our everyday surroundings.

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This is true of a lot of things.

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It's this that I love about science.

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What science teaches us
is that our image of the world,

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our perception of the world,

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is very often wrong, limited,

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working only in our usual surroundings.

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The human race is like
someone born in a small town

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where everyone behaves in the same way,

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until they leave and say,
"Oh, but there's more.

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We can eat different things,
say different things,

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speak different languages,
have different ideas."

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Humanity leaves behind
the smallness of its thoughts

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and discovers that everything's different:

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species transform from one to another,

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"high" and "low" are not real,

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time is not what it seems.

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The world is bigger, more beautiful,
more diverse, and more thought-provoking

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than what it seems at first sight,

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this thing, a little banal,
with "high" and "low,"

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with people that move,
and rocks that fall.

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It's much richer.

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And to understand that,
we have little need of ancient knowledge.

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Ancient knowledge, all ancient knowledge,

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what our forefathers taught us,

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really only applies here.

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If we look a little further,
it's no longer valid.

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As was said in the first video today,
the universe is endless.

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We were born in a tiny,
little corner of it,

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have ideas that apply
only to this tiny, little corner,

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when we then start
to look a little further afield.

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I think what we discover at each step -

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and I'm concluding -

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is far more extensive,
more beautiful, more complex,

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than any of the ideas
our forefathers told us about,

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or our moms and dads taught us.

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And this beauty that overwhelms us,

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this mystery that always lies before us

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to which we gain access,
step by step, little by little,

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but which forever remains boundless,

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draws us, fascinates us,
and we want to get to see it.

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This, for me, is science.

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Thank you.

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(Applause)